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ELEMENTS 


OF 


CHEMISTKY, 


,     INCLUDING  THE 

MOST  RECENT  DISCOVERIES  AND  APPLICATIONS  OF  THE  SCIENCE  TO 
MEDICINE  AND  PHARMACY,  AND  TO  THE  ARTS. 


BY  ROBERT^KANE,  M.D.,  M.R.I.A., 

PBOFESSOK  OF  NATURAL  PHILOSOPHY  TO  THE  BOYAL  DUBLIN  SOCIETY  ; 

PBOFBSSOB  OF  CHEMISTRY  TO  THE  APOTHECARIES'  HALL  OF  IRELAND  ;  MEMBER  OF  TBI 

SOCIETY  OF  PHARMACY   OF  PARIS,  AND   OF  THE   GERMAN  PHARMACEUTICAL 

SOCIETY,  ETC.,  ETC.,  ETC. 


AN   AMERICAN   EDITION, 

WITH    ADDITIONS    AND    CORRECTIONS,   AND    ARRANGED    FOR   THE    USE    OF 

THE    UNIVERSITIES,  COLLEGES,  ACADEMIES,  AND    MEDICAL 

SCHOOLS    OF    THE    UNITED    STATES, 

BY  JOHN  WILLIAM  DRAPER,  M.D 

PROFESSOR   OF   CHEMISTRY   IN  THE   UNIVERSITY   OF  NEW- YORK,  FORMERLT 

PROFESSOR  OF   PHYSICAL  SCIENCE   AND   PHYSIOLOGY  IN   HAMPDEN  SIDNEY   COLLEQB, 

VIRGINIA;   MEMBER   OF   THE   LYCEUM  OF   NATURAL   HISTORY  OF   NEW-YORK, 

dec,  &C.,  &C. 


qD3o 


NEW-YORK: 


Published   by  Harper  &   Brothers, 
No.  82  Clipf-Street. 


185  1. 


S4457 


A  no 


Entered,  according  to  Act  of  Congress,  in  the  year  184  ,  by 

Harper  &  Brothers, 
2R  the  Clerk's  Office  of  the  Sp-*hern  District  of  New- York. 


PREFACE  TO  THE  AMERICAN  EDITION. 


In  preparing  the  work  of  Dr.  Kane  for  the  use  of  Amer- 
ican students,  I  have  preserved  the  original  entire,  and  have 
only  made  those  alterations  in  it  which  the  system  of  instruc- 
tion pursued  in  the  United  States  seems  to  require. 

This  work,  which,  as  a  text-book,  is  undoubtedly  the  best 
extant  in  the  English  language,  representing  the  present  con- 
dition of  chemical  science,  necessarily  contains  much  detail. 
To  give  it  completeness,  it  was  needful  to  include  the  de- 
scription of  many  bodies  of  little  technical  importance,  to 
describe  experimental  processes,  and  sometimes  to  dwell  on 
facts  of  minor  value. 

The  period  of  instruction  in  the  schools  of  this  country  is 
short,  so  that  many  standard  books  are  unavailable  from 
their  extent.  From  an  experience  of  several  years  in  public 
teaching,  I  have  perceived  the  importance  of  separating,  for 
the  student,  the  leading  principles  from  the  accompanying 
detail.  This  will,  perhaps,  to  a  certain  extent,  be  accom* 
plished  by  the  mechanical  contrivance  of  printing  such  works 
with  different  types,  the  important  matter  being  in  the  larger 
letters. 

The  magnitude  of  the  original  prevented  me  from  making 
additions  to  any  great  extent ;  what  has  been  introduced  in 
this  way  will  be  readily  distinguished,  from  being  inserted 
between  brackets. 

From  its  having  been  repeatedly  and  carefully  read,  and 
the  errors  and  misprints  revised,  this  will  probably  be  found 
more  correct  than  the  foreign  edition. 

John  William  Draper. 

University  of  New-York,  June  1st,  1843. 


PREFACE. 


My  object  in  the  following  pages  is  to  present  to  the  stu- 
dent an  account  of  the  general  principles  and  facts  of  Chem- 
istry, and  of  its  applications  to  Pharmacy,  to  Medicine,  and 
to  the  Useful  Arts. 

In  the  arrangement  of  a  work  like  the  present,  if  the  gen- 
eral principles  of  the  science  are  first  described,  it  is  impos- 
sible to  avoid  the  difficulty  of  introducing  the  names  of  many 
substances  with  whose  history  the  reader  cannot  be  supposed 
conversant ;  and  by  entering,  in  the  commencement,  on  the 
description  of  individual  substances,  reference  to  the  princi- 
ples of  affinity  and  the  laws  of  constitution  is  continually  ne- 
cessary, in  order  that  the  reactions  of  these  bodies  may  be 
understood.  In  both  cases  the  student  is  liable  to  some  em- 
barrassment, but  I  believe  it  to  be  greater  in  the  latter,  and 
hence  I  have  adopted  the  plan  of  fully  describing  all  the 
general  principles  and  laws  of  chemical  action,  before  enter- 
ing on  the  description  of  the  chemical  substances  in  detail. 

Chemistry  being  itself  but  a  department  of  Natural  Philos- 
ophy, although  the  most  extensive  in  its  objects  and  the  most 
important  in  its  uses,  it  is  connected  so  intimately  with  the 
other  branches  of  Physics,  that  a  knowledge  of  at  least  their 
general  principles  is  necessary  for  the  proper  understanding 
of  the  nature  of  chemical  phenomena.  I  have  consequent- 
ly embraced  within  the  design  of  the  present  work  a  de- 
scription of  the  physical  properties  of  bodies,  so  far  as  they 
serve  to  complete  their  chemical  history,  or  influence  their 
chemical  relations ;  and  thus,  upon  the  one  hand,  supply 
characters  by  which  chemical  substances  may  be  recognised, 
and,  upon  the  other,  modify  the  affinities  by  which  thp  ac- 
tion of  chemical  substances  upon  each  other  is  determined. 
With  this  twofold  object,  the  chapters  on  Cohesion,  Light, 
Heat,  and  Electricity  have  been  drawn  up. 

The  portion  of  the  work  which  treats  of  the  general  laws 
of  chemical  combination,  is  followed  by  an  account  of  the 
mode  of  preparation  and  properties  of  all  inorganic  substan- 
ces of  interest  to  Science,  to  Medicine,  or  to  the  Arts.  But 
in  this  part  I  will  pass  over  very  briefly  the  history  of  nu- 
merous bodies  which,  from  their  rarity,  are  objects  only  of 


n  PREFACE. 

scientific  curiosity,  referring  those  who  would  wish  to  study 
their  history  more  closely  to  the  extended  works  of  Thomp- 
son, of  Graham,  of  Dumas,  or  of  Berzelius. 

In  the  department  of  Organic  Chemistry  my  object  will  be 
fully  to  discuss  the  history  of  all  such  bodies  as  are  of  im- 
portance, from  their  bearing  upon  general  principles  or  ex- 
isting theories,  from  their  use  in  medicine  or  pharmacy,  their 
employment  in  the  arts  or  in  ordinary  life.  The  numerous 
series  of  bodies  which  are  every  day  discovered  in  Organic 
Chemistry,  but  which  do  not  come  under  any  of  the  above 
heads,  shall  be  dismissed  with  only  a  notice  of  their  exist- 
ence. 

The  relations  of  chemical  action  to  the  functions  of  organ- 
ized matter,  the  applications  of  Chemistry  to  Physiology  and 
to  Pathology,  will  be  treated  of  so  far  as  our  accurate  knowl- 
edge extends  ;  and,  finally,  a  succinct  description  of  the  mode 
of  analysis  of  organic  and  inorganic  bodies  will  be  given. 

As  this  work  is  not  intended  to  be  a  complete  system  of 
Chemistry,  nor  to  satisfy  the  wants  of  those  who  wish  to  make 
Chemistry  their  special  study,  I  have  in  almost  all  cases 
avoided  references  or  quotations,  which  would  needlessly 
occupy  much  space ;  for,  in  the  larger  works  already  men- 
tioned, the  original  authorities  on  all  subjects  will  be  found. 

The  object  of  a  work  like  the  present  being  to  represent 
faithfully  the  general  aspect  and  extent  of  science  at  the  time 
of  publication,  its  details  must  be  in  great  part  founded  on 
the  results  of  others.  Hence  originality  cannot  in  any  great 
degree  be  either  expected  or  desired ;  but  I  have  not  hesi- 
tated, in  many  instances,  where  the  best  consideration  I" 
could  give  the  subject  induced  me  to  dissent  from  views 
generally  heldj  to  make  this  work  the  vehicle,  in  a  popular 
form,  of  such  suggestions  as  I  thought  deserved  to  be  adopted. 

The  processes  given  for  the  preparation  of  the  various 
substances  described  are,  with  very  few  exceptions,  those 
followed  either  in  my  private  laboratory  or  in  the  manufac- 
turing laboratory  of  the  Apothecaries'  Hall  of  Ireland  ;  and 
the  apparatus  figured  in  the  woodcuts  are  generally  similar 
to  those  which  I  employ  in  experiments  of  research  or  at 
lecture. 


CONTENTS. 


Pago 

INTRODUCTION. 
Origin  and  Objects  of  Chemistry     .      9 

CHAPTER  I. 

or     GRAVITY    AND     COHESIVE     FORCES,     AS 
CHARACTERIZING      CHEMICAL      SUBSTAN- 


Specific  Gravities  of  Bodies     . 

.     11 

Constitution  of  Matter     . 

.     17 

Capillarity  and  Elasticity 

.     19 

Phenomena  of  Solution    . 

.     22 

Crystallization 

.     23 

Systems  of  Crystallization 

.     26 

CHAPTER  11. 

OF    THE     PROPERTIES    OP    LIGHT   AS    CHAR- 
ACTERIZING   CHEMICAL    SUBSTANCES. 

Reflection  and  Refraction  of  Light  .  32 
Double  Refraction  .  .  .  .34 
Polarization  of  Light  .  .  .38 
Circular  Polarization  .  .  .41 
Wave  Theory  of  Light    ...    42 

CHAPTER  m. 

OF   HEAT  CONSIDERED  AS   CHARACTERIZING 

CHEMICAL    SUBSTANCES. 

Section  I. 

Of  Expansion        .         .         .  .46 

Nature  of  Temperature        .  .    49 

Thermometers     .        .        .  .50 

Pyrometers          .        .        .  .54 

Expansion  of  Air  and  Gases  .    56 

Liquids    .         .  .58 

Solids     ...    60 

Section  II. 

Specific  Heat         .         .         .  .63 
Connexion  of  Specific  Heat  and 

the  Chemical  Constitution  .    66 

Specific  Heats  of  Gases       .  .    69 

Section  III. 

Of  liquefaction     .         .         .  .70 

Latent  Heat  of  Liquids         .  .     71 

Freezing  Mixtures       .        .  .73 

Sbction  IV. 

Of  Vaporization    .         .         .  .75 

Latent  Heat  of  Vapours       .  .     76 

Elasticities  of  Vapours         .  .     78 

Nature  of  the  Boiling  Point  .    83 

Spontaneous  Evaporation     .  .    87 
Of  Steam  as  a  Moving  Power      .    89 

Section  V. 

Of  the  Transmission  of  Heat  through 

Bodies 91 

Conduction  of  Heat     .        .  .92 


Radiation  of  Heat  .  .  .94 
Absorption  and  Reflection  of  Heat  96 
Researches  of  Melloni  and  Forbes  98 
Polarization  of  Heat  .  .  .  'Ol 
Relations  of  Heat  to  Light  .  .  102 
Section  VI. 

Of  the  Cooling  of  Bodies  .  .  103 
Theory  of  Dew  and  Frost  .  .  104 
Central  Heat  of  the  Earth    .        .  105 

CHAPTER  rV. 

OF  ELECTRICITY  CONSIDERED  AS  CHA- 
RACTERIZING CHEMICAL  SUBSTAN- 
CES        106 

Section  L 

Of  Statical  Electricity  .        .         .  107 
Distribution  of  Electricity    .        .110 
Electrical  Attractions  and  Repul- 
sions         113 

Theories  of  Electricity  .  .114 
Electrical  Induction  .  .  .118 
Theory  of  the  Leyden  Jar  .  .  120 
Nature  of  Induction  .  .  .  122 
Atmospheric  Electricity       .        .  125 

Section  II. 

Of  Dynamical  Electricity  .  .126 
Simple  Galvanic  Circles  .  .128 
Of  Electrotype  Copying  .  .  130 
Theory  of  the  Galvanic  Battery  .131 
Volta's  Theory  of  Contact  .  .  133 
Construction  of  Galvanic  Batteries  134 
Constant  Batteries  .  .  .136 
Thermo-electric  Currents     .        .  139 

Magnetism 143 

Electro-magnetic  Phenomena  .  145 
Of  the  Galvanometer  .        .        .  147 

CHAPTER  V. 

OF    CHEMICAL    NOMENCLATURE    .    149 

Names  of  the  Simple  Bodies    .        .  150 

Primary  Compounds  .  152 

Secondary  Compounds  154 

Symbolical  Nomenclature        .        .156 

CHAPTER  VI. 

OF  CHEMICAL  AFFINITY,  AND  ITS  RELA- 
TIONS TO  HEAT,  TO  LIGHT,  AND  TO  CO- 
HESION. 

Elective  Decomposition  .  .  .157 
Order  of  Affinity  not  Constant  .  159 
Relation  of  Affinity  to  Cohesion  .  163 
Influence  of  Elasticity  on  Affinity  .  168 
Influence  of  Light  on  Affinity  .  .  172 
Influence  of  the  Chemical  Rays  of 
Light 173 


VUl 


CONTENTS. 


Page 

Photography     and     Daguerreotype 
Drawing 175 

CHAPTER  VII. 

or   THE  HEAT  AND  LIGHT  DISENGAGED 

DURING   CHEMICAL    COMBINATION     .    178 

Products  of  Slow  Combustion  .  179 

Constitution  of  Flame      .        .  .181 

Of  the  Safety  Lamp         .        .  .183 

Theories  of  Combustion  .        .  .  185 

CHAPTER  VIII. 

OF   THE   INFLUENCE    OP   ELECTRICITY 

ON   CHEMICAL   AFFINITY   .  .    187 

Electro-chemical  Classification  .  189 
Electro-chemical  Theories  .  .190 
Electrolysis  and  Electrolytes  .  .194 
Origin  of  the  Galvanic  Current  .  197 
Synthetic  Action  of  Electricity  .  199 
Relations  of  Electricity  to  Affinity  .  201 

CHAPTER  IX. 

OP    THE    LAWS    OF    COMBINATION      .    202 

Scales  of  Chemical  Equivalents       .  205 

.  207 

.  210 

.  213 


Law  of  Multiple  Proportions 
Definiteness  of  Composition 
Theory  of  Volumes 

CHAPTER  X. 


OP  THE  RELATIONS  OF  CHEMICAL  CONSTI- 
TUTION TO  THE  MOLECULAR  STRUCTURE 
OF   BODIES. 

Section  I. 

Of  the  Atomic  Theory  .  .  .217 
Physical  and  Chemical  Atoms     .218 

Section  II. 

Of  Isomorphism  .  .  .  .221 
Isomorphous  Groups  .  .  .  223 
Relation  of  Form  to  Constitution  226 

Section  III. 

Of  Dimorphism  and  Isomerism,  and 

of  the  Theory  of  Types  .  .  227 
Approximate  Dimorphism  .  .  230 
Principle  of  Isomerism         .        .231 

Compound  Radicals  .  233 

Theory  of  Organic  Types     .        .  234 

Section  IV. 

Of  Catalysis  ....  235 

Communication  of  Motion    .        .  237 


CHAPTER  XL 

the    CLASSIFICATION    OP    THE    EL- 
EMENTARY  BODIES 

CHAPTER  XIL 


238 


at  THE  SIMPLE  NON-METALLIC  BODIES, 
AND  OP  THEIR  COMPOUNDS  WITH  EACH 
OTHER. 

1.  Of  Oxygen:  Its  Preparation  and 
Properties         ....  241 

a.  Of  Hydrogen :  Its  Preparation  .  246 
The  Hydro-oxygen  Blowpipe  .  251 
Of  Water :  its  Composition  .  253 

Peroxide  of  Hydrogen         .        .  258 


3.  Of  Nitrogen  .  .  .  .260 
Of  the  Atmosphere  .  .  .  262 
Nitrous  Oxide  ....  272 
Nitric  Oxide  ....  273 
Hyponitrous  Acid,  Nitrous  Acid  .  275 
Nitric  Acid 277 

4.  Of  Sulphur  .  .  .  .283 
Sulphurous  Acid  ....  284 
Sulphuric  Acid  ....  286 
Hyposulphurous  and  Hyposulphu- 

ric  Acids 290 

Sulphuret  of  Hydrogen         .        .  292 

5.  Of  Selenium        ....  294 
Its  Compounds  with  Oxygen,  Hy- 
drogen, and  Sulphur         .        .  294 

6.  Of  Phosphorus     ....  295 
Oxide  of  Phosphorus,  Phosphor- 
ous Acid 296 

Phosphoric  Acid  ....  297 
Phosphuret  of  Hydrogen      .        .  299 

7.  Of  Chlorine  ....  300 
Hypochlorous  and  Chloric  Acids  .  304 
Chlorous  Acid  ....  305 
Hydrochloric  or  Muriatic  Acid  .  307 
Chlorides  of  Sulphur  and  Phospho- 
rus     310 

8.  Of  Iodine 311 

Iodic  and  Periodic  Acids  .  .313 
Hydriodic  Acid  ....  316 
Iodine  with  Phosphorus,  Sulphur, 

&c 316 

Hydriodate  of  Phosphuretted  Hy- 
drogen       316 

9.  Of  Bromine  .  .  .  .317 
Bromic  and  Hydrobromic  Acids  .  318 
Other  Compounds  of  Bromine      .318 

10.  Of  Fluorine  .  .  .  .319 
Hydrofluoric  Acid        .        .        .  320 

11.  Of  Silicon  .  .  .  .321 
Silicic  Acid  or  Silica  .  .  .  322 
Chloride  of  Silicon       .        .        .323 

■    Fluoride  of  Silicon        .        .        .  324 

12.  Of  Boron 325 

Boracic  Acid  ....  326 
Chloride  and  Fluoride  of  Boron    .  326 

13.  Carbon    referred    to    Organic 
Chemistry        ....  327 

CHAPTER  XIL* 

OF  THE  GENERAL  CHARACTERS  OP  THB 
METALS,  AND  OF  THEIR  COMPOUND* 
WITH  THE  NON-METALLIC  BODIES. 

Classification  of  the  Metals ;  their 
State  in  Nature ;  the  Mode  of  Re- 
duction of  their  Ores    .        .        .  327 

CHAPTER  XIII. 

OP  THE  INDIVIDUAL  METALS,  AND  OP  THEIB 
COMPOUNDS  WITH  OXYGEN,  SULPHUR, 
SELENIUM,  AND  PHOSPHORUS  :  THEIB 
ALLOYS. 

Section  I.  Metals  of  the  First  Class. 
Potassium  :  its  Preparation  .  336 

Potash,  Peroxide  of  Potassium    .  337 


CONTENTS. 


IX 


Page 

Sulpharets  of  Potassium  .  .  339 
Sodium  and  Soda  .  .  .340 
Sulphurets  of  Sodium  .  .  .342 
Lithium :  its  Oxide  and  Sulphuret  342 
Barium :  its  Preparation  .  .  342 
Barytes,  Hydrate  of  Barytes  .  342 
Sulpiiuret  of  Barium  .  .  .344 
Strontium ;  its  Oxide  and  Sulphu- 
ret     344 

Calcium :  its  State  in  Nature  .  345 
Preparation  and  Properties  of  Lime  346 
Sulphurets  of  Calcium  .        .  347 

Magnesium,  Magnesia,  &c.  .  348 

iacTioN  IL  Metals  of  the  Second  Class. 
Aluminum  :  its  State  in  Nature  .  349 
Alumina,  Sulphuret,  &c.  .  .  350 
Glucinum  and  its  Compounds  .  351 
Tttrium,  Thorium,  Zirconium  .  351 
Cerium,  Lanthanum  .  .  .351 
Of  Manganese  .  .  .  .352 
Oxides  of  Manganese  .  .  .  353 
Technical  Valuation  of  Manganese 

Ore 355 

Manganic  and  Permanganic  Acids  356 
Other  Compounds  of  Manganese  .  357 
Section  IIL  Metals  of  the  Third  Class. 
Of  Iron  :  its  State  in  Nature  .  357 
Manufacture  of  Cast  and  Soft  Iron  359 
Manufacture  of  Steel  .  .  .360 
Passive  Condition  of  Iron  .  .301 
Oxides  of  Iron  .  .  .  .362 
Sulphurets  of  Iron  .  .  .  363 
Of  Nickel  and  its  Compounds  .  365 
Of  Cobalt  and  its  Compounds  .  366 
Of  Zhic  and  its  Compounds  .  367 
or  Cadmium.     Of  Tin  .        .  369 

Oxides  and  Sulphurets  of  Tin  .  .370 
Of  Chrome  :  its  Oxide.     Chromic 

Acid 371 

Of  Vanadium       .        .        .        .  373 
Skction  IV.  Metals  of  the  Fourth  Class. 
Tungsten  and  Molybdenum  .  373 

Osmium  and  its  Compounds  .  374 
Columbium  and  Titanium    .         .  375 

Of  Arsenic 376 

Arsenious  Acid,  Arsenic  Acid  .  377 
Arseniuret  of  Hydrogen  .  .  378 
Sulphuret  of  Arsenic  .  .  .  379 
Detection  of  Arsenic  .  .  .  380 
Of  Antimony  .  .  .  .384 
Compounds  of  Antimony  with  Ox- 
ygen          385 

Sulphurets  of  Antimony  .  .  386 
Antimoniuret  of  Hydrogen  .  .  388 
Of  Tellurium  and  its  Compounds  389 
Of  Uranium  and  its  Compounds  .  390 
Section  V.  Metals  of  the  Fifth  Class. 
Of  Copper,  Reduction   from   its 

Ores 390 

Oxides  of  Copper  .         .        .  392 

Sulphurets  of  Copper    .         .         .  393 
Brass,  Bronze,  Gun  Metal,  Specu- 
lum Metal         ....  393 
Of  Lead:  its  Oxides    .        .        .  394 


Sulphurets  and  Alloys  of  Lead     .  395 
Bismuth  and  its  Compounds        .  397 
Section  VI.  Metals  of  the  Sixth  Class. 
Of  Silver,  its  Natural  State  and  I 

Properties  ....  399 
Oxides  and  Sulphurets  of  Silver  .  401 
Of  Mercury  :  its  Preparation  and 

Properties         ....  402 
Oxides  and  Sulphurets  of  Mercury  403 
Of  Gold :  its  Oxides  and  Sulphu- 
rets   405 

Of  Palladium  and  its  Compounds  406 
Of  Platinum :  its  Oxides  and  Sul- 
phurets      407 

Of  Iridium  and  Rhodium      .        .  409 

CHAPTER  XIV. 
OP   the   general  properties  and  con- 
stitution OF   SALTS. 

Neutral,  Acid,  and  Basic  Salts ;  Dou- 
ble Salts;  Sulphur  Salts;  Theo- 
ries of  the  intimate  Constitution  of 
Acids  and  Salts ;  Binary  Theory 
of  Salts        .        .        .        ,        .410 

CHAPTER  XV. 

SPECIAL  HISTORY  OP  THE  MOST  IMPORTANT 
SALTS  OF  THE  INORGANIC  ACIDS  AND 
BASES. 

Of  the  Salts  of  Potash.— Chloiide,  lo 
dide,  Bromide,  and  Fluoride  of  Po- 
tassium ;  Fluosilicate  of  Potash ; 
Sulphates  of  Potash ;  Nitrate  of 
Potash;  Manufacture  of  Gunpow- 
der ;  Hypochlorite  and  Chlorate  of 
Potash ;  ifercjilc^atei  lodate,  and 
Sihcate  of  Potash         .        ,        .  421 

Of  the  Salts  of  Sodium. — Chloride  of 
Sodium  ;  of  Sea- water ;  Bromide 
and  Iodide  of  Sodium ;  Sulphate, 
Nitrate,  Hypochlorite,  and  Hypo- 
nitrite  of  Soda;  Various  Phos- 
phates of  Soda ;  Borate  and  Sili- 
cate of  Soda         ....  426 

Of  the  Salts  of  Lithium — Salts  of  Ba- 
rium.— Chloride  of  Barium ;  Sul- 
phate and  Nitrate  of  Barytes.  Salts 
of  Strontium. — Chloride  of  Stron- 
tium; Sulphate  and  Nitrate  of 
Strontian     .         .        ;         .         .  429 

Of  the  Salts  of  Calcium. — Chloride, 
Bromide,  Iodide,  and  Fluoride  of 
Calcium  ;  Sulphate  and  Nitrate  of 
Lime;  Phosphateof  Lime  ;  Hypo- 
chlorite of  Lime  ;  Manufacture  of 
Bleaching  Salt ;  Chlorometry       .  430 

Salts  of  Magnesia. — Epsom  Salts     .  434 

Salts  of  Aluminum. — Manufacture  of 

Alum 435 

Constitution  of  Glass  and  Porce- 
lain;   Manufacture    of  Glass; 
Manufacture  of  Earthenware    .  437 
Of  the  Salts  of  Manganese   .        .  443 

Of  the  Salts  of  /ron.— Chlorides  of 


CONTENTS. 


Page 

Iron ;  Manufacture  of  Copperas ; 
Nitrates  of  Iron        .        .        .  444 
Salts  of  Nickel  and  Cobalt   .        .  446 
Salts  of  Zinc  and  Cadmium  .  447 

Salts  of  Tin  .        .        .        .448 

Salts  of  Chrome  and  Vanadium ; 

Chromates  ....  449 
Salts  of  Tungsten,  Molybdenum, 

Osmium,  and  Columbium  .  451 

Salts  of  Arsenic,  Arsenites,  Ar- 

seniates  .....  452 
Salts  of  Antimony,  Antimoniates  453 
Salts  of  Titanium,  Tellurium,  and 

Uranium 454 

Salts  of  Copper. — Manufacture  of 
Blue  Vitriol ;  Scheele's  Green ; 
Emerald  Green         .        .  ..     .  455 
Salts  of  Lead  ;  Chrome  Yellow ; 

Chrome  Red  .  .  .  .  457 
Salts  of  Bismuth  .        .        .458 

Salts  of  Silver,  Lunar  Caustic      .  459 
Salts  of  Ji^rcury. — Corrosive  Subli- 
mate,   Calomel,    Iodides,    Sul- 
phates, and  Nitrates  of  Mercury  461 
Salts  of  Gold        .         .        .        .465 
Salts  of  Palladium  and  Platinum  466 
Salts  of  Iridium  and  Rhodium      .  466 

CHAPTER  XVI. 

OF  THE   GENERAL  PRINCIPLES  OP  THE   CON- 
STITUTION   OF    ORGANIC    BODIES. 

Elements  of  Organic  Bodies  ;  Rela- 
tion of  Vital  Force  to  Affinity; 
Compound  Radicals ;  Theory  of 
Organic  Acids  ;  Theory  of  Types  ; 
Decomposition  of  Organic  Bodies  467 

CHAPTER  XVn. 

OF   CARBON  AND   ITS   COMPOUNDS  WITH    OX- 
YGEN,   SULPHUR,    AND    CHLORINE. 

Forms  of  Carbon  ;  Organic  Analysis  476 
Carbonic  Acid  ;  Carbonates  of  Pot- 
ash and  Soda ;  Manufacture  of 
Potashes  and  Soda-ash ;  Alkalim- 
etry ;  Earthy  Carbonates ;  Car- 
bonates of  Iron,  Copper,  Lead, 
&c.  ;  of  Carburets  .  .  .  485 
Carbonic  Oxide,  Oxalic  Acid,  and  the 
Oxalates ;  Chlorocarbonic  Acid ; 
Oxycarburet  of  Potassium  ;  Rho- 
dizonic,  Croconic.  and  Mellitic 
Acids ;  Sulphuret  of  Carbon ;  Chlo- 
rides of  Carbon    .        .        .      ^ .  492 

CHAPTER  XVIII. 

OF  THE  COMPOUNDS  OF  NITROGEN  4ND  HY- 
DROGEN. OP  AMMONIA,  ITS  DERIVATIVES 
AND    COMPOUNDS. 

A.mmonia ;  Amidogene  ;  Iodide  and 
Chloride  of  Azote  ;  Ammoniurets, 
Amidides  ;  Azoturets  ;  Ammonia- 
Salts  of  Zinc,  Copper,  Nickel,  Co- 


balt, Silver,  Palladium,  Platinum, 
and  Mercury;  White  Precipitate  498 
Ammonia  and  Anhydrous  Acids; 
Common  Ammoniacal  Salts ;  The- 
ory of  Ammonium ;  Sal  Ammoni- 
ac, Sulphates,  Phosphates,  Oxal- 
ates, &c.,  of  Ammonia ;  Double 
Chlorides  of  Ammonium      .        .  507 

CHAPTER  XIX. 

OF  CYANOGEN  AND  ITS  COMPOUNDS,  AND 
OF  THE  BODIES  DERIVED  PROM  IT. 

Cyanogen.  Cyanic,  Fulminic,  and 
Cyanuric  Acids.  Prussic  Acid: 
its  Preparation  and  Detection; 
Valuation  of  its  Strength.  Chlo- 
rides and  Iodides  of  Cyanogen     .  613 

Of  the  Metallic  Cyanides,  Potassium, 
Mercury,  Iron.  Complex  Cyan- 
ides ;  Prussian  Blue ;  Yellow  and 
Red  Ferroprussiates  of  Potash ; 
Theory  of  the  Complex  Cyanides  520 

Of  Sulphocyanogen  and  its  Com- 
pounds ;  of  Mellon,  Melam,  Mela- 
mine,  and  their  Derivatives  .  525 

CHAPTER  XX. 

OF  STARCH,  LIGNINE,  GUM,  AND  SUGAE, 
WITH  THE  PRODUCTS  OF  THEIR  DECOM- 
POSITION   BY    ACIDS    AND    ALKALIES. 

Varieties  of  Starch ;  Lignine  ;  Vari- 
eties of  Gum  ;  Varieties  of  Sugar ; 
Action  of  Acids  on  Sugar ;  Saccha  • 
rine  Fermentation  ;  Lactine ;  Mu- 
cic  Acid  ;  Mannite ;  Lactic  Acid; 
Glycyrrhizine       ....  527 

CHAPTER  XXL 

OF  THE  ALCOHOLIC  AND  ACETIC  FERMENT- 
ATIONS. OF  ALCOHOL ;  THE  ETHERS ; 
ALDEHYD  ;  ACETIC  ACID,  AND  OTHBB 
BODIES    DERIVED    FROM    IT. 

Vegeto-animal  Bodies ;  Yeast ;  Man- 
ufacture of  Spirit ;  Preparation  of 
Ether;  Theory  of  the  Process; 
Nature  of  Ether ;  its  Compounds 
with  Acids ;  Sulphovinic  Acid  ; 
Oil  of  Wine  ;  Compound  Ethers  ; 
of  defiant  Gas  and'  the  derived 
Compounds  ....  537 

Oxidation  of  Alcohol;  Aldehyd;  Ace- 
tous Fermentation ;  Acetic  Acid, 
Acetates  of  Potash,  Lime,  &c  ,  Su- 
gar of  Lead,  Verdigris,  other  Ace- 
tates ;  of  Acetone;  Compounds  of  • 
Kacodyl ;  of  Marsh  Gas      .        ,  553 

Action  of  Chlorine  on  Alcohol,  and 
the  Bodies  derived  from  it ;  The- 
ory of  the  Ethers  .         .         .  564 

Secondary  Products  of  the  Alcoholic 
Fermentation  :  GEnanthic  Acid  ; 
Amilic  Alcohol ;  Corn  Oil    .        .  567 


CONTENTS. 


Xi 


CHAPTER  XXII. 


Page 


OP    THE    ESSENTIAL    OILS,    CAMPHORS,    AND 
RESINS. 

Of  the  Oils  forming  Acids,  not  exist- 
ing in  the  Plants ;  Oil  of  Bitter 
Almonds  ;  Amygdaline ;  Benzoic 
Acid ;  Benzyl ;'  Oils  and  Acids  of 
Cinnamon,  Cloves,  Mustard,  and 
Spirea 569 

Oils  pre-existing  in  the  Plant,  Prop- 
erties not  Acid     ....  574 

Camphors  or  Stearoptens  of  the  Oils 
of  Resins     .         .         .        .         •  576 

Amber,  Succinic  Acid,  Succinates; 
Caoutchouc         ....  579 

CHAPTER  XXIII. 

OF   THE    SAPONIFIABLE   FATS   AND    OILS. 

Glycerine,  Stearine,  Oleine,  Marga- 
rine ;  Products  of  the  Action  of 
Acids  on  Fatty  Bodies;  Vegeta- 
ble Fats  and  Oils ;  Fish  Oils :  Man- 
ufacture of  Soaps  and  Plasters     .581 

Spermaceti,  Ethal,  and  the  derived 
Bodies.     Wax     .        .        .        .591 

CHAPTER  XXIV. 

OP  THE  ORGANIC  ACIDS  WHICH  DO  NOT 
PRE-EXIST  IN  PLANTS,  AND  DO  NOT  BE- 
LONG   TO    ANY    ESTABLISHED    SERIES. 

Tartaric  Acid  ;  Tartrates  of  Potash, 
Soda,  Iron,  Antimony,  &c.  .         .  692 

Action  of  Heat  on  Tartaric  Acid ; 
Raccmic  Acid      ....  595 

Citric  Acid  ;  Citrates ;  its  Decompo- 
sition by  Heat      .        .        .       '.  597 

Malic,  Maleic,  and  Fumaric  Acids   .  598 

Meconic,  Komenic,  and  Pyromecon- 
ic  Acids 599 

Tannic  Acid ;  Valuation  of  Tannin ; 
Tannates 600 

Gallic  Acid ;  the  Products  of  its  De- 
composition ....  601 

Tannic  Acid  from  Catechu,  Cincho-    , 
na,  and  Kino        ....  603 

Other  Vegetable  Acids     .        .        .604 

CHAPTER  XXV. 

OF  THE  NEUTRAL  ORGANIC  SUBSTANCES, 
AND  OF  THE  PRODUCTS  OF  THEIR  DE- 
COMPOSITION. 

Pectine ;  Salicene ;  Phloridzine ;  As- 
paragine  ;  Caffeine  ;  Piperine  ; 
Cantharadine  ;  Anemonine  ;  Ce- 
trarine ;  Picrotoxine  ;  Columbine  ; 
Cusparine;  Elaterine;  Meconine; 
Peudecanine  ;  iEsculine ;  Popu- 
line  ;  Quassine  ;  Santonine  ;  Sapo- 
nine  ;  Scillitine  ;  Senegine ;  Smi- 
lacine ;  Absinthi'ine  ;  Lactucine  .  605 

Of  Extractive  Matter;  Apotheme  ; 
Extracts 612 


CHAPTER  XXVI. 

OF  THE  COLOURING  MATTERS. 

Of  Madder;  Anchusa  ;  Carthamine; 
Carmine ;  Logvi^ood ;  Persian  Ber- 
ries ;  Anotta  ;  other  Yellow  Bod- 
ies ;  Indigo,  and  the  Substances 
derived  from  it ;  Lichen  Colours ; 
Archil  and  Litmus ;  Colours  of 
Leaves  and  Flowers ;  Theory  of 
Dyeing 613 

CHAPTER  XXVII. 

OP     THE     VEGETABLE     ALKALIES     AND     OF 
THEIR    SALTS. 

Quinine ;  Cinchonine ;  Aricine ;  Mor- 
phia ;  Narcotine  ;  Codeine  ;  The- 
baine ;  Narceine ;  Pseudomor- 
phine  ;  Strychnine  ;  Brucine ;  Del- 
phinine  ;  Veratrine  ;  Sabadilline  ; 
Jervine  ;  Colchicine ;  Einetine ; 
Solanine ;  Chelerythrine  ;  Cheli- 
donine ;  Aconitine ;  Atropine ;  Bel- 
ladonine ;  Daturine ;  Hyoscya- 
raine ;  Coneine ;  Nicotine ;  Men- 
ispermine ;  Cissampeline  ;  Glau- 
cine ;  of  the  Constitution  of  the 
Vegetable  Alkalies       .        .        .  623 

CHAPTER  XXVIII. 

OF  THE   PRODUCTS   OF   THE  DECOMPOSITIOW 
OP    WOOD    AND   THE   ALLIED    BODIES. 

Section  I. 

Of  the  slow  Decomposition  of  Wood. 
Constitution  of  Ulmine.    Of  Turf 

and  Coal 637 

Section  II. 

Of  the  Products  of  the  destructive 
Distillation  of  Wood,  Coal,  and 
Resin 646 

Pyroxylic  Spirit ;  Compounds  of 
Methyl ;  Formic  Acid ;  Coal 
Gas ;  Napthaline ;  Kreosote,  &c,  647 

CHAPTER  XXIX. 

OF    THE    CHEMICAL    PHENOMENA    OF    VEGE- 
TATION. 

Germination,  Assimilation  of  the 
Food  of  Plants  ;  Sources  of  Car- 
bon and  Nitrogen ;  Ashes  of  Plants ; 
Composition  of  Soils  and  Manures ; 
Rotation  of  Crops ;  Action  of  Light 
on  Plants 650 

CHAPTER  XXX. 

OP   ANIMAL  CHEMISTRY. 

Section  I. 

Of  the  Composition  of  the  Animal 
Tissues. 

Of  the  Albuminous  Constituents ; 
Albumen  ;  Fibrine  ;  Proteine  ; 
Gelatine  ;  Chondrine  ;  Fats  of 
the  Brain ;  Ozmazome ;  Zomi- 
dine 663 

Skin,    Epidermis,    Hair,    Horn, 


xn 


CONTENTS. 


Feathers ;  Cellular  and  Serous 
Tissues ;  Tendons ;  Muscular 
Tissue ;  Brain ;  Composition  of 
Bones,    Teeth,    and   Enamel; 

Shells 

Section  II. 

Of  the  Composition  of  the  Blood,  and 
the  Phenomena  of  Respiration. 

Blood  Globules  and  Serum ;  Clot ; 
Hematosine.   Blood  in  Disease ; 
Respiration ;  Modes  of  Action 
of  the  Air ;  Animal  Heat 
Section  III. 

Composition  of  the  Digestive  Or- 
gans,  and  of  their  Secretions; 
Chemical  Phenomena  of  Diges- 
tion. 

Mucus ;  Gastric  Juice ;  Pepsine ; 
Analyses  of  the  Bile;  Bilin; 
Taurine;    Cholic    and    other 


Fage 


670 


673 


Acids;  Bilifulvine;  Chyle  and 
Lymph,  Saliva  and  Pancreatic 

Juice 

Section  IV. 

Constitution  of  the  Urine  in  Health 

and  in  Disease. 
Urea ;  Uric  Acid ;  AUantoine,  Al- 
loxan,  AUoxantine,   and  other 
Products  of  the  Decomposition 
of  Uric  Acid ;  Hippuric  Acid 
Urinary  Deposites  and  Calculi 
Mode  of  recognising  Calculi 
Urine  in  Diabetes  and  other 


679 


Section  V. 

Of  various  Natural  and  Morbid 

Products. 
Milk;   Caseine;  Eggs;  Amnios; 
Tissues  of  the  Eye ;  Earwax ; 
Pus;  Ambergris 


ELEMENTS   OF   CHEMISTRY. 


The  science  of  chemistry  has  its  origin  in  the  principle,  that  the 
bodies  which  constitute  the  external  world  are  composed  of  a  va- 
riety of  elements,  united  according  to  certain  laws.  If  we  could 
conceive  a  universe  consisting  only  of  iron,  or  quicksilver,  or  sul- 
phur, the  objects  of  the  astronomer  might  still  remain  as  extensive 
and  as  sublime  as  they  are  in  the  actual  state  of  things  ;  for,  in 
tracing  the  constitution  of  planetary  and  satellitic  systems,  or  re- 
ducing to  precise  laws  the  forces  by  which  the  motions  of  the 
heavenly  bodies  might  be  produced,  all  the  resources  of  his  science 
would  still  be  brought  into  play.  In  like  manner,  the  physical  sci 
ences  could  attain  perfection,  for  the  relations  of  these  bodies  to 
heat,  to  light,  to  electricity,  the  various  problems  and  laws  of  stat- 
ical and  dynamical  forces,  could  have  been  known,  and  thus  all 
that  is  essential  to  the  science  of  natural  philosophy  might  be 
attained.  But  not  even  an  idea  of  chemistry  could  have  been 
formed.  The  duty  of  chemistry  is  to  find  the  constituent  ele- 
mentary substances,  which,  by  uniting,  form  the  various  compound 
bodies  which  we  observe  ;  to  ascertain  the  nature  of  the  forc-es  by 
which  they  unite,  and  the  laws  by  which  their  union  or  separation 
may  be  regulated ;  to  trace  the  effects  of  their  mutual  action  in 
the  properties  of  the  new  substances  formed  by  their  combination, 
and  in  the  phenomena,  independent  of  composition,  which  accom- 
pany the  exertion  of  chemical  force. 

This  object  of  chemistry  has  been  at  all  periods  fully  recognised ; 
for  the  earliest  philosophers,  even  before  the  science  had  received 
a  name,  considered  its  objects  as  well  defined  in  the  arrangement 
of  the  elements  of  fire,  air,  earth,  and  water.  When  the  methods 
of  chemistry,  and  the  reasonings  to  which  they  led,  acquired  a 
better  form,  these  elements,  which  had  been  assumed  from  specu- 
lations in  natural  history  and  metaphysics,  gave  way  to  others,  as 
sulphur,  spirit,  salt,  oil,  and  earth,  equally  incorrect,  but  still  those 
which,  in  the  rough  trials  of  the  period,  were  obtained  by  decom- 
.  posing  compound  bodies.  As  more  accurate  ideas  and  better  pro- 
cesses were  acquired,  these  elementary  principles  changed  again 
their  character,  until,  finally,  the  philosophical  idea  of  chemistry 
was  clearly  stated  and  established  by  Lavoisier :  1st,  that  we  study 
to  resolve  the  various  compound  bodies  found  in  nature  into  others 
which  resist  our  power,  and  which  we  term  undecompounded  or  sim- 
ple substances^  without  pretending  that  they  are  elements ;  for  the 
advance  of  science  enables  us  to  decompose,  in  each  generation, 
bodies  which  to  our  own  predecessors  had  appeared  simple  ;  2d, 
that  we  study  to  effect  the  recombination  of  those  simple  boJiej^, 


10  ORIGIif     AND     USES     OF     CHEMISTRY. 

either  in  the  same  proportions,  and  thus  regenerate  the  natural 
compound  bodies,  or  in  new  proportions,  and  t'hus  add  to  the  cata- 
logue of  bodies  which  may  exist  in  nature. 

Of  these  two  operations,  the  first,  or  separation  of  a  compound 
body  into  the  simple  substances  which  constitute  it,  is  termed  anal- 
ysis. The  second,  or  combination  of  simple  to  form  a  compound 
substance,  is  called  synthesis.  All  chemical  processes  are  conducted 
upon  the  principle  of  one  or  other  of  these  two,  and  occasionally 
they  are  both,  successively  or  synchronously,  accomplished. 

The  objects  of  chemistry  cannot,  however,  be  considered  as 
limited  to  the  mere  abstract  study  of  the  laws  of  elementary  com- 
position; to  it  also  belongs  the  improvement  of  processes  in  the 
useful  arts  by  the  more  accurate  knowledge  of  their  theory  which 
chemistry  confers,  and  the  invention  of  new  processes  or  of  new 
arts,  by  the  application  or  discovery  of  substances  previously  neg 
lected  or  unknown;  the  alleviation  of  disease,  by  new  remedies 
which  may  be  placed  at  the  command  of  the  physician,  or  by  more 
correct  ideas  of  the  origin  and  results  of  morbid  action,  to  which 
the  attentive  study  of  the  chemical  processes  of  the  great  labora- 
tory of  the  human  frame  may  ultimately  lead,  ranks  also  among 
the  most  important  of  its  applications :  and,  although  an  abstract 
science,  which  reveals  some  of  the  most  beautiful  of  nature's  laws, 
deserves  our  best  attention,  yet  it  becomes  invested  with  more 
general  interest,  and  commands  more  universal  homage,  when,  as 
with  chemistry,  it  appears  to  be  the  basis  of  those  practical  arts  on 
which  so  much  of  health,  of  national  prosperity,  and  of  civilization 
may  depend. 

The  origin  or  derivation  of  the  word  chemistry  is  unknown.  It 
was  first  found  as  xw^^^i  indicating  the  art  of  making  gold  and 
silver  among  the  Egyptians  and  Greeks  of  the  Empire,  at  the  com- 
mencement of  that  extraordinary  perversion  of  the  idea  of  ele- 
mentary constitution  which  fascinated  mankind  for  nearly  five  hun- 
dred years.  From  the  Greeks  it  was  naturally  adopted,  with  the 
rain  pursuit  which  it  denoted,  by  the  Arabians,  and,  passing  with 
the  Arabic  prefix  into  the  languages  of  modern  Europe,  became 
alchemy.  When  the  just  objects  and  powers  of  the  science  were 
finally  recognised,  it  was  termed  chemia  or  chemistry. 

In  studying  those  properties  of  the  difierent  kinds  of  matter  by 
which  they  are  recognised  to  be  distinct  and  independent  chemical 
substances,  it  is  unavoidable  to  include  those  qualities  which,  al- 
though common  to  all  forms  of  matter,  yet  difier  in  degree  among 
the  different  kinds,  and  thus  serve  as  distinguishing  characteristics 
of  them.  The  physical  properties  of  various  bodies  are  hence  in 
common  use  among  chemists,  as  serving  to  perfect  their  description  j 
and,  indeed,  the  limit  between  properly  physical  and  properly  chem- 
ical properties  of  substances  is  not  always  capable  of  being  dis- 
tinctly drawn. 


PECIFIC     GRAVITY     OP     GASES.  11 


CHAPTER  L 

OF    GRAVITY   AND    COHESIVE    FORCES    AS    CHARACTERIZING    CHEMICAL   SUB 

STANCES.  > 

The  physical  forces  which  are  of  most  importance  in  determin- 
ing the  characteristic  properties  of  bodies  are  gravity  and  cohesion. 
These  differ,  however,  remarkably  in  principle  from  each  other, 
and  are  applied  to  quite  independent  purposes.  Gravity  is  com- 
mon to  all  forms  of  matter,  and  is  totally  independent  of  its  nature. 
It  is  exerted  at  all,  even  the  greatest  conceivable  distances,  and  is 
the  invisible  yet  insuperable  tie,  which,  connecting  together  the 
satellites  and  planets  of  our  system  with  the  central  sun,  assigns  to 
each  of  the  tenants  of  our  boundless  skies  its  place  and  motions. 
Acting  thus  only  on  the  mass,  gravity  is  a  measure  of  the  quantity 
of  matter  present  in  a  body  j  and  what  we  term  weight  is  only  the 
gravitating  force  exerted  by  the  substance  which  we  weigh.  By 
no  natural  operation  can  the  smallest  particle  of  matter  be  annihi- 
lated or  destroyed ;  throughout  the  most  complicated  processes  the 
quantity  of  matter  remains  constant,  and  hence  we  are  enabled  to 
verify  the  accuracy  of  our  chemical  operations,  by  proving  the 
weight  of  the  bodies  ultimately  formed  to  be  equal  to  the  weight 
of  the  substances  by  whose  action  they  have  been  produced. 

Under  the  same  volume  different  bodies  have  very  different 
weights,  and  hence  contain  different  quantities  of  matter.  Bodies 
are  said  to  be  more  or  less  dense,  according  as  in  a  given  bulk  they 
contain  a  greater  or  less  quantity  of  gravitating  matter  j  and  when 
a  certain  body  is  taken  as  a  standard,  and  their  density  reduced  to 
numbers,  there  is  obtained  the  specific  gravity  of  each  body,  or  the 
comparative  quantity  of  matter  it  contains  in  a  given  bulk,  which, 
being  almost  always  the  same  for  the  same  body,  is  an  important 
element  in  its  history,  and  may  often  serve  for  its  recognition. 

The  determination  of  specific  gravities  is  easily  performed  where 
the  volume  of  the  substance  can  be  exactly  measured.  Thus,  for 
liquids,  as  water,  oil  of  vitriol,  or  alcohol:  if  a  small  bottle  be 
taken  containing  an  ounce  of  water,  or  480  grains,  it  will  contain 
343  grains  of  sulphuric  ether,  or  885  grains  of  sulphuric  acid.  Now 
the  densities  will  be  as  these  numbers ;  or  water  being  taken  as  the 
standard,  and  its  specific  gravity  being  assumed  as  1000,  the  spe- 
cific gravities  of  the  others  become  proportional  to  it ',  as, 

Water  ...  480  :  1000 
Ether  ...  343  :  715 
Sulphuric  acid     885  :  1845 

To  save  this  little  calculation,  the  bottle  in  use  is  generally  made 
to  hold  1000  grains  of  pure  water,  and  then,  filling  it  with  the  fluid 
to  be  tried,  the  weight  gives  directly  the  specific  gravity. 

Where  the  substance  exists  naturally  in  the  state  of  gas,  a  pre- 
cisely similar  process  may  be  had  recourse  to  ;  in  place  of  a  bottle 


12  SPECIFIC     GRAVITY     OP     GASES. 

with  a  ground  glass  stopper,  there  is  used  a  globe,  g,  with  a  stop 
cock,  capable  of  holding  from  twenty  to  thirty  cubic  inches.  A 
quantity  of  air  having  been  removed 
from  the  globe,  the  gas,  which  must  pre- 
viously be  either  perfectly  dried  or  per- 
fectly saturated  with  moisture,  is  admit- 
ted to  supply  its  place ;  and  as  the  volume 
of  gas  which  passes  in  is  exactly  equal  to 
the  volume  of  air  which  had  been  taken 
out,  the  relative  weights  give  their  den- 
sities, and  hence  the  specific  gravity  of 
the  gas.  For,  suppose  that  the  globe  full 
of  air  weighed  656  grains ;  that,  having 
been  exhausted  of  air,  it  weighed  647*5, 
and  then,  having  received  28  cubic  inches  of  carbonic  acid  gas,  it 
weighed  660*3  grains.  We  thus  know  that  the  28  cubic  inches  of 
air  had  weighed  8*5  grains,  and  that  28  cubic  inches  of  the  gas  had 
weighed  12*8  5  hence  the  densities  are  as  8*5  to  12*8,  and  the  specific 

12-8 
gravity  of  the  gas,  air  being  taken  as  1000,  is  -^;^^  1000= 1*506. 

This  brief  description  being  intended  only  to  explain  the  princi- 
ple which  the  words  "  specific  gravity"  involve,  it  has  been  consid- 
ered as  not  liable  to  alteration  ;  but,  in  reality,  the  volumes  of  bodies, 
particularly  of  gases,  are  constantly  in  a  state  of  change.  Accord- 
ing as  the  air  is  warmer  or  colder  j  according  as  the  pressure  to 
which  it  is  subjected,  as  indicated  by  the  barometer,  diminishes  or 
augments,  the  volume  which  a  certain  weight  occupies  is  altered, 
and  the  specific  gravity  is  changed.  Hence,  when  we  take  air  as  a 
standard  of  specific  gravities  for  gases,  we  do  so  only  with  refer- 
ence to  a  certain  standard  of  temperature  and  pressure,  as  at  32  on 
the  scale  of  Fahrenheit's  thermometer,  and  at  30  inches  of  mercury 
in  the  barometer  tube.  It  is  only  by  accident  that  an  experiment- 
might  happen  to  be  made  at  this  standard  temperature  and  pressure, 
and  hence  it  is  necessary  to  reduce  the  observed  result  to  what  the 
result  should  have  been  at  the  standard  points.  If  the  gas  be  damp, 
it  is  necessary  also  to  correct  for  the  presence  of  the  watery  va- 
pour, and  hence  the  determination  of  the  specific  gravity  of  a  gas, 
although  so  simple  in  theory,  is  in  practice  a  most  delicate  opera- 
tion. Under  the  proper  heads  of  the  constitution  of  gases  and 
vapours,  with  regard  to  heat  and  pressure,  the  mode  of  making 
these  corrections  will  be  described. 

The  determination  of  the  specific  gravity  of  a  solid  body  involves 
in  practice  some  principles  in  addition  to  those  above  stated.  We 
cannot  regulate  the  bulk  of  a  solid  body  as  we  wish,  and  hence  the 
volume  must  be  determined  indirectly.  This  is  done  by  finding  how 
much  water  it  displaces.  Thus,  if  the  solid  be  in  many  small  frag- 
ments, weighing  altogether,  for  example,  357  grains,  they  may  be 
introduced  into  a  specific  gravity  bottle  containing  1000  grains  of 
water.  A  quantity  of  water  overflows  exactly  in  bulk  to  the  solid 
which  is  introduced.  The  bottle  being  full,  the  solid  body  and  the 
remaining  water  are  then  found  to  weigh  1285  grains.  Now,  if  no 
water  had  been  expelled,  the  water  and  solid  body  should  have 


SPECIF  I«C     GRAVITY     OF      SOLIDS.  13 

weighed  1357  grains.  The  difference  72  is  the  weight  of  the  water 
expelled ;  and,  consequently,  the  weights  of  equal  volumes,  or  the 
densities  of  the  water  and  of  the  solid,  are  as  72  and  357  j  or,  the 
specific  gravity  of  the  water  being  taken  as  1000,  that  of  the  solid 

357 
is X  1000,  or  4958.     If  the  solid  be  unsuited  for  that  method,  its 

72  ' 

volume  is  next  determined  by  the  principle  that  a  solid  body  im- 
mersed in  a  fluid  is  partly  supported  by  the  upward  pressure  of  the 
liquid  which  it  displaces.  The  solid,  in  order  to  sink  in  the  liquid, 
has  to  displace  and  push  upward  a  quantity  of  it  equal  to  its  own 
bulk,  and  to  resist  its  weight  or  tendency  to  sink  down  again ;  for 
this  purpose  a  portion  of  the  weight  of  the  solid  must  be  entployed, 
and  it  is  only  the  overplus  that  is  counterpoised  by  the  weights 
when  we  proceed  to  weigh  the  solid  body  immersed  in  any  fluid. 
A  solid  weighs,  therefore,  less  when  immersed  in  a  fluid  than  when 
weighed  in  the  ordinary  manner,  the  difference  being  the  portion 
of  the  weight  of  the  solid  which  is  employed  to  sink  it,  or  to  resist 
the  force  of  the  liquid  which  tends  to  float  it  up,  and  this  is  equal 
to  the  weight  of  the  liquid  which  the  solid  pushes  out  of  its  place, 
and  which  is  of  the  same  volume  as  the  solid.  To  effect  this  op- 
eration, a  balance,  as  in 
the  figure,  is  taken,  gen- 
erally with  one  scale  dish. 
The  solid  is  hung  to  the 
other  extremity  of  the 
beam  by  a  fine  hair  or 
thread  of  cocoon-silk,  ^, 
and  is  thus  weighed  as 
usual ;  let  us  suppose  that 
it  weighed  295  grains. 
A  vessel  of  pure  water  is  then  so  arranged  that  the  solid  shall  be 
immersed  as  nearly  as  possible  in  the  centre  of  it  (as  a  in  figure), 
and  it,  being  then  again  weighed,  is  found  to  be  lighter  than  before  j 
let  us  suppose  that  it  shall  weigh  243  grains.  This  is  the  overplus 
of  its  weight  after  having  neutralized  the  tendency  of  the  water  to 
float  it  up.  The  difference  of  the  two  weighings  295 — 243=52 
grains  is  therefore  the  amount  of  the  upward  pressure,  or  the 
weight  of  the  water  which  the  solid  displaced.  Equal  volumes 
thus  of  the  solid  and  of  the  water  are  found  to  weigh  respectively 
295  and  52  grains,  and  the  comparison  of  these  numbers,  water 
being  taken  as  1000,  gives  the  specific  gravity  of  the  solid,  which 

295 
is -—-x  1000=5673. 

A  variety  of  other  instruments  are  made  use  of  for  measuring 
the  specific  gravities  of  solids  and  of  fluids,  as  areometers,  hydrom- 
eters, &c. ;  but  as  here  it  is  rather  the  general  principles  than  the 
practical  details  of  such  operations  that  are  of  importance,  I  shall 
not  enter  into  their  description. 

The  specific  gravity  of  compound  gases  is  found  to  have  a  highly  important  rela- 
tion to  their  ultimate  constitution,  and  throws  great  light  upon  some  of  the  most 
general  laws  of  chemistry ;  but  as  yet,  notwithstanding  some  interesting  specula 
lions  of  Perzoz  and  of  Boullay  which  I  shall  hereafter  notice,  no  connexion  be 

B 


14 


SPECIFIC      GRAVITY      OF     A^  A  P  O  L"  R  S. 


tvveen  the  chemical  properties  or  composition  of  liquid  or  solid  booies  and  their 
specific  gravities  has  been  discovered.  The  physical  constitution  of  vapours  and 
gases  being,  however,  identical,  those  bodies  which,  being  volatile,  are  capable  of 
assuming  the  form  of  vapour,  may  render,  by  the  examination  of  the  specific  grav- 
ities of  their  vapours,  most  interesting  indications  of  the  manner  in  which  their 
elements  are  combined,  and  methods  of  performing  this  operation  have  been  con- 
trived by  some  of  the  most  illustrious  of  chemists,  as  by  Dumas  and  by  Gay  Lussac. 
The  method  of  (Jay  Lussac  is  the  simpler  of  the  two,  and,  for  substances  which 
are  volatilized  at  moderate  temperatures,  easily  applied.  A  basin,  c,  is 
taken,  which  rests  upon  a  little  furnace,  and  contains  mercury.  In 
this  basin  the  graduated  bell  glass,  a,  is  inverted  full  of  mercury.  Let 
us  suppose  we  wish  to  determine  the  specific  gravity  of  vapour  of  wa- 
ter. One  or  two  little  bulbs  are  taken  and  filled  with  water  as  follows  : 
the  bulb  is  warmed  with  a  lamp,  and  allowed  to  cool  with  the  ijoint 
dipped  into  the  water;  in  this  manner  a  little  water  gets  admission  ; 
this  is  then  boijed  in  the  bulb  until  all  air  has  been  expelled,  and  the 
bulb  is  filled  with  pure  steam ;  the  point  being  then  dipped  under  the 
^  surface  of  the  water,  as  the  steam  condenses,  the  water  rushes  up  to 
^/  supply  its  place,  and  the  whole  becomes  full ;  the  point  being  then 
touched  to  the  flame  of  a  lamp,  it  is  melted,  and  the  orifice  is  closed. 
A  small  quantity,  three  or  four  grains,  of  water  being  tlius  enclosed, 
the  little  bulbs  are  passed  under  the  edge  of  the  jar,  a,  an'.l  rise  to  the 
top,  where  they  float  upon  the  mercury ;  a  glass  cylinder,  b,  open  at 
both  ends,  is  now  placed  round  the  jar,  resting  on  and  secured  to  the 
dish,  c,  and  into  it  is  poured  so  much  colourless  oil  as  shall  completely  cover  the 
jar,  a,  but  allow  of  the  graduation  being  distinctly  seen  ;  the  furnace  is  then  light 
ed,  and  as  the  temperature  of  the  oil  and  mercury  rises,  the  vvater  in  the  little  bulbs 
forms  steam,  which  at  last  bursts  the  bulbs,  and  the  level  of  the  quicksilver  in  the 
jar  immediately  falls,  the  steam  occupying  tlie  space  above  it.  When  the  mercury 
ceases  to  descend,  it  is  known  that  all  liquid  has  been  converted  into  vapour;  the 
temperature  of  the  oil,  which  is  necessardy  the  same  as  that  of  the  vapour  inside, 
is  ascertained,  and  by  the  graduation  on  the  jar  the  volume  occupied  by  the  vapour 
is  accurately  read  off;  the  weight  of  the  vapour  is  knovim,  for  it  is  the  weight  of 
the  vvater  in  the  bulbs,  and  its  volume  at  this  high  temperature  is  thus  found. 
Knowing  thus  the  volume  of  a  few  grains  of  steam  at  250",  the  volume  at  33°  may- 
be calculated  ;  and  as  the  volume  of  so  many  grains  of  air  at  32°  is  already  known, 
the  specific  gravity  of  the  vapour  of  water  is  obtained.  The  temperature  of  the 
oil  must  be  at  least  thirty  or  forty  degrees  above  the  boiling  point  of  the  liquid,  and 
hence  it  is  likely  to  become  coloured,  to  fume,  or  even  to  risk  taking  fire,  unless 
great  caution  is  emj3loyed. 

The  method  invented  by  Dumas  has  the  advantage  of  being  applicable  to  all  tern 
peratures  below  the  melting  point  of  glass,  and  it  is  consequently  by  its  application 
that  the  greatest  benefit  has  been  conferred  on  science.  It  is,  however,  more  com- 
plex in  principle,  though  not  less  dehcate  in  practice.  A  globe  holding  from  ten  to  fif- 
teen cubic  inches,  and  drawn  out  at  its  beak  to  a  capillary  orifice,  is  carefully  weigh- 
ed, containing,  as  usual,  atmospheric  air.  It  is  then  v/armed,  and  its  beak  being 
dipped  into  the  fluid  to  be  tried,  it  is  allowed  to  cool,  until  by  the  contraction  of  the 

air  a  sufficient  quantity  of  the 
fluid  has  made  its  way  in.     The 
globe  is  then  fitted  in  a  sort  of 
cage,  by  which  it  is  securely  held 
in  the  centre  of  the  liquid  bath, 
by  which  the  heat  is  to  be  appli- 
ed, and  which  may  be  water  oi 
oil,  a  solution  of  chloride  of  zinc, 
^.?s=^or,  best  of  all,  the  fusible  alloy 
^^^55^:=**^'^       of  bismuth,  tin,  and  lead.     The 
^^f''''^  capillary  beak  of  the  tube  just 

(T  projects  over  the  surface  of  the 

^  bath,  as  in  the  figure.    When  the 

. — I  Jv.^  globe  becomes  sufliciently  heat- 

/    Y  —         f    ^\  ed,  the  liquid  boils,  and  its  va- 

/      \       (         /-    \         ])      \       y  P^*^*"'  ^'^  passing  away,  carries  oflF 

I  1 — J '    O  ^ L_      ^^-^ — ^  the  air  which  had  previously  fill- 


DIVISIBILITY     OF     MATTER.  15 

ed  the  globe.  The  liquid  should  be  present  in  such  quantity  that  its  vapour,  after 
carrying  off  all  air,  should  occupy  the  interior  of  the  globe  completely  pure.  The 
excess  of  vapour  is  known  to  have  passed  away  when  there  is  no  longer  a  jet  pro- 
ceeding from  the  capillary  beak,  and  then  by  means  of  a  blowpipe  the  orifice  is 
closed,  and  the  temperature  of  the  bath  being  taken  at  the  same  moment,  the  globe 
is  removed  from  the  bath,  perfectly  cleaned  and  weighed.  The  liquid  condensing, 
as  soon  as  the  globe  grows  cold,  leaves  its  interior  practically  empty,  and,  on  break- 
ing off  the  capillary  beak  under  the  surface  of  quicksilver,  this  last  enters  into  the 
vessel,  and,  if  the  operation  had  been  well  managed,  fills  it  completely.  The  globe, 
full  of  quicksilver,  is  then  emptied  into  a  graduated  jar,  by  which  the  quEintity  of 
the  quicksilver  being  measured,  the  volume  of  the  globe  is  known ;  when  this  has 
been  done,  all  requisites  for  calculating  the  specific  gravity  of  the  vapour  have  been 
obtained.  For,  knowing  the  volume  of  the  globe,  the  weight  of  the  air  it  contained 
is  known,  and,  subtracting  that  from  the  first  weighing  of  the  globe,  the  weight  of 
the  globe  when  empty  is  obtained.  Subtracting  this  from  the  second  weighing  of 
the  globe,  the  weight  of  the  vapour  is  obtained  ;  and  as  the  air  and  vapour  occupied 
the  same  volume,  the  densities  should  be  as  these  weights,  if  they  had  been  at  the 
same  temperature ;  but,  as  this  was  not  the  case,  a  farther  calculation  is  required 
to  reduce  them  to  the  standard,  and  obtain  the  numerical  specific  gravities. 

No  process  has  been  more  fruitful  in  important  results  than  this  mode  of  detei- 
mining  the  specific  gravity  of  vapours,  for  it  is  only  in  this  way  that  such  substances 
as  sulphur,  arsenic,  phosphorus,  and  mercury,  as  well  as  numerous  compound  bodiea 
with  high  boiling  points,  could  have  been  tried. 

The  force  of  gravity  is  thus  of  importance  in  chemistry,  by  giv- 
ing a  measure  of  the  quantity  of  matter  upon  which  we  experiment, 
and  by  affording  characteristics  of  individual  substances,  by  the 
comparison  of  the  quantity  of  matter  they  possess  in  a  standard 
vokime.  The  force  of  cohesion,  although  not  so  universally  exist- 
ant  as  that  of  gravity,  is  of  equal  interest,  from  the  numerous  pecu- 
liarities in  its  activity  which  almost  everybody  is  capable  of  pre- 
senting, and  by  which  bodies  are  remarkably  distinguished  from 
each  other.  To  understand,  however,  the  nature  of  cohesive  forces, 
and  the  causes  of  the  variation  of  their  energy,  it  is  necessary  to 
notice  those  ideas  of  the  peculiar  constitution  of  matter  on  which 
philosophers  have  generally  agreed,  and  which  result  from,  while 
they  best  serve  to  explain,  those  remarkable  phenomena. 

From  the  earliest  period  in  science,  discussions  have  arisen  as  to 
whether  the  masses  of  matter  which  we  ordinarily  employ  should 
be  considered  capable  of  infinite  division,  or  whether,  by  continuing 
to  divide,  a  term  should  ultimately  be  found  at  which  no  farther  sub- 
division could  be  made  j  that  thus  the  ultimate  constituent  and  indi- 
visible particles,  or  atoms,  which,  by  their  aggregation,  form  sensible 
masses,  should  be  discovered.  By  no  appeal  to  experiment  can  this 
question  be  resolved ;  when  we  call  in  the  assistance  of  our  most 
powerful  means  of  mechanical  division,  we  attain  only  to  producing 
powders,  of  which  the  finest  particle  is,  in  miniature,  all  that  the 
mass  from  which  it  had  been  formed  was  upon  a  larger  scale,  and 
capable  evidently  of  just  as  much  subdivision,  if  our  mechanical 
processes  were  perfect  enough  to  enable  us  to  proceed. 

That  this  divisibility  may  actually  occur  to  an  almost  incredible 
degree,  may  be  easily  demonstrated  by  experiment.  In  gilding  sil- 
ver wire,  a  grain  of  gold  is  spread  over  a  surface  of  1400  square 
inches ;  and  as,  when  examined  in  a  microscope,  the  gold  upon  the 
thousandth  of  a  linear  inch,  or  one  millionth  of  a  square  inch,  is 
distinctly  visible,  it  is  proved  that  gold  may  be  divided  into  particles 
of  at  least  ^-^^.J-- __-  of  a  square  inch  in  size,  and  yet  possess 


16  DIVISIBILITY     OF     MATTER. 

the  colour  and  all  otKer  characters  of  the  largest  mass.  If  a  graiB 
of  copper  be  dissolved  in  nitric  acid,  and  then  in  water  of  ammonia, 
it  will  give  a  decided  violet  colour  to  392  cubic  inches  of  water. 
Even  supposing  that  each  portion  of  the  liquor  of  the  size  of  a  grain 
of  sand,  and  of  which  there  are  a  million  in  a  cubic  inch,  contains 
only  one  particle  of  copper,  the  grain  must  have  divided  itself  into 
392  million  parts.  A  single  drop  of  a  strong  solution  of  indigo, 
wherein  at  least  500-000  distinctly  visible  portions  can  be  shown, 
colours  1000  cubic  inches  of  water  ;  and  as  this  mass  of  water  con- 
tains certainly  500*000  times  the  bulk  of  the  drop  of  indigo  solution, 
the  particles  of  the  indigo  must  be  smaller  than  jjuTTooiiooTrffoo  ^^'' 
twenty-five  hundred  millionth  of  a  cubic  inch.  A  rather  more  dig 
tinct  experiment  is  the  following :  if  we  dissolve  a  fragment  of  sil- 
ver, of  O'Ol  of  a  cubic  line  in  size,  in  nitric  acid,  it  will  render  dis- 
tinctly milky  500  cubic  inches  of  a  clear  solution  of  common  salt. 
Hence  the  magnitude  of  each  particle  of  silver  cannot  exceed,  but 
must  rather  fall  far  short  of,  a  billionth  of  a  cubic  line.  To  render 
the  idea  of  this  degree  of  division  more  distinct  than  the  mere  men- 
tion of  so  imperfectly  conceivable  a  number  as  a  billion  could  effect, 
it  may  be  added,  that  a  man,  to  reckon  with  a  watch,  counting  day 
and  night,  a  single  billion  of  seconds,  would  require  31*675  years. 

In  the  organized  kingdoms  of  nature  even  this  excessive  tenuity 
of  matter  is  far  surpassed.  An  Irish  girl  has  spun  linen  yarn  of 
which  a  pound  was  1432  English  miles  in  length,  and  of  which,  con- 
sequently, 17  lbs.  13  oz.  would  have  girt  the  globe  5  a  distinctly  visible 
portion  of  such  thread  could  not  have  weighed  more  than  tc;t  o  K  o  o  o 
of  a  grain.  Cotton  has  been  spun  so  that  a  pound  of  thread  was 
203*000  yards  in  length,  and  wool  168-000  yards.  And  yet  these, 
so  far  from  being  ultimate  particles  of  matter,  must  have  contained 
more  than  one  vegetable  or  animal  fibre  j  that  fibre  being  itself  of 
complex  organization,  and  built  up  of  an  indefinitely  great  number 
of  more  simple  forms  of  matter. 

The  microscope  has,  however,  revealed  to  us  still  greater  wonders 
as  to  the  degree  of  minuteness  which  even  complex  bodies  are  ca- 
pable of  possessing.  Each  new  improvement  in  our  instruments 
displays  to  us  new  races  of  animals,  too  minute  to  be  observed  be- 
fore,  and  of  which  it  would  require  the  heaping  together  of  millions 
upon  millions  to  be  visible  to  the  naked  eye.  And  yet  these  ani- 
mals live  and  feed,  and  have  their  organs  for  locomotion  and  prehen- 
sion, their  appetites  to  gratify,  their  dangers  to  avoid.  They  possess 
circulating  systems  often  highly  complex,  and  blood,  with  globules 
bearing  to  them,  by  analogy,  the  same  proportion  in  size  that  our 
blood  globules  do  to  us ;  and  yet  these  globules,  themselves  organ- 
ized, possessed  of  definite  structure,  lead  us  merely  to  a  point  where 
all  power  of  distinct  conception  ceases ;  where  we  discover  that 
nothing  is  great  or  small  but  by  comparison,  and  that  presented  by 
Nature  on  the  one  hand  with  magnitudes  infinitely  great,  and  on  the 
other  with  as  inconceivable  minuteness,  it  only  remains  to  bow  down 
before  the  omnipotence  of  Nature's  Lord,  and  own  our  inability  to 
understand  Him. 

These  proofs  of  great  divisibility,  however,  leave  the  question  of 
infinite  divisibility  quite  untouched.     There  are,  however,  many  and 


MOLECULAR     CONSTITUTION.  17 

powerful  reasons' which  have  decided  almost  all  modern  philosophers 
to  consider  the  possible  division  as  being  finite.  On  the  other  view 
the  mind  has  no  resting-place,  until,  by  the  total  disappearance  ot 
material  conceptions,  the  constitution  of  bodies  resolves  itself  into 
a  collection  of  mathematical  points,  from  which,  as  centres,-  certain 
forces  are  exerted ;  but  with  such  abstract  speculation  chemistry- 
has  no  connexion.  Its  fundamental  condition,  that  there  exist  many- 
kinds  of  elementary  matter,  of  which  the  quantity  is  measured  by 
their  weight,  is  totally  independent  of  our  abstract  idea  of  what  mat 
ter  is,  or  how  its  properties  have  their  source. 

In  proof  of  the  division  of  matter  having  a  limit,  experiments 
made  principally  by  Faraday  and  Wollaston  have  been  quoted.  Thus, 
it  is  ascertained  that  our  atmosphere  does  not  extend  into  spaced 
but  is  confined  within  comparatively  a  trifling  distance  from  the 
earth,  about  45  miles.  Wollaston,  considering  the  particles  of  air 
as  being  balanced  between  their  mutual  repulsion  and  the  general  at- 
traction towards  the  earth,  suggested  that,  if  these  particles  could  be 
divided  to  an  infinite  degree,  there  should  be  an  infinite  source  of 
repulsive  power,  and  hence,  at  a  certain  distance,  this  repulsion  over- 
coming the  gravitating  force,  the  atmosphere  should  spread  into 
space,  and,  being  attracted  to  the  other  planets  in  proportion  to  their 
masses,  should  form  round  the  larger,  as  Jupiter,  and  especially  the 
Sun,  vast  and  dense  atmospheres,  the  existence  of  which  should 
easily  be  recognised.  No  such  atmospheres  exist,  and  hence,  as 
was  argued  by  Wollaston,  the  force  of  repulsion  must  have  a  finite 
limit,  and  the  number  of  repelling  particles  cannot  be  infinite.  In 
like  manner,  Faraday  found  that  bodies,  in  evaporating,  form  atmo- 
spheres of  certain  definite  depths  above  the  surface  of  the  body,  and 
drew  from  hence  the  same  conclusion.  This  argument  cannot,  how- 
ever, be  considered  as  decisive.  It  is  not  at  all  certain  that,  because 
the  elasticity  of  air  is  thus  found  to  have  a  limit,  the  number  of 
particles  of  air,  in  a  given  space,  might  not  be  infinite. 

I  shall  consider  the  masses  of  matter,  whose  properties  we  pur- 
pose to  examine,  as  being  made  up  of  a  great  number  of  lesser  masses, 
to  which  the  name  of  molecules  or  particles  may  be  assigned.  It 
is  totally  indifferent  whether  these  molecules  may  be  infinitely  di- 
visible or  not ;  there  is  no  fact  in  either  chemistry  or  physics  which 
requires  the  positive  adoption  of  either  one  side  or  the  other.  These 
molecules  are  subjected  to  the  influence  of  two  forces,  which  oppose 
each  other,  and  by  the  relative  balancing  or  preponderance  of  which, 
all  the  forms  and  physical  properties  of  ordinary  substances  are  pro- 
duced. One  of  these  forces  is  attractive  ;  it  is  the  attraction  of  ag- 
gregation, as  it  has  been  termed,  or  cohesion.  If  it  acted  unimpeded, 
the  molecules  of  every  portion  of  matter  would  cohere  with  insuper- 
able power ;  unconquerable  solidity,  hardness,  and  tenacity  would 
alone  characterize  external  nature.  The  other  force  is  one  of  repul- 
sion, which,  from  a  variety  of  evidence,  is  assumed  as  identical  with 
the  cause  of  heat.  If  it  alone  prevailed,  no  other  form  of  matter 
could  exist  but  that  of  gas ;  the  solid  globe,  the  liquid  waters,  would 
change  to  atmospheres  of  vapours,  and  the  beneficent  uses  to  which 
our  earth  is  now  adapted  could  not  exist. 

Such  is,  perhaps,  approximatively  what  occurs  in  those  extreme 


18  STATES     OF     AGGREGATION. 

members  of  our  planetary  system,  Herschel  and  Mercury.  The  for- 
mer receiving  from  the  Sun  but  j ^^  P^^*  ^^  the  heat  which  our  earth 
derives,  must  be  reduced  to  the  temperature  of  empty  space  ;  and, 
with  few  exceptions,  the  bodies  which  on  this  earth  are  gaseous  or 
liquid,  if  they  exist,  are  there  as  rocky  masses.  The  latter  must  at 
certain  periods  be  so  hot,  that  quicksilver  would  naturally  be  a  gas 
upon  its  surface,  and  those  metals  which  here  constitute  our  examples 
of  solidity,  should  there  form  liquid  oceans.  On  this  earth,  however, 
according  as  the  forces  of  heat  and  cohesion  vary  in  different  bodies, 
they  pass  through  different  states  of  aggregation.  Those  bodies  in 
which  cohesion  prevails  are  solid,  and  by  their  tenacity  and  resist- 
ance to  breakage  or  change  of  form,  display  the  force  which  binds 
their  molecules  together.  Where  cohesion  has  been  suppressed,  and 
the  repulsive  agency  of  heat  acts  uncontrolled,  the  body  become? 
gaseous,  and  its  particles,  devoid  of  the  least  trace  of  cohesive  power, 
repel  each  other.  In  intermediate  cases,  where  the  two  forces  ap- 
pear balanced,  the  particles  do  not  cohere,  and  hence  may  move 
upon  and  separate  from  each  other  without  any  external  force  ;  but 
they  do  not  repel,  and  thus  remain  in  contact  if  no  external  force 
tends  to  disturb  them.  This  is  the  liquid  condition ;  it  is  that  of 
water,  of  alcohol,  of  oil,  while  air  and  steam  are  gaseous,  and  iron, 
wood,  and  stone  are  instances  of  the  solid  form. 

The  peculiar  nature  of  each  body  determines  whether,  under  com- 
mon circumstances,  it  shall  have  one  or  the  other  of  these  forms ; 
but  there  are  few  bodies  which  are  not  capable  of  assuming  all  the 
three.  This  is  artificially  effected  by  diminishing  or  increasing  the 
degree  of  heat,  and  thus  by  cooling  a  liquid,  it  may,  by  the  cohesion 
becoming  greater,  be  converted  into  a  solid  j  or  by  increasing  the 
heat  to  which  a  solid  is  subjected,  it  may  be  converted  into  a  li- 
quid, and  from  thence  into  a  gas.  One  liquid,  pure  alcohol,  has  not 
yet  been  frozen  ;  some  solids,  as  charcoal,  have  not  yet  been  melted  : 
organized  bodies  are  generally  decomposed  too  easily  to  allow  of 
a  change  of  state ;  but,  with  these  exceptions,  the  principle  of  the 
change  of  form,  artificially  caused  by  the  increase  or  diminution  of 
the  quantity  of  heat,  is  universal.  These  forms  of  matter,  consid- 
ered as  effects  of  heat,  will  require  and  obtain  hereafter  a  more 
extended  notice. 

This  force  of  molecular  cohesion  acts  only  at  distances  so  minute 
as  to  escape  the  most  delicate  examination.  The  fragments  of  a 
piece  of  glass  or  metal  which  has  been  just  broken,  when  laid  ever 
so  closely  together,  have  no  tendency  to  unite  again  ;  but,  if  the 
surfaces  be  pressed  together,  union  may  take  place,  though  only 
in  a  few  points,  and  imperfectly.  Yet,  when  pieces  of  plate  glass, 
laid  flat  on  each  other,  and  subjected  to  considerable  pressure,  are 
allowed  so  to  remain  for  a  certain  time,  they  are  found  to  grow  to- 
gether so  completely,  that  thick  masses  may  often  be  ground  as  if 
they  had  always  formed  a  single  piece.  If  two  surfaces  of  lead  be 
cut  quite  clean  and  bright,  and  forcibly  pressed  together,  they  unite 
also,  and  may  require  a  force  of  eighty  or  one  hundred  pounds  to 
effect  their  separation.  In  fluids,  although  the  force  of  cohesion 
is  very  nearly  absent,  yet  it  is  not  entirely  so  ;  the  viscidity  of 
fluids  depending  upon  the  traces  of  it  which  remain.  The  globular 
form  of  a  rain  dtop,  or  of  a  drop  of  any  fluid  allowed  to  fall  from 


COHESION.- 


APILLARITY. 


19 


ti  point)  arises  also  from  the  cohesive  attraction  of  its  particles,  and 
different  fluids  difl^er  remarkably  in  their  relations  to  heat,  from  the 
various  degrees  of  force  with  which  this  residue  of  cohesion  is  ex- 
erted. The  particles  of  a  fluid  cohere  not  only  to  each  other,  but 
even  more  powerfully  to  solid  bodies  in  many  cases.  It  is  thus 
that  solid  bodies  are  wetted  by  fluids.  If  the  finger  be  dipped  into 
water,  the  particles  of  the  water  in  contact  with  the  finger  adhere 
to  it  more  powerfully  than  they  do  to  the  other  particles  of  the 
fluid,  and  when  the  finger  is  removed,  they  accompany  it,  and  thus 
it  becomes  wet.  Mercury  does  not  wet  the  finger,  for  its  particles 
cohere  too  powerfully  to  each  other ;  but  mercury  adheres  to,  or 
wets  a  piece  of  gold,  as  water  wets  the  finger.  From  this  cohe- 
sion of  fluids  to  solids,  all  the  phenomena  of  capillary  attraction 
result,  as  the  filtering  of  liquids  in  pharmacy  and  chemistry,  to  sep- 
arate solids  which  had  been  mixed  with  them ;  the  absorption  of 
liquids  by  porous  solid  bodies,  and  many  others. 

The  existence  of  this  form  of  cohesion  may  be  very  simply  shown 
by  an  experiment,  such 

as  is  illustrated  in  the       ^  -JliL^^     .T/    ,.^-^.Ji^  ^^ 

figure.  A  disk  of  any 
substance  which  may 
be  wetted  by  water  is 
to  be  hung  evenly  from 
the  extremity  of  the 
beam  of  the  balance, 
and  brought  exactly 
into  contact  with  the 
water  in  the  cup  be- 
low. It  will  be  found  necessary  to  augment  considerably  the  weights 
in  the  scale  dish  opposite,  to  separate  them  j  and,  when  the  disk  has 
been  torn  away  from  the  surface  of  the  water,  the  force  overcome 
will  be  found  to  have  been,  not  that  of  the  solid  to  the  liquid,  which 
was  still  more  intense,  but  the  cohesion  of  the  liquid  particles  to  each 
others  for  the  solid  is  found  to  be  wetted  by  a  layer  of  liquid  par- 
ticles which  it  had  torn  from  the  general  mass  of  liquid  underneath. 
If  the  experiment  be  tried  with  a  disk  of  polished  iron,  and  mercury 
as  the  fluid,  there  is  no  wetting,  and  the  force  measured  is  really 
the  cohesion  of  the  solid  to  the  fluid. 

[Clairaut  found,  as  the  result  of  his  mathematical  investigations, 
that  all  the  phenomena  of  capillary  tubes  depend  upon  the  relation 
of  two  forces :  1st,  The  cohesion  of  the  particles  of  the  fluid  for 
each  other  ;  and,  2d,  The  attraction  of  the  particles  of  the  solid  for 
those  of  the  fluid.  When  a  glass  tube  is  dipped  into  different 
liquids:  if  the  force  of  attraction  of  the  glass  is  less  than  half  the 
force  of  cohesion  of  the  fluid,  the  fluid  will  be 
depressed,  and  not  rise  to  its  hydrostatic  level ;  ^  ^ 
if  it  be  equal  to  half,  the  fluid  will  come  pre- 
cisely to  its  level ;  and  if  it  be  more  than  half, 
the  fluid  will  rise  in  the  tube.  a 

Connected  with  these  conditions  is  the  figure 
of  the  boundary  surface  of  the  fluid.     If  three 
glass  tubes,  be,  de,  fg,  be  placed  in  fluids  which  ^ 
respectively  are  depressed,  at  the  true  level,  or  at 


20  COMPRESSIBILITY. 

an  elevation,  it  will  be  seen  that  in  h  c  the  surface  a  a  of  the  fluid 
is  convex,  in  c/  e  it  is  plane,  and  in  fg  it  is  concave.] 

The  particles  of  a  body  being  held  at  certain  distances  from  each 
other  by  the  balance  of  their  attraction  and  repulsion  :  if,  by  the  ap- 
plication of  an  external  force,  as  pressure,  they  be  brought  nearer, 
so  as  to  occupy  a  smaller  volume,  the  body  is  said  to  be  compress- 
ible. If,  when  the  external  force  is  removed,  the  body,  by  the  mutual 
repulsion  of  its  particles,  regain  its  original  volume,  it  is  said  to  be 
elastic ;  if,  on  the  contrary,  it  remains  as  when  compressed,  it  is 
called  inelastic.  In  nature  there  are  few  bodies  perfectly  elastic,  and 
none  which  can  be  said  to  be  perfectly  inelastic.  In  solid  bodies, 
when  pressure  produces  a  change  of  volume,  some  traces  of  it  are 
permanent ;  but  in  liquids  and  in  gases,  the  restoration  to  the  origi- 
nal bulk  appears  to  be  complete. 

The  amount  to  which  solid  and  liquid  bodies  may  be  compressed 
is  Very  small,  so  much  so  that  very  delicate  methods  are  necessary 
to  determine  it.  Thus  it  requires  a  pressure  of  about  400  lbs.  upon 
each  square  inch  of  the  surface  of  water  to  diminish  its  volume  by 
the  joVo  part.  In  gases,  however,  the  repulsive  force  acting  without 
interference,  and  the  particles  being  at  much  greater  distances  from 
one  another  than  in  the  liquid  or  solid  form,  the  amount  of  com- 
pressibility becomes  very  much  increased,  and  the  law  by  which  it 
is  regulated  extremely  simple,  being,  that  the  volume  of  any  gas 
varies  inversely  as  the  pressure  upon  it ;  that  it  is  doubled  if  the 
pressure  be  diminished  to  one  half,  and  reduced  to  one  half  if  the 
pressure  upon  its  surface  be  doubled.  Thus,  supposing  a  gas  to 
measure  100  volumes  under  the  pressure  of  20  lbs., 

Then  with  pressures  of  80    .    40     .     20     .     10     .       5  lbs. 
The  volume  becomes     25    .    50     .  100     .  200     .  400. 

The  gases  which  are  used  in  chemical  operations  are  liable  to 
constant  changes  of  volume,  from  the  alterations  in  the  weight  of 
the  surrounding  atmosphere,  by  which  they  are  always  pressed ;  and 
hence,  before  we  can  tell  how  much  of  a  gas  we  really  have  obtained 
by  any  process,  it  is  necessary  to  ascertain  the  amount  of  atmo- 
spheric pressure,  and  to  allow  for  it.  The  pressure  which  the  air 
exercises  is  measured  by  the  barometer,  in  which  a  column  of  quick- 
silver balances  the  pressure  of  the  air,  and  varies  in  height  according 
as  this  changes ;  the  height  of  this  mercurial  column  being  accurately 
measured  by  a  scale  applied  to  the  tube  of  the  barometer.  In  these 
countries,  the  height  of  the  barometric  column  fluctuates  between 
28  and  31  inches,  but  the  average  height  of  a  year  is  about  29-8 
inches.  For  simplicity,  a  number  very  near  this,  30  inches,  is  taken 
as  the  standard  pressure  ;  and  whenever  the  specific  gravity,  or  the 
volume  of  a  gas  is  given,  without  particular  remark,  this  standard 
height  of  the  barometer  is  understood  to  be  the  pressure. 

If,  therefore,  we  have  a  gas  at  a  different  pressure,  it  is  usual,  and  often  neces- 
sary, to  reduce  its  volume  to  what  it  should  have  been  under  the  standard  pressure, 
or,  as  it  is  generally  termed,  to  correct  for  pressure  :  to  do  this,  we  use  the  rule 
given  above  for  the  change  of  volume  with  the  pressure.  Thus,  if,  in  an  analysis 
of  morphia,  we  obtain  454  cubic  inches  of  nitrogen  gas  when  the  barometer  is  at 
285  inches,  we  say  that,  expressing  the  volume  at  30  inches  by  V, 

V  •  28-5  :  :  4-54  :  30,  or  V=— x4-54=4-313. 


LIQUEFACTION     OF     GASES. 


21 


Knowing,  then,  the  weight  of  100  cubic  inches  of  nitrogen  gas  at  30  inches,  the 
weight  of  4-313  is  easily  obtained. 

In  this  manner,  the  corrections  for  pressure,  alluded  to  in  the  description  of  the 
modes  of  taking  the  specific  gravities  of  gases  and  of  vapours,  are  introduced. 
Thus,  in  taking  the  specific  gravity  of  steam  by  Gay  Lussac's  process  (page  14), 
the  vapour  occupying  but  a  portion  of  the  tube,  there  remains  a  column  of  mercury, 
suppose  5  inches  high  :  the  pressure  on  the  vapour  is  therefore  only  the  diflference 
between  that  and  the  external  pressure,  and  if  this  be  30  inches,  is  (30 — 5)=25. 
Then  the  measured  volume  of  the  steam  is  to  what  it  should  be  at  the  standard 
pressure,  as  30  to  25. 

In  certain  cases,  of  which  atmospheric  air  may  be  taken  as  an 
example,  this  rule,  of  the  volume  being  inversely  as  the  pressure, 
holds  exactly  ;  but  there  are  many  other  gases,  in  which,  when  the 
compression  is  very  great,  the  particles  appear  to  be  brought  within 
the  sphere  of  their  respective  cohesive  forces,  and  the  volume  di- 
minishes more  rapidly  than  it  ought  by  the  rule.  Thus,  if  a  tube 
full  of  air  and  a  tube  full  of  sulphurous  acid  gas  be  exposed  to  ex- 
actly the  same  pressure,  the  volumes  will  not  diminish  in  the  same 
degree  when  the  pressure  becomes  high,  but  as  follows : 

The  air  as  .     .     .     1000      .      853      .      559      .      314. 
Sulphurous  acid  as   1000      .      851      .      554      .      301 

In  some  other  gases  the  same  variation  has  been  observed. 

If  such  a  gas  be  still  more  violently  compressed,  its  particles  may 
be  brought  so  completely  within  the  sphere  of  cohesive  action,  that 
this  force  comes  into  active  play,  and  the  body  changes  from  the 
gaseous  to  the  liquid  form.  Thus  many  gases  have  been  liquefied 
by  a  degree  of  pressure  which  differs  for  each  gas,  and  is  at  3?° 
Fahrenheit  as  follows: 


Name  of  gas. 


Nitrous  Oxide  .  .  . 
Carbonic  Acid  .  .  . 
Muriatic  Acid  .  .  . 
Sulphuretted  Hydrogen 

Ammonia 

Cyanogen  

Sulphurous  Acid  .     .     . 


Pounds  to 

the  Inch. 

44 

660 

36 

540 

24 

360 

15 

225 

5 

75 

3 

45 

2 

30 

Other  gases,  such  as  oxygen,  hydrogen,  and  nitrogen,  have  been 
subjected  to  a  pressure  of  800  atmospheres,  not  only  without  becom- 
ing liquid,  but  without  even  deviating  from  the  rule  which  implies 
perfect  elasticity,  and  hence  without  even  approximating  to  the 
term  at  which  they  should  abandon  the  gaseous  state.  Notwith- 
standing this,  we  cannot  •consider  that  there  is  any  physical  differ- 
ence of  constitution  between  those  liquefiable  and  non-liquefiable 
gases,  and  hence  the  conclusion  is,  that,  by  a  suitable  increase  of 
pressure,  the  molecules  of  all  gases  might  be  so  brought  into  cohe- 
rent approximation,  and  converted  into  liquids. 

"With  regard  to  the  means  of  applying  such  pressure,  and  actually 
obtaining  those  gases  in  the  liquid  form,  it  is  necessary  to  consider 
the  manner  in  which  such  gases  are  generated,  and  such  methods 
will  consequently  be  described  in  the  history  of  those  bodies. 

Cohesion  is  thus  antagonistic  to  the  force  of  heat,  which  tends  to 
render  the  molecules  of  a  body  repulsive  to  each  other,  and  to  sep- 
arate them  to  greater  distances  from  each  other  than  they  had  been 


22 


PHENOMENA     OF     SOLUTION. 


before.     Cohesion  is  therefore  diminished,  and  even  annulled,  by 
applying  heat. 

When  the  cohesion  between  the  particles  of  a  solid  and  those  of 
a  fluid  is  more  powerful  than  between  the  particles  of  the  solid  it- 
self, the  latter  is  not  merely  moistened  by  the  fluid,  but  it  abandons 
altogether  the  solid  form,  and,  becoming  liquid,  mixes  uniformly  with 
the  fluid,  and  is  said  to  have  been  dissolved  by  it.  By  this  peculi- 
arity of  cohesion,  bodies  are  divided  into  the  soluble  and  the  insoluble. 
Thus  common  salt  and  Glauber's  salt  are  soluble,  while  chalk  and 
white  lead  are  insoluble,  in  water.  These  classes  are,  however,  con- 
nected by  a  series  of  intermediate  degrees  of  sparingly  soluble 
bodies,  such  as  cream  of  tartar  and  plaster  of  Paris.  Bodies  which 
are  insoluble  in  water  may  be  yet  easily  dissolved  by  other  fluids ; 
thus,  resinous  bodies,  which  do  not  dissolve  in  water,  dissolve  in  al- 
cohol. A  great  deal  of  the  success  of  vegetable  proximate  analysis 
depends  on  the  skill  with  which  the  solvent  powers  of  various  fluids 
may  be  successively  applied. 

From  the  tendency  of  heat  to  diminish  the  force  of  cohesion,  it  naturally  results 
that  the  solubility  of  most  bodies  is  increased  by  heat ;  thus,  100  parts  of  water,  at 
60°  F.,  dissolve  11  of  sulphate  of  potash,  and  at  212  dissolve  25.  At  60°,  32  parts 
of  dry  sulphate  of  magnesia  are  dissolved  by  100  of  water,  bvlt  74  at  212°.  This, 
however,  i^  not  always  the  case ;  some  bodies,  as  common  salt,  are  exactly  equally 
soluble  in  water  at  all  temperatures,  while  in  other  cases  the  solubility  is  greater  at 
particular  temperatures  than  either  above  or  below  them.  Of  this  peculiarity,  the 
sulphate  and  nitrate  of  soda  are  examples.  Thus,  100  parts  of  water  dissolve  of 
dry  sulphate  of  soda,  at  32°,  502 ;  at  52^,  1022  ;  at  76o,  28 ;  at  93°,  53;  at  122°, 
47 ;  and  at  212^,  42 :  the  solubility  increasing  up  to  93°,  and  from  thence  dimin- 
ishing. 100  parts  of  water  dissolve  of  nitrate  of  soda,  at  21°,  63  ;  at  32°,  80  ;  at 
50°,  23  ;  60°,  55  ;  and  at  246°,  218  parts.  Here  the  pecuharity  is  of  the  opposite 
kind  to  what  occurs  with  sulphate  of  soda :  the  solubility  diminishing  up  to  50°, 
and  from  thence  progressively  increasing. 

The  solubility  of  bodies  in  water  may  be  strikingly  represented  to  the  eye  by 
means  of  a  kind  of  map,  such  as  is  given  in  the  figure.  The  horizontal  lines  rep- 
resent the  quantities  of  the  salt  dissolved  by  100  parts  of  water,  while  the  vertical 
lines  represent  the  temperatures.    Thus  the  line  of  sulphate  of  soda  commences 

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FORMATION     OFCRYSTALS.  23 

at  the  temperature  of  32°  at  the  horizontal  line  5,  and,  rising  rapidly,  cuts  the  hori- 
zontal line  10  at  52°,  cuts  the  line  of  40  at  88^,  and  attains  its  highest  point  of  53 
at  93°  ;  from  thence  it  commences  to  redescend,  until  at  232°  there  are  only  43 
parts  dissolved.  The  line  of  chloride  of  sodium  is  horizontal,  showing  that  it  is 
equally  soluble  at  all  temperatures,  and  in  the  other  ceises  the  construction  of  the 
scale  is  easily  seen  on  inspection. 

In  general,  when  solid  bodies  dissolve  in  a  fluid,  there  is  cold  produced,  but  oc- 
casionally the  solution  is  accompanied  with  a  remarkable  evolution  of  heat ;  this 
last  occurs  when  bodies  which  naturally  contain  water,  chemically  combined,  are 
deprived  of  it  by  heat,  and  when  thus  dried,  dissolved ;  in  such  cases,  it  is  probable 
that  the  one  portion  of  water  is  taken  by  the  salt  into  a  state  of  intimate  chemical 
combination,  and  thus  more  heat  produced  than  counteracts  the  cold  which  should 
arise  from  the  mere  solution  of  the  hydrated  salt  thus  formed.  Such  examples  may 
be  found  in  dry  chloride  of  calcium,  the  dry  sulphates  of  copper,  or  of  zinc  and  iron. 

Solution  is  very  much  promoted  by  agitation,  by  the  minute  di- 
vision of  the  solid,  and  generally  by  all  causes  which  tend  to  facil- 
itate the  contact  of  the  solid  and  liquid  particles.  When  the  liquid 
has  dissolved  as  much  of  the  solid  as  possible,  it  is  said  to  be  satu- 
rated. The  cohesion  of  the  liquid  to  the  solid  having  been  reduced 
to  an  equality  with  that  of  the  particles  of  the  solid  for  each  other, 
it  can  dissolve  no  more. 

If  a  saturated  solution  be  so  circumstanced  as  to  diminish  the 
cohesion  of  the  particles  of  the  solid  to  each  other,  a  portion  of 
the  solid  separates,  the  amount  of  which  depends  on  the  new  con- 
ditions under  which  the  liquid  is  placed.  Thus,  if  to  a  solution  of 
nitre  in  water  there  be  added  spirits  of  wine,  the  water  mixes  with 
the  spirits  of  wine  and  abandons  the  nitre,  which  is  precipitated 
If  strong  muriatic  acid  be  added  to  a  solution  of  chloride  of  barium 
in  water,  the  water  is  taken  by  the  acid,  and  the  salt  falls  down  as  a 
white  powder.  But  the  most  usual  case  is  where  the  separation 
of  the  solid  is  produced  by  the  cohesion  of  its  own  particles,  which, 
slowly  abandoning  the  liquid,  dispose  themselves  according  to  cer- 
tain laws,  and,  assuming  regular  geometrical  forms,  are  termed 
crystals.  Solid  bodies,  in  separating  slowly  from  liquids  in  which 
they  had  been  dissolved,  in  general  thus  crystallize,  and  the  figures 
of  these  crystals  being,  to  a  great  extent,  characteristic  of  the 
bodies,  deserve  minute  attention. 

To  obtain  substances  regularly  crystallized,  several  processes 
may  be  followed,  according  to  the  nature  of  the  body.  Where  the 
substance  is  soluble,  and  more  soluble  in  a  hot  than  in  a  cold  liquid, 
a  saturated  boiling  solution  may  be  made  and  allowed  to  cool.  The 
excess  of  the  solid  body  crystallizes  out  on  cooling.  Thus,  if  151 
parts  of  sulphate  of  magnesia  in  crystals  be  dissolved  in  100  parts 
of  boiling  water,  and  allowed  to  cool  to  60°,  a  quantity  of  crystals 
will  be  obtained  weighing  86  parts ;  for  at  60^  the  100  of  water  can 
only  dissolve  65,  and  the  difference  between  that  and  the  151, 
which  had  been  dissolved  by  the  boiling  water,  must  crystallize. 
If  the  body  be,  like  common  salt,  equally  soluble  in  water  at  all 
temperatures,  the  above  process  cannot  be  applied,  and  a  quantity 
of  the  liquid  must  be  removed  by  evaporation ;  the  portion  of  salt 
corresponding  to  the  quantity  of  water  which  has  passed  away,  is 
thus  obtained  solid.  If  the  evaporation  be  slowly  carried  on,  so 
that  the  formation  of  the  crystals  is  not  disturbed  by  the  boiling  of 
the  liquid,  they  form  regularly,  and  may  attain  to  considerable  size. 

In  many  cases  the  bodies  which  it  is  necessary  to  obtain  crys- 


24  CRYSTALLIZATION. 

tallized  are  not  soluble,  or  it  may  be  wished  to  obtain  crystals  oth- 
erwise than  by  solution.  By  melting  a  solid  substance,  its  particles 
are  allowed  liberty  of  motion  ',  and  when  it  again  commences  to 
solidify,  they  may  arrange  themselves  regularly,  and  crystallize. 
Almost  all  bodies,  when  melted,  and  then  allowed  to  solidify,  do 
thus  crystallize;  but  the  spaces  left  between  the  crystals  which 
first  form  being  completely  filled  up  by  the  portions  which  solidify 
afterward,  there  remains  only  a  general  crystalline  structure,  visi- 
ble in  the  fracture  of  the  body.  Thus  cast  iron,  sulphur,  zinc,  &c., 
have  crystalline  fractures.  The  beautiful  feathered  appearance 
given  to  sheet  tin  by  washing  with  dilute  acid,  and  which  was  so 
popular  some  years  ago  under  the  name  of  moir^e  metallique,  was 
simply  this  crystalline  structure,  displayed  by  removing  the  thin 
layer  of  metal  on  the  outside,  which  had  solidified  too  rapidly  to 
have  acquired  any  trace  of  crystallization.  To  obtain,  therefore, 
the  metals  crystallized  by  fusion,  the  excess  of  liquid  metal  must 
be  removed  from  around  the  crystals  that  are  first  formed.  A 
quantity  of  the  metal  or  of  sulphur,  having  been  melted  in  a  cup, 
is  to  be  allowed  to  cool  until  a  solid  crust  has  formed  upon  the 
surface  and  at  the  sides  to  a  certain  depth;  two  apertures  must 
then  be  made  in  the  upper  crust,  and  the  fluid  metal 
remaining  be  poured  out  at  the  one  aperture,  while 
the  air  enters  at  the  other  to  supply  its  place.  On 
then  breaking  the  vessel,  the  interior  of  the  solid 
layer  of  metal  or  sulphur  is  generally  found  lined 
with  well-formed  and  characteristic  crystals,  as  rep- 
resented in  the  figure. 
Bodies  may  also  be  crystallized  by  sublimation.  When  a  sub- 
stance has  been  converted  into  vapour,  and  that,  in  condensing,  it 
assumes  at  once  the  solid  form,  its  particles  arrange  themselves  so 
as  to  form  crystals.  Thus  are  obtained  in  fine  crystals,  arsenic, 
arsenious  acid,  corrosive  sublimate,  benzoic  acid,  &c. 

It  frequently  happens  that  the  same  body  may  be  obtained  crys- 
tallized by  more  than  one  of  these  processes.  Thus,  corrosive  sub- 
limate may  be  crystallized  by  solution  or  by  sublimation  j  sulphur 
may  be  crystallized  either  by  fusion  or  by  solution.  It  is  remark- 
able that,  when  this  occurs,  the  crystals  obtained  by  the  two  pro- 
cesses are  never  of  the  same  shape  ;  they  have  not  even  any  simple 
relation  of  figure  to  one  another,  but  indicate  a  totally  different 
mode  of  arrangement  of  particles,  induced  probably,  at  least  in 
part,  by  the  different  temperatures  at  which  the  change  of  state  of 
aggregation  may  have  occurred.  A  body  which  crystallizes  thus 
in  two  ways  is  said  to  be  dimorphous,  and  this  character  will  be 
found  hereafter  of  the  highest  importance  in  the  theory  of  the 
atomic  constitution  of  compound  bodies. 

The  more  slowly  the  change  of  state  occurs,  the  more  regular, 
and  the  larger,  are  the  crystals  that  are  formed.  Hence,  in  practice, 
solutions  are  left  to  cool  very  slowly,  or  to  evaporate  spontaneously ; 
and  sublimation  is  effected  by  the  most  gentle  heat  that  can  be  ad- 
vantageously applied.  To  favour  the  deposition  of  the  particles, 
a  variety  of  artificial  acids  may  be  applied.  Thus,  crystallization 
takes  place  better  in  a  pan  with  some  little  roughness  at  the  sides 


CRYSTALLIZATION.  25 

than  when  it  is  quite  smooth,  and  threads  are  hung  in  sirup  to  pro 
mote  the  crystallization  of  the  sugar-candy  j  a  little  crystal  of  the 
same  kind  of  salt  is  often  introduced,  to  serve  as  a  nucleus  round 
which  the  new  crystals  may  gather  j  and,  in  a  solution  containing 
many' salts,  the  nature  of  the  salt  which  shall  crystallize  may  be 
determined  by  the  nature  of  the  little  crystal  introduced :  thus,  if 
equal  parts  of  nitre  and  of  Glauber's  salt  be  mixed  and  dissolved 
in  five  parts  of  water,  and  the  solution  divided  between  two  similar 
dishes  j  on  a  crystal  of  nitre  being  laid  in  one  dish  and  a  crystal 
of  Glauber's  salt  being  laid  in  the  other,  a  crystallization  of  pure 
nitre  will  occur  in  the  former,  while  nothing  but  Glauber's  salt  will 
crystallize  in  the  latter  dish.  Salts  which  are  mixed  together  in 
solution  may  also  be  separated  from  one  another  by  their  respective 
solubilities :  thus,  if  sea-water  be  evaporated,  common  salt  alone 
will  be  deposited  according  as  the  liquor  boils  away ;  when  it  has 
been  removed  from  the  fire  no  more  common  salt  separates,  but 
Epsom  salt  will  crystallize,  and,  after  it  has  been  removed,  the  liquor 
will  be  found  to  contain  chloride  and  iodide  of  magnesium.  The 
liquor  from  which  crystals  have  separated  is  called  the  Mother 
liquor. 

Crystals  occasionally  form  in  a  body,  although  it  may  remain 
completely  solid.  Thus,  when  copper  wire  has  been  kept  some 
time  in  the  laboratory,  it  becomes  a  mass  of  cubical  crystals,  and 
its  tenacity  is  almost  completely  lost.  When  sugar  is  melted  and 
allowed  to  cool,  it  forms  a  perfectly  transparent  hard  mass,  desti- 
tute of  any  trace  of  crystalline  arrangement,  but  after  some  months 
it  becomes  opaque  and  white,  having  changed  into  ordinary  crystal- 
lized sugar.  In  cases,  also,  where  bodies  are  dimorphous,  one 
form  is  generally  unstable,  and  the  body,  when  crystallized  in  it, 
changes  after  some  time  into  the  other  form.  This  takes  place  re- 
markably with  sulphur,  and  will  hereafter  be  again  referred  to. 

A  solution  of  a  salt,  saturated  at  a  high  temperature,  is  found 
occasionally  to  remain  without  crystallizing,  although  cooled  to  a 
very  low  degree.  In  such  case,  on  introducing  a  little  crystal,  or 
agitating  the  liquor,  it  suddenly  crystallizes,  and  frequently  solidi- 
fies into  one  mass.  Sulphate  of  soda  is  remarkable  for  its  tenden- 
cy to  assume  this  indifl^erence  to  crystallization.  If  two  parts  of 
crystallized  sulphate  of  soda  be  dissolved  in  one  part  of  water,  at 
93%  and  the  solution  be  laid  aside  to  cool,  without  being  disturbed, 
it  remains  quite  clear  and  liquid  j  but,  on  producing  crystallization 
by  any  of  the  means  just  stated,  the  whole  becomes  solid. 

In  all  cases  of  crystallization  there  is  heat  evolved,  consequent 
on  the  general  law  of  heat  being  given  out  when  a  liquid  or  va- 
pour becomes  solid.  There  is  sometimes  a  remarkable  evolution 
of  light,  to  which  I  shall  refer  again.  Indeed,  crystallization  is 
sensibly  affected  by  the  presence  or  absence  of  light.  If  a  dish, 
half  covered  by  paper,  be  set  aside  with  a  solution  to  crystallize, 
but  few  crystals  will  form  in  the  dark,  although  there  may  be  an 
abundant  crop  on  the  illuminated  portion  of  the  vessel. 

It  has  been  noticed,  that  when  a  body  has  been  obtained,  crys- 
tallized at  difi^erent  temperatures,  as  by  solution  and  fusion,  the 
crystalline  form  is  generally  different,  and  the  body  is  said  to  be 


26 


PRIMARY     AND     SECONDARY     CRYSTALS. 


dimorphous.  In  this  case,  the  two  forms  are  totally  different  m 
their  geometrical  character.  But  independent  of  this,  a  body  may, 
even  simply  by  solution,  be  obtained,  crystallized  in  a  great  variety 
of  forms.  In  a  crop  of  crystals  of  sulphate  of  iron  or  of  alum,  obtain- 
ed by  cooling  from  a  hot  solution,  a  great  many  different  figures  may 
be  observed,  which,  however,  are,  on  examination,  all  referrible  to 
one  more  regular  and  fundamental  form.  Each  substance  has  thus 
a  characteristic  form  of  crystal,  which  is  termed  its  primary  form  j 
and  it  may  assume  a  great  variety  of  figures,  produced  by  modifi- 
cations of  this  form:  these  are  termed  secondary  forms.  Thus, 
carbonate  of  lime  has  been  found  crystallized  in  more  than  six 
hundred  different  secondary  forms,  all  derivable,  however,  from  the 
one  original  primary  figure,  the  rhombohedron.  The  growth  of  a 
crystal  depending  on  the  deposition  of  new  layers  of  particles 
over  its  external  surface,  any  change  in  the  quantity  deposited  on 
each  side  will  naturally  produce  a. change  of  form.  It  is  there- 
fore necessary,  when  crystals  are  left  long  in  a  solution,  to  turn 
them,  and  change  their  position  frequently,  as  otherwise  the  growth 
would  take  place  on  some  sides  rather  than  others,  and  secondary 
forms  would  be  produced,  by  which  the  characteristic  figure  of  the 
crystal  would  be  injured. 

The  most  ordinary  source  of  change  of  figure  consists  in  the  replacement  of  an 
edge  or  of  an  angle  by  a  plane.  Thus  one  of  the  simplest  figures  of  crystals  is 
the  cube  a ;  it  has  eight  edges  and  eight  solid  angles.  The  effect  of  substituting 
plane  surfaces  for  the  edges  is  to  produce  the  secondary  form  b,  and  by  replacing 
the  solid  angles  by  planes,  the  form  c ;  when  these  replacements  occur  together, 


.^^^ 


the  more  complex  figure  d  is  produced.  If  the  edges  of  the  cube  be  replaced  until 
ail  traces  of  the  original  planes  disappear,  the  figure  e,  the  rhombic  dodecahedron, 
is  produced ;  and  if  the  replacement  of  the  solid  angles  by  planes  be  carried  on  to 


inc  same  extent,  there  is  formed  a  regular  octohedron  /.  These  last  are  again  sim- 
ple and  primary  forms,  for  by  a  similar  move  of  replacement  they  may  be  reduced 
to  each  other  or  to  the  cube. 

When  a  crystal  augments  in  size  by  the  deposition  of  layers  of 
fresh  material  upon  its  faces,  the  molecular  cohesion  in  each  new 
layer  is  greater  than  its  cohesion  to  the  layer  underneath,  and  hence, 
by  skilful  splitting,  a  crystal  may  be  separated  into  a  number  of 
plates,  exhibiting  the  order  of  its  formation.  The  direction  in 
which  a  crystal  may  be  split  is  termed  its  cleavage,  and  it  is  of  great 
importance  in  the  determinatioft  of  the  primary  form  of  the  crys- 


.REGULARSYSTEM.  27 

f;al,  for  it  often  occurs  that  the  same  secondary  form  may  be  pro- 
duced by  two  different  primary  forms,  and  in  such  case,  the  cleav- 
age being  simply  related  to  the  surfaces  of  the  true  primary  form, 
determines  which  it  is. 

Notwithstanding  the  immense  variety  of  forms  of  crystals  which  exist,  they  may 
yet  be  reduced  to  a  very  few  classes,  by  conceiving  them  to  be  formed  by  their  par- 
ticles being  built  up  around  certain  axes,  which  pass  through  the  centre  of  the  crys- 
tal, and  the  relative  position  and  magnitude  of  which  determine  the  manner  in  which 
the  particles  are  arranged. 

In  this  way  there  may  be  formed  six  systems  of  crystallization,  characterized  as 
follows : 

1st  System.  The  Regular  System.  The  three  axes  are  all  equal  in  length,  and 
are  at  right  angles  to  each  other. 

2d  System.  The  Rhombokedral  System  has  three  axes  equal  in  length,  which 
are  placed,  however,  at  equal  angles  (60°)  with  each  other,  and  are  all  in  the  same 
plane,  while  a  fourth  and  unequal  axis  is  at  right  angles  to  that  plane. 

3d  System.  The  Square  Prismatic  System  has  the  three  axes  at  right  angles  to 
each  other,  but  there  are  only  two  of  them  equal ;  the  third  is  either  longer  or  shorter 
than  the  other  two. 

4th  System.  The  Right  Prismatic  System  has  the  three  axes  at  right  angles  to 
each  other,  but  there  are  no  two  of  them  of  the  same  length. 

5th  System.  The  Oblique  Prismatic  System  has  two  of  the  axes  making  an  acute 
angle  with  each  other,  while  the  third  is  placed  at  right  angles  to  both.  The  three 
axes  are  all  unequal  in  length. 

6th  System.  The  Doubly  Oblique  Prismatic  System  has  all  the  axes  unequal  in 
length,  and  making  acute  angles  with  one  another. 

The  various  actual  forms  of  crystals,  both  primary  and  secondary,  are  derivable 
from  the  manner  in  which  the  plane  surfaces  of  the  crystals  may  be  applied  around 
these  axes.  In  order  to  conceive  the  application  of  the  planes,  the  axes  shall  be 
considered  as  placed  with  one  in  a  vertical  position,  and  it  is  called  the  principal 
axis.     The  nature  of  the  system  determines  which  axis  should  be  selected. 

In  the  Regular  System,  the  axes  being  all  equal,  it  is  a  matter  of  indifference 
which  is  chosen  as  the  principal  axis,  and  their  perfect  symmetry  is  also  a  reason 
that  the  portions  of  the  crystal  around  each  axis  must  be  completely  similar.  The 
number  of  forms  belonging  to  this  system  is  consequently  not  very  large,  and  they 
are  remarkable  for  their  simplicity.  Thus,  when  each  plane  cuts  the  axes  at  equal 
distances  from  the  centre,  the  form  is  the  octohedron,  and  as  the  planes  must  be 
equally  inclined  to  all  the  axes,  it  is  the  regular  octohedron  /,  of  which  each  plane 
is  an  equilateral  triangle.  When  each  face  of  the  crystal  cuts  one  axis  at  right  an- 
gles, and  is  hence  parallel  to  the  other  two,  the  form  is  the  cube  a.  When  each 
face  cuts  two  axes  at  equal  distances  from  the  centre,  and  is  parallel  to  the  third, 
the  figure  which  results  is  the  rhombic  dodecahedron  e.  By  the  combined  positions 
of  sets  of  planes,  other  and  more  complicated  (secondary)  b,  c,  d,  forms  are  produced, 
arising  from  the  partial  coexistence  of  the  conditions  of  the  formation  of  two  sim- 
ple forms. 

The  crystals  belonging  to  this  system  are  generally  veiy  well  defined  and  easily 
recognised :  a  great  number  of  important  bodies  crystallize      ^ 
in  the  forms  belonging  to  it :  thus  common  salt,  fluor  spar,    /y 
galena,  and  iron  pyrites,  are  found  in  cubes  ;  alum  in  octohe-  ^  ■ 
drons ;  the  garnet  is  found  in  dodecahedrons.     When  pure 
metallic  substances  are  found  crystallized,  it  is  always  in 
forms  belonging  to  this  system ;  thus,  bismuth,  copper,  sil- 
ver, gold,  crystallize  in  cubes,  and  lead  in  octohedrons. 

A  peculiarity  of  crystals,  belonging  particularly  to  this  sys- 
tem and  to  the  next,  is,  that  every  alternate  face  shall  become 
developed  to  such  a  degree  as  to  obliterate  the  intervening 
planes,  and  thus  to  generate  a  new  form,  having  one  half  of 
the  number  of  planes.  Thus  a  crystal  of  alum  is  very  sel- 
dom truly  octohedral ;  it  has  usually  the  figure  of  g  where 
four  of  the  sides  of  the  octohedron  have  become  very  large, 
while  the  other  four  remain  very  small.  When  the  oblitera- 
tion becomes  complete,  there  is  produced  the  tetrahedron,  or 
three-sided  pyramid  of  fig.  h,  which  is  hence  properly  called 


28 


RHOMBOHEDRAL     AND     SQUARE, SYSTEMS. 


the  hemioctohedron.  Such  crystals  are  called  hemihedral,  from  their  containing 
half  the  proper  number  of  sides.  Certain  bodies  have  a  natural  tendency  to  hemi- 
hedral crystallization,  and  are  but  very  rarely  found  with  the  proper  number  of 
planes.  The  diamond  is  a  remarkable  instance  of  this.  Its  proper  form  is  the  reg- 
ular octohedron,  but  its  crystals  are  universally  hemihedral. 
In  the  Rhambohedral  system,  the  supplementary,  or  fourth  axis,  is  taken  as  the 
principal  axis,  and  the  crystals  are  formed 
by  the  planes  being  apphed  to  these  axes, 
as  in  the  former  system.  If  the  planes 
be  all  inclined  at  the  same  angles  to  the 
three  horizontal  axes,  and  cut  the  verti- 
cal axis,  there  is  formed  a  double  six- 
sided  pyramid  {i) ;  and  when  the  planes 
are  perpendicular  to  the  horizontal  axes, 
and  parallel  to  the  vertical  axis,  the  six- 
sided  prism  (k)  is  produced.  These  forms 
generally  coexist  in  quartz,  as  in  the  figure 
k.  By  the  replacement  of  the  edges  in  these  forms  there  may 
be  produced  others  with  twelve  sides  in  place  of  six ;  as  a  twelve- 
sided  prism  and  a  twelve-sided  pyramid,  of  which  quartz  also 
affords  examples. 

This  system  is  more  remarkable  for  its  modified  forms  than  for  those  simple  fig- 
ures above  described,  although  the  six-sided  prism  and  six- 
sided  pyramid  are  characteristic  of  very  many  substances.  If 
we  suppose,  in  the  terminal  six-sided  pyramid,  every  alternate 
side,  above  and  below,  to  grow  at  the  expense  of  those  next 
it  at  each  side,  I  will  be  formed.  Ultimately  the  sides  of  the 
prism  disappear,  and  there  will  remain 
a  figure  of  six  planes,  of  which  all  the 
sides  shall  be  equal  and  similar  rhombs, 
the  rhombohedron,  m,  which  gives  its 
name  to  this  system,  although  it  be  but 
a  hemihedral  modification  of  the  true 
typical  form.  The  principal  axis  of  the 
rhombohedron  is  the  vertical  axis  of  the 
pyramid,  and  the  horizontal  axes  are  found  by  joining  the 
solid  angles  to  the  centres  of  the  opposite  faces,  where  ori- 
ginally the  lateral  angles  of  the  pyramid  had  been. 

The  carbonates  of  lime,  of  iron,  and  magnesia  are  remarkable  for  crystallizing 
with  this  hemihedral  figure.  Even  in  the  six-sided  prism  of  carbonate  of  lime,  the 
rhombohedral  tendency  is  evident  by  the  crystal  being  terminated,  not  by  the  six- 
sided  prism,  as  in  quartz,  but  by  its  three  hemihedral  replacing  planes. 
3.  T7ie  Square  Prismatic  System. — The  crystals  of  this  class  differ  from  those  of 
the  regular  system  in  the  vertical  axis  not  being  necessarily 
equal  to  the  other  two ;  but,  on  the  contrary,  being  in  almost 
all  cases  either  longer  or  shorter.  Where  there  is  formed 
an  octohedron,  n,  it  differs  from  the  regular  octohedron  in 
the  terminal  angle  of  each  plane  being  not  60°,  but  more  or 
less.  Its  basis  is,  however,  a  square  ;  and 
to  distinguish  it  from  the  octohedron  of  the 
following  system,  it  is  termed  the  octohedron  with  the  square  base. 
By  the  application  of  planes  perpendicular  to  the  horizontal  axes,  a 
four-sided  pyramid  with  a  square  base  is  formed,  o,  and  by  the  re- 
placement of  the  terminal  edges  of  this  prism,  four-sided  pyramids 
may  be  formed  on  its  base  and  summit.  By  this  property  the  square 
prisms  and  octohedrons  are  distinguished  from  all  modifications  of 
the  cube  and  octohedron  of  the  regular  system.  When  the  edge 
of  a  cube  is  replaced,  the  plane  substituted  for  it  gains  equally  on 
the  two  surfaces,  and  hence,  when  one  is  effaced,  the  other  must 
be  so  also.  But  in  the  square  prisms  the  replacement  may  efface  the  terminal  plane, 
giving  a  four-sided  pyramid,  and  yet  the  lateral  planes  be  but  little  encroached  upon. 
The  sides  of  the  crystal  in  this  system  are  thus  independent  of  the  top  or  bottom, 
and  may  be  modified,  while  the  top  and  bottom  remain  unaltered  ;  this  never  takes 
place  in  the  regular  system,  where,  there  being  no  one  side  particularly  upper  or 
ower,  all  modifications  must  affect  all  sides  alike. 


^ 

f\ 

V     0 

Or/ 

■~"-Ov^ 

vJ 

■? 

PRISMATIC     SYSTEMS. 


29 


4.  The  right  Prismatic  System. — In  this  system  the  three  axes 
being  all  unequal,  the  length,  breadth,  and  thickness  of  the  crys- 
tal may  be  different  from  each  other.  Thus,  in  the  octohedron,j9, 
formed  by  the  application  of  planes,  each  connecting  the  extremi- 
ties of  the  three  axes,  the  three  dimensions  of  the  crystal,  as  in 
the  figure,  which  is  the  primitive  form  of  sulphur,  are  unequal ; 
the  octohedron  has  a  rhombic  base ;  and  by  planes  which  are  in- 
clined to  the  horizontal  axes,  and  parallel  to  the  vertical  axis,  a 
prism  with  a  rhombic  base  may  be  produced.  This  also,  by  com- 
bination of  the  two  forms,  may  obtain  pyramidal  terminations,  as 
in  some  forms  of  native  sulphur. 

An  important  character  of  this  system,  which  arises  from  there 
being  no  necessary  connexion  between  the  two 
horizontal  axes,  is,  that  the  lateral  edges  may  be 
alternately  modified  in  a  different  manner ;  or,  in  other  words,  that, 
looking  at  the  crystal,  its  back  and  front  may  be  differently  aflfected 
from  its  sides.  Of  this  an  example  may  be  found  in  a  common 
modification  of  the  sulphur  octohedron  given  in  figure  q. 

5.  The  oblique  Prismatic  System. — From  the  manner  in  which 
the  crystals  belonging  to  this  system  form,  one  of  the  oblique  axes 
is  generally  by  much  the  most  developed,  and  is  taken  as  the  prin- 
cipal axis.  The  remaining  axes,  which  are  at  right  angles  to  each 
other,  are  taken  as  horizontal,  the  principal  axis  making  with  them  the  acute  angle, 
which  belongs  to  the  peculiar  body. 
By  means  of  planes  which  are  inclined  to  all  the  axes,  there  is  formed  the  ob- 
lique rhombic  octohedron,  such  as  characterizes  gypsum 
(sulphate  of  lime),  as  in  figure  r;  and  by  means  of  planes 
which  are  inclined  to  two  axes,  but  parallel 
to  the  third,  an  oblique  rhombic  prism  may 
be  formed,  s.  A  remarkable  character  of 
,  these  crystals  is,  that  from  the  crossing  of  the  axes  and  their  inde- 
pendence of  each  other,  the  front  and  back  of  the  crystal  may  be 
quite  different  in  relation  to  the  sides.  The  crystals  of  sulphate 
of  soda,  of  carbonate  of  soda,  of  borax,  of  sulphate  of  iron,  and  of 
feldspar,  may  be  taken  as  examples  of  the  numerous  forms  deriva- 
ble from  this  system. 

6.  The  doubly  oblique  Prismatic  System. — The  axes  are  all  une- 
qual, and  all  form  acute  angles  with  each  other,  and  it  is  hence  in- 
different which  is  taken  as  the  principal  axis  of  the  crystal.  The 
consequence  is  complete  absence  of  symmetry  between  any  two  surfaces  of  the 
crystal,  except  such  as,  being  at  the  ends  of  the  same  axis,  are  parallel  to  each  other. 
The  complexity  of  crystals  of  this  system  is  hence  usually 
very  great.  The  simplest  forms  are  the  oblique  rhombic 
octohedron,  t,  and  the  oblique  rhombic  prism,  formed  by 
planes  inclined  to  all  the  axes,  or  to  two,  and  parallel  to  the 
third,  respectively.  The  soda  feldspar  (albit)  and  sulphur 
of  copper  are  examples  of  this  system ;  the  octohedron  of 
this  system  is  figured  in  the  margin. 

It  might  be  at  first  supposed  that  the  assumption  of  these  axes,  or  lines  round 
which  we  have  supposed  the  crystalline  particles  to  be  regularly  arranged,  was 
merely  a  geometrical  fiction,  by  which  the  form  of  the  crystal  might  be  more  easily 
represented  to  the  mind ;  but  such  is  not  the  case.  Evidence  derived  from  a  vari- 
ety of  sources  agrees  in  demonstrating  that  this  diversity  of  crystalline  systems 
arises  from  fundamental  differences  in  the  laws  of  molecular  cohesion,  by  which 
the  formation  of  the  crystal  is  regulated,  and  that  these  axes,  which  have  been  so 
much  alluded  to,  are  real  centres,  the  proportion  and  position  of  which  determine 
all  the  physical  properties  of  the  body.  It  is  peculiarly  from  the  action  of  crystal- 
lized bodies  upon  light  that  accurate  and  extraordinary  information  has  been  ob- 
tained of  their  internal  structure,  and  the  discoveries  that  have  been  made  in  this 
department  were  the  means  of  advancing  the  physical  theory  of  light  to  its  present 
ahnost  perfect  state. 

Substances  may  assume  crystalline  forms  which  do  not  properly  belong  to  them 
in  many  ways.  Thus,  a  group  of  crystals  being  imbedded  in  a  rock,  they  may,  by 
the  filtration  of  the  water  of  springs  across  the  rock,  be  dissolved  out,  leaving  a  hoi- 


^^©5* 


30         FORMS     MODIFIED     BY     FOREIGN     BODIES. 

low  mould  of  their  form  ;  and,  subsequently,  substances  of  another  kind  may  be  in- 
troduced into  this  cavity,  and,  solidifying  there,  may  simulate  the  external  form  of 
the  original  inhabitant.  But  these  are  no  more  real  crystals  than  a  mass  of  plaster 
of  Paris,  which  has  solidified  in  a  hollow  mould,  and  comes  out  as  an  Apollo's  head, 
can  be  said  to  have  so  crystallized.  By  cleavage,  and  by  the  operation  of  polarized 
light,  the  unsuited  internal  structure  is  recognised,  and  the  crystal  is  stated  to  have 
been  merely  pseudomorphous.  Another  mode  in  which  a  body  may  come  to  have  a 
form  not  its  own,  is  by  remaining  behind  after  the  decomposition  of  the  substance 
which  had  really  crystallized.  Thus,  when  hydrated  chloride  of  copper,  which 
crystallizes  in  fine  green  prisms,  is  carefully  heated,  the  water  is  expelled,  and  the 
chloride  of  copper  remains  dry,  and  of  a  fine  yellowish-brown  colour,  in  the  original 
crystalline  form,  and  with  the  surfaces  quite  bright.  The  red  iodide  of  mercury 
combines  with  ammonia  to  form  a  substance  which  crystallizes  in  long  prisms  of  a 
snow-white  colour ;  these,  when  exposed  to  the  air,  lose  all  ammonia,  and  the 
iodide  of  mercury  remains  behind,  pure,  and  of  a  brilliant  red,  but  with  the  perfect 
figure,  and  bright,  smooth  surfaces  and  sharp  angles  of  the  body  originally  crys- 
tallized. 

It  has  been  thought  that  the  presence  of  foreign  bodies  in  a  solution,  even  where 
they  did  not  enter  into  combination  with  the  substances  M^hich  crystallized  from  it, 
might  modify  their  form.  Thus,  when  common  salt  crystaUizes  in  a  solution  of 
urea,  it  is  deposited  in  octohedrons,  and  by  dissolving  alum  in  a  solution  of  urea,  it 
may  be  obtained  crystallized  in  cubes.  But  in  this  case,  the  substances  which  crys- 
taUize  are  no  longer  common  salt  nor  alum,  but  the  one,  a  combination  of  urea  with 
common  salt,  and  the  other,  a  basic  alum  produced  by  the  mutual  decomposition 
of  the  urea  and  the  alum.  The  presence  of  a  trace  of  lead  or  tin  in  a  large  quanti- 
ty of  iodide  of  potassium,  has  been  supposed  to  modify  its  form  ;  but  it  is  more  likely 
that  the  mechanical  presence  of  an  impurity  of  the  kind  maybe  supposed  to  produce 
a  tendency  to  macled  crystals,  and  thus  the  external  form  be  somewhat  altered,  al- 
though the  true  constitution  of  the  crystal  may  remain  the  same. 

Certain  bodies,  when  they  exist  together  in  solution,  may  re- 
markably modify  each  other's  form,  by  crystallizing  together  so* 
completely  that  every  individual  crystal  shall  contain  a  quantity  of 
each.  Yet  these  bodies  will  not  have  combined  chemically  with 
each  other,  for  the  quantity  of  each  present  in  each  crystal  is  quite 
indefinite  ;  they  are  mixed  together  mechanically  in  the  crystals, 
and  hence  the  form  of  the  actual  crystal  is  intermediate  between 
those  which  the  separate  bodies  should  have  had  if  they  were 
pure.  In  order  that  bodies  may  so  crystallize  together,  it  is  not 
only  necessary  that  they  should  be  of  the  same  crystalline  system, 
but  the  crystalline  forms  must  resemble  one  another  very  closely 
in  all  their  angles  and  sides.  Thus,  not  only  will  iodide  of  potas- 
sium and  sulphate  of  soda,  which  belong  to  different  systems  of 
crystallization,  not  crystallize  together,  but  Glauber  salt  and  car- 
bonate of  soda,  which  do  belong  to  the  same  system,  will  not  crys- 
tallize together,  because  the  relations  of  their  angles  and  sides  be- 
ing completely  different,  they  cannot  mix  together  so  as  to  form  a 
uniform  solid.  But  sulphate  of  zinc  and  sulphate  of  magnesia  be- 
long not  merely  to  the  same  crystalline  system,  but  they  are  al- 
most identical  in  their  figures  ;  the  eye  cannot  make  any  distinction 
between  their  crystals ;  and  hence,  when  a  crystal  is  being  formed 
in  a  solution  containing  these  two  bodies,  the  molecular  and  crys- 
talline forces  being  the  same  for  both,  they  concur  in  the  building 
of  the  crystal  without  interfering  with  each  other.  Hence,  as  there 
is  a  very  small  difference  between  the  angles  of  the  rhombic  prisms 
of  the  two  salts,  the  one  being  90°  30',  and  the  other  91°  8',  if  they 
be  mixed  in  equal  proportions  in  the  crystal,  its  angle  must  be  90° 
49'.     Carbonate  of  lime  and  carbonate  of  magnesia  are,  like  the 


ISOMORPHISM.  31 

sulphates  of  zinc  and  magnesia,  almost  identical  in  crystalline  form, 
and  they  exist  in  nature  mixed  together,  forming  the  dolomite  or 
magnesian  limestone.  The  quantity  of  carbonate  of  lime  is  to  the 
quantity  of  carbonate  of  magnesia  as  50*6  to  42*8  ;  and  as  the  angle 
of  the  rhomb  of  carbonate  of  lime  is  105°  ¥,  and  that  of  carbonate 
of  magnesia  is  107^  40',  the  angle  of  the  mixed  crystal  is  found 
by  multiplying  the  angle  of  each  constituent  by  its  quantity,  adding 
these  products  together,  and  dividing  by  the  quantity  of  the  mixture, 
and  the  result  is  106"^  15',  the  angle  of  the  rhombic  crystal  of  mag- 
nesian limestone. 

The  peculiarity  of  crystallization  which  such  bodies  possess  may 
be  illustrated  in  another  manner.  Ordinary  alum  is  a  sulphate  of 
alumina  and  potash ;  but  there  are  a  great  variety  of  other  double 
sulphates  which  crystallize  in  the  same  form,  and  which  constitute 
a  well-defined  crystalline  genus.  If  an  octohedral  crystal  of  com- 
mon alum  be  placed  in  a  solution  of  the  sulphate  of  alumina  and 
ammonia,  the  crystal  augments  in  size  by  the  addition  of  layers  of 
It.  If  it  be  then  removed  to  a  solution  of  sulphate  of  potash  and 
peroxide  of  iron,  it  acquires  another  layer ;  by  a  solution  of  sul- 
phate of  ammonia  and  peroxide  of  iron  another  still ;  and  by  means 
of  solutions  of  the  alums,  which  consist  of  oxide  of  chrome  united 
to  potash  or  ammonia,  with  sulphuric  acid,  the  crystal  may  grow  to 
a  still  greater  size.  The  chemical  constituents  of  the  crystal  may 
thus  vary,  but  it  retains  its  form  j  the  number  of  equivalents  of 
chemical  substaiices  contained  in  it  remains  also  the  same,  although 
they  may  not  remain  identical  in  nature.  The  potash  and  the  am- 
monia on  the  one  hand,  the  oxide  of  iron,  the  alumina,  and  the  ox- 
ide of  chrome  on  the  other,  agree  in  producing  the  same  crys- 
talline arrangement  of  particles  ;  in  impressing  upon  their  com- 
pounds, with  the  same  bodies,  the  same  crystalline  form.  Bodies 
so  related  are  called  isomorphous.  Oxide  of  zinc  and  magnesia  are 
isomorphous  j  while  lime  is  a  dimorphous  body,  being  in  one  form 
isomorphous  with  magnesia,  and  in  the  other  with  oxide  of  lead. 
Isomorphous  bodies  are  remarkably  similar  in  their  chemical  prop- 
erties j  they  follow  generally  the  same  laws  of  combination,  and 
hence,  as  shall  be  farther  shown  in  the  chapter  on  chemical  affinity, 
the  principle  of  isomorphism  has  been  of  the  highest  importance 
in  developing  the  true  relations  of  chemical  substances  to  each 
other,  and  the  intimate  connexion  of  the  forces  which  produce  the 
chemical  combination,  and  those  which  direct  the  crystalline  ar- 
rangement of  the  particles  of  bodies. 

It  was,  some  time  ago,  considered  an  important  question,  whether  the  ultimate 
particles  of  bodies  had  the  same  figure  as  their  primary  crystalline  form,  or  wheth- 
er they  were  globular  or  ellipsoidal.  The  law  of  isomorphism  was  considered,  at 
one  time,  to  result  from  the  ultimate  particles  of  those  bodies,  being  themselves 
isomorphous  ;  and  hence,  when  entering  into  similar  combinations,  giving  to  them 
also  the  same  form.  It  was  at  another  time  referred  to  the  principle  that,  in  any 
chemical  combination,  the  crystalline  form  was  determined  by  the  number  of  mole- 
cules or  atoms  present,  and  was  independent  of  their  nature.  Neither  of  these 
ideas  has  been  found  sufficient ;  but  the  complete  discussion  of  the  relations  of  the 
isomorphous  bodies  will  be  found  in  a  future  chapter. 

The  angular  dimensions  of  crystals  being  thus  the  measures  by 
which  they  are  recognised  and  compared  with  one  another,  the 
instruments  by  means  of  which  their  measurement  is  effected  re- 


32  GONIOMETER  S. L  t  G  H  T. 

quire  a  few  words'  notice.  They  are  called  goniometers  (yovioq^  an 
angle  ;  fisrpo),  I  measure).  The  simplest  form  consists  of  a  semicir- 
cular scale  of  degrees  attached  to  a  pair  of  blades,  which,  crossing 
each  other  at  the  centre,  allow  of  the  crystal  being  adjusted  exactly 
to  their  edges,  and  then  show  the  value  of  the  angle  by  the  number 
of  degrees  intercepted  on  the  scale  between  the  blades.  For  all 
purposes  requiring  accuracy,  the  goniometer  of  Wollaston  must  be 
applied.  In  it,  the  angle  of  the  crystal  is  determined  by  measuring 
the  number  of  degrees  through  which  it  is  necessary  to  turn  the 
crystal  in  order  that  two  rays  of  light,  reflected  successively  from 
the  two  surfaces,  including  the  angle,  may  be  in  exactly  the  same 
direction.  To  the  adoption  of  this  principle  of  measurement  we 
owe  almost  all  the  great  advance  that  has  been  lately  made  in  the 
relations  of  the  crystalline  forms  of  bodies  to  their  chemical  and 
molecular  constitution. 

In  all  that  has  formed  the  subject  of  the  chapter  which  has  now 
closed,  the  forces  brought  into  play,  and  the  efl^ects  which  were  pro- 
duced by  means  of  their  action,  were  not  such  as  to  involve  the 
principle  upon  which  all  purely  chemical  phenomena  are  based,  the 
existence  of  a  variety  of  elements.  The  laws  of  cohesion,  from  its 
simplest  action  in  a  liquid  to  its  most  complex  manifestation  in  a 
double  oblique  crystal,  might  have  existed  in  nature,  and,  being 
studied,  make  a  part  of  science,  independent  of  any  consideration 
of  true  chemical  force,  although  serving  most  usefully  for  the  iden- 
tification of  chemical  substances,  and  capable  of  modifying  the  cir- 
cumstances of  their  mutual  action  in  an  eminent  decree. 


CHAPTER  II. 

OF  THE  PROPERTIES  OF  LIGHT  AS  CHARACTERIZING  CHEMICAL  SUBSTANCES 

I  SHALL  not  attempt  to  enter  into  the  details  of  the  history  of  the 
mechanical  properties  of  light,  as  they  constitute  one  of  the  most 
purely  mathematical  of  the  physical  sciences,  and  have  but  indirectly 
a  relation  to  chemical  phenomena :  a  short  notice  of  these  properties 
is,  however,  necessary,  in  order  that  the  means  of  recognising  chem- 
ical substances  may  be  fully  given. 

Light,  emanating  from  any  luminous  body,  moves  in  straight  lines ; 
the  smallest  portion  of  it  which  can  be  admitted  through  an  aperture 
being  termed  a  ray.  When  a  ray  of  light  falls  upon  the  surface  of 
a  body,  it  is  either  bent  back  again,  or  it  passes  into  the  substance 
of  the  body;  the  bending  back  is  termed  reflection^  and  is  regulated 
by  the  law,  that  the  angles  of  incidence  upon  the  surface,  and  of 
reflection  from  it,  are  always  equal.  It  is  thus  that  the  images  are 
formed  in  a  looking-glass ;  for  we  see  objects  in  the  direction  in 
which  the  ray  of  light  arrives  at  the  eye,  and  hence  we  judge  the 
image  to  be  as  much  behind  the  mirror  as  the  object  is  before  it. 

When  the  ray  of  light  has  passed  into  the  substance  of  the  body, 


PROPERTIES     OF     LIGHT.  33 

it  may  be  absorbed^  in  which  case  the  substance,  not  sending  any  light 
to  the  eye,  appears  completely  black,  or  is,  rather,  totally  invisible, 
except  by  contrast  with  some  other  body  placed  behind  it ;  or  the 
light  may  be  transmitted,  in  which  case  the  body  is  said  to  be  trans- 
farent^  as  the  light  may  arrive  at  the  eye  after  passing  through  the 
substance.  Bodies  which  do  not  transmit  light  are  said  to  be  opaque  ; 
but  there  are  two  kinds  of  opacity,  that  of  blackness,  where  the  light 
which  falls  upon  the  object  is  totally  lost  by  being  absorbed,  and  that 
of  whiteness,  where  the  light  is  reflected,  and  we  can  see  the  object 
itself,  though  we  cannot  see  anything  through  it.  Where,  in  an 
opaque  body,  the  light  is  partly  reflected  to  the  eye  and  partly  ab- 
sorbed, there  arises  the  diversity  of  colours  which  opaque  bodies 
may  possess. 

When  the  ray  of  light  is  neither  totally  reflected  from  the  surface 
nor  lost  within  the  substance  of  the  body,  but  passes  through  it,  it 
is  refracted  ;  that  is,  its  direction  is  changed  j  and  if  its  path  be  rep- 
resented by  a  line,  it  is  broken  at  the  surface  of  the  medium,  and 
hence  the  name.  It  is  thus  that  an  oar,  partly  immersed  in  water, 
appears  broken  at  the  surface.  Any  substance  through  which  light 
is  moving  is  termed  a  medium^  and  the  refraction  occurs  at  the  lim- 
iting surface  of  the  two  media,  as  air  and  water,  air  and  glass,  though 
not  to  the  same  degree  as  if  the  light  had  passed  into  the  most  re- 
fractive medium  directly  from  an  emptj?'  space.  This  refractive 
power  is  of  importance  as  a  characteristic  property  of  bodies,  but 
to  the  chemist  it  is  specially  of  use  in  the  study  of  crystallized  bodies ; 
and  it  is  hence  with  reference  to  the  principles  of  the  molecular 
structure  of  those  substances  already  noticed,  that  the  refraction 
of  white  light  shall  be  examined. 

This  reflection,  absorption,  or  transmission  of  the  luminous  rays 
which  fall  upon  the  surface  of  a  body  is,  however,  in  no  case  abso- 
lute and  simple.  All  bodies  reflect  some  light,  and  there  are  none 
which  allow  light  to  pass  through  them  without  its  undergoing  some 
absorption.  In  general,  light  incident  upon  a  body  is  divided  into 
three  unequal  parts,  of  which  one  is  reflected,  another  absorbed,  and 
the  third  transmitted,  and  the  nature  of  the  body  determines  which 
action  shall  be  most  powerful. 

In  uncrystallized  bodies,  a  ray  of  light,  in  passing  from  a  rarer 
to  a  denser  medium,  is  generally  bent  towards  a  line  perpendicular 
to  the  surface  of  the  medium,  and  in  passing  from  a  denser  to  a  rarer 
medium,  the  refraction  is  from  the  perpendicular.  In  this  case,  the 
law  of  refraction  is  such  that  the  sines  of  the  angles  of  incidence 
and  refraction  are  to  each  other  in  a  constant  proportion,  no  matter 
how  the  direction  of  the  incident  ray  may  change,  and  the  number 
which  expresses  this  ratio  is  called  the  index  of  refraction. 

The  velocity  with  which  light  is  transmitted  is  exceedinglj'-  great ; 
the  light  of  the  sun  arrives  at  the  earth  in  eight  minutes,  being  at 
the  rate  of  195,000  miles  in  a  second.  This,  however,  is  but  the 
mean  velocity  of  the  coloured  lights  which  a  solur  ray  contains,  for 
these  differ  in  velocity,  those  which  are  least  refrangible  being  trans- 
mitted with  the  greatest  quickness.  The  velocity  of  light  is  changed 
when  it  passes  from  one  substance  to  another,  and  it  is  this  change 
m  which  originates  refraction.     In  general,  the  denser  the  medium 

E 


34 


REFRACTION. 


dies  in  the  follow 

ing  table  : 

.  2  549 

Garnet 

.  1  815 

.  2-500 

Oil  of  cassia 

.  1-614 

.  2-439 

Plate  glass 

.  1-542 

.  2-322 

Oil  of  turpentine 

.  1-475 

.  2-224 

Water 

.  1-336 

.  2-148 

Chlorine     . 

.  1-000772 

.  2-028 

Air    . 

.  1  000294 

.  1  830 

Vacuum     . 

.  1-000000 

the  more  is  the  velocity  diminished ;  and  it  was  by  the  experimental 
proof  of  this  that  one  of  the  most  triumphant  testimonies  in  favour 
of  the  undulatory  theory  of  light  was  found. 

The  refractive  power  of  a  body  is  not  connected  with  its  chemical 
constitution  in  any  positive  manner ;  but  inflammable  substances 
are  generally  possessed  of  high  refractive  powers.  It  was  this 
which  led  Newton  to  the  celebrated  prophecy  that  the  diamond 
should  be  combustible,  and  that  water  should  possess  an  inflammable 
constituent ;  but  many  bodies  of  high  refracting  powers  are  not  at 
all  combustible. 

The  refracting  power,  as  measured  by  the  refractive  index,  is  given  for  some  of 
the  more  remarkable  bodi 
Realgar  . 
Octohedrite     . 
Diamond 
Nitrate  of  lead 
Phosphorus     . 
Sulphur  . 
Flint  glass,  from 
to 

In  uncrystallized  bodies,  the  molecular  arrangement  being  irreg- 
ular and  indefinite,  the  action  upon  light  is  the  same  in  every  direc- 
tion, and  hence  a  ray  of  light  undergoes,  when  passing  from  air  into 
water  or  glass,  simple  ordinary  refraction  ;  it  is  bent  out  of  its  path 
by  an  angle  which  depends  upon  the  angle  of  incidence,  by  the  law 
of  the  proportionality  of  their  sines.  In  bodies  which  crystallize 
in  the  regular  system,  where  there  are  three  precisely  similar  axes, 
the  molecular  constitution,  although  subjected  to  definite  laws,  must 
be  the  same  in  all  directions,  and  hence  a  ray  of  light  will  be  acted 
upon,  in  such  a  crystal,  in  the  same  manner,  no  matter  in  what  di- 
rection it  may  go.  Hence,  in  crystals  of  the  regular  system,  there 
is  only  ordinary  refraction  and  a  single  image. 

When  a  ray  of  light  passes,  however,  into  a  crystal  of  the  rhom- 
bohedral  system,  it  is  diflerently  acted  upon,  according  to  the  part 
of  the  crystal  it  passes  through.  If  it  pass  along  the  principal  axis, 
it  is  equally  related  on  all  sides  to  the  crystalline  forces,  and  hence, 
as  in  the  crystals  of  the  regular  system,  there  is  only  a  single  re- 
fracted ray.  But  if  the  light  pass  in  any  other  direction,  it  is  divi- 
ded into  two  portions,  one  of  which  is  refracted  according  to  the 
ordinary  law  of  the  sines,  while  the  other,  following  a  totally  new 
law,  is  termed  the  extraordinary  ray.  The  angle  which  these  two 
rays  make  with  each  other  increases  according  as  the  path  of  the 
incident  fky  is  farther  from  the  principal  axis  ;  and  when  the  light 
falls  perpendicular  to  the  sides  of  the  prism,  and  hence  to  the  prin- 
cipal axis,  the  divergence  of  the  two  refracted  rays  is  the  greatest 
possible.  In  the  square  prismatic  system,  the  same  peculiar  action 
upon  light  exists  ;  when  a  ray  of  light  passes  along  the  principal 
axis  of  the  crystal,  it  undergoes  simple  refraction  according  to  the 
ordinary  law,  but  in  any  other  direction  the  ray  is  subdivided  into 
two,  of  which  one  is  refracted  in  the  ordinary  way,  and  the  other 
follows  a  new  and  peculiar  law. 

The  existence  of  double  refraction,  and  the  change  in  its  amount, 
according  to  the  direction  in  which  the  light  passes  through  the 


DECOMPOSITION     OF     LIGHT. 


35 


crystal,  may  easily  be  observed.  If  a  round  dot  be  marked  with 
ink  on  a  sheet  of  paper,  and  a  rhomb  of  calc-spar  be  laid  upon  it, 
the  dot  will  appear  double,  and  on  moving  the  crystal  round,  one 
image  will  be  seen  to  revolve  round  the  other.  By  changing  the 
posidon  of  the  eye,  the  distance  between  the  two  images  of  the  dots 
will  be  found  to  change  j  it  will  be  greatest  when  the  eye  is  in  a  line 
connecting  a  solid  angle  and  the  centre  of  the  opposite  plane  j  but 
to  efface  the  double  image  and  obtain  single  refraction,  new  sur- 
faces would  require  to  be  cut  perpendicular  to  the  principal  axis.  In 
a  natural  crystal  there  are,  therefore,  always  two  images  of  an  object 
seen  through  it. 

In  the  remaining  three  classes  of  crystals,  where  the  rhombic  octohedron, 
whether  right  or  oblique,  gives  the  predominant  character  to  the  forms,  the  exist- 
ence of  a  molecular  constitution,  regulated  by  the  same  cause  as  the  external  fig- 
ure, is  displayed  in  a  peculiarly  striking  manner.  There  is  no  longer  a  single  line 
in  the  crystal,  in  which  ordinary  refraction  alone  occurs,  but  there  are  two  such 
lines,  or  axes  of  simple  refraction.  These  axes,  however,  do  not  now  coincide 
with  the  principal  crystalline  axis,  as  was  the  case  when  there  was  only  one,  but 
their  position  is  so  dependant  on  that  of  the  crystalline  axes  as  to  show  that  they 
are  the  resultants  of  the  forces  which  emanate  from  them,  and  which  govern  all 
the  molecular  actions  of  the  crystal.  If  the  ray  of  light  does  not  pass  exactly  along 
one  of  these  axes,  but  at  some  distance  from  it,  it  is  divided  into  two  rays ;  and 
of  these  rays,  both  follow  new  and  pecuhar  laws  of  refraction,  the  proportionality  of 
the  sines  being  totally  abandoned.  The  real  distinction  of  the  crystalhne  systems 
is  thus  completely  proved  by  the  existence  of  these  remarkable  optical  properties 
by  which  they  are  characterized  ;  and  so  perfect  is  this  distinction,  that  in  cases 
where  the  external  form  and  cleavage  would  lead  us  totally  astray,  tha  optical 
properties  of  the  body  may  show  us  its  true  crystalline  position.  Thus  the  mineral 
boracite  (borate  of  magnesia)  crystallizes  in  cubes,  which  are  remarkable,  how- 
ever, for  an  anomalous  replacement  of  the  opposite  solid  angles  by  triangular  planes. 
When,  however,  boracite  was  optically  examined,  it  was  found  to  possess  double 
refraction,  and  to  appear  cubical  only  from  the  accidental  circumstances  of  its  rec- 
tangular axes  being  exactly  equal  to  each  other. 

When  a  ray  of  white  light,  S,  P,  admitted  ^into  a  darkened  room 

L     through  an  aperture, 


H,  passes  mto  a  re- 
fracting substance,  «, 
A,  B,  C,  whose  surfa- 
ces are  parallel,  its 
path  after  refraction 
is  parallel  to  its  ori- 
ginal course,  and  the 
ray  continues  white  ; 
but  if  the  surfaces  of 
the  refracting  medium  be  not  parallel,  if  it  be  a  prism.  A,  B,  C,  the 
ray  of  white  light  is  separated  into  a  num.ber  of  rays  of  light,  of 
different  colours  and  of  different  refrangibilities,  as  at  g  ;  and  if  it 
has  been  derived  from  the  sun,  in  place  of  a  round  white  image,  P, 
there  is  formed  a  series  of  solar  images  of  different  colours,  which, 
overlapping  each  other,  produce  a  long  band,  which  is  termed  the 
prismatic  spectrum,  or  image  of  the  sun.  The  order  of  colours,  the 
same  as  that  seen  in  the  rainbow,  is,  commencing  with  the  rays  of 
greatest  refrangibility,  violet,  indigo,  blue,  green,  yellow,  orange, 
and  red ;  the  length  of  the  spectrum,  and  the  space  occupied  by 
each  colour,  varying  vv'^ith  the  nature  of  the  refracting  body,  ac- 
cording to  what  is  termed  its  dispersive  power.  White  light  is, 
therefore,  not  a  simple,  but  a  highly  complex  phenomenon,  con- 


36  PRISMATIC     COLOURS. 

sisting  of  impressions  made  simultaneously  on  the  eye  by  the 
lights  of  these  various  colours.  This  may  be  verified  by  experi- 
ments of  very  simple  performance :  if  a  circular  disk  be  painted 
with  the  colours  of  the  spectrum,  in  segments  proportional  to  the 
spaces  which  each  colour  occupies  in  the  length  of  the  spectrum, 
and  then  be  made  to  revolve  rapidly  on  a  central  axis,  the  eye  loses 
the  sensation  of  the  individual  colours,  and  a  uniform  grayish- 
white  tinge  is  produced :  if  we  had  colours  as  perfect  as  those  of 
pure  solar  light,  their  reunion  would  form  pure  white,  and  this  ac- 
tually may  be  produced  by  receiving  the  spectrum  on  a  lens,  by 
which  all  the  coloured  rays  are  brought  to  bear  upon  a  single  point, 
the  focus,  where  reproduction  of  the  original  white  light  takes  place. 
Herschel  has  recently  discovered  that  there  exists  in  the  spec- 
trum, beyond  the  limits  of  the  violet  rays,  other  rays  of  a  still 
higher  refrangibility,  and  of  a  colour  which  he  proposes  to  term 
lavender.  This  lavender  light  cannot  be  merely  a  weaker  form  of 
violet  light ;  for,  on  concentrating  it  by  means  of  a  lens,  it  remains 
still  unaltered,  and  appears  to  have  no  tendency  to  assume  a  violet 
tinge  when  it  becomes  more  intense.  If  this  proposal  be  adopted, 
there  are  then  eight  prismatic  colours ;  and  although  some  peculi- 
arity of  vision,  with  regard  to  colours,  may  cause  a  difference  of 
opinion,  yet  the  evidence  obtained  by  Herschel  of  the  real  exist- 
ence of  simple  lavender-coloured  light  appears  to  be  satisfactory. 
Of  the  seven  prismatic  colours,  there  are  four  which  cannot  be 
considered  as  simple  lights,  but  as  being  formed  by  the  mixing  of 
rays  of  two  different  colours  having  the  same  refrangibility :  these 
are  orange,  green,  indigo,  and  violet ;  the  first  being  the  mixture 
of  the  superposing  extremes  of  the  red  and  yellow,  the  second  of 
the  yellow  and  blue,  and  the  third  and  fourth  of  blue  with  red  re- 
maining in  excess.  There  are,  in  fact,  blue,  red,  and  yellow  lights 
spread  over  every  portion  of  the  spectrum  j  and  if  they  were  so  in 
equal  quantities,  the  spectrum  would  be  white,  and  we  could  not 
have  any  decomposition  of  light  by  refraction  ;  but,  although  there 
are  blue  rays  of  every  degree  of  refrangibility,  yet  the  larger  pro- 
portion of  them  have  a  refrangibility  greater  than  those  of  any 
other  colour,  and  they  are  hence  collected  nearer  the  upper  extrem- 
ity of  the  spectrum.  A  portion  of  red  light  is  spread  also  over  the 
whole  surface,  but  the  majority  of  the  red  rays,  having  low  refran- 
gibility, are  thrown  to  the  opposite  extremity,  while 
the  great  proportion  of  the  yellow  rays,  having  a  mean 
refrangibility,  occupy  the  centre.  In  every  portion  of 
the  spectrum  there  is  therefore  mixed,  blue,  red,  yel- 
N^  low,  and  hence  white  light ;  but  where  these  simple 
lights  prevail,  the  colours  of  the  spectrum  are  pro- 
duced, and  where  two  are  present  in  excess  over  the 
quantities  which  form  white  light,  the  secondary  col- 
ours, orange,  green,  indigo,  and  violet,  are  formed. 
The  intensity  of  these  spectra  of  simple  light  in  each 
portion  of  the  prismatic  spectrum  is  represented  in 
the  figure  by  the  distance  of  the  curved  lines,  R,  Y,  B, 
from  the  ground,  M,  N.  Where  the  red  rises  beyond 
the  yellow  and  blue,  the  red  space  of  the  spectrum  is  produced  ; 
where  the  curve  of  the  yellow  light  prevails,  the  space  is  coloured 


ABSORPTIO  N. N  ATURAL     COLOURSOF     BODIES.    37 

yellow,  and  similarly  in  the  blue  ;  at  the  point  where  the  curves 
of  the  red  and  yellow  meet,  the  tint  is  orange  j  where  the  yellow  and 
blue  are  equal,  the  colour  produced  is  green  ;  and  where  the  red  and 
blue  are  both  in  excess  over  the  intermediate  yellow,  there  is  violet. 
This  view  of  the  constitution  of  the  solar  spectrum,  leading  to 
the  remarkable  and  unexpected  consequence  that  there  may  be 
white  light  unalterable  by  the  prism,  its  coloured  rays  having  all  the 
same  degree  of  refrangibility,  was  obtained  by  Brewster,  by  means 
of  the  absorliing  power  of  coloured  bodies.  If  a  ray  of  white  light 
be  incident  upon  a  glass  coloured  red  by  suboxide  of  copper,  it  is 
decomposed  in  passing  through  it,  the  yellow  and  blue  lights  being 
intercepted  or  absorbed,  and  the  red  rays  alone  being  transmitted. 
A  glass  does  not  possess  this  property  of  absorbing  certain  kinds 
of  light,  because  it  is  coloured ;  but  it  appears  coloured  to  our  vi- 
sion, because  it  acts  so  upon  white  light.  The  colours  so  given  to 
glass  are  of  great  importance,  from  the  use  which  is  made  of  them 
for  ornamental  purposes  in  the  arts  ',  but  they  afford  also  to  the 
chemist  one  of  the  most  delicate  and  most  certain  means  of  detect- 


many 


metallic  substances,  thus 


Cobalt  is  known  by  colouring  glass  blue. 


Nickel 

i( 

u 

orange. 

Chrome  and  vanad 

ium 

(C 

green. 

Copper         " 

(C 

u 

green  or  red. 

Iron              « 

(C 

(( 

yellow  or  green. 

Manganese 

(( 

C( 

purple. 

Silver           « 

(( 

u 

yellow  or  orange. 

Gold 

(( 

u 

crimson. 

And  these  are  not  the  only  cases  in  which  colours  are  produced. 

The  colours  of  chemical  compounds  are  so  varied,  that  there 
cannot  he  laid  down  any  principle  by  which  they  could  be  arranged : 
thus,  lead  forms  with  other  simple  bodies  compounds  which  are 
brown,  or  red,  or  yellow,  or  white ;  mercury  has  a  still  greater 
range.  There  are,  however,  certain  general  facts  worth  bearing  in 
mind,  in  which  classes  of  bodies,  to  a  certain  extent,  are  character- 
ized by  colour :  thus,  the  ordinary  compounds  of  copper  are  us»i 
ally  green  or  blue  ;  those  of  nickel,  green;  those  of  cobalt,  ri^iit 
or  blue  ;  those  of  chrome,  green  or  purple.  A  singular  property 
of  certain  bodies  consists  in  what  is  termed  dichroism^  that  is,  when 
seen  by  light  which  has  passed  in  different  directions,  they  appear 
of  different  colours,  which  are  often  complementary,  or  such  as, 
when  mixed  together,  would  form  white  light.  This  dichroism  oc- 
curs only  in  crystals  which  refract  doubly,  and  in  which  the  absorp- 
tion takes  place  unequally  along  the  two  refracted  rays. 

The  colours  of  natural  bodies,  seen  by  transmitted  light,  depend 
thus  upon  the  analysis  which  they  effect  of  the  light  incident  upon 
them,  and  of  which  they  absorb  one  portion  and  transmit  another. 
Where  the  object  is  seen  by  reflected  light,  its  colour  is  generally 
different  from  that  given  by  transmitted  light,  for  it  frequently  re- 
flects, in  considerable  quantity,  the  light  which  it  does  not  transmit. 
Thus,  solution  of  litmus,  when  seen  by  transmitted  light,  is  of  a 
rich  reddish  purple,  but,  seen  by  reflected  light,  of  a  fine,  pure  blue. 
In  general,  a  portion  of  the  light  is  reflected  from  the  second  sur- 


38  POLARIZATION     OF     LIGHT. 

face,  tinged  like  the  transmitted  portion,  which,  mixing  with  that 
properly  reflected  at  the  first  surface,  modifies  its  colour.  The 
transmitted  and  reflected  lights  are  sometimes  truly  complementa- 
ry; thus,  sea- water,  seen  by  reflection,  is  of  a  fine  green,  but  the 
light  which  it  transmits  is  pink. 

When  a  ray  of  light  is  reflected  from  any  surface  at  a  particular 
angle,  which  is  for  glass  56°  45',  and  for  water  53^  11',  it  acquires 
peculiar  properties  which  it  had  not  previously  possessed,  and  is 
said  to  be  polarized.  If  the  ray  be  then  made  to  falf  upon  a  sec- 
ond reflecting  surface,  the  effect  varies  according  to  the  position 
of  the  plane  of  the  second  reflected  ray.  The  reflection,  if  it  be 
in  the  same  plane  as  the  first,  is  complete  ;  but  if  it  be  at  right  an- 
gles to  the  first,  there  is  no  light  reflected  :  in  intermediate  positions, 
the  quantity  of  light  reflected  varies  according  to  the  angle  which 
the  second  makes  with  the  original  plane.  Light  is  thus  said  to  be 
polarized  by  reflection.  In  all  cases  of  reflection  there  is  some  of 
the  light  thus  modified ;  for,  although  the  angles  above  mentioned 
are  those  at  which  alone  the  polarization  is  complete,  at  all  other 
angles  the  light  reflected  is  partially  polarized  in  a  degree,  accord- 
ing to  its  deviation  on  either  side  from  the  proper  angles. 

Polarization  may  be  effected  by  various  other  means,  as  by  re- 
fraction or  absorption.  Even  in  ordinary  refraction  some  of  the 
light  transmitted  is  polarized,  but  it  is  mixed  with  so  much  ordina- 
ry light  that  its  properties  are  obscured :  however,  if  the  same 
quantity  of  light  be  refracted  often,  it  may  be  polarized  completely  j 
and  hence,  transmitting  a  ray  of  ordinary  light,  at  a  certain  angle, 
through  a  pile  of  parallel  glass  plates,  is  a  usual  mode  of  polari- 
zing it.  In  double  refraction,  the  polarization  of  the  refracted  light 
is  perfect,  and  the  two  emergent  rays  are  found  to  be  polarized  in 
planes  at  right  angles  to  each  other.  If  these  proceed  together  to 
the  eye,  they  mix  again,  and  thus  recompose  the  original  ray  of 
common  light ;  but  by  contrivances,  such  as  in  Nichol's  prism,  one 
may  be  turned  aside  or  absorbed,  and  then  the  other  used.  In  po- 
larizing light  by  absorption,  the  mineral  tourmaline  is  generally 
used ;  this  is  a  doubly  refracting  substance,  of  such  a  nature  that 
it  absorbs  completely  one  refracted  ray  and  transmits  the  other.  It 
therefore  gives  only  a  single  image  of  any  object,  but  this  image 
is  formed  by  light  completely  polarized.  If  two  pieces  of  tourma- 
line be  laid  together,  and  the  direction  of  their  crystalline  axes 
be  the  same  in  both,  they  act  similarly  upon  the  light,  and,  the  same 
polarized  ray  being  transmitted  by  both,  the  brightness  of  the  im- 
age is  almost  the  same  with  the  two  as  with  only  one  ;  but  if  they 
be  placed  with  their  crystalline  axes  at  right  angles  to  each  other, 
the  ray  that  is  transmitted  by  the  first  is  absorbed  by  the  second, 
and  no  light  can  pass.  If  a  ray  of  light  be  polarized  by  reflection 
or  refraction,  it  is  known  that  the  polarization  has  been  complete 
when  the  ray  is  totally  absorbed  by  a  tourmaline,  the  axis  of  which 
is  perpendicular  to  the  plane  of  polarization  of  the  ray. 

When  a  ray  of  light  so  polarized  passes  through  a  doubly  refracting  substance,  it 
undergoes  double  refraction  like  a  beam  of  ordinary  light,  being  divided  into  two 
rays,  polarized  in  two  new  planes  at  right  angles  to  each  other ;  and  when  these- 
two  rays  are  received  upon  another  polarizing  instrument,  they  are  each  divided 
into  two  portions,  again  at  right  angles,  which  unite,  as  the  planes  of  polarization 
coincide  two  and  two,  and  by  their  union  produce  some  of  the  most  beautiful  phe- 


POLARIZED     LIGHT. 


39 


nomena  in  optics ;  for  as,  in  the  doubly  refracting  substance  through  which  the  ray 
has  passed,  the  two  portions  move  with  different  velocities  according  to  the  refract- 
ive indices  of  the  body,  one  issues  in  advance  of  the  other  by  a  certain  distance, 
and  according  to  this  distance,  which  depends  on  the  difference  between  the  two 
refractive  indices  of  the  body,  a  series  of  colours  is  produced  the  most  gorgeous 
that  can  be  imagined,  for  every  little  difference  of  thickness  a  different  colour  is 
shown ;  with  the  same  thickness  the  colour  passes  through  all  the  prismatic  tints, 
according  as  the  plane  of  polarization  of  the  ray  of  light  is  altered,  and  thus  the  ac- 
tion exercised  upon  the  ray  by  the  doubly  refracting  substance,  shows  itself  in  a 
manner  equally  beautiful  and  strange. 

The  apparatus  used,  in  so  employing  polarized  light  to  exhibit  these  properties  of 
bodies,  consists  in,  first,  a  means  of  polarizing  the  ray,  which  may  be  any  of  those 
before  described,  but  which  is  generally  a  flat  plate  of  obsidian  or  blackened  glass, 
by  which  a  polarized  reflected  ray  is  given.  The  substance  to  be  examined  is  sup- 
ported upon  a  frame,  in  a  plane  perpendicular  to  the  direction  of  the  ray ;  or,  if  it  be 
fluid,  a  glass  tube  is  filled  with  it,  and,  being  closed  by  plates  of  glass  with  parallel 
surfaces,  it  is  so  placed  that  the  ray  shall  pass  along  the  axis  of  the  tube.  The  ray, 
after  emergence,  is  examined  in  order  to  detect  the  modifications  which  it  has  un- 
dergone, by  an  apparatus  termed  the  analyzing  piece,  which  may  be,  where  two 
images  are  required,  a  doubly  refracting  prism,  or,  where  only  one,  the  Nichol's 
prism,  a  doubly  refracting  prism  in  which  one  image  is  destroyed  ;  a  tourmaline 
might  also  be  used,  but  the  brown  or  olive  colour  which  tourmalines  possess  would 
deprive  the  phenomenon  to  be  observed  of  much  of  the  interest  it  derives  from  the 
beautiful  display  of  colours. 
In  nothing  is  the  action  of  polarized  light  so  interesting  as  in  the  evidence  which 

it  gives  of  the  internal  constitution  of  crystals 
of  the  different  systems  that  have  been  descri- 
bed ;  for  the  real  difference  of  molecular  ar- 
rangement, in  crystals  belonging  to  these  various 
systems,  is  rendered  still  more  remarkably  dis- 
tinct by  the  action  which  they  exercise  upon 
light  in  this  peculiar  state  of  plane  polarization. 
,  I  If  a  ray  of  polarized  light  pass  along  the  Princi- 
pe pal  axis  of  a  crystal  belonging  to  the  rhombo- 
hedral  or  to  the  square  prismatic  system,  and 
on  issuing  be  examined  by  means  of  an  analy- 
zing plate,  the  axis  of  the  crystal  is  seen  to  be 
surrounded  by  a  series  of  beautifully  rainbow- 
coloured  rings,  the  centre  being  occupied  either 
by  a  cross  which  is  alternately  black  and  white, 
according  as  the  analyzing  plate  revolves,  as 
with  calc  spar,  fig.  a,  or  a  circular  space  which  is  occupied  successively  by  a  series 
uf  colours  similar  to  those  which  form  the  rings,  as  in  quartz.  / 

If  the  crystal  belong  to  any  of  the  more  complex  systems,  and  its  optical  axes 
^:;!|-;:^  be  not  much  inclined  to  one  another,  there  will 

be  seen,  on  transmitting  a  ray  of  polarized  light 
along  the  crystalline 
axis  intermediate  to  the 
two,  a  double  system 
of  rings,  which,  uniting, 
form  a  very  beautiful 
curved  figure,  such  as 
is  represented  in  figure 
h,  which  is  the  phenom- 
jCnon  as  seen  with  ni- 
tre. The  curves  are  fj 
crossed  by  two  bands,  g 
black  or  white,  accord- 
ing as  the  analyzing 
plate  revolves,  but 
which,  when  the  crys- 
tal is  turned  round  on 
its  principal  axis,  open 
out,  revolving  each  on 
its  axis,,  A  or  B,  and 


40 


OPTICAL  PROIERTIES  OF  CRYSTALS. 


bend  with  the  convexity  towards  the  centre  of  the  figure.  In  substances,  as  topai 
and  carbonate  of  soda,  where  the  axes  make  a  large  angle  with  each  other,  tho 
complete  system  of  rings  cannot  be  at  once  seen,  and  only  one  half,  or  the  portion 
round  one  axis,  as  in  the  case  of  topaz  in  figure  c,  is  visible  in  one  direction. 
The  angle  of  the  axes  in  topaz  is  18°  30',  but  in  other  cases  it  may  be  much  greater ; 
thus  with  green  sulphate  of  iron  they  are  at  right  angles  with  each  other. 

The  physical  production  of  these  beautiful  phenomena  involves  optical  principles 
too  recondite  to  be  here  introduced.  It  is,  for  the  purposes  of  the  chemist,  sufticient 
to  say  that  they  arise  from  the  mutual  action  of  the  two  rays,  which  are  produced 
by  the  double  refraction  of  the  crystal ;  and  hence,  if  there  be  not  double  refraction, 
there  can  be  no  colours  produced.  With  crystals  of  the  regular  system  there  ia 
consequently  no  such  result,  and  hence  such  crystals  are  recognised  by  the  com 
plete  absence  of  coloured  rings. 

The  optical  properties  of  the  different  systems  of  crystallization  may  be  thuf 
summed  up. 


Single  refraction. 
.  )  Double  refraction 
.    J      with  one  axis. 

'    (  Double  refraction 
with  two  axes. 


No  rings  by  polarized  light 
Simple  system  of  rings  b} 
polarized  light. 

Double  system  of  rings  by 
polarized  light. 


Regular  system. 

2.  Rhombohedral  system 

3.  Square  prismatic  system 

4.  Right  prismatic  system 

5.  Oblique  prismatic  system  .       .    > 

6.  Doubly  oblique  prismatic  system  ) 
When  crystals  form  in  a  crowded  or  confused  manner,  it  frequently  happens  that 

not  merely  are  their  surfaces  modified  in  a  complicated  way,  but  that  several  crys- 
tals become  soldered  together  so  completely  as  to  simulate  a  single  form  which 
does  not  belong  to  the  substance  of  which  the  crystal  is  composed.  These  crystals 
are  called  macks,  or  twin  or  hemitrope  crystals.  Some  bodies  have  a  remarkable 
tendency  to  crystallize  in  this  way  ;  thus,  sulphate  of  potash  had  been  long  consid- 
ered as  crystallizing  in  six-sided  prisms,  terminated  by  six-sided  pyramids ;  and 
such  crystals  of  it  occur  with  almos^  exactly  the  proportions  of  the  rhombohedral 
system';  but  by  optical  examination,'  this  figure  was  found  to  be  composed  of  three 
or  six  of  the  true  crystals,  which  are  right  rhombic  prisms  of  the  fourth  system. 
These  being  laid  together,  form,  by  their  angles  exactly  joining,  a  six-sided  prism ; 
but  when  tested  by  polarized  hght,  they  show,  in  place 
of  the  system  of  rings  which  a  true  crystal  should  pro- 
duce, the  tesselated  structure  of  the  figure.  In  many 
cases,  the  agglutination  of  the  crystals  is  less  complete, 
and  irregular  figures,  with  the  sides  channelled  by  the 
imperfect  joints,  are  found.  A  substance  which  il- 
lustrates remarkably  this  tendency  to  the  macled  form 
is  the  mineral  analcime,  which  is  termed  also  cubizite, 
from  its  forms  belonging  most  perfectly,  so  far  as  ex- 
ternal characters  go,  to  the  regular  system.  It  has, 
however,  no  distinct  cleavage  planes,  and  refracts 
When  examined  by  a  ray  of  polarized  light,  the  cube  of  analcime  gives  a 
most  beautiful  appearance.  The  diagonals  of  each 
surface  become  occupied  by  lines,  which  are  alter- 
nately black  and  white,  according  as  the  analyzer 
is  made  to  revolve,  and  in  the  intervening  triangu- 
lar spaces  the  richest  colours  of  the  rainbow  sue 
ceed  one  another,  according  to  the  optical  laws. 
This  crystal  is  therefore  made  up  of  a  great  number 
of  other  crystals  belonging  to  some  one  of  the 
more  complex  systems  ;  but  its  structure  is  so  ex- 
traordinary, that  the  determination  of  the  form  of 
its  real  crystal  has  been  as  yet  impossible  In 
this  instance,  and  in  that  of  boracite  alrea  ly  no- 
ticed, the  optical  properties  have  been  the  means 
of  showing  the  true  nature  of  bodies  which,  from  their  external  form,  should  oth- 
erwise have  been  ranked  among  those  which  crystallize  in  the  forms  of  the  regular 
system. 

It  has  been  noticed  as  a  general  character  of  the  crystals  of  the  rhombohedral 
and  square  prismatic  systems,  that  by  the  analysis  of  a  beam  of  polarized  light 
transmitted  along  the  principal  axis,  there  is  seen  a  system  of  coloured  rings  trav- 
ersed by  a  cross,  alternately  black  and  white,  as  the  analyzing  plate  revolves,  but 


doubly. 


ROTATIVE     POWER     OF     LIQUIDS.  41 

farther,  that  in  the  case  of  quartz  the  cross  is  not  produced,  the  central  space  being 
occupied  in  succession  by  all  the  prismatic  colours.  Even  in  quartz  there  have 
been  found  two  modifications  of  this  property ;  with  one,  the  analyzing  plate  must 
be  turned  from  right  to  left,  to  obtain  the  spectral  colours  from  red  to  violet ;  but 
with  the  other,  the  rotation  must  be  in  the  opposite  direction,  to  show  them  in  the 
same  order.  The  molecules  of  the  quartz  cause  these  colours  to  appear  along  the 
axis  by  turning  the  plane  of  polarization  of  each  colour  round  in  a  different  degree, 
and  thus  opening  out  into  a  fan  shape  those  combined  lights,  which  had  previously 
affected  the  eye  only  as  white  or  black.  This  faculty  does  not  depend  upon  the 
manner  of  arrangement  of  the  particles  of  the  quartz  ;  it  involves  the  chemical  na 
ture  of  the  molecules ;  and,  although  some  observations  appeared  to  connect  it  with 
the  crystaUine  structure,  it  is  now  fully  established  to  be  independent  of  it.  In 
fact,  this  property  of  circular  polarization,  as  it  is  termed,  belongs  to  certain  bodies, 
independent  of  their  arrangement,  and  even  in  many  cases  accompanies  them  whei 
they  enter  into  combination.  It  is  even  found  in  liquids,  particularly  the  volatilfi 
oils ;  and  when  oil  of  turpentine  is  converted  into  vapour,  its  molecules  preserve 
unaffected  their  rotative  power.  Its  existence  is,  however,  subjected  to  remarka- 
ble anomalies  ;  thus,  when  oil  of  turpentine  combines  with  muriatic  acid  and  forms 
artificial  camphor,  it  retains  its  power  of  rotation  ;  but  when  the  artificial  camphor 
is  decomposed  and  the  oil  of  turpentine  got  back  again,  its  power  of  changing  the 
plane  of  polarization  of  the  ray  of  light  has  totally  disappeared. 

[These  phenomena  of  circular  polarization  may  be  readily  traced.  If  from  a 
crystal  of  quartz  a  disk  is  cut  transversely,  a  system  of  rings  will  be  seen  enclosing 
a  circular  coloured  space.  If  the  disk  be  turned  round,  no  change  takes  place ;  but 
if  the  analyzing  plate  turns,  the  colour  passes  through  a  series  of  tints,  which,  after 
100°  of  rotation,  may  end  in  a  sombre  violet..  If,  now,  we  cut  from  the  same  crys- 
tal another  disk  twice  the  thickness  of  the  former,  and  make  use  of  it,  we  shall  find 
the  tint  different  from  what  it  last  was ;  but,  by  turning  the  analyzing  plate  100°, 
we  may  bring  it  back  again  to  the  same  sombre  violet :  with  a  plate  three  times 
as  thick,  we  should  have  to  turn  100°  still  farther  to  produce  the  same  tint,  and  for 
each  additional  thickness  an  additional  100°.  We  therefore  infer  that,  when  polar- 
ized light  passes  along  the  axis  of  a  crystal  of  quartz,  its  planes  of  polarization  ro- 
tate circularly,  or,  rather,  spirally,  in  the  crystal ;  and  this  takes  place  in  some  spe- 
cimens from  right  to  left,  and  in  others  from  left  to  right.  Under  these  circum- 
stances, light  is  said  to  undergo  circular  polarization.] 

In  cases,  therefore,  where  bodies  exhibit  this  action  upon  light,  their  power  of 
rotation  becomes  an  important  numerical  fact  in  their  descriptions,  and  it  may  be 
measured  by  the  angle  through  which  a  certain  thickness  of  the  body  is  capable  of 
moving  the  plane  of  polarization  of  a  ray  of  homogeneous  light,  such  as  the  pure 
red  given  by  glass  coloured  by  sub-oxide  of  copper.  It  may  also  be  expressed, 
when  white  light  is  used,  by  the  angle  at  which  the  pure  violet  is  produced,  and  the 
direction  of  rotation  is  expressed  by  an  arrow  turned  either  to  the  right  or  left,  ac- 
cording as  it  is  necessary  to  make  the  analyzing  crystal  revolve  to  the  one  or  the 
other  side.  Thus,  the  rotative  power  of  oil  of  turpentine,  contained  in  a  tube  six 
inches  long,  is  for  red  light  45°< — ^,  and  of  oil  of  lemons,  in  the  same  length, 
84°9a»-^.  The  rotative  power  of  quartz  is  about  685  times  greater  than  that  of 
oil  of  turpentine.  This  property  is  beautifully  applied  to  trace  the  changes  which 
occur  during  the  saccharine  fermentation :  a  solution  of  starch  possesses  a  high 
^8^ — >-  power ;  but  it  gradually  changes  into  the  sugar  of  grapes,  the  rotative  power 
of  which  is  -< — ^:.  Hence  the  action  of  the  starch,  when  fermentation  has  com- 
menced, rapidly  diminishes,  until  there  is  so  much  sugar  formed  that  the  ^ — >  and 
< — ««s  exactly  balance,  and  the  solution  is  totally  without  action  upon  a  polarized 
ray  ;  alter  that,  the  quantity  of  sugar  still  increasing,  the  rotation  becomes  < — ^, 
»nd  increases  until  all  the  starch  has  been  decomposed.  With  such  a  solution, 
knowing  the  total  quantity  of  starch  originally  dissolved,  the  measure  of  its  rotative 
power  enables  the  quantity  of  sugar  present  to  be  at  once  calculated.  The  juices  of 
plants  which  contain  sugar,  as  the  beet-root,  the  maple,  the  sugar-cane,  may  be  ex- 
actly valued  by  a  simple  determination  of  their  rotative  power  compared  with  their 
specific  gravities.  This  property  of  the  circular  polarization  of  a  ray  of  light,  which 
at  the  first  aspect  might  appear  so  far  removed  from  proper  chemical  inquiry 
or  useful  application,  becomes  thus  an  instrument  from  which  the  distiller  or  sugar- 
boiler  may  every  day  derive  advantage ;  and  when  we  come  to  discuss  the  means 
by  which  we  endeavour  to  learn  the  internal  constitution  of  bodies  produced  by 
chemical  affinity,  we  shall  find  that  the  light  which  ordinary  polarization  throws  upon 

F 


fiS  "     WAVE     THEORY     OF     LIGHT. 

the  internal  mechanical  stracture  of  the  crystal  is  not  more  brilliant  than  that  which 
we  obtain  of  the  arrangement  of  the  chemical  constituents  by  their  circularly  po- 
larizing power. 

Some  specimens  of  quartz  appear  destitute  of  this  rotative  power :  the  purple 
quartz,  amethyst,  is  generally  so,  and  gives  with  polarized  light  the  ordinary  black 
cross.  But  these  peculiarities  of  quartz  are  related  to  their  crystalline  arrangement. 
Thus,  in  those  specimens  which  possess  rotative  power,  the  sohd  angles  of  the  pyr- 
amid {k,  page  28)  are  generally  replaced  by  planes  which  are  unequally  inclined  to 
the  axes  ;  and  where  these  planes  are  present,  the  direction  of  the  rotation  can  be 
foretold,  it  being  to  the  right  or  to  the  left,  according  as  these  unsymmetrical  facea 
are  inclined.  Such  crystals  are  termed  plagihedral ;  as  in  the  cases  where  no  such 
faces  can  be  traced,  the  rotative  power  is  generally  absent,  and  this  arises,  as  is  re- 
markably evident  in  amethyst,  from  the  crystal  being  formed  of  separate  crystals 
rolled  up  together ;  and  as  these  may  possess  opposite  rotations,  and  so  neutralize 
each  other,  the  action  on  light  should  be  like  that  of  calcareous  spar,  which  has  no 
rotative  power.  Such  crystals  are  truly  macles ;  and  hence  the  circular  polarization 
may  show  a  still  more  intimate  crystalline  arrangement  than  could  be  detected  by 
light  in  its  ordinary  polarized  condition. 

With  such  an  example,  it  was  not  difficult  to  conclude  that  the  power  of  rotation 
depended  on  the  crystalline  arrangement,  particularly  as  quartz,  in  all  its  uncrys- 
tallized  conditions,  is  devoid  of  all  rotative  power ;  and,  accordingly,  until  the  dis- 
covery of  the  power  of  rotation  in  liquids,  and  that  this  property  was  found  to  ac- 
company the  molecules  of  the  body  through  all  states  of  aggregation,  it  was  con- 
sidered to  have  its  origin  in  the  mechanical  structure  of  the  body ;  but  we  must  now 
invert  the  argument,  and  infer  that  the  difference  of  rotative  power  in  right-handed 
and  left-handed  quartz  does  not  result  from  the  difference  of  crystalline  arrangement, 
but  that  this  last  is  caused  by  actual  difference  of  properties  in  the  molecules  them- 
selves, of  which  the  most  remarkable  is  detected  by  the  opposite  actions  upon  light. 

The  impression  of  light  was  at  one  time  considered  to  be  produ- 
ced by  a  series  of  exceedingly  minute  particles,  of  a  peculiar  sub- 
stance, emanating  from  the  sun  and  from  burning  or  luminous  bodies, 
and  which  strike  upon  the  eye.  This  idea  has  been,  however,  now 
almost  totally  abandoned,  and  all  the  phenomena  are  considered  to 
arise  from  the  vibrations  of  an  exceedingly  attenuated  medium, 
thrown  into  waves  by  luminous  bodies  of  every  kind,  and  v/hich,  fill- 
ing all  space,  and  being  diffused  through  the  substance  of  the  most 
solid  bodies,  and  occupying  the  spaces  between  their  more  substan- 
tial molecules,  transmits  and  modifies  these  vibrations,  and  confers 
upon  substances  transparency  or  opacity,  colour,  and  all  other  proper- 
ties of  acting  upon  light  which  they  may  possess. 

This  medium,  or  luminiferous  ether,  as  it  is  termed,  is  supposed 
capable  of  vibrating  in  waves  of  different  lengths,  and  from  this 
difference  in  length  of  wave  arises  the  difference  in  colour  of  the 
light  produced.  The  shortest  wave  produces  violet,  the  most  re- 
frangible light ;  the  longest  wave,  red,  the  least  refrangible  light : 
the  length  of  the  wave  being  in  all  cases  inversely  proportional  to 
the  refrangibility  of  the  light.  The  impression  of  the  different  col- 
ours arises,  therefore,  precisely  as  the  impression  of  different  sounds 
is  produced,  by  a  difference  in  the  length  of  the  waves  in  the  vibra- 
ting air  j  the  shortest  wave,  in  sound,^  giving  the  highest  note  and 
in  light  giving  the  violet  colour  The  actual  length  of  these  waves 
of  light  is  extremely  small :  for  violet  light  there  are  57-490  in  an 
inch;  for  red,  39-180;  the  average  of  the  different  colours  being 
50-000  ;  and  hence,  in  Avhite  light,  there  acts  upon  the  eye  in  every 
second  610-000000-000000  luminiferous  vibrations. 

In  the  case  of  doubly  refracting  crystals  with  one  axis,  that  is, 
those  belonging  to  the  rhombohedral  and  the  square  prismatic  sys- 


WAVE     THEORYOF     LIGHT.  43 

tern,  the  elasticity  of  the  ether  is  supposed  to  be  so  far  modified 
by  the  arrangement  of  the  molecules  of  the  body,  that  the  velocity 
of  propagation  of  the  waves  is  more  rapid  in  one  direction  than  in 
another  at  right  angles  to  it,  and  hence  there  are  two  refracted  rays. 
In  the  three  systems,  the  crystals  of  which  have  double  refraction 
with  two  axes,  the  elasticity  of  the  ether  is  supposed  to  be  differ- 
ent in  each  of  three  perpendicular  directions,  and  hence  neither 
refracted  ray  can  follow  the  ordinary  law.  It  is  thus,  as  has  been 
already  stated,  that  the  classification  of  all  crystallized  bodies  in 
these  systems  is  shown,  not  to  be  an  arbitrary  assumption,  but  a 
principle  based  upon  our  most  decisive  evidence  of  molecular  ar 
rangement. 

The  rays  of  light  derive  some  of  their  most  remarkable  proper 
ties  from  the  principle  that  the  vibrations  are  accomplished  in  a 
direction  perpendicular  to  the  direction  of  the  rays.  Thus,  if  we 
conceive  a  ray  of  light  moving  from  north  to  south,  the  little  vi- 
brations which  constitute  it  are  efiected  in  a  direction  east  or  west, 
and  in  every  other  direction  equally  perpendicular  to  its  path  j  and 
ordinary  light  is  characterized  by  the  fact  that  its  vibrations  are 
accomplished  in  every  imaginable  plane.  If  we  reduce  these  vi- 
bratory movements  to  a  single  plane,  the  light  becomes  polarized, 
and  is  then  in  the  condition  for  dissecting  the  interior  of  crystal- 
lized bodies,  and  exhibiting  the  beautiful  illustrations  of  their  struc- 
ture that  have  been  already  noticed.  But  it  would  lead  us  too  far 
away  from  our  proper  subject  to  enter  into  the  description  of  polar- 
izing apparatus,  or  even  of  its  principles,  in  detail,  as  the  indication 
just  given  of  its  nature  is  suflicient. 

Perhaps  the  most  remarkable  and  the  most  important  principle 
of  the  theory  of  waves  is,  that  two  portions  of  light  may  act  on 
each  other  so  as  to  interfere  and  produce  darkness,  though  at  an- 
other point  they  may  form  light  of  double  brilliancy.  To  effect 
this,  it  is  only  necessary  they  should  be  in  opposite  states  of  vibra- 
tion, that  is,  while  the  waves  of  one  ray  should  be  rising  up,  those 
of  the  other  should  be  falling  down :  these  motions  then  compen- 
sate each  other,  and  the  result  is  the  same  as  if  no  vibratory  mo- 
tion had  existed,  that  is,  as  if  no  light  had  arrived  at  the  points 
where  the  rays  met.  It  is  only,  however,  when  one  of  the  simple 
coloured  lights  is  employed,  that  actual  blackness  occurs  by  the 
mutual  destruction  of  the  rays  :  if  white  light  be  used,  there  is  pro- 
duced a  brilliant  series  of  prismatic  colours ;  for  at  the  moment 
when  the  red  light  is  destroyed,  the  remaining  blue  and  yellow  form 
a  bright  green  ;  when  the  yellow  is  destroyed,  the  red  and  blue  pro- 
duce a  purple.  Cases  of  this  kind  of  interference  are  extremely 
common:  it  is  thus  that  the  coloured  rings  of  crystals,  and  the 
colours  of  the  soap-bubble  or  oil-film  are  produced.  The  brilliancy 
of  the  plumage  of  birds,  the  lustre  of  many  minerals,  as  of  labrado- 
rite,  arise  from  the  interference  of  the  portions  of  light  which  after 
reflection  thus  act  on  each  other. 

Under  ordinary  circumstances,  light  is  always  associated  with 
heat  5  the  sun,  the  source  of  warmth  to  the  surface  of  our  globe, 
being  also  the  natural  origin  of  light :  and  in  most  cases  where  light 
is  artificially  produced,  it  is  associated  with  heat,  which  is  also  ca- 


44 


PHOSPHORESCENCE. 


pable  of  being  transmitted  in  a  radiant  form.  It  was,  indeed,  once 
considered,  that  at  certain  temperatures  heat  became  converted 
into  light,  and  that  the  colour  of  the  light  depended  on  the  degree 
of  heat  j  a  body,  when  first  rendered  luminous  by  being  heated, 
emitting  a  dull  red  light,  which  gradually  becomes  brighter  as  the 
temperature  rises,  until  at  the  highest  degree  of  heat  the  light 
emitted  is  pure  white,  and  similar  in  constitution  to  the  solar  ray. 
The  powers  of  emitting  heat  and  of  emitting  light  are,  however, 
although  so  frequently  associated,  quite  independent  and  distinct  j 
and  the  rays  of  heat  and  those  of  light  may  be  perfectly  separated 
from  each  other.  It  would  anticipate  too  much  the  account  of  radi- 
ant heat  to  describe  the  means  of  separating  the  heating  from  the 
luminous  qualities  of  ordinary  light;  but  elsewhere  they  will  be 
described  in  full.  A  body  may  become  luminous  when  very  mod- 
erately heated,  as  is  the  case  with  many  minerals,  as  fluor  spar 
Light  may  be  produced  also  by  the  friction  of  bodies,  as  by  rubbing 
two  pieces  of  sugar  briskly  together,  or  by  striking  together  two 
pieces  of  quartz ;  and  in  these  cases  it  is  difficult  to  assign  its  true 
origin,  as,  possibly,  a  minute  trace  of  the  substance  may  be  very 
intensely  heated.  There  are  also  many  bodies  which,  when  ex- 
posed to  the  light  of  the  sun  after  having  been  made  red  hot,  ap- 
pear to  absorb  a  portion  of  it,  and  become  capable  of  emitting  it 
slowly,  giving  a  pale  bluish  light  for  some  time  afterward  in  the 
dark.  This  occurs  particularly  with  chloride  of  barium,  native  sul- 
phate of  barytes,  carbonate  of  lime,  and  a  great  number  of  other 
bodies.  Such  substances  are  said  to  be  phosphorescent.  Thus  fluor 
spar  is  rendered  so  by  heat,  sugar  and  quartz  become  so  by  friction, 
and  the  electric  spark  is  capable  of  conferring  the  phosphorescent 
property  on  a  great  variety  of  bodies. 

Organized  substances  become  phosphorescent  in  the  first  stages 
of  their  decay ;  thus,  rotten  wood,  and  fish  before  actual  putrefac- 
tion has  commenced.  The  light  emitted  is,  in  such  cases,  the  re- 
sult of  an  exceedingly  slow  but  distinct  process  of  combustion  ;  it 
requires  the  presence  of  atmospheric  air,  or  oxygen,  although  an 
exceedingly  small  quantity  may  suffice,  and  it  is  extinguished  and 
revived  by  all  such  means  as  facilitate  or  retard  the  chemical  ac- 
tion of  the  air  upon  organic  bodies.  The  light  emitted  by  the  glow- 
worm and  the  fireflies,  as  well  as  by  the  great  variety  of  marine 
zoophytes,  appears  also  to  be  not  merely  an  evolution  of  light  as  a 
product  of  vital  action,  but  to  arise  similarly  from  the  secretion  of 
a  substance,  which,  slowly  combining  with  the  oxygen  of  the  at 
mosphere,  produces  the  light  as  a  consequence  of  combustion 
Animal  phosphorescence  is,  therefore,  to  be  ascribed  to  chemical 
action. 

The  white  light,  derived  from  diflerent  sources,  does  not  always 
possess  the  same  physical  constitution.  If  the  coloured  spectrum 
produced  by  the  solar  ray  be  closely  examined,  it  will  be  found 
crossed  by  a  multitude  of  black  lines,  indicating  the  total  absence 
in  the  sun's  light  of  rays  of  certain  refrangibilities.  That  this  is 
inherent  in  the  light  is  shown  by  the  fact,  that  when  we  change 
the  nature  of  the  prism,  the  position  of  the  space  in  which  these 
black  lines  occur  may  alter,  but  the  lines  preserve  all  their  relative 


CHEMICAL     RAYS     IN     THE     SPECTRUM.  45 

distances  from  each  other  totally  unchanged.  Hence,  in  place  of 
referring  to  the  colours  of  the  spectrum  in  order  to  characterize  its 
properties,  those  lines,  of  which  the  most  remarkable  is  a  double  line 
situated  in  the  yellow  space,  are  used  as  marks.  The  light  of  the 
sun,  of  the  moon  and  planets,  as  well  as  white  light  produced  by 
our  processes  of  combustion,  all  consist  of  the  same  elements  of 
yellow,  red,  and  blue,  and  all  are  distinguished  by  the  same  set  of 
lines.  In  the  light  of  some  of  the  fixed  stars  the  same  lines  are 
found,  as  is  the  case  with  Pollux ;  but  in  the  spectrum  formed  by 
rays  from  Sirius  or  from  Castor,  this  double  line  does  not  occur, 
but  is  replaced  by  one  broad  line  in  the  yellow  space,  and  two  re 
markable  dark  lines  in  the  blue.  It  is  very  curious,  that  if  we  ex- 
amine the  spectrum  through  certain  coloured  media,  as  the  vapours 
of  iodine  or  bromine,  we  find  additional  black  lines,  and  by  using 
gaseous  nitrous  acid  these  become  almost  innumerable,  and  in- 
crease so  much  when  the  gas  is  heated  that  the  spectrum  is  oblit- 
erated and  the  gas  becomes  opaque.  It  is  possible  that  such 
takes  place  at  the  origin  of  the  light  of  the  heavenly  bodies,  and 
that  the  sun  and  the  fixed  stars  are  involved  in  absorbing  atmo- 
spheres, which  allow  only  certain  rays  to  pass,  and  that  hence  there 
may  exist  in  nature  kinds  of  light  from  which  the  eye  of  man  is 
screened  forever  by  means  of  such  an  impervious  veil. 

Some  classes  of  chemical  substances  are,  to  a  certain  extent, 
characterized  by  the  facility  with  which  they  are  decomposed  when 
under  the  influence  of  light.  The  salts  of  silver,  of  gold,  of  plati- 
na,  and,  in  some  instances,  of  mercury,  are  subject  to  this  influence. 
A  great  variety  of  vegetable  and  animal  bodies  undergo  important 
changes  in  their  constitution  by  the  action  of  the  solar  rays,  the 
development  of  certain  colours  requiring  the  agency  of  light,  and 
the  majority  of  colours  being  destroyed  when  its  action  is  too  great : 
hence  the  fading  of  dyes  arises.  The  power  of  light  thus  to  mod- 
ify the  affinity  by  which  chemical  combination  is  produced,  has 
been  found  to  be  exercised  specially  by  the  violet  or  more  refran- 
gible extremity  of  the  spectrum,  and  even  with  great  intensity  by 
invisible  rays  quite  outside  of  the  luminous  space,  and  extending 
beyond  the  lavender-coloured  prismatic  space  of  Herschel.  It  has 
been  also  considered  that  the  rays  of  the  red  extremity  of  the  spec- 
trum possessed  chemical  properties  of  an  inverse  kind,  and  that  the 
decomposition  produced  by  violet  light  might  be  counteracted,  and 
the  elements  brought  to  recombine  by  the  red  rays.  This  is  not 
certain.  All  that  has  been  established  is,  that  there  exist  in  solar 
light,  and  probably  in  all  light  derived  from  sources  of  combustion, 
three  distinct  sets  of  rays,  the  one  of  proper  light,  which  produces 
only  luminous  effects,  the  second  of  radiant  heat,  the  nature  of 
which  will  be  specially  examined  in  the  following  chapter,  and  the 
third  of  rays  which,  though  neither  luminous  nor  heating,  exercise 
an  influence  on  chemical  affinity,  and  the  nature  of  which  will  be 
discussed  with  more  detail  when  the  subject  of  chemical  aflinity 
and  its  relations  to  the  other  physical  forces  has  been  described. 


46  EFFECTS     OF     HEAT. 


CHAPTER  III. 

OF    HEAT    CONSIDERED   AS    CHARACTERIZING   CHEMICAL    SUBSTANCES. 

At  almost  every  step  of  chemical  inquiry  it  is  necessary  to  in- 
troduce the  action  of  heat,  either  as  modifying  the  results  of  the 
chemical  action  of  bodies  upon  each  other,  or  as  affording  charac- 
ters by  which  the  substances  we  operate  upon  may  be  distinguished. 
The  doctrine  of  heat  and  the  history  of  its  effects  have  consequent- 
ly, at  all  periods,  formed  an  important  portion  of  the  studies  of  the 
chemist ;  and  it  is,  indeed,  only  lately,  since  the  brilliant  course  oi 
discoveries  that  was  opened,  and  so  successfully  prosecuted  by 
Melloni  and  by  Forbes,  has  identified  the  theories  of  heat  and  light, 
that  this  subject  has  been  contemplated  in  its  proper  aspect  as  a 
physical  science,  and  its  application  and  influence  in  chemistry  have 
ceased  to  be  considered  as  making  up  the  science,  properly  so  call- 
ed, of  heat. 

Of  all  the  physical  sciences,  however,  that  of  Heat^  or  Thermotia^, 
as  it  is  now  termed,  is  the  most  important  to  the  chemist  in  guiding 
him  in  his  operations,  and  in  the  accurate  description  of  their  results 
On  this  account  it  will  be  necessary  to  describe  the  properties  of  heai 
more  in  detail  than  those  of  any  other  of  the  physical  agents,  and 
to  illustrate  these  properties  by  more  numerous  references  to  cases 
in  which  their  utility  in  chemistry  is  apparent. 

The  effects  of  heat,  by  which,  according  to  their  degrees,  bodies 
may  be  characterized,  are, 

1st.  Change  of  volume  for  a  given  change  of  temperature.  K::^ 
pansion. 

2d.  Quantity  of  heat  required  to  produce  a  given  change  of  te¥> 
perature.     Specific  heat. 

3d.  Temperature  necessary  for  liquefaction.     Melting  points. 

4th.  Temperature  necessary  for  giving  a  certain  elasticity  to  j. 
vapour.     Boiling  points. 

5th.  Quantity  of  heat  required  to  produce  a  given  change  of  a^' 
gregation.     Latent  heat  of  liquids  and  vapours. 

6th.  Manner  and  rapidity  of  communicating  or  receiving  he.-il 
Conduction  and  radiation  of  heat. 

The  subject  of  heat  will  therefore  be  studied  specially  under 
these  heads ;  and  it  will  be  necessary  to  introduce  an  account  of 
our  mode  of  measuring  heat  and  temperature  by  the  thermometer 
and  pyrometer,  and  to  add  some  observations  on  the  physical  rela- 
tions of  heat  and  light,  and  on  the  physical  theory  of  heat. 

SECTION  I. 

OF    EXPANSION. 

When  describing  the  effects  of  cohesion,  I  have  already  noticed 
that  the  molecular  constitution  of  all  bodies  might  be  considered 


REPULSIVE  POWER  OF  HEAT.  47 

to  depend  on  the  relative  power  of  the  attractive  force,  cohesion^ 
and  the  repulsive  force  of  heat^  upon  their  particles.  That  where 
the  attraction  was  in  excess,  the  molecules  were  knitted  firmly  to- 
gether to  form  a  solid  body ;  but  that  where  repulsion  was  most  pow- 
erful, all  cohesion  was  lost,  and  the  body  assumed  the  form  of  a  va- 
pour or  a  gas.  In  the  intermediate  condition,  where  the  forces  ap- 
peared to  be  nearly  in  equilibrium,  the  liquid  state  was  produced, 
in  which  the  molecules  of  the  body  appeared  still  to  unite  by  a  trace 
of  remaining  cohesion,  but  that  they  moved  among  one  another 
with  perfect  ease,  and  the  slightest  external  force  might  disarrange 
them  entirely.  Now  the  change  from  one  to  the  other  of  any  two 
of  these  conditions  is  not  quite  abrupt.  If  a  cold  body  be  gradu- 
ally heated  until  it  shall  begin  to  liquefy,  its  particles  do  not  remaki 
in  the  same  condition  up  to  the  moment  when  they  separate  so  far 
as  to  change  their  state  of  aggregation ;  on  the  contrary,  from  the 
instant  that  the  substance  becomes  warm,  the  change  begins  j  the 
molecules  of  the  body  gradually  separate,  occupy  more  space  than 
before,  and  from  the  very  commencement  of  the  increase  of  heat, 
the  body,  though  it  may  remain  solid,  yet  expands.  In  the  same 
manner,  if  a  liquid  be  heated,  the  change  of  aggregation  does  not 
commence  until  the  increase  of  heat  has  reached  a  certain  degree  ; 
but  from  the  beginning  a  change  of  volume  occurs,  the  increase  of 
which  marks  the  gradual  diminution  of  cohesion.  In  gases  there 
can  take  place  no  farther  change  of  form,  and  the  only  effect  which 
heat  can  produce  upon  them  is  expansion. 

This  power  of  repulsion  which  we  suppose  heat  to  exercise,  in  causing  the  tran- 
sition from  one  state  of  aggregation  to  another,  as  well  as  the  expansion  which  oc- 
curs without  change  of  form,  may  become  directly  evident  to  the  senses,  at  least 
in  a  partial  way,  in  many  cases.  Thus,  many  powders,  if  sprinkled  on  a  warm 
capsule,  or,  still  better,  on  a  silver  plate,  are  thrown  into  violent  motion,  and  dissi- 
pated by  the  mutual  repulsion  of  their  particles,  independent  of  any  currents  of  air 
which  might  affect  them.  When  liquids,  particularly  alcohol  and  the  oils,  are 
brought  to  boil,  the  drops  which  are  mechanically  thrown  up  out  of  the  liquid  do 
not  mix  with  it  on  falling  back,  but  roll  about  on  the  surface,  and  appear  to  repel 
each  other,  and  to  be  repelled  by  the  hot  glass  of  the  vessel  in  a  remarkable  de- 
gree. If  a  brass  poker,  strongly  heated,  be  allowed  to  rest  against  a  cold  iron  bar, 
or,  still  better,  if  a  rounded  bar  of  brass  be  made  very  hot  and  laid  upon  a  flat  block 
of  lead,  the  surface  of  the  cold  metal  becoming  heated,  repels  the  warmer  brass, 
which  instantly  falls  down  again,  by  its  weight  overcoming  the  repulsion,  when  the 
metal  cools.  When  the  brass  again  touches  the  metal  or  lead,  the  latter  is  again 
heated  at  the  point  of  contact,  and  again  there  is  repulsion  succeeded  by  a  new 
contact,  and  these  repeated  motions  throw  the  bar  of  brass  into  a  state  of  tremulous 
agitation,  which  being  conveyed  to  the  ear  by  the  intervening  air,  gives  a  remark- 
ably distinct  and  agreeable  musical  tone.  The  better  conductor,  the  heated  body, 
and  the  worse  conductor  (provided  both  are  metals),  the  cold  body  can  be,  the  more 
successful  is  the  result. 

This  force  of  repulsion  is  iTxade  still  more  distinct,  and  even  measurable,  by  an 
experiment  devised  by  Powell.  When  a  flat  and  a  convex  glass  plate  are  strongly 
pressed  together,  they  still  do  not  touch,  but  are  separated  by  an  exceedingly  thin 
space,  by  the  action  of  light  on  which  there  are  produced  coloured  rings,  like  those 
seen  on  the  surface  of  a  soap-bubble,  or  in  a  film  of  oil  floating  upon  water.  Each 
colour  belongs  to  a  distinct  and  measurable  thickness  of  this  space ;  and  when  such 
an  apparatus  is  gradually  heated,  the  rings  close  in  towards  the  centre,  showing 
that  the  glass  plates  recede  from  one  another,  and  the  degree  of  repulsion  may  be 
determined  from  the  narrowing  which  occurs  in  the  breadth  of  any  particular  col- 
oured ring,  according  as  the  temperature  rises. 

In  gases,  the  expanding  effect  of  heat  is  unaffected  by  any  dis- 
turbing cause  5  there  is  no  cohesion  remaining  to  impede  its  oper- 


48  MEASURE      OF     HEAT. 

ation ;  hence  a  certain  increase  of  heat  afTects  all  gases  alike  j  and 
no  matter  how  hot  or  how  cold  a  gas  maybe,  a  certain  increase  of 
heat  produces  the  same  increase  of  volume  in  every  case.  In  sol- 
ids and  in  liquids,  however,  it  is  different ;  the  expansion  which  oc- 
curs is  but  the  result  of  the  opposing  forces  of  cohesion  and  of 
heat,  and  hence  the  amount  of  expansion  depends  not  only  on  the 
quantity  of  heat  which  is  applied,  but  also  on  the  power  of  cohe- 
sion by  which  it  is  resisted,  and  which  depends  upon  the  nature  of 
the  body.  Consequently,  every  fluid  and  every  solid  expands  in  a 
degree  which  is  peculiar  to  it.  There  is  yet  another  consequence 
of  the  influence  of  cohesion  upon  the  expansion  of  solids  and  of 
liquids.  Let  us  represent  the  cohesive  force  of  a  certain  substance, 
for  example,  copper,  by  10,  and  let  us  suppose  that  we  apply  to  it  a 
quantity  of  heat  which  will  expand  it  through  a  space  which  we 
will  call  1,  and  will  diminish  its  cohesion  from  10  to  9.  If,  then, 
we  apply  another  quantity  of  heat  exactly  equal  to  the  former,  it 
will  not  have  to  contend  against  a  cohesion  of  10,  but  of  9,  and 
will,  consequently,  be  able  to  produce  an  expansion  of  more  than 
1,  say  1|,  and  it  will  reduce  the  cohesion  more  than  it  did  before, 
as  from  9  to  7^.  If,  then,  another  equal  quantity  of  heat  be  added, 
it  having  still  less  opposing  force  to  overcome,  will  act  still  more 
powerfully,  reducing,  for  example,  the  cohesion  from  7|  to  5,  and 
the  increase  of  volume  becoming,  in  place  of  1^,  2.  In  solids  and 
liquids,  the  rate  of  expansion  increases  thus,  with  the  temperature, 
from  the  diminution  of  cohesion ;  but  in  gases,  where  the  cohesion 
remains  the  same,  or,  rather,  is  completely  absent,  the  expansion  is 
proportional  to  the  additional  quantity  of  heat,  no  matter  how  much 
may  have  been  sensibly  present  in  the  gas  before. 

I  shall  now  proceed  to  consider  in  detail  the  rates  of  expansion 
of  various  bodies,  commencing  with  those  of  gases,  for  which  the 
simplest  results  have  been  obtained.  Before  doing  so,  however,  it 
is  necessary  to  study  the  means  by  which  we  ascertain  the  quanti- 
ties of  heat  which  we  add  or  subtract  from  bodies  to  eflect  their 
expansion  or  contraction;  to  investigate,  in  fact,  the  principle  on 
which  the  thermometer  and  pyrometer  are  founded,  and  such  de- 
tails of  their  construction  as  shall  hereafter  be  found  necessary  to 
be  known. 

Let  abhea  glass  bulb  with  a  long  and  narrow  neck,  which  is  divided 


o 


^ 


M    M    i   i   I    I    i    M    M    M    M 


KD 


by  a  scale,  as  in  the  figure,  of  which  each  division  is  a  certain  part,  as 
ToV 0  ^^  ^^^^  volume  of  the  bulb.  Let  us  suppose  the  bulb  a  to  be  fill- 
ed with  pure  dry  air,  at  the  same  degree  of  heat  as  that  at  which  ice 
melts,  and  separated  completely  from  the  external  air  by  means  of 
a  globule  of  mercury,  c,  which  is  exactly  settled  at  the  commence- 
ment of  the  scale.  If,  now,  the  instrument  be  warmed,  the  air  in 
the  bulb  expands,  and,  according  as  it  increases  in  volume,  pushes 
before  it  into  the  tube  the  globule  of  mercury.  This  last  serves, 
therefore,  as  an  index  of  the  increase  of  volume  which  the  air  gains 
as  it  is  heated,  and  by  its  position  we  can  read  off'  the  exact  proper- 


NATURE     OF     TEMPERATURE.  49 

tion.  If  the  source  of  heat  be  water  boiling,  under  ordinary  cir- 
cumstances, at  Dublin,  at  the  level  of  the  sea,  as  soon  as  the  air 
has  been  heated  to  exactly  the  same  degree  as  the  water,  the  glob-, 
ule  will  be  found  to  have  arrived  at  the  365th  division  on  the  scale. 
Therefore,  1000  measures  of  air,  on  being  heated  from  the  degree 
of  melting  ice  to  that  of  boiling  water,  become  1365.  Now  as,  from 
the  constitution  of  air  and  gases,  the  effect  of  each  increase  of 
heat  is  the  same,  we  may  consider  the  whole  quantity  of  heat  which 
it  received  from  the  boiling  water  to  be  divided  into  365  parts  or 
degrees,  and  each  of  these  parts  being  applied  separately  to  the 
bulb,  should  have  increased  the  volume  of  air  by  y  ^V o  P^^^j  o^'  should 
have  converted  the  1000  volumes  into  1001.  There  is  thus  obtain- 
ed a  scale  of  expansion  which  is  quite  artificial  and  arbitrary  cer- 
tainly, but  which,  having  been  once  contrived,  may  be  with  perfect 
accuracy  applied  to  measure  different  quantities  of  heat.  Thus,  if 
we  warm  water  to  blood  heat,  and  immerse  in  it  the  air  bulb  as  de- 
scribed, the  expansion  of  the  air  will  move  the  globule  of  mercury 
to  the  degree  122,  which  is  almost  exactly  the  one  third  part  of 
the  365,  and  hence  the  water,  in  being  heated  from  the  degree  of 
melting  ice  to  that  of  blood  heat,  received  almost  exactly  one  third 
of  the  quantity  of  heat  which  should  have  made  it  boil,  and  its  tem- 
perature is  one  third  as  high. 

I  have  here  spoken  of  measuring  the  successive  quantities^  of 
heat  which  the  air  received,  and  in  this  case  the  manner  of  expres- 
sion is  sufficiently  accurate,  as  well  as  the  most  simple.  But  it  is 
necessary  to  explain  the  true  meaning  of  the  words  quantity  of  heat 
and  temperature.  The  amount  of  expansion  which  a  hot  body  is 
capable  of  producing  in  the  air  or  mercury  of  the  thermometer, 
measures  truly  what  is  called  its  temperature.  The  temperature  has 
nothing  whatsoever  to  do  with  the  quantity  of  heat  which  the  body 
may  contain,  it  refers  only  to  its  expanding  power.  If  a  quantity 
of  water,  of  oil,  of  ether,  of  mercury,  or  of  iron  produce  all  the 
same  amount  of  expansion  in  the  air  or  mercury  of  the  thermometer, 
we  say  they  have  the  same  temperature,  without  pretending  to  know 
anything  of  the  quantity  of  heat  which  they  may  actually  possess. 
The  thermometer  and  pyrometer  are  therefore  instruments  for 
measuring,  not  heat,  but  temperature^  and  we  denote  by  degrees  of  tem- 
perature the  amount  of  expansion  produced,  marked  off  on  any  arbi- 
trary scale  which  we  may  think  proper  to  adopt. 

Gases  expanding  more  than  any  other  bodies,  the  air  thermom- 
eter is  the  most  sensible  that  can  be  made,  and  in  the  form  just 
described  it  is  an  exact  measure  of  heat,  subject  only  to  one  cor- 
rection, which  is,  that  although  the  air,  in  being  heated  from  the 
degree  of  melting  ice  to  that  of  boiling  water,  actually  expands 
fVVo  ^^  ^^^  volume,  yet  that  expansion  is  not  all  visible,  for  the  glass 
bulb  expands  also  on  being  heated,  although  in  a  very  small  propor- 
tion, and  holds  ^-^„^  more  than  it  did  when  cold  ;  the  visible  expan- 
sion on  the  scale  is  therefore  only  363  degrees,  and  this  must  be 
allowed  for  to  have  complete  accuracy.  The  form  of  the  air  ther- 
mometer which  has  been  just  described  is,  however,  quite  unfit  for 
ordinary  use ;  the  adjustment  of  the  index  globule,  the  necessity 
that  the  instrument  should  be  perfectly  horizontal,  which  is  quite 

G 


50 


AIR     THERMOMETER. 


impossible  in  the  majority  of  practical  cases,  renders  this  kind  of 
an  air  thermometer  too  unmanageable  ;  and  since  the  air  changes  its 
volume  very  much  for  every  change  of  pressure,  and  our  atmo- 
sphere varies  in  its  weight  almost  every  hour,  an  air  thermometer 
left  open,  as  at  the  orifice  ^,  would  change  continually  without  ref- 
erence to  the  degrees  of  heat  at  all,  and  would  thus  give  false  in- 
dications. The  end  of  the  tube  must  therefore  be  accurately 
closed. 

When,  however,  the  air  inside  is  thus  confined,  the  simple  rule 
of  the  dilatation  being  proportional  to  the  increase  of  heat,  ceas- 
es completely.  For  if  the  point  b  be  closed,  and  the  bulb  a  be 
heated,  the  globule  of  mercury,  in  moving  along  the  scale,  con- 
denses the  air  before  it,  and  thus  generates  an  elastic  force,  by 
which  the  expansion  is  resisted  and  diminished  in  amount  j  the  de- 
grees would  therefore  be  no  longer  equal,  but  rapidly  diminish  in 
size,  so  that  on  the  upper  parts  of  the  scale  they  could  not  be  dis- 
tinguished from  one  another,  and  would  hence  be  useless.  But  by 
having  a  second  bulb,  in  the  next  figures,  the  elasticity  of  the  air 
'ompressed  in  the  cold  bulb  increases  much  less  rapidly,  and  the 
*cale  to  be  applied  to  the  stem  connecting  the  bulbs  is  easily  con- 
structed. As  the  stems  of  these  air  thermometers  are  generally 
upright,  mercury  would  be  too  heavy  a  fluid  to  introduce  in  a  column, 
and  the  mere  globule  which  we  supposed  in  the  example  first  taken 
-would  not  answer,  from  the  facility  with  which  it  might  be  broken 
or  displaced :  to  any  watery  or  spirituous  fluid  there  is  also  an  ob- 
jection, that  the  amount  of  expansion  would  be  increased  to  an 
uncertain  degree  by  the  portion  of  fluid  converted  into  vapour.  To 
avoid  these  errors,  oil  of  vitriol  may  best  be  employed,  and  it  is 
generally  coloured  red  to  render  the  motion  of  the  fluid  column 
more  easily  visible. 

An  air  thermometer,  closed  perfectly,  indicates  a  change  of  tem- 
uerature  only  by  the  difference  between  the  elasticity  of  the  air  in 
the  two  bulbs.  No  matter  how  high  or  how  low 
the  temperature  may  be,  if  it  affects  both  bulbs  to 
the  same  degree,  the  air  in  each  bulb  presses  on 
the  liquid  column  with  the  same  force,  and  exactly 
balances  the  other.  The 
instrument  indicates,  there- 
fore, such  temperatures  only 
as  affect  one  bulb  and  not 
the  other;  the  difference,  in 
fact,  between  the  tempera- 
tures of  the  two  bulbs,  and 
hence  is  properly  called  the 
differential  thermometer.  In 
fig.  A  the  one  bulb  is  much  above  the  other. 
In  fig.  B  the  stem  which  terminates  above  in 
a  bulb  is  open  below,  and  plunges  into  the 
fluid  which  the  inferior  bulb  contains.  This 
lower  bulb  is  soldered  or  cemented  at  its  or- 
ifice round  the  tube,  so  as  perfectly  to  pre- 
vent the  action  of  the  air.     Fig  C  represents 


MERCURIAL      THERMOMETER.  51 

the  most  ordinary  form  j  the  bulbs  are  on  a  level,  and  are  connected 
by  a  U-shaped  stem. 

The  air  thermometer  is  thus,  in  all  its  forms,  liable  to  so  many  in- 
conveniences from  the  limited  range  of  its  scale,  if  it  be  not  open 
to  the  air,  and  from  the  complex  form  which  the  scale  assumes  if 
the  external  air  be  prevented  from  communication,  that  it  is  never 
made  use  of  in  practice  except  in  some  particular  cases,  which 
shall  hereafter  be  specially  noticed.  We  are  therefore  obliged  to 
have  recourse,  for  our  accurate  measures  of  temperature,  to  other 
bodies,  which,  though  not  so  sensible  as  air,  ofier  more  practical 
advantages. 

The  liquids  which  are  generally  used  to  measure,  by  their  expan- 
sion, change  of  temperature,  are  alcohol  and  mercury.  The  former, 
in  being  raised  from  the  melting  point  of  ice  to  that  at  which  itself 
boils,  expands  y§^,  whereas  air  within  the  same  limits  would  have 
expanded  y^o)  heing  about  three  and  a  half  times  as  much  as  alco- 
hol :  and  mercury,  in  having  its  temperature  raised  from  the  melt- 
ing point  of  ice  to  the  boiling  point  of  water,  expands  y^f oj  ^^ 
about  ^V  ^f  ^^®  quantity  of  air.  Hence  these  liquids  are  much  less 
sensible,  as  thermometers,  than  air ;  but  their  other  advantages  are 
decidedly  in  their  favour.  Alcohol  is  only  employed  where  the 
object  is  to  measure  very  great  degrees  of  cold  j  and  for  this  pur- 
pose it  is  admirably  fitted,  as  it  is  the  only  liquid  that  has  not  yet 
been  frozen.  Mercury,  on  the  other  hand,  may  be  applied  to  an 
extensive  range  of  temperatures,  as  it  freezes  only  by  the  applica- 
tion of  an  intense  cold ;  and  it  does  not  boil  until  it  arrives  nearly 
at  a  red  heat.  It  has  the  largest  interval  between  its  freezing  and 
boiling  points  of  any  liquid  that  is  known.  Mercury  is  also  admi- 
rably suited  to  be  a  measure  of  heat,  by  the  accidental  circumstance 
that  its  expansion,  when  contained  in  a  glass  bulb,  is  accurately 
proportional  to  the  temperature,  and  its  indications  therefore  abso- 
lutely true. 

This  is  occasioned  by  the  circumstance  that,  as  in  all  liquids  and  solids  the  ex- 
pansion increases  with  the  temperature,  the  rate  of  increase  of  the  capacity  of  the 
glass  bulb  exactly  corresponds  to  the  increase  of  the  rate  of  expansion  of  the  mer- 
cury, and  absorbs  it ;  so  that  the  visible  expansion  of  the  mercury  is  uniform,  and  a 
degree  in  every  part  of  the  scale  is  of  the  same  length.  For  instance,  if  mercury 
and  air  be  together  heated  from  the  freezing  to  the  boiling  point  of  water,  1  000 
measures  of  air  become  1-365,  and  10000  measures  of  mercury  become  10- 180. 
If,  then,  they  be  both  heated  as  much  more,  the  air,  expanding  at  the  same  rate, 
becomes  1-730;  but  the  mercury,  expanding  more  rapidly,  becomes  10-363:  and 
hence,  if  a  scale  was  so  applied,  there  would  be  shown  180  degrees  in  the  lower, 
and  183  degrees  in  the  upper  part  of  the  scale,  to  the  same  quantity  of  heat.  This 
is  corrected  by  the  expansion  of  the  glass  bulb  which  holds  the  mercury.  At  the 
temperature  of  melting  ice,  the  bulb  holds,  for  example,  10  000  measures  of  mer- 
cury ;  but,  on  being  heated  to  that  of  boiling  water,  it  holds  10026.  The  mercury, 
however,  having  become  10- 180,  the  difference,  (10180 — 10026)=154  measures, 
passes  into  the  stem,  and  makes  the  rise  of  temperature  upon  the  scale.  When, 
now,  the  second  portion  of  heat  is  applied,  the  mercury  becomes  10 -363  ;  and  the 
glass  bulb,  expanding  at  the  same  time,  becomes  able  to  hold  10055 :  and  hence 
the  difference,  (10-363 — 10-055)r=308  measures,  passes  into  the  stem  and  moves 
along  the  scale.  Thus  the  visible  portion  of  the  expansion  is  rendered  exactly  pro- 
portional to  the  increase  of  heat ;  and  the  mercurial  thermometer  becomes,  not 
merely  the  most  convenient,  but  the  most  accurate  measure  of  heat  which  we 


In  constructing  a  thermometer,  the  first  requisite  is,  that  the  bore  of  the  tube 
shall  be  perfectly  uniform,  for  otherwise  the  result  above  described,  which  gives  all 


52  OF  THE  STANDARD  INTERVAL. 

Its  real  value  to  the  quicksilver  thermometer,  would  be  completely  inapplicable  in 
practice.  This  is  ascertained  by  finding  that  a  small  quantity  of  mercury,  moved  up 
and  down  the  tube,  occupies  exactly  the  same  length  in  every  part.  A  proper  tube 
having  been  thus  obtained,  one  extremity  is  closed,  and  a  bulb  is  blown  upon  it ; 
another  is  formed  near  the  open  end,  leaving  a  space  between  the  two  bulbs  some- 
what longer  than  the  thermometer  is  intended  to  be.  The  tube  and  bulbs  having 
been  heated,  are  allowed  to  cool,  with  the  open  end  immersed  in  pure  and  recently- 
boiled  mercury.  By  the  contraction  of  the  internal,  and  the  pressure  of  the  exter- 
nal, air,  a  quantity  of  mercury  is  forced  into  the  first  bulb,  and  ultimately  the  bulb 
at  the  closed  end  is  filled  completely  by  a  repetition  of  the  process.  When  the  in- 
troduction of  the  mercury  has  been  completed,  the  open  end  of  the  tube  is  closed 
by  a  little  sealing-wax,  to  prevent  the  admission  of  air  or  dust,  and  the  tube  is  al- 
lowed to  cool  with  the  terminal  bulb  down.  When  it  has  cooled  completely,  it  is 
again  heated  to  the  highest  degree  it  is  intended  to  indicate  ;  and  the  fine  flame  of 
a  blowpipe  being  directed  upon  the  point  which  is  to  be  the  extremity  of  the  tube, 
it  is  melted,  and  the  orifice  completely  closed.  When  the  instrument  then  cools, 
there  remains  over  the  mercury  in  the  stem  a  perfectly  empty  space. 

It  remains,  then,  to  attach  the  scale.  When  describing  the  general  principle  of 
the  thermometer,  in  the  example  of  dry  air,  pushing,  by  its  expansion,  an  index 
globule  of  mercury  along  the  stem,  the  scale  which  included  the  interval  from  the 
freezing  to  the  boiling  points  of  water  was  supposed  to  be  divided  into  365  parts. 
This  was,  however,  merely  because  the  1000  measures  of  air,  in  being  heated 
through  that  interval,  expand  in  that  proportion.  The  scales  that  are  actually  used 
are  different,  although  quite  as  arbitrary.  The  simplest  scale  is  that  in  which  the 
interval  between  the  freezing  and  boiling  points  of  water,  which  is  universally  ta- 
ken as  the  standard,  is  divided  into  100  parts ;  it  is  termed  the  centigrade  scale, 
and  is  employed  in  France,  and  generally  in  Germany  and  the  north  of  Europe.  In 
it  ice  is  said  to  melt  at  0°,  and  water  to  boil  at  100°.  On  the  scale  generally  used 
in  this  country  and  Great  Britain,  the  standard  interval  is  divided  into  180  degrees, 
but  the  melting  point  of  ice  is  not  taken  as  0°,  but  as  32°,  from  a  very  absurd  idea  of 
Fahrenheit,  who  was  the  inventor  of  this  scale.  He  mixed  together  snow  and  salt, 
and  having  thus  produced  a  more  intense  cold  than  anybody  before  him  had  done, 
he  imagined  that  he  had  attained  a  point  at  which  the  bodies  had  no  heat  at  all, 
that  he  had  arrived  at  what  was  afterward  called  the  absolute  zero,  and  he  called 
that  point  0°  ;  the  melting  point  of  ice  was  then  32°,  and  water  boiling  at  180^ 
higher,  its  temperature  was  marked  212°.  There  is  another  scale,  sometimes,  but 
not  often  used ;  that  of  Reaumur,  in  which  the  melting  point  of  ice  is  the  com- 
mencement or  0°,  and  the  boiling  point  of  water  is  marked  80°.  The  first  step  in 
the  graduation  is  to  mark  the  extreme  points  of  the  standard  interval :  the  melting 
point  of  ice,  and  the  boiling  point  of  water.  To  do  this  correctly,  some  precautions 
must  be  taken.  I  have  frequently  spoken  of  the  melting  point  of  ice  and  the  freez- 
ing point  of  water  as  meaning  the  same  temperature,  and  under  ordinary  circum- 
stances they  do  so  ;  but  they  do  not  so  nece&sarily.  The  freezing  of  water  is  a 
crystallization,  and,  like  all  other  cases  of  crystallization,  may  take  place  with  great- 
er or  less  facility.  If  water  be  agitated,  or  if  it  be  contained  in  rough  vessels,  af- 
fording prominences  to  which  the  crystals  of  ice  may  attach  themselves,  it  freezes 
exactly  at  32°  on  Fahrenheit's  scale  ;  but  if  the  water  be  kept  carefully  at  rest,  and 
be  contained  in  smooth  glass  vessels,  free  from  dust,  it  maybe  easdy  cooled  to  25°, 
and  has  been  cooled  even  to  15°,  without  becoming  solid.  Hence,  if  we  wished  to 
determine  the  zero  by  means  of  freezing  water,  an  error  might  easily  be  committed. 
Ice,  however,  under  all  circumstances,  melts  at  32° ;  and  hence,  by  plunging  the  bulb 
of  the  thermometer  into  a  mixture  of  ice  and  water,  and  marlcing  on  the  stem  the 
point  at  which  the  level  of  the  mercury  settles,  the  first  fixed  point  upon  the  scale  is 
had.  To  determine  the  second  point,  that  at  which  water  boils,  it  is  necessary  to  at- 
tend to  the  condition  of  the  barometer.  It  will  be  hereafter  described  how  the  boil- 
ing point  of  every  liquid  varies  with  the  atmospheric  pressure  ;  it  is  here  enough 
to  notice,  that  either  the  boiling  point  must  be  determined  when  the  barometer 
stands  at  29  8  inches,  or  a  correction,  which  will  be  hereafter  given,  applied  for  any 
difference  of  height  which  may  exist.  The  water  must  boil  also  in  a  metallic  ves- 
sel, for  water  in  a  glass  or  porcelain  vessel  has  its  boiling  point  somewhat  raised, 
and  as  the  thermometer  is  to  be  used  for  chemical  purposes,  the  bulb  and  only  a 
small  portion  of  the  stem  should  be  immersed  in  the  boiling  water.  The  two  fixed 
points  having  been  thus  obtained,  the  interval  is  to  be  divided  into  180  equal  parts 
or  degrees  for  the  ordinary  scale  of  Fahrenheit,  and  then  32  of  these  degrees 
counted  downward  from  the  point  of  melting  ice  to  obtain  the  zero  ;  for  the  zero 


THERMOMETRIC     SCALES.  53 

ctt^.-oi  be  truly  got  in  the  manner  in  which  Fahrenheit  is  supposed  originally  to 
have  invented  it,  for  a  mixture  of  snow  and  salt  is  found  to  produce  always  a  cold 
of  about  2°  below  zero,  or  — 2°.  As  our  range  of  temperature  passes  far  below 
the  zero  of  the  scale,  we  count  downward  precisely  as  we  count  upward,  only 
prefixing  in  the  former  case  the  —  minus  sign,  whereas,  in  the  degrees  above  zero, 
the  -|-  plus  sign  is  usually  omitted.  Thus,  4-50°,  or  simply  50°,  is  fifty  degrees 
above  zero,  but  — 50°  is  the  same  number  below  zero.  To  construct  the  centi 
grade  scale,  the  method  is  precisely  the  same,  except  that  we  make  the  point  of 
melting  ice  0°,  and  that  of  boiling  water  100°,  and  a  degree  being  the  y-J-^  of  the 
interval,  we  count  up  and  down  from  zero,  precisely  as  in  the  other  case. 

It  is  generally  proper  to  lay  a  thermometer  aside  for  a  few  weeks  after  having 
filled  it  before  proceeding  to  apply  the  scale.  For  it  is  found  that  as  there  is  a  vac- 
uum in  the  instrument  above  the  mercury,  the  external  pressure  acting  on  the  thin 
glass  of  the  bulb  gradually  changes  its  form  a  little,  and  would  move  up  the  fixed 
points,  sometimes  through  one  or  two  degrees,  if  they  had  been  marked  before  the 
change. 

The  centigrade  scale  is  of  such  extensive  use  in  the  works  of  most  distinguished 
chemists,  that  it  is  well  to  show  more  closely  its  relation  to  the  ordinary  scale  of 
Fahrenheit,  and  the  means  of  reducing"  one  to  the  other.  The  standard  interval  is 
divided  into  ISO'*  Fahrenheit,  and  into  100  centigrade  degrees,  and  hence  a  degree 
of  the  former  is  equal  to  j^^-,  or  |ths  of  a  centigrade  degree.  To  reduce  any  inter- 
val in  centigrade  degrees  to  Fahrenheit's,  it  is  therefore  to  be  multiplied  by  9  and 
divided  by  5  ;  and  for  the  reduction  from  Fahrenheit  to  centigrade,  the  number  is 
to  be  multiplied  by  5  and  divided  by  9  :  but  as  the  degrees  do  not  in  number  start 
from  the  same  point,  the  Fahrenheit  scale  being  already  32*^  when  the  centigrade 
begins,  it  is  necessary  to  add  32°  to  the  number  of  Fahrenheit  degrees  which  have 
been  attained  by  calculation  from  the  centigrade,  and  to  subtract  32°  from  the  num- 
ber of  degrees  on  Fahrenheit,  which  are  to  be  converted  into  degrees  upon  the  oth- 
er scale. 

Thus,  to  reduce  167°  of  Fahrenheit,  we  proceed  : 

167—32=135,  and  135xf=75<=, 
Jtiii  find  it  to  correspond  to  75°  centigrade.    And  to  reduce  65°  centigrade  to  Fah- 
renheit's scale,  we  say, 

65  X  1=117,  and  117+32=149°, 
corresponding,  therefore,  to  149°  of  Fahrenheit. 

Reaumur's  scale  being  to  the  centigrade  scale  as  4  to  5,  similar  reductions  are 
made  to  and  from  it,  by  using  ^  in  place  of  f ,  as  has  been  employed  in  the  example. 

The  range  of  temperatures  observable  with  a  mercurial  thermom- 
eter on  Fahrenheit's  scale  is  from  — 39^  to  +630°.  The  mercury- 
freezes  a  little  below  — 40°  ;  and  though  it  does  not  boil  until  it  ar- 
rives at  660°,  yet  the  quantity  of  vapour  which  it  forms  when  very 
near  its  boiling  point,  prevents  its  indications  from  being  quite  ex- 
act between  that  point  and  630°. 

Our  means  of  estimating  temperatures  above  the  boiling  point 
of  mercury  are  not  at  all  so  perfect  as  those  that  have  been  de- 
scribed for  the  lower  degrees  of  heat.  Mercury,  when  boiling,  is 
not  in  the  slightest  degree  luminous,  but  the  temperature  at  which 
a  heated  body  becomes  visible  in  the  dark,  by  emitting  a  dull  red 
light,  is  not  much  higher.  Numerous  instruments  have  been  in- 
vented for  the  purpose  of  determining  the  higher  temperatures, 
particularly  of  furnaces,  and  hence  they  have  been  called  pyrome- 
ters. Of  these,  the  only  one  which  appears  to  give  accurate  re 
suits,  and  hence  deserves  description,  is  that  of  Daniell. 

In  this  pyrometer,  the  change  of  temperature  is  shown  by  the  excess  of  the  ex- 
pansion of  an  iron  bar  over  the  expansion  of  a  black-lead  case  in  which  it  is  en- 
closed. The  iron  rod  a  is  somewhat  shorter  than  the  black-lead- ware  case,  and  a 
plug  of  earthenware,  b,  which  fits  tight  in  the  case,  abuts  against  the  iron  rod  in- 
side, and  projects  as  at  c  in  the  figure.  Let  us  suppose  the  length  of  the  case  to  be 
5  inches,  that  of  the  iron  rod  4^  inches,  and  that  of  the  earthenware  plug  to  be  1 
inch.  If  tlie  whole  be  heated  until  the  case  shall  have  expanded  by  12  parts,  the 
iron  rod  will  have  increased  in  length  by  44,  and  the  earthenware  piece  by  7,  which., 


64 


daniell's    pyrometer. 


added  to  44,  makes  51.  If  the  black-lead  case  did  not  increase  in  size,  all  these 
51  parts  should  project ;  but  as  there  is  additional  room  made  for  12,  the  project- 
ing portion  is  only  39.  If  the  parts  of  the  apparatus  were  all  free  to  move,  each 
contracting  again  on  cooling,  the  result  would  be  that  all  would  be  restored  to  their 
original  position  ;  but  this  is  not  the  case.  The  bar  of  iron,  in  expanding,  pushes 
out  before  it  the  plug  of  earthenware,  which,  however,  is  held  so  tight  in  the  case 
that  it  cannot  go  back  again  when  the  apparatus  has  become  cold.  The  protrusion 
of  the  earthenware  plug  is  therefore  a  permanent  index  of  the  greatest  amount  of 
expansion  that  had  been  produced  while  the  instrument  was  exposed  to  heat.  This 
expansion  is,  however,  very  small.  The  three  pieces  being,  as  stated,  5,  4i,  and  1 
inch,  the  expansion,  when  heated  from  32°  to  212°,  is  only  yf  |^  of  an  inch ;  and  as 
this  indicates  180  degrees,  the  expansion  for  a  degree  is  only  about  f-^o  of  an 
inch.  It  is  therefore  necessary  to  magnify  this  expansion,  in  order  that  the  indi- 
cation maybe  read  off;  and  this  is  done  by  means  of  a  graduated  circular  arch,  d  e 
/,  with  a  movable  index,  kept  by  means  of  a  spring  constantly  at  0^  when  undis- 
turbed. On  fitting  this  scale  to  the  pyrometric  black-lead  case,  after  it  has  been 
in  the  fire,  the  projection  of  the  earthenware  plug,  c,  catches  in  the  prolonged  heel 
of  the  index,  e,  and  moving  it  round,  the  point  of  the  index  travels  over  a  portion 
of  the  graduated  scale,  and  indicates  the  number  of  degrees  through  which  the 
temperature  had  been  raised.  This  instrument  is  not  always  made  of  the  same 
size,  and  hence  the  absolute  amount  of  expansion  may  vary,  which,  however,  is  re- 
duced to  the  same  proportion  on  the  scale,  by  which,  also,  the  increase  in  the  rat« 
of  expansion  of  the  metallic  bar  at  very  high  temperatures  must  be  allowed  for. 
By  means  of  this  very  ingenious  and  useful  instrument,  Professor  Daniell  has  de- 
termined the  melting  point  of  most  of  the  important  metals,  and  also  several  other 
temperatu]  es  at  which  remarkable  phenomena  occur. 

The  p  Tometers  of  Wedgewood,  of  Guyton,  and  many  others 
that  have  been  proposed,  must  be  considered  as  now  totally  aban- 
doned, and  do  not  require  notice. 

The  most  delicate,  and  perhaps  the  most  important,  measure  of 
heat  that  has  been  contrived,  is  one  totally  independent  of  expan- 
sion, and  founded  on  the  measurement  of  an  electric  current  which 
a  change  of  temperature  produces  under  certain  circumstances.  It 
is  the  Thermo-multiplier  invented  by  Nobili.  The  principle  which 
the  instrument  involves  in  its  construction  and  its  form  will  be  de- 
scribed under  the  head  of  electricity,  and  the  remarkable  results 
obtained  by  means  of  it,  and  which  have  completely  remoielled 


TABLE     OP     TEMPERATURES. 


55 


our  ideas  of  the  physical  constitution  of  heat,  will  be  noticed  in 
another  place. 

It  may  be  of  interest  to  subjoin  the  temperatures  on  Fahrenheit's 
scale  at  which  some  of  the  most  remarkable  effects  of  heat  are 
produced : 

—  135°.  The  greatest  cold  that  has  been  produced. 

—  121°.  The   solid  compound   of  alcohol  and  carbonic   acid 

melts. 

Greatest  cold  by  ordinary  freezing  mixtures. 

Temperature  of  the  planetary  spaces. 

Greatest  cold  observed  in  the  arctic  regions. 

Sulphuric  ether  congeals. 

Nitric  acid  congeals. 

Mercury  congeals. 

Oil  of  vitriol  freezes. 

Oil  of  turpentine  freezes. 

Wine  freezes. 

Blood  freezes. 

Ice  melts. 

Olive  oil  freezes. 

Heat  of  human  blood. 

Phosphorus  melts. 

Alcohol  boils. 

Rose's  metal  melts. 

Newton's  metal  melts. 

Water  boils. 

Sulphur  melts. 

Mercury  boils. 

Antimony  melts. 

Red  heat. 

Heat  of  a  common  fire. 

Brass  melts. 

Silver  melts. 
1996°.  Copper  melts. 
2200°.  Gold  melts. 
2786°.  Cast  iron  melts. 
The  details  which  have  been  given,  regarding  the  construction  of  the  air  ther- 
a  >meter,  will  show  sufficiently  the  principle  upon  which  the  detennination  of  the 
rhye  of  expansion  of  gaseous  bodies  has  been  effected.     The  exact  amount  of  dila- 
taion  was  first  ascertained  by  Dalton  and  Gay  Lussac  nearly  at  the  same  time. 
Tt«e  apparatus  of  Gay  Lussac  consisted  of  a  tin  vessel,  A,  having  five  apertures^ 




91°. 



58°. 



60°. 



47°. 



45°. 

, 

39°. 

+ 

1°. 

+ 

14°. 

+ 

20°. 

+ 

25°. 

+ 

32°. 

+ 

36°. 

+ 

98°. 

+ 

108°. 

+ 

174°. 

+ 

201°. 

+ 

211°. 

•4- 

212°. 

+ 

218°. 

+ 

662°. 

+ 

810°. 

+ 

980°. 

+ 

1141°. 

+ 

1869°. 

+ 

1873°. 

By  means  of  the  aperture  in  the  side,  o',  there  is  introduced  the  tube  with  the  boH^ 


56 


EXPANSION     OF     AIR. 


fr  g\  containing  air  dried  by  the  tube  h  h',  and  arranged  with  the  graduated  scale  and 
index  globule  of  mercury  m,  as  described  in  page  48.  By  the  opposite  orifice,  o,  is 
fixed  a  thermometer,  h  s,  the  bulb  b  of  which  is  on  the  same  level  as  the  bulb  of 
the  air  tube.  By  means  of  the  central  orifice  in  the  top,  a  second  thermometer,  v, 
is  introduced,  the  bulb  of  which  is  situated  exactly  in  the  centre  of  the  box.  The 
other  orifices  in  the  top  are  for  the  free  escape  of  steam.  The  apparatus  so  being 
arranged,  water,  rendered  ice-cold  by  some  snow  or  ice  floating  on  it,  is  introduced, 
until  the  thermometers  and  the  air  bulbs  are  covered  to  the  depth  of  a  couple  of 
inches,  and  the  index  globule  of  mercury  is  thus  brought  to  the  zero  of  the  scale. 
The  box  is  then  placed  on  a  furnace,  B,  and  gradually  heated  :  the  rise  of  temper- 
ature is  indicated  by  the  thermometer,  t,  the  expansion  by  the  motion  of  the  index 
globule,  and  at  each  degree  the  thermometer  and  air  bulb  may  be  compared  to- 
gether until  the  water  is  brought  to  boil. 

By  substituting  other  substances  for  water,  such  as  oil,  or  a  bath  of  fusible  metal, 
the  rate  of  expansion  may  be  determined  for  still  higher  temperatures,  and  has  been 
thus  ascertained  by  Dulong  and  Petit  up  to  the  boiling  point  of  mercury. 

From  such  experiments,  conducted  by  Dalton,  Gay  Lussac,  and  Dulong,  it  result- 
ed, that  1000  volumes  of  air,  when  heated  from  32°  to  212°,  became  1375,  and  that 
the  change  was  in  proportion  for  higher  or  lower  temperatures.  The  numbers  ac- 
tually obtained  may  be  stated  as  in  the  following  table  : 


Temperature    on   a 
Mercurial     Ther- 
monfeter  by  Fah- 
renheit's Scale. 

10000  Volumes 
of  Air  at  32" 
become 

Expansion    for    one 
Degree  on  F.  Scale 
in  Parts  of  the  Vol- 
ume at  32°. 

—  33 

-\-  32 
212 
300 
387 
473 
559 
660 

8650 
10000 
13750 
15576 
17389 
•  19189 
20976 
23125 

20-77 

20-83 
20-70 
20-82 
20-84 
20-83 
20-90 

The  mean  of  these  results  gives  the  expansion  for  one  degree  at  20-81,  or  almosi 
exactly  ^1^  of  the  volume  at  32°,  which  result  had  been  adopted  universally,  with- 
out any  suspicion  of  its  being  imperfect.  Circumstances  having,  however,  induced 
Rudberg  to  submit  the  subject  to  an  accurate  reinvestigation,  conducted  with  ex- 
ceeding care  and  attention,  particularly  to  the  state  of  dryness  of  the  air  employed, 
he  has  found  that  the  amount  of  expansion  assigned  by  Gay  Lussac  and  Dalton  ia 
somewhat  too  great,  and  that  a  volume  of  air,  in  being  heated  from  32°  to  212°, 
expands  from  1000  volumes  to  1365. 

The  method  which  he  employed  was  almost  exactly  the  inverse  of  that  of  Gay 
Lussac.  Having  dried  with  great  care  the  air  in  a  glass  bulb,  the  tube  of  whic.'. 
Avas  drawn  to  a  fine  point,  like  that  described,  page  14,  for  taking  the  specific  gravity 
of  vapours,  he  heated  it  for  a  long  time  in  a  vessel  of  boiling  water,  taking  care 
that  all  parts  of  the  bulb  and  tube  were  equally  heated,  and  then,  being  completely 
certain  that  all  the  air  had  attained  the  maximum  temperature,  he  sealed,  by  the 
blowpipe,  the  minute  orifice,  and  thus  had  the  bulb  containing  air  in  the  expanded 
state.  The  vessel  being  then  removed  to  a  trough  of  mercury,  the  orifice  of  the 
tube  was  placed  deep  below  the  surface,  and  carefully  opened ;  a  quantity  of  ice 
was  then  laid  upon  the  globe,  and  being  supplied  as  fast  as  it  melted,  the  whole 
was  thus  left  for  some  hours  until  the  temperature  was  well  established  at  32°, 
and  all  the  mercury  which  would  rise  into  the  globe  by  the  contraction  of  the  air 
by  cooling,  had  entered.  The  height  of  the  mercury  was  then  noticed,  and  the 
height  of  the  barometer,  and  the  corrections  necessary  for  its  positive  amount,  or 
for  any  change  which  occurred  during  the  experiment,  allowed  for,  as  already  de- 
scribed. The  volume  of  the  mercury  which  had  entered  into  the  globe  was  then 
ascertained,  and  the  volume  of  the  globe  itself  also  determined ;  and  by  a  compar- 
ison of  these,  corrected  for* the  expansion  of  the  glass,  and  for  any  variation  in  the 
boiling  point  from  212°,  the  rate  of  expansion  and  its  amount  were  calculated. 

From  very  numerous  experiments,  Rudberg  inferred  that,  in  being 
heated  from  32°  to  212°,  1000  volumes  of  air  became  between  1364 
and  ISGG'^ ;  we  may  consider  1365,  which  is  between  the  two,  as 


CORRECTION  FOR  CHANGE  OF  TEMPERATURE.  57 

being  absolutely  the  most  correct,  and  hence  that  for  each  degree 
lOOd'volumes  expand  f|f =2-028,  or  ^f  ^  of  its  volume  at  32^ 

In  all  operations  upon  gaseous  mixtures,  the  rate  of  expansion 
of  air  comes  into  play  j  for  as  all  gases  expand  alike,  and  the  vapours, 
even  of  these  bodies  which  are  least  volatile,  as  camphor  and  cor- 
rosive sublimate,  expand,  while  in  the  elastic  form,  precisely  as 
gases  do,  their  volumes  are  corrected  for  temperature  and  pressure 
in  the  same  manner.  In  determining  the  specific  gravity  of  a  va- 
pour, it  is  also  usual  to  reduce  it  to  the  same  standard  as  those  of 
gases,  that  is,  air  at  32^,  even  where  the  substance  is  of-  such  a  na- 
ture as  that  at  32°  it  may  not  produce  any  sensible  vapour  at  all. 
In  doing  so,  it  is  assumed  that  the  vapour  should,  in  cooling  to  32*^, 
follow  the  same  law  as  common  air  ;  and  hence  an  error,  even  though 
very  slight,  in  the  rate  of  expansion  of  air,  might  lead  to  incorrect 
results  in  many  cases. 

The  application  of  such  corrections  follows  very  simply  from  what  has  been  de- 
scribed. If  there  be  a  certain  quantity,  as  155  cubic  inches  of  hydrogen  gas  at  142° 
Fahrenheit,  and  we  wish  to  know  tlie  volume  there  should  be  when,  cooled  to  32*^, 
we  say  that,  as  142°  is  110°  above  32°,  the  155  cubic  inches  are  equal  to  the  vol- 
ume at  32°,  and  in  addition  to  |-^|  of  it ;  that  being  the  quantity  by  which  it  is  ex- 
panded from  32°  to  142°.  Therefore,  denoting  the  volume  at  32°  by  the  letter  V, 
there  is  the  equation : 

129-5  cubic  inches  are  therefore  the  volume  at  32°. 

If,  on  the  other  hand,  we  have  a  gas  at  a  low  temperature,  and  we  wish  to  as- 
certain what  its  volume  should  be  at  32°,  it  is  evident  that  the  mode  is  the  same, 
except  that,  in  place  of  subtracting  the  amount  of  expansion,  we  add  it  to  the  origi- 
nal volume.  Thus,  if  the  155  cubic  inches  of  hydrogen  had  been  at  6°  Fahrenheit, 
then  the  equation  should  have  been  32° — 6°  being  26. 
,r^      Tr     Tr26  ,.      155x493      ,^oo       k  ••      u       • 

155=V — V-— -,  or  V=:-  ^^   -  ^  =1683  cubic  mches  in  exact  numbers. 
493  493 — 26 

It  frequently  happens  that  it  is  necessary  to  reduce  a  gas  at  one  temperature  to 
Its  volume  at  another,  neither  of  which  being  32°,  it  would  require  two  different  sums 
to  be  worked  by  the  above  process.  But  it  may  be  effected  as  follows  by  a  single 
calculation. 

The  volumes  at  the  two  temperatures  are  to  one  another  in  the  same  propor- 
tion as  the  standard  volume,  493,  increased  by  the  amount  of  expansion  proper  to 
the  temperatures.  Thus,  at  the  temperatures  of  75°  and  42°,  the  standard  volume, 
which  is  493°,  at  32°  becomes  respectively  536  and  503.  Now  any  volume  of 
gas,  when  heated  from  42°  to  75°,  or  cooled  from  75°  to  42°,  changes  its  volume 
in  these  proportions  ;  and  hence,  if  we  have,  for  example,  127  cubic  inches  of  a  gas 
at  75°,  and  we  wish  to  calculate  its  volume  when  at  the  temperature  of  42°,  we 
say,  calling  the  unknown  volume  V  ; 

V  :  127  :  :  503  :  536,  and  Y=^:^^I^^==ll9fi. 

536 
The  formulae  for  these  corrections  may  be  very  simply  written  in  a  general  form . 
thus,  to  reduce  a  volume  to  32°,  denoting  the  temperature  on  Fahrenheit's  scale 
by  t ;  by  V,  the  volume  of  gas  which  we  have  measured  at  that  temperature ;  and 
by  Vi,  the  volume  at  32°,  the  formula  is  : 

y  ^ 493.  V 

^     493  ±  (f— 32°)' 
And  to  reduce,  without  reference  to  32°  ;  denoting  the  known  volume  by  V,  and 
the  unknown  by  Vi ;  the  temperature  of  V  by  /,  and  that  of  V,  by  ti,  there  is  found  : 
V.__493±  (^,-32)  y,     .,493-i:  (^,-32) 

V  ~493±  (i-32) '  ^""^     '-    493  :f  ^-32)- 
Air  which  has  been  heated  becomes,  from  its  great  increase  in 
volume,  specifically  much  lighter  than  cold  air,  in  which  it  there- 
fore ascends  with  a  velocity  due  to  the  difference  between  their 

H 


58  EXPANSION     OF     LIQUIDS. 

specific  gravities.  It  is  thus  that  over  every  lamp  or  candle  there 
may  be  felt  a  current  of  heated  air  ascending  from  the  flame  j  that 
the  heavy  dark  smoke  rises  in  its  heated  form  from  the  chimneys  of 
our  houses  ;  and  that,  in  crowded  apartments  or  theatres,  the  upper 
portion  of  the  space  will  be  occupied  by  oppressively  hot  air,  while 
that  near  the  floor  will  be  quite  cool.  By  the  ascent  of  the  heated 
air  from  our  furnaces  and  fireplaces,  there  is  generated  the  draught 
which  gives  the  supply  of  air  necessary  for  continued  burning  ;  and 
as  the  intensity  of  the  combustion  and  consequent  heat  produced 
depends  on  the  rapidity  of  draught,  the  hot  air  is  kept  from  being 
cooled  by  mixing  with  the  cold  external  air,  by  being  collected  in 
the  chimney,  where  it  obtains  an  ascensional  power  corresponding 
to  its  height,  and  by  which  we  are  enabled  to  regulate  with  accu- 
racy the  temperature  which  shall  be  produced.  On  this  ascensional 
power  of  heated  air  is  founded  also  the  construction  of  the  fire  or 
Montgolfier  balloon,  a  bag  of  hot  air,  rising  in  the  surrounding  colder 
atmosphere,  precisely  as  a  light  flask,  filled  with  oil  or  alcohol, 
would  ascend  if  let  loose  at  the  bottom  of  a  vessel  full  of  water. 

It  has  been  already  noticed  that  liquids  do  not,  in  expanding, 
follow  any  simple  proportion,  such  as  that  which  exists  for  gaseous 
bodies,  but  that  each  fluid  has  a  peculiar  dilatability  of  its  own,  and 
that  the  rate  of  expansion  varies  with  the  temperature,  being  greater 
in  the  higher  portion  of  the  thermometric  scale  than  in  the  lower. 
Liquids  expand  much  less  than  gases,  but  much  more  than  solids; 
for,  as  is  particularly  instanced  in  the  thermometer,  the  visible  ex- 
pansion of  a  fluid  is,  in  most  cases,  only  the  excess  of  its  expansion 
over  the  expansion  of  the  solid  vessel  in  which  it  may  be  contained. 
To  measure  the  amount  of  expansion  in  liquids,  they  may  be  introduced  into 
graduated  thermometer  tubes  ;  and  then,  when  exposed  to  the  same  degree  of  heat, 
they  will  indicate  temperatures  proportional  to  their  expansibilities.  Thus  alcohol 
rising  more  into  the  stem  than  water,  and  water  more  than  mercury,  will  stand  at 
different  marks  on  the  stem,  although  the  temperature  be  really  the  same.  It  may, 
however,  be  more  easily  and  more  accurately  done  by  means  of  the  apparatus  in 

the  figures,     a  d  b  is  a  glass  tube,  the  neck  of 
fr  '*'  "^  ^  ^^  which  is  very  narrow,  and  bent  as  in  either  fig- 

'  ure.     This  tube  is  to  be  filled  completely,  at  the 

lowest  temperature,  with  the  liquid,  whose  expansion  is  to  be  examined  and  then 
,_-...--„._....„..  weighed,  the  weight  of  the  tube  itself  being  previously 
jj  ^J]i_£  known,  and  the  quantity  of  liquid  which  it  contains  is  thus 
I  frj-^Ji-^  determined.  The  tube  is  to  be  then  placed  upright  in  a 
I  I  IllJlIf  cylinder  of  water  or  oil  &,  to  which  heat  may  be  applied 
I  P^lf  by  a  furnace  below ;  and  the  liquid  expanding  according 
I  l|i'|0  as  its  temperature  is  raised,  the  excess  of  volume  flows 
I  111  ^  out  at  the  capillary  beak  c,  and  may  be  collected  as  in  d,  or 
I  1  w  let  to  waste.  When  the  apparatus  has  been  brought  to  the 
I  \||  -  highest  temperature  required,  and  all  farther  expansion  has 
I  I  "    ceased,  as  is  known  by  no  more  liquid  passing  out  at  c,  the 

I   /W  '^fe  t^be  is  to  be  removed  from  the  bath,  carefully  cleaned,  and, 
^^il^^^P  when  again  cool,  accurately  weighed.     The  loss  of  weight 
"  is  the  quantity  of  liquid  that  had  been  expelled,  and  this, 

compared  with  the  whole  original  quantity  of  liquid,  gives  the  proportion  of  expan- 
sion. In  this  manner,  however,  the  result  appears  to  be  less  than  it  really  is,  for 
the  expansion  of  the  glass  tube  itself  diminishes  the  quantity  of  liquid  expelled. 
Such  results  require,  therefore,  to  be  corrected  for  the  expansion  of  the  glass,  which 
is,  however,  so  small,  that  in  the  more  dilatable  liquids  it  may  be  neglected.  In 
mercury,  however,  it  affects  the  apparent  expansion  very  much  :  mercury  expanding 
in  glass  through  180°,  augments  in  volume  only  ^,  while  its  real  expansion  is  -^■^. 
The  amount  of  expansion  of  different  fluids  in  passing  through  180°  of  Fahren- 
heit is  thus  found  to  be  : 


EXPANSION     OF     LIQUIDS. 


59 


Alcohol ^ 

Nitric  acid ^ 

Fixed  oils -j^ 

Sulphuric  ether  •     .     •    •  t¥ 


Oil  of  turpentine 
Sulphuric  acid  . 
Water  .  .  .  . 
Mercury    .     .     . 


•51! 


The  actual  amount  of  expansion,  independent  of  the  expansion  of  the  containing 
vessel,  is  best  observed  by  the  apparatus  used  by  Dulong  and  Petit.     It  consists  of 

a  glass  tube  a  h  c,  bent  in  the  form  of  a 
U,  of  which  the  horizontal  portion  c  is  nar- 
row, but  the  vertical  legs  pretty  wide. 
When  mercury  is  poured  into  the  tube,  it 
stands  at  the  same  height  in  both  legs  if 
the  temperature  be  the  same ;  but  one  leg 
being  immersed  in  a  vessel  of  oil  or  water 
I,  by  which  heat  can  be  applied  to  it,  and 
thereby  the  mercury  in  it  caused  to  expand, 
the  height  of  the  hquid  column  must  in- 
crease in  order  to  balance  the  colder  column  of  mercury  in  the  proportion  of  the 
augmented  volume.  The  difference  between  the  heights  being  read  off,  by  means  of 
an  accurate  scale,  with  a  telescope  o,  the  amount  of  absolute  expansion  may  be  ea- 
sily calculated  from  it. 

By  means  of  this  instrument  Dulong  and  Petit  determined  the  rate  at  which  the 
expansion  of  mercury  increases  with  the  temperature,  as  has  been  noticed  generally 
in  the  description  of  the  thermometer.  Their  result  was,  that  between  32*^  and  212°, 
measured  on  the  air  thermometer,  the  expansion  is  ■^^.-^.  From  212°  to  392°,  it  is 
^y.i_^  ;  and  from  392°  to  572°,  it  is  ^.o^.  The  consequence  is,  that,  measured  by 
its  own  expansion,  mercury  boils  at  680°  Fahrenheit ;  but  from  the  expansion  of 
the  glass  of  an  ordinary  thermometer  bulb,  it  boils  at  660°  on  the  visible  scale, 
which  coincides  almost  exactly  with  662°,  the  temperature  given  by  the  dilatation 
of  air.  The  apparent  expansion  of  mercury  in  glass  is  therefore  taken  as  being 
uniform  for  180°.  ^  of  its  volume. 

Considerable  simplicity  is  given  to  the  laws  of  dilatation  of  liquids  by  an  observa- 
tion of  Gay  Lussac,  that,  in  order  to  obtain  any  common  rule  for  them,  such  as  is 
found  for  gaseous  bodies,  we  must  examine  them  when  in  the  same  molecular  con- 
dition ;  that  is  to  say,  the  cohesive  powers  of  the  liquids  we  employ  must  be  brought 
into  the  same  state.  This  is  most  nearly  done  by  taking  these  liquids  when  heat- 
ed to  their  boiling  points,  for  then  the  cohesion  of  each  liquid  is  about  to  cease  alto- 
gether. Thus  alcohol  boils  at  173°,  water  at  212°,  sulphuret  of  carbon  at  134°,  and 
sulphuric  ether  at  963° ;  and,  taking  1000  volumes  of  each  at  their  boiling  points, 
and  aliowmg  them  to  cool,  they  contract  as  follows : 


By  cooling 
through 

Water 

contracts 

Alcohol 
contracts 

Sulphuret 
of  Carbon 
contracts 

Ether 
contracts 

18° 
36° 
54° 
72° 
90° 
108° 

661 
1315 
18-85 
2410 
28-56 
32  42 

11-43 
24  34 
34-74 
45-68 
5602 
65  96 

1201 
23-80 
3506 
45-77 
56-28 
6621 

1617 
31-83 
46-42 
58-77 
7201 

We  by  this  means  find  a  very  interesting  relation  between  alcohol  and  sul- 
phuret of  carbon,  two  fluids  remarkably  different  in  their  specific  gravities,  and  in 
their  chemical  constitution  and  properties.  It  appears  that  their  molecular  force 
must  increase  at  the  same  rate ;  for  in  cooling  the  same  number  of  degrees  below 
their  boiling  points,  they  contract  to  exactly  the  same  amount :  and  a  still  farther 
connexion  is  exhibited  between  their  molecular  conditions  by  the  remarkable  fact 
that,  in  being  converted  into  vapour,  the  augmentation  of  volume  which  they  un- 
dergo is  the  same. 

Many  liquids  possess  the  property  of  contracting,  by  reduction 
of  temperature,  only  to  a  certain  point ;  below  which,  if  the  cool- 
ing be  continued,  they  expand.  As  the  volume  at  this  temperature 
is  the  least  possible,  it  is  called  the  point  of  maximum  density. 
This  peculiarity  was  first  recognised  in  water  j  but  it  has  since  been 


60  EXPANSIONOF     SOLIDS. 

found  in  many  other  fluids,  even  in  a  still  more  remarkable  degree 
It  is,  however,  in  water  that  the  phenomenon  is  of  most  importance, 
in  consequence  of  the  extensive  agency  of  that  fluid  in  natural  op- 
erations. The  point  of  maximum  density  of  water  has  been  deter- 
mined by  the  experiments  of  very  many  persons  to  be  39.5"  of  Fah- 
renheit. When  water  below  that  temperature  is  heated,  it  con- 
tracts J  when  heated  above  it,  it  expands :  when  cooled  from  above 
it,  it  contracts  j  Avhen  cooled  below  it,  it  expands :  and  when  the 
experiment  is  made  in  glass  vessels,  the  contraction  of  the  glass  has 
.  ne  eflfect  of  rendering  the  expansion  of  cooling  below,  or  of  heat- 
mg  above,  through  the  same  number  of  degrees,  exactly  equal.  Thus 
100*000  volumes  of  water  become  100*012  equally  by  being  cooled 
from  39*5  to  32"",  or  by  being  heated  from  39*5  to  46^,  and  the  spe- 
cific gravity  of  water  at  46"^  and  at  32°  is  consequently  the  same. 

A  great  deal  of  the  permanence  of  the  existing  order  of  nature 
depends  upon  this  property  of  water :  it  is  by  means  of  it  that  the 
great  mass  of  water  in  our  lakes  and  rivers  is  preserved  from  being 
converted  into  solid  ice.  When,  by  the  cooling  process  of  the 
winds,  the  water  has  been  all  reduced  to  the  temperature  of  39*5°, 
the  surface  acts  as  a  screen  to  prevent  the  farther  loss  of  heat,  and 
thus  retains  the  deeper  portions  at  a  temperature  sufliciently  high 
for  the  existence  of  its  organized  inhabitants  j  for,  by  the  continued 
action  of  the  cold  wind,  the  superficial  water  being  cooled  below 
39*5°,  it  becomes  lighter,  and  floats  upon  the  heavier  and  warmer 
water  underneath ;  and  from  the  bad  conducting  power  which  water 
will  be  hereafter  demonstrated  to  possess,  the  loss  of  heat  is  efix3ct- 
ually  prevented.  If  it  w^ere  not  for  this  property  of  water,  all  large 
collections  of  it  in  lakes  and  rivers  would,  with  few  exceptions, 
be  permanently  frozen. 

The  dilatation  of  solids  is  much  inferior  in  amount  to  that  of 
liquids,  and  as  with  these,  the  rate  of  dilatation  is  not  uniform,  but 
increases  with  the  temperature.  The  increase  is,  however,  so  ex- 
ceedingly minute,  that  in  almost  all  cases  it  may  be  neglected,  and 
hence  need  not  occupy  much  attention.  The  dilatation  of  solids, 
although  so  small,  may  yet  be  demonstrated  to  be  real  by  many 
simple  experiments.  Thus,  if  an  iron  rod  be  made  to  fit,  when  cold, 
in  length  and  breadth,  an  exact  scale,  it  will  be  found,  when  heated, 
to  be  too  large  to  enter  it.  An  iron  ring,  which  is,  when  cold,  too 
small  to  pass  over  a  cylinder,  becomes  sufliciently  large  on  being 
heated ;  and  if  the  cylinder  could  have  passed  through  when  cold, 
its  diameter  becomes  too  great  to  allow  its  passage  when  its  tem- 
perature is  raised.  In  the  arts,  the  expansion  of  solids,  particularly 
of  the  metals,  in  this  way  becomes  the  source  of  numerous  incon- 
veniences, and  of  many  useful  applications.  Thus,  the  iron  rim  of 
a  carriage  wheel  is  secured  by  the  power  of  its  own  contraction, 
it  having  been  slipped  upon  the  wooden  frame  while  in  a  hot  and  ex- 
panded state.  The  force  of  contraction  of  iron  bars  in  cooling  has 
been  applied  successfully  to  restore  to  the  proper  position  buildings 
which  had  been  about  to  fall,  and  the  rate  of  expansion  has  also,  as 
in  the  pyrometers  of  Daniell  and  others,  served  as  a  useful  meas- 
ure of  high  temperatures  j  on  the  other  hand,  by  the  alternate  ex- 
pansions and  contractions,  under  the  successive  influence  of  win- 


EXPANSION     OF     SOLIDS. 


61 


ters  and  summers,  of  the  metallic  bars  which  had  imprudently  been 
laid  in  the  masonry  of  some  important  public  buildings,  with  the 
idea  of  giving  additional  security,  the  courses  of  stone  or  brick 
have  been  loosened  from  one  another,  and  reconstruction  rendered 
necessary,  in  order  to  prevent  their  being  gradually  pulled  to  pieces. 
In  estimating  the  amount  of  expansion  of  a  solid  body,  the  great 
difficulty  is  the  accurate  measurement  of  the  small  increase  in 
length  which  takes  place.  For  this  purpose,  a  great  variety  of  me- 
chanical arrangements  have  been  constructed.  As  they  are  all  in 
principle  the  same,  and  the  detailed  description  of  any  exact  form 
would  occupy  too  much  space,  it  will  be  sufficient  to  notice  one, 
which,  though  not  that  by  which  very  accurate  numbers  may  be 
obtained,  is  calculated  to  give  a  very  satisfactory  idea  of  their  gen- 
eral construction:  a 
h  is  the  bar  of  which 
the  expansion  is  to 
be  determined  j  it  is 
fastened  securely  at 
the  extremity  «,  and 
rests  at  A  in  a  groove 
along  which  it  is  free 
to  move,  as  in  the 
figure.  This  end  of 
the  bar  at  b  presses 
against  a  rod  c,  which 
is  a  lever  of  the  sec- 
ond order,  very  near 
the  fulcrum,  and  this 
transfers  its  motion 
to  the  end  of  the  lev- 
er, increased  in  the  proportion  of  the  distance.  This  lever  acts  on 
another  similar  one,  (/,  the  extremity  of  which  serves  as  an  index 
on  the  graduated  circular  arc  e,  by  which  the  amount  of  expansion 
is  read  off.  Thus,  if  the  acting  lengths  of  the  arms  of  the  levers 
are  respectively  1  and  20,  and  the  end  of  the  bar  a  2it  b  moves 
ToVir  of  an  inch,  the  end  of  the  index  d  will  move  on  the  scale  e 

through  ~"fAA7r==Trj  ^^  ^'i  'mc\  a  space  capable  of  being  divided 

by  a  microscope  and  vernier  into  200  measurable  spaces,  so  that  an 
expansion  of  the  two  hundred  thousandth  of  an  inch  can  be  accu- 
rately determined.  For  a  popular  illustration,  the  source  of  heat 
may  be  lamps,  as  in  the  figure ;  but  for  accurate  experiments,  the 
bar  is  completely  immersed  in  a  bath  of  oil  or  water,  and  the  tem- 
perature ascertained  by  a  suitable  arrangement  of  thermometers. 

The  most  important  results  thus  obtained  are  the  following.    The  temperature 
being  raised  from  32°  to  212°,  the  increase  in  length  of  a  bar  of 


Glass  varies  from 
to  . 
Copper      .    .     . 
Brass    .... 


•  ToVo 


Steel 

Gold 

SQver 

Lead 

Tin. 


1 

TT2 


Softiron ^j 

The  increase  in  length  is  called  the  linear  dilatation  of  a  sub 


62 


EXPANSION    INCREASES    WITH    TEMPERATURE. 


Stance,  lut  its  increase  of  volume  is  called  the  cubical  dilatation, 
and  is  three  times  the  former.  Thus  the  cubical  dilatation  of  glass 
^®  72^45  ^^  4:ij'  Hence  a  glass  ball  which  holds  428  measures  at 
32°,  becomes  capable  of  holding  429  at  212°  j  or  if  it  hold  10-000  at 
32°,  it  holds  10-023  at  212°.  In  this  manner  the  correction  for  the 
expansion  of  glass  is  in  all  cases  made.  But  it  is  necessary  to  ap- 
ply the  amount  of  expansion  belonging  to  the  particular  sort  of 
glass  j  thus,  in  the  account  of  the  thermometer  in  page  51,  the 
cubic  dilatation  of  glass  was  taken,  not  as  10*023,  but  10-026. 

[The  reason  that  the  cubic  dilatation  may  be  taken  as  equal  to  three  times  the 
linear,  without  sensible  error,  is  due  to  the  circumstance  that  the  linear  dilatation 
is  always  a  small  fraction  of  the  primitive  length.  If  l-\-l  represent  the  dilated 
length,  (1-f /)%  or  1-f  3  l-\-2  P-\-P  will  be  the  true  volume ;  but  as  /  is  a  small 
fraction,  its  triple  square  and  cube  may  be  neglected.] 

Although  it  is  abundantly  proved  that  solid  bodies  expand  more  rapidly  at  high 
than  at  low  temperatures,  yet,  except  in  the  case  of  some  p£irticular  substances,  as 
glass,  iron,  and  platinum,  whose  utility  as  measurers  of  heat  rendered  a  knowledge 
of  the  law  of  their  expansion  necessary,  the  subject  has  been  little  examined  ;  the 
degree  to  which  the  rate  of  expansion  is  affected  by  temperature  will  be  sufficiently 
shown  in  the  table  which  follows.  At  the  temperature  of  212°  Fahrenheit,  as  given 
by  an  air  thermometer,  the  dilatation  for  one  degree  is  thus,  for 


Glass. 

Platinum. 

Iron. 

Copper. 

d'TToTo" 

FtIs-o 

S0T6  0 

34I20 

while  at  572°  of  Fahrenheit  it  becomes,  for 


Glass. 

Platinum. 
65^40 

Iron.         Copper. 

59220 

4  0¥T7  3T1-60 

and  the  temperature  deducible  from  the  expansion  of  a  thermometer  made  of  each 
of  these  substances  should  be,  in  passing  from  212°  to  572°,  as  compared  with  air, 


Air. 

Glass. 

Platinum. 

Iron. 

Copper. 

623° 

572° 

667° 

592° 

702° 

Platinum  expands  thus  the  most  regularly  of  those  bodies,  and  should,  therefore,  be 
best  fitted  for  a  metallic  thermometer. 

It  is  remarkable  that  the  rate  of  expansion  is  not  increased  by 
rise  of  temperature  for  all  solid  bodies,  but,  on  the  contrary,  in 
some  cases  there  exists,  for  solids  as  for  liquids,  a  point  of  maxi- 
mum density,  so  that  the  body  shall  expand  whether  it  be  cooled 
or  heated  from  that  degree.  This  is  peculiarly  the  case  in  Rose's 
fusible  metal,  which  has  been  so  often  mentioned  as  a  means  of  ap- 
plying a  steady  heat.  When  heated  from  32°  to  111°,  this  metallic 
alloy  increases  in  volume  from  100-000  to  100-830  parts,  but  there 
the  expansion  stops,  and  when  farther  heated  it  contracts,  until, 
when  at  156°,  the  volume  is  only  99-291,  being  less  than  at  32° 
By  a  farther  rise  of  temperature  it  again  expands,  and  at  178°  is  at 
its  original  volume  of  100-000,  and  continues  expanding  until,  being 
100-862  at  201°,  almost  exactly  what  it  had  been  at  111°,  it  begins 
to  melt.  It  is  curious  that  it  has  no  point  of  maximum  density 
when  in  the  liquid  state. 

The  diiferent  rates  of  expansion  of  different  solid  bodies  are  sub- 
servient to  some  very  important  uses  in  the  arts  and  in  scientific 
research.  Thus,  the  difference  between  the  expansibilities  of  plati- 
num and  brass,  or  any  other  two  metals  which  differ  much,  may  be 
used  as  a  very  delicate  thermometric  means.     If  we  take  a  flat  rule 


EXPANSION     OF     COMPOUND     METALLIC     BARS.     63 


of  platinum  exactly  ten  inches  long  at  32°,  and  lay  it  on  a  similar 
rule  of  brass,  to  which  it  is  firmly  screwed  at  one  extremity,  and 
on  which,  at  the  free  end,  there  is  engraved  a  scale  of  parts  of  an 
inch  for  a  small  space,  the  compound  rule  will  serve  as  a  thermom- 
eter. For  the  two  rules  being  exactly  of  the  same  length  at  32°,  if 
we  place  them,  fastened  together,  in  boiling  water,  the  brass  rule 
will  be  elongated  by  0-019,  while  the  platina  rule  will  expand  only 
through  0'009  ;  hence  the  end  of  the  brass  rule  will  project  beyond 
the  platina  rule  by  0*0 10  of  an  inch  j  and  as  the  expansion  is  uniform 
for  these  moderate  temperatures,  each  degree  of  Fahrenheit's  scale 
will  be  indicated  on  the  scale  of  the  brass  rule  by  ^-^^^^^  of 
an  inch.  In  this  form  the  spaces  would  be  too  minute  to  be  easily 
determined  j  but  by  modifying  the  form,  and  connecting  the  rules 
through  their  whole  length,  the  beautiful  metallic  thermometer  of 
Breguet  has  beeii  invented.  Its  principle  is  as  follows  :•  if  the  two 
rules  be  soldered  completely  together,  as  in  «,  in  place  of  being  con- 
nected only  at  a  single  point,  the  result  of  the  unequal  expansion  is 
to  bend  the  bar,  as  in  6,  until,  the  most  expansible  metal  being  on 
the  outside,  it  forms  an  arch  longer  than  that 
formed  by  the  inside  rule,  by  the  difference 
^^  of  their  expansions.  If  the  compound  bar  be 
o  already  bent  into  a  circle,  the  ends  of  which 

are  not  opposed,  the  effect  of  the  expansion  is  to  make  these  edges 
project,  and  to  diminish  the  diameter  of  the  circle ;  by  having  a 
number  of  such  circles,  the  expansion  of  all  being  added  together, 
a  considerable  circular  motion  is  produced  in  the  extremity.  In 
the  thermometer  of  Breguet  there  is  such  a 
compound  spiral  b,  b,  fastened  at  the  upper  end, 
and  having  attached  to  its  lower  extremity  an 
index,  c,  which  moves  round  a  dial,  dj  d,  and 
indicates  the  temperature  of  the  instrument. 
On  this  relative  expansion  is  also  founded  the 
construction  of  the  compound  pendulum.  A 
metallic  bar,  when  used,  as  in  an  ordinary  clock, 
to  measure  time  by  its  vibrations,  being  con- 
stantly changing  in  length  according  as  the  ex- 
ternal temperature  varies,  affects  the  rate  of  the 
clock,  making  it  go  too  fast  or  too  slow  by  its 
shortening  or  elongation.  This  is  corrected  by  having  two  or  more 
bars,  by  the  expansion  of  one  of  which  the  vibrating  length  of  the 
pendulum  is  increased,  while  by  the  expansion  of  the  other  it  is 
just  as  much  shortened  ;  the  consequence  of  this  opposing  action 
is,  that  the  pendulum  remains  indifferent  to  all  changes  of  temper- 
ature, and  the  clock  becomes  an  exact  measure  of  time  at  all  sea- 
sons. 


SECTION  II. 

OF    SPECIFIC    HEAT. 


It  is  now  necessary  to  examine  into  the  quantity  of  heat  which 
each  substance  requires  to  raise  its  temperature  a  certain  number 
of  degrees ;  for,  although  it  be  quite  impossible  to  assign  the  absolute 


64  ME  TH  OD     OF     MIXT  U  RE  S. 

proportion,  yet,  by  obtaining  the  relative  proportions,  we  may  arrive 
at  results  which  may  serve  to  characterize  those  substances,  and 
may,  as  shall  be  hereafter  shown,  lead  us  to  important  views  of  the 
relations  between  their  physical  and  chemical  constitution.  The  rel- 
ative quantity  of  heat  necessary  to  raise  the  temperature  of  any 
body  through  a  certain  number  of  degrees,  as  ten,  for  example,  is 
termed  its  specific  heat. 

If  we  take  a  pint  of  water  at  150°,  and  another  pint  of  water  at 
50^,  and  mix  them  well  in  a  very  thin  vessel,  the  temperature  of 
the  mixture  is  found  to  be,  if  we  allow  for  some  sources  of  er- 
ror to  which  this  process  is  exposed,  exactly  100°.  Thus  the  one 
part  of  the  water  has  transferred  to  the  other  a  quantity  of  heat 
sufficient  to  raise  its  temperature  50°  ;  and  whether  this  addition  was 
from  50°  to  100"^,  or  from  100°  to  150°,  the  result  was  the  same.  In 
water,  thej'efore,  the  specific  heat  does  not  change  within  these 
limits  J*  but  it  will  be  found  that  in  high  temperatures  a  trifling  in- 
crease does  occur  ;  for  the  present  purpose,  however,  it  may  be  neg- 
lected. If,  now,  a  pint  of  water  be  taken  at  150°  as  before,  and  a 
pint  of  mercury  at  50°,  and  they  be  well  and  rapidly  mixed  together 
until  both  have  attained  the  same  temperature,  this  will  be  found  to 
be  118°.  The  mercury  here  rises  from  50°  to  118°,  through  68°, 
while  the  water  cools  only  through  32°,  or  not  quite  half  as  much, 
so  that  the  same  quantity  of  heat  can  raise  the  temperature  of  mer- 
cury through  twice  as  many  degrees  as  that  of  water. 

Taking  thus  equal  volumes,  the  specific  heats  of  water  and  mer- 
cury are  as  68  :  32 ;  or  water  being  adopted  as  the  standard  for 
liquid  and  solid  bodies,  and  its  specific  heat  taken  as  1,  the  specific 
heat  of  mercury  is  0*47  nearly.^  Such  bodies  are,  however,  gener- 
ally taken,  not  in  equal  volumes,  but  in  equal  weights,  and  hence 
it  is  necessary  to  divide  the  0*47  by  13*5,  the  specific  gravity  of*mer- 
cury,  and  thus  there  is  obtained  0-035,  its  specific  heat. 

The  process  now  given  is  known  as  the  method  of  mixtures,  and 
has  been  selected  for  example,  as  that  by  which  the  meaning  of  the 
term  specific  heat  is  best  explained ;  but  it  is  not  the  only  one,  nor 
even,  perhaps,  the  best,  by  which  specific  heat  may  be  determined. 
The  sources  of  error  are,  that  a  certain  quantity  of  heat  is  absorbed 
by  the  vessel  in  which  the  mixture  is  made,  and  that,  as  the  mixture 
requires  some  time  to  make,  a  certain  loss  occurs  by  the  cooling 
power  of  the  air.  But  it  is,  however,  in  skilful  hands,  capable  of  ex- 
ceeding accuracy ;  and,  with  the  recent  improvements  that  have  been 
made  in  its  details  by  Regnault,  it  has  yielded  results  of  the  highest 
value  to  science.  The  various  forms  of  apparatus  used  in  such  ex- 
periments need  not  be  described.  For  the  use  of  the  method  of 
mixtures,  it  is  not  necessary  that  the  two  bodies  should  be  liquid. 
Thus,  if  a  pound  of  pure  copper  in  a  bar  be  heated  in  an  oil  bath  to 
300°,  and  be  then  immersed  in  a  pound  of  water  at  50°,  the  copper 
will  give  out  its  excess  of  heat  to  the  water,  and  both  will  arrive  at 
a  temperature  of  72°.  The  copper  has  therefore  lost  228°,  and  the 
water  has  gained  22°,  and  the  specific  heats  being  inversely  as  these 
aumbers,  that  of  copper  is  found  thus  to  be  gVf— 0*096,  water  being 
l-OOO. 
One  process  employed  by  Dulong  and  Petit  consisted  in  heating 


THECALORIMETER.  65 

to  the  same  degree  the  bodies  to  be  tried,  and  allowing  them  to  cool 
exactly  under  the  same  circumstances.  It  is  evident  that,  if  we  know 
exactly  the  rate  at  which  a  body  cools,  and  the  time  which  it  takes  to 
cool,  we  can  calculate  exactly  how  much  heat  it  parts  with.  Thus, 
if  we  have  two  bodies  heated  to  300^,  and  circumstanced  in  all  re- 
spects alike,  one  requires  15  minutes  to  cool  to  50^,  and  the  other 
25,  the  latter  will  have  parted  with  more  heat,  in  the  proportion  of 
25  to  15,  and  the  specific  heat  is  expressed  by  the  quantity  of  heat 
the  body  gives  out  in  cooling.  Hence  those  substances  which  have 
high  specific  heats  require  more  time  to  heat  or  cool,  through  a  cer- 
tain number  of  degrees,  than  those  bodies  whose  specific  heat  is  less. 

It  was  by  a  process  of  this  kind  that  the  relative  specific  heats  of 
bodies  was  first  discovered.  Boerhaave  having  remarked  that,  when 
two  thin  glass  vessels,  containing,  one  a  pound  of  water  and  the 
other  a  pound  of  mercury,  were  equally  exposed  to  the  heat  at  the 
front  of  a  strong  fire,  the  temperature  of  the  mercury  rose  much 
more  rapidly  than  that  of  the  water,  and  that  it  attained  its  greatest 
degree  in  one  half  of  the  time  which  the  water  required ;  and  also, 
when  both,  equally  hot,  were  removed  from  the  fire,  the  mercury 
cooled  twice  as  fast.  For  accurate  purposes,  however,  there  are 
many  precautions  necessary  in  order  to  place  the  substances  under 
the  same  conditions,  so  as  to  render  the  rapidity  of  cooling  depend- 
ant only  on  their  difl^erent  specific  heats ;  thus,  equal  weights  of 
the  different  bodies  are  placed  in  the  same  thin  polished  silver  ves- 
sel, so  that  their  external  surface  may  be  the  same  in  extent  and  na- 
ture, and  this  vessel  cools  in  an  exhausted  receiver  in  order  that 
there  may  be  no  loss  of  heat  from  contact  with  the  external  air. 
The  internal  surface  of  the  receiver  must  also  be  always  in  the  same 
state,  that  the  heat  given  out  may  pass  off  in  all  cases  with  equal 
facility. 

An  extensive  series  of  researches  on  the  specific  heats  of  bodies,  conducted  by 
the  illustrious  associates  Lavoisier  and  Laplace,  has  been  found  on  repetition  to 
have  been  rendered  useless  by  the  imperfections  of  the  apparatus  they  employed : 
it  was  termed  the  Calorimeter,  and  consisted  of  a  vessel  containing  ice,  in  the  centre 
of  which  the  heated  body  was  placed,  and  the  quantity  of  heat  this  gave  out  in 
cooling  was  measured  by  the  quantity  of  ice  which  was  melted  into  water.  Outside 
there  was  another  case  of  ice  to  defend  the  instrument  from  the  action  of  the  air. 
It  was  found  in  practice  impossible  to  collect  all  the  water.  A  quantity  remained 
infiltrated  among  the  ice,  some  solidified  in  one  part  of  the  vessel  after  having  been 
melted  in  another,  and,  consequently,  the  numbers  given  by  two  of  the  greatest  men 
that  have  ever  been  attached  to  science  must  be  considered  as  quite  without  au- 
thority. In  cases,  however,  where  the  quantity  of  heat  was  very  large,  as  when 
the  Calorimeter  was  employed  to  determine  the  quantity  of  heat  produced  in  com- 
bustion, these  sources  of  error  became  less  influential,  and  such  results  will  be  util- 
ized in  a  future  chapter. 

The  specific  heats  of  a  number  of  the  most  important  solid  and 
liquid  bodies,  determined  by  such  methods,  are  given  in  the  foUow- 
inof  table : 


Water =1000 

Ether =0520 

Alcohol =0-660 

Sulphuric  acid     .     .     .  =0-333 

Nitric  acid      ....  =0-442 

Sulphur =0-202 

Carbon =0  241 

Mercury =0  033 


Iron =0114 

Copper =0  095 

Lead =0  031 

Gold =0  032 

Antimony  .    .     .     .    .  =0  051 

Tin =0-056 

Iodine =0  054 

Phosphorus    .    .     .     .  =0  188 


66      SPECIFIC     HEAT. CHEMICAL     CONSTITUTION. 


Lime =0-205 

Magnesia =0-276 


Arsenic =0  081  Glass =0177 

Platinum =0  032  Calomel =0  041 

Silver =0057  Common  salt      .     .     .  =0225 

Zinc =:0095  Nitrate  of  soda   .     .     .  =0240 

Tellurium =0051 

Nickel =0109 

Cobalt =0107 

The  numbers  given  are  generally  those  lately  obtained  by  Reg-» 

nault. 

The  specific  heats  of  bodies  are  not  the  same  at  all  temperatures ; 

thus  Dulong  and  Petit  have  found  that  the  specific  heats,  calculated 

from  the  change  of  temperature  from  32°  to  212°,  and  from  32°  to 

572°,  differ,  as  in  the  following  table : 


Substance. 

Sp.  Heat  from 
320  to  212°. 

Sp.  Heat  from 

320  to  672°.   1 

Mercury  .... 

0  0330 

00350 

Zinc 

00927 

01015 

Antimony    .     .    . 

0  0507 

00549 

Silver      .... 

00557 

00611 

Copper    .... 

00949 

01013 

Platinum     .    .    . 

00355 

00397 

Glass      .... 

01770 

01900 

Iron 

01098 

01218 

The  specific  heat  increases,  therefore,  with  the  temperature,  and 
Nauman  and  Regnault  have  found  that  this  holds,  even  with  water  ; 
for,  according  to  their  experiments,  the  specific  heat  of  water  at  32° 
being  1-000,  that  water  at  212°  is  1*010,  consequently  the  equal  dis- 
tribution of  heat  between  warm  and  cold  water,  which  was  described 
at  the  commencement  of  this  section,  does  not  exactly  hold  ;  the 
temperature  of  the  mixture  should  be  a  very  little  above  the  mean. 
This  was,  however,  omitted,  in  order  not  to  complicate  the  account 
of  that  manner  of  finding  the  specific  heats. 

The  specific  heats  of  bodies  are  connected  very  intimately  with 
their  chemical  and  molecular  constitution,  although  we  are  not  yet 
able  to  trace  the  exact  cause  of  this  connexion  in  all  its  forms.  The 
discovery  of  such  connexion  was  the  most  remarkable  result  of  the 
experiments  of  Dulong,  and  it  may  be  expressed  as  follows.  If  we 
take  the  specific  heats  of  any  of  the  bodies  given  in  the  table,  and 
divide  by  each  of  them  the  number  3*1,  we  obtain  a  series  of  num- 
bers which  are  found  to  be  either  those  which  shall  be  hereafter 
described  as  the  chemical  equivalents  of  the  bodies,  or  to  stand  in 
some  remarkably  simple  relation  to  those  equivalents,  thus : 


Sp.  Heat. 

31 

True 
Kqulvalent. 

Sp.  Heat. 

Lead  .... 
Tin    .    .    .     . 

0031 
0  056 
0095 

1000 
55  4 
326 

1036 
57-9 
323 

Zinc   .... 

Bismuth .     .     . 

0  030 

1007 

710 

Carbon    .     .     . 

0-24 

129 

61 

1263 

31-4 

•108- 

Iodine     .     .     . 
Phosphorus 
Silver      .     .     . 

0054 
•0188 
0057 

57-4 
165 
54-4 

In  the  first  division  of  this  table,  the  quotient  is  so  close  to  the 
true  equivalent  as  sufficiently  to  show  that,  were  it  not  for  the  un- 


SPECIFIC     HEATS     OF     ATOMS. 


67 


avoidable  errors  of  experiment,  they  would  coincide.  In  bismuth 
the  result  is  1^  times  the  true  equivalent.  In  carbon  it  is  double 
the  true  equivalent.  In  iodine,  in  phosphorus,  and  in  silver,  it  is 
one  half.  Each  of  these  illustrations  might  be  much  extended,  their 
numbers  being  only  intended  as  examples  of  the  fact. 

The  above  are  all  simple  bodies ;  but  Nauman  and  Avogadro  have 
shown,  that  also  in  compound  bodies  this  connexion  between  the 
equivalent  number  and  the  specific  heat  exists,  although  the  connect- 
ing dividend  is  no  longer  3*1,  but  is  a  different  number  for  each 
class  of  bodies. 

Thus,  for  the  following  carbonates,  the  specific  heats  being  made 
the  divisors  of  the  number  10'4,  there  is — 


Substances. 

Sp.  Heat. 

10-4 

True 
Equivalent- 

Sp.  Heat. 

Carbonate  of  lime  .     . 
Carbonate  of  iron  .     . 
Carbonate  of  zinc  .     . 
Magnesian  limestone  . 

0-2044 
0-1819 
0-1712 
0-2161 

509 
57-2 
60-7 
48-1 

506 
581 
62-4 
46-7 

For  certain  sulphates  the  number  is  12*4     Thus 


Sulphate  of  barytes 
Sulphate  of  strontia 
Sulphate  of  lime 


Sp.  Heat. 


01068 
0-1300 
01854 


95-4 
66-8 


Sp.  Heat.  Equivalent. 

116-1     116-1 


91-9 
68-6 


For  a  number  of  metallic  oxides,  the  constant  appears  to  be  5'4 
Thus: 


Substances. 

Sp.  Heat. 

0-276 
0049 
0132 
0-137 

5-4 
Sp.  Heat. 

19.6 

110-2 

40.9 

39-4 

Equivalent. 

20-7 

109-4 

40-3 

396 

Magnesia      .... 
Red  oxide  of  mercury- 
Oxide  of  zinc    .     .    . 
Oxide  of  copper     .     . 

The  relation  between  the  specific  heats  of  bodies  and  their  chem- 
ical equivalents  is  thus  remarkably  shown  to  extend  not  merely  to 
the  simple  substances,  but  even  to  saline  bodies,  and  indicates  a  con- 
nexion between  the  chemical  equivalents  and  the  molecules  upon 
which  the  heat  exerts  its  action,  of  an  intimate  description.  In  fact, 
the  specific  heat  of  a  certain  weight  of  any  body  is  thus  shown  to  be 
proportional  to  the  number  of  chemically  equivalent  masses  contain- 
ed in  that  weight ;  and  the  constant  numbers,  which  were  divided 
by  the  specific  heats,  are  the  specific  heats  of  the  ultimate  chemi- 
cally equivalent  particles.  Thus,  the  specific  heat  of  chemical  mole- 
cules of  zinc,  of  lead,  and  tin,  is  3*1 ;  that  of  the  oxides  of  zinc,  of 
copper,  and  of  mercury,  5*4  ;  the  specific  heat  of  the  chemical  atom 
or  ultimate  particle  of  carbonate  of  lime  or  of  zinc,  10*4  j  and  that  of 
the  sulphates  of  barytes,  strontia,  and  lime,  12*4'  Attempts  have  been 
made  to  connect  these  constants  together,  but  without  good  found- 
ation ;  for  5*4  and  12*4,  although  nearly  the  double  and  quadruple 
of  3*1,  are  yet  too  far  removed  to  show  any  necessary  connexion, 
and  10-4  is  completely  out  of  the  series  of  3'1,  though  nearly  the 
double  of  5-4. 

I  shall  have  occasion  to  discuss  this  remarkable  relation  between  the  physical  and 


68  HEAT    BY     CHEMICAL     COMBINATION. 

chemical  characters  of  these  bodies  when  I  come  to  examine  the  subject  of  the  laws 
of  chemical  combination  in  their  full  extent.  For  the  present,  the  details  now  given 
are  sufficient. 

It  is  not  likely  that  any  law  connecting  the  specific  heats  of  dif- 
ferent bodies  can  be  obtained  perfectly  consistent,  for  the  various 
bodies  necessary  cannot  be  examined  exactly  in  the  same  state. 
Regnault  has  well  observed,  that  the  quantity  of  heat  which  w« 
measure  as  specific  heat  consists  of  several  different  portions :  1st, 
the  true  specific  heat ;  2d,  the  heat  which  produces  dilatation ;  3d, 
the  heat  which  causes  the  rise  of  temperature  ;  and,  4th,  when  a 
solid  is  near  its  fusing  point,  the  quantity  employed  in  giving  the 
softness  and  ductility,  which  most  bodies  at  certain  temperatures  ac- 
quire. These  last  three  portions  being  very  small,  do  not  conceal 
the  law  by  which  the  true  specific  heat  is  regulated ;  but  they  influ- 
ence it  so  far  as  to  prevent  the  law  from  being  verified  in  its  nu- 
merical results  with  the  accuracy  which  otherwise  might  have  been 
obtained. 

When  bodies  combine  chemically,  there  is  generally  found  to  be 
a  diminution  of  specific  heat ;  and  it  has  been  attempted  to  account 
thereby  for  the  rise  of  temperature,  by  which  combination  is  in  most 
cases  accompanied.  Thus,  the  specific  heat  of  sulphuric  acid  is 
0'33 ;  and  when  mixed  with  an  equal  weight  of  water,  the  specific 
heat  of  the  mixtures  should  be,  were  there  no  action,  ^=0,665; 
but  the  true  specific  heat  of  the  combined  acid  and  water  is  found 
to  be  only  0-587.  The  excess,  therefore,  0-665— 0-587=0-078,  be- 
comes free,  and  shows  itself  by  raising  the  temperature  of  the  mix- 
ture ;  and,  accordingly,  on  mixing  together  sulphuric  acid  and  water, 
it  is  well  known  that  a  temperature  higher  than  that  of  boiling  water 
may  be  produced.  It  was  even  supposed  at  one  time,  when  heat 
was  looked  upon  as  being  a  positive  substance  which  combined  with 
bodies  in  different  proportions,  that  the  absolute  quantity  of  heat 
which  a  body  contained  might  be  determined  by  such  an  experi- 
ment, thus :  if  the  rise  of  temperature  produced  by  0.078  of  heat 
becoming  free  is  expressed  by  180^  above  32^,  then  the  quantity  of 
heat  which  stays  behind  must  be  greater  than  that  in  the  proportion 
of  587  to  78  ;  and  hence  is  equivalent  to  ~  180  =  1335'' :  and  thus,  at 
the  temperature  of — 1303°  of  Fahrenheit's  scale,  a  body  should  con- 
tain no  heat  at  all ;  it  should  be  the  absolute  zero.  But  no  two  such 
experiments,  with  different  bodies,  ever  gave  the  same  result :  and 
it  is  evident,  from  the  fact  of  the  specific  heat  diminishing  as  the 
temperature  sinks,  that  the  term  at  which  the  two  quantities  should 
vanish  must  be  infinitely  remote,  and  that  there  is  no  such  thing  as 
an  absolute  zero  at  all.  In  fact,  the  physical  existence  of  an  abso 
lute  zero  is  inconsistent  with  the  more  accurate  ideas  of  the  nature 
of  heat,  which  modern  investigation  has  suggested. 

The  development  of  heat,  in  chemical  combination,  is  also  only 
in  some  cases  accompanied  by  a  diminution  of  specific  heat ;  in  at 
least  as  many  it  is,  on  the  contrary,  remarkably  augmented. 

The  specific  heat  of  gases  and  vapours  has  obtained  considerable 
attention ;  and  yet,  from  the  extreme  delicacy  of  the  processes  neces- 
sary, and  the  small  quantity  of  material  which  can  be  operated  on, 
the  results  hitherto  obtained  have  not  acquired  that  degree  of  posi- 


SPECIFIC     HEAT 


OF     GASES. 


69 


tive  accordance  which  should  render  repetition  unnecessary.  The 
principal  experimenters  in  this  department  have  been  Delaroche  and 
Berard,  Delarive  and  Marcet,  Haycraft,  Dulong,  and,  latterly,  Apjohn 
and  Suerman. 

The  method  adopted  by  Haycraft,  and  by  Delaroche  and  Berard, 
consisted  in  heating  a  quantity  of  gas  to  a  certain  temperature,  and 
then,  by  passing  it  through  a  tube  in  a  vessel  of  water,  determining 
how  much  it  raised  the  temperature  of  the  water  in  being  cooled 
through  a  certain  number  of  degrees.  In  principle,  this  mode  is 
perfect ;  but  the  extreme  accuracy  necessary  in  the  management  of 
the  apparatus  does  not  appear  to  have  been  attained  by  Haycraft : 
and  Delaroche  and  Berard  deprived  their  results  of  most  of  their 
value  by  the  oversight  of  using  the  gases  in  a  damp  state.  The  pro- 
cess of  Delarive  and  Marcet  was  not  such  as  could  lead  to  results 
worthy  of  much  confidence.  A  glass  globe  full  of  gas,  to  which 
was  attached  a  thermometer,  with  the  bulb  exactly  in  the  centre, 
was  plunged  into  a  vessel  of  hot  water,  in  the  expectation  that  the 
lime  occupied  by  each  gas,  in  having  its  temperature  raised  a  cer- 
tain number  of  degrees,  would  be  proportional  to  the  specific  heat 
under  a  constant  volume.  But  the  communication  of  the  heat 
would  be  so  much  and  so  variously  affected  by  currents,  according 
to  the  density  of  the  gas  and  the  quantity  of  heat  absorbed  by  the 
gas,  so  trifling  in  comparison  to  that  which  would  be  required  to 
heat  the  globe,  that  the  amount  of  liability  to  error  was  very  great. 

The  process  employed  by  Dulong  was  very  beautiful  in  principle, 
and  calculated  to  give  experimental  results  of  great  accuracy.  It 
consisted  in  determining  the  velocity  of  sound  in  each  gas,  which 
was  measured  by  finding  the  note  the  same  organ-pipe  gave  with 
each :  from  this,  by  very  ingenious  methods,  which,  however, 
need  not  here  be  introduced,  farther  than  that  the  gases  with  higher 
specific  heats  give  more  acute  tones,  he  calculated  the  specific  heats. 
The  calculations  were,  however,  based  on  certain  other  principles, 
which  are  not  necessarily  true. 

The  method  contrived  by  Apjohn  is  that  which  appears  to  be  the 
best  calculated  to  give  accurate  results,  and  those  which  he  obtained 
have  been  verified  by  the  experiments  of  Suerman. 

Apjohn's  method  cannot  be  completely  described  until  we  come  to  speak  of  the 
latent  heat  of  vapours  and  their  relation  to  space  ;  but  the  general  principle  of  it  is, 
that  if  several  gases  be  employed  to  convert  a  certain  quantity  of  water  into  vapour, 
the  gases  will  be  cooled  thereby  in  inverse  proportion  to  their  specific  heats.  Thus, 
if  one  gas  have  double  the  specific  heat  of  another,  it  will  saturate  itself  with  va- 
pour by  cooling  through  only  half  the  number  of  degrees  necessary  for  that  with 
the  less  specific  heat ;  and  thus,  by  measuring  simply  the  cooling  power  of  each 
gas,  the  specific  heat  may  be  calculated. 

The  numbers  obtained  by  Delaroche  and  Berard,  by  Dulong  and  by  Apjohn,  for 
the  specific  heats  of  the  gases  in  equal  volumes,  are  given  in  the  following  table  • 


[Apjohn, 


Air      .     .     .  . 

Nitrogen  .    .  . 

Oxygen    .     .  . 

Hydrogen      .  . 

Carbonic  acid  . 
Carbonic  oxide . 

Nitrous  oxide  . 


1000 
1048 

•808 
1-459 
1195 

•996 
1193 


1000 
1006 
•976 
•900 
1-258 
1-034 
1-350 


Dulong. 


1000 
1-000 
1000 
1  300 
1-172 
1-000 
1159 


70    *  LIQUEFACTION. 

These  numbers  show  the  diversity  which  exists  among  even  the  best  expert 
menters ;  and  they  also  show  that  the  different  gases  follow  no  simple  law  regard- 
ing their  specific  heats.  The  principle  laid  down  by  Haycraft,  Delarive,  and  Marcet, 
that  in  equal  volumes  all  gases  have  the  same  specific  heat,  is  thus  shown,  by  the 
combined  evidence  of  all  the  best  results,  to  be  totally  unfounded. 

It  is  sometimes  necessary  to  compare  the  specific  heats  of  gases 
with  that  of  water ;  this  being  1-000,  that  of  air  is  0-267  for  equal 
weights,  and  so  on  for  the  other  gases  in  proportion. 

We  do  not  know  the  specific  heats  of  many  bodies  in  the  state 
of  vapour.  For  watery  vapour,  however,  it  is  found  to  be  0-847, 
water  being  1-000,  or  3-172,  air  being  1-000,  for  equal  weights. 
Water  is  thus  the  only  substance  of  which  we  know  the  specific 
heat  in  the  three  states  of  aggregation,  that  of  ice  being  -900,  water 
1*000,  and  steam  -847,  for  equal  weights. 

When  the  volume  of  a  gas  or  of  a  vapour  increases,  its  specific 
heat  increases  also,  and  vice  versa.  Hence,  when  air  is  suddenly 
condensed,  so  much  heat  is  evolved  that  tinder  may  be  lighted,  and 
the  barrel  of  a  condensing  syringe  may  become  too  hot  to  hold  ; 
thus,  also,  in  some  kinds  of  machinery  where  air  suddenly  expands, 
so  great  a  degree  of  cold  is  produced  that  water  may  be  frozen. 

The  exact  degree  of  connexion  between  the  amount  of  expansion 
of  the  gas  and  the  increase,  or  of  condensation  and  the  diminution 
of  specific  heat,  has  not  been  ascertained.  They  are  not  propor- 
tional ;  that  is  to  say,  when  the  volume  of  a  gas  is  doubled,  its  spe- 
cific heat  is  not  doubled,  and  vice  versa  ;  and  yet  it  would  appear 
that  it  does  not  fall  much  below  that  ratio. 

SECTION  III. 

OF   LIQUEFACTION. 

It  has  already  been  frequently  explained,  that  by  the  application 
of  heat  to  a  solid  body,  it  commences,  when  its  temperature  has 
risen  to  a  certain  degree,  to  become  liquid,  and  that  this  point,  the 
melting  point  of  such  solid  body,  is  one  of  the  most  determinate 
and  characteristic  of  its  physical  properties.  Accordingly,  the 
melting  point  is  often  used  as  a  means  of  distinguishing  and  recog- 
nising substances  otherwise  very  similar  in  properties ;  as,  for  ex- 
ample, the  numerous  fatty  acids  can  scarcely  be  otherwise  distin- 
guished from  each  other,  exclusive  of  analysis,  than  by  the  tem- 
peratures at  which  they  melt.  There  has  been  already  given  a  list 
of  the  melting  points  of  a  number  of  solid  bodies,  and,  in  the  his- 
tory of  each  individual  substance,  its  fusibility  will  be  described. 

The  change  from  the  solid  to  the  liquid  state  is  accompanied, 
however,  by  a  phenomenon  difl^ering  from  any  yet  described,  and 
deserving  of  great  attention  from  the  important  consequences  which 
flow  from  it.  It  is,  that  at  the  moment  of  liquefaction  a  very  large 
quantity  of  heat  is  absorbed,  combining,  as  it  were,  with  the  solid 
to  form  the  liquid  body,  and  after  combination  being  insensible  to 
the  thermometer,  and  having  thence  obtained  the  name  of  latent  heat. 
A  pound  of  water  at  32^  and  a  pound  of  ice  at  32°  give  on  the 
thermometer  precisely  the  same  degree,  and  yet,  independent  of  all 
considerations  of  specific  heat  discussed  in  the  last  section,  and 
which  we  now  lay  aside,  the  water  contains,  in  a  state  of  intimate 


ABSORPTION    OF     HEAT    DURING    LIQUEFACTION.    71 

combination,  a  great  quantity  of  heat,  by  virtue  of  which  it  is  liquid 
water,  and  by  losing  which  it  would  be  reduced  to  the  state  of  solid 
ice.  In  melting,  therefore,  every  body  renders  latent  a  quantity  of 
heat. 

This  principle  may  be  demonstrated  by  experiments  of  a  very  sim- 
ple kind.  Thus,  if  a  pound  of  ice  be  taken  at  32%  and  added  to  a 
pound  of  water  at  172"",  the  ice  dissolves  immediately,  but  the  tem- 
perature of  the  resulting  two  pounds  of  water  is  found  to  be  32^ 
There  has  thus  disappeared  a  quantity  of  heat,  which  had  previous- 
ly raised  the  temperature  of  the  water  to  172^,  or  through  14>0^. 
This  heat  has  been  absorbed  by  the  ice  in  becoming  liquid,  and  ren- 
dered latent ;  and  it  is  therefore  said  that  the  latent  heat  of  liquid 
water  is  140^.  If  a  vessel  of  water,  at  the  temperature  of  52°,  be 
exposed  freely  to  air  below  the  freezing  point,  it  will  rapidly  cool 
until  it  arrives  at  32°,  but  there  the  lowering  of  the  temperature 
ceases  j  it  begins  to  freeze,  and,  until  the  entire  mass  is  reduced  to 
solid  ice,  no  loss  of  heat  sensible  to  the  thermometer  is  observed : 
yet  it  must  still  be  giving  out  heat  precisely  as  it  was  when  it  cool- 
ed from  52°  to  32°,  this  heat  being,  however,  that  which  gave  to  it 
the  form  of  liquid  water,  and  which  had  been  perfectly  insensible, 
or  latent,  until  the  formation  of  ice  commenced.  If  the  water  had 
taken  ten  minutes  to  cool  from  52°  to  32°,  it  will  be  found  to  require 
one  hour  and  ten  minutes  to  become  completely  frozen  ;  and  hence, 
as  in  the  same  time  it  loses  the  same  quantity  of  heat,  the  external 
air  remaining  equally  cold,  the  latent  heat  is  20°  x  7=140°,  as  in  the 
former  experiment.  Another  mode  of  verifying  the  result  consists 
in  exposing  a  pound  of  ice  at  32°,  and  a  pound  of  water  at  the  same 
temperature,  to  the  same  source  of  heat,  as  on  a  steady  fire,  and  it 
will  be  found  that,  by  the  time  the  ice  has  completely  melted,  the 
temperature  of  the  water  will  have  risen  to  172°. 

Water  is,  of  all  liquids,  that  which  contains  the  greatest  quantity 
of  latent  heat,  and  hence  that  which  changes  from  the  liquid  to  the 
solid  state  most  slowly ;  and  inversely,  ice  is  the  solid  which  ab- 
sorbs most  heat,  and  requires  most  time  to  liquefy.  This  property 
of  water  is  of  the  highest  importance  in  the  economy  of  nature, 
for  by  means  of  it  the  change  of  seasons  is  rendered  much  less 
sudden  than  could  otherwise  occur.  If  water  passed  from  32°  to 
31°,  and  became  solid  by  losing  only  the  same  quantity  of  heat  as 
it  gives  out  in  cooling  from  33°  to  32°,  the  change  of  seasons  would 
be  so  rapid  and  so  uncertain  as  to  interrupt  almost  entirely  the 
proper  cultivation  of  the  soil,  and,  by  the  vicissitudes  of  heat  and 
cold,  become  injurious  to  the  health.  But,  as  these  properties  of 
water  are  now  arranged,  each  particle,  in  freezing,  becomes  a  source 
of  warmth  to  all  around,  and  mitigates  the  severity  of  the  cold; 
there  can  be  but  a  comparatively  small  quantity  of  water  rendered 
solid  ;  and  when,  on  the  return  of  a  warmer  season,  a  sudden  lique- 
faction might  prove  equally  injurious,  ice  and  snow,  in  melting,  ab 
sorb  all  excess  of  heat,  and  render  the  change  gradual,  and 'suitable 
to  the  functions  of  those  plants  and  animals  to  which  a  sudden  tran- 
sition might  prove  fatal. 

We  do  not  know  the  latent  heat  of  many  liquid  bodies,  but  those 
given  in  the  following  table  will  suffice  to  show  the  renaarkable 


72  HEAT     EVOLVED     IN     SOLIDIFICATION. 

pre-eminence  of  water  in  that  respect.  The  numbers  are  given  in 
two  cohimnsj  the  first  showing  the  interval  through  which  the 
body  itself,  in  its  liquid  form,  would  be  heated  by  the  heat  it  absorbs 
in  melting,  and  the  second  showing  the  interval  through  which 
that  heat  would  elevate  the  temperature  of  an  equal  weight  of  water 
Thus : 

Latent  Heat  of  Measured  by  itself.  Measured  by  Water 

Water 140 140 

Sulphur 144 2714 

Lead 370 110 

Zinc 493 483 

Bismuth 550  .......     .  23  25 

In  every  case  a  solid  body  begins  to  melt  at  the  same  temperature 
Thus,  ice  never  begins  to  melt  until  it  arrives  at  32°,  and  can  never 
be  raised  above  32°  without  melting  ;  consequently,  the  fixed  point 
is  the  melting  point  of  ice,  and  not  the  freezing  point  of  water  ;  for, 
if  water  be  cooled  carefully  without  agitation,  its  temperature  may 
be  lowered  easily  to  25°,  and  has  been  reduced  to  15°  without  so- 
lidifying. This  is  a  phenomenon  like  that  which  has  been  (page  25) 
noticed  in  the  crystallization  of  sulphate  of  soda,  where  the  solution 
may  remain  perfectly  liquid  until  agitated,  and  then  suddenly  crys- 
tallizes with  the  evolution  of  considerable  heat.  If  water,  so  cooled 
below  32°,  be  agitated,  it  freezes  suddenly,  and  the  temperature 
rises  to  32°  ;  the  latent  heat  of  that  portion  which  freezes  becoming 
sensible,  and  thus  warming  the  entire  mass. 

Substances  which  crystallize  easily  generally  expand  in  solidify- 
ing, and  in  doing  so  exert  great  force.  Thus  water  is  capable  of 
bursting  the  strongest  vessels  if  they  be  filled  completely  with  it, 
and  tightly  closed  so  as  to  prevent  expansion  otherwise.  It  is  by 
the  agency  of  this  force  that  the  gradual  deterioration  of  the  sur- 
face of  rocks,  and  the  formation  of  the  soil  on  the  lower  grounds, 
depends ;  the  rain-water  being  absorbed  into  the  pores  and  small 
cavities  which  even  the  hardest  rocks  contain,  and  being  there,  in 
winter,  frozen,  breaks  open  the  substance  of  the  rock,  and  causes 
it  gradually  to  fall  to  powder,  thus  generating  the  soft  and  porous 
soil  fitted  for  the  reception  and  sustenance  of  the  seeds  and  roots 
of  plants.  It  is  also  by  the  action  of  this  force  of  expansion,  exert- 
ed by  many  bodies  when*they  crystallize,  that  we  are  enabled  to 
take  accurate  copies  of  the  moulds  into  Avhich  such  substances,  in 
the  liquid  state,  are  poured.  Cast  iron,  antimony,  and  the  alloy  of 
antimony  used  for  printers'  types,  the  alloy  used  for  stereotype 
plates,  brass,  bronze,  and  all  such  bodies,  are  capable  of  making 
good  castings  by  virtue  of  this  expanding  power ;  while  bodies 
which  do  not  distinctly  crystallize,  as  gold,  silver,  and  copper,  are 
not  capable  of  giving  accurate  castings,  and  hence  the  coinage  of 
these  metals  is  made  by  stamping  the  necessary  marks  upon  them 
by  means  of  a  violent  blow. 

By  the  addition  of  small  quantities  of  salts  or  vegetable  acids, 
the  freezing  point  of  water  may  be  considerably  lowered :  thus,  sea- 
water  does  not  easily  freeze.  When  such  a  solution  is  brought  to 
solidify,  it  is  pure  ice  which  first  crystallizes  out.  Thus,  from  a 
strong  solution  of  potash,  ice  has  been  obtained  in  large  six-sided 
prisms  j  and  the  ice  mountains  which  form  in  the  Polar  Seas  are 


COLD     BY     LIQUEFACTION.  73 

found  to  be  almost  completely  fresh.  This  principle  has  been  ap- 
plied also  to  the  concentration  of  vinegar  and  lemon-juice  by  freez- 
ing, a  large  quantity  of  mere  ice  being  formed  round  the  sides  of 
the  vessel,  and  a  central  cavity  remaining  filled  with  concentrated 
acid. 

The  principle  of  latent  heat  has  been  applied  to  the  production 
of  artificial  cold.  For  if  a  solid  body  suddenly  liquefies  without 
the  application  of  external  heat,  it  must  abstract  from  the  surround 
ing  bodies  the  heat  necessary  to  its  liquefaction,  and  thus  reduce 
their  temperature  and  its  own.  Hence,  when  salts  are  dissolved  iit 
water  without  any  chemical  combination,  there  is  cold  produced. 
Thus,  by  mixing  nitrate  of  ammonia  with  an  equal  weight  of  water, 
the  thermometer  sinks  46°  ;  and  carbonate  and  sulphate  of  soda, 
dissolved  in  three  times  their  weight  of  water,  reduce  the  temper- 
ature, the  first  16°,  and  the  second  12°. 

In  many  cases  where,  by  double  decomposition,  those  soluble 
substances  may  be  formed,  more  powerful  effects  are  produced  by 
mixing  two  salts  together  than  by  either  separately.  Thus  neither 
nitre  nor  sal  ammoniac  produce  much  cold,  but  when  mixed  they 
generate  nitrate  of  ammonia,  which  is  very  powerful,  and  hence 
cause  a  reduction  of  40°.  In  other  cases  the  cold  results  from  a 
quantity  of  water  of  crystallization  being  set  free  and  suddenly 
liquefying.  Thus,  when  crystallized  sulphate  of  soda  is  dissolved 
in  muriatic  acid,  there  are  formed  bisulphate  of  soda  and  chloride 
of  sodium,  with  which  but  i  of  the  quantity  of  water  remains ;  and 
the  remaining  |  being  disengaged,  and  abstracting  from  the  sur- 
rounding bodies  the  heat  necessary  for  their  liquefaction,  depress 
the  temperature  through  50°. 

By  using  snow  or  pounded  ice,  freezing  mixtures  of  still  greater 
power  may  be  produced.  The  cold  is  the  greatest  when  a  substance 
is  employed  which  contains  itself  a  large  quantity  of  water  in  a 
combined  from.  Thus  crystallized  chloride  of  calcium  contains 
half  its  weight  of  water,  and,  when  mixed  with  an  equal  weight  of 
snow,  the  whole  becomes  liquid,  and  the  quantity  of  heat  absorbed 
is  proportionally  large.  By  combining  such  freezing  mixtures  in- 
tense degrees  of  cold  have  been  produced ;  Mr.  Walker,  to  whom 
the  invention  of  most  of  them  is  due,  having  obtained  a  depression 
of  temperature  to  — 91°  of  Fahrenheit. 

The  following  table  contains  the  proportions  for  some  of  the  most  useful  freezing 
mixtures,  and  the  degree  of  cold  which  can  be  obtained  by  means  of  them.  It  is  to 
be  remarked,  that  in  using  freezing  mixtures  a  great  deal  of  the  success  depends  on 
the  rapidity  with  which  the  Uquefaction  is  produced ;  the  thinnest  possible  vessels, 
and  a  tolerably  large  quantity  of  materials  should  be  used.  For  producing  a  great 
degree  of  cold,  it  is  also  necessary  to  cool  the  materials  previously  as  much  as  pos- 
sible ;  thus,  to  produce  the  intense  cold  of  — 91°,  Mr.  Walker  had  cooled  the  sub- 
stances to  be  mixed  down  to  — 68°  by  means  of  other  freezing  mixtures. 

K 


74     ARTIFICIAL     COLD     BY     FRIGORIFIC     MIXTURES. 


FRIGORIFIC  MIXTURES  WITHOUT  ICE. 

Mixtures. 

Parts 

Thermometer  sinks 

Degree 
of  cold. 

Nitrate  of  ammonia 
Water 

1 
1 

5 

5 

16 

1  from  +50°  to  +4° 

46° 
40° 
63° 

Muriate  of  ammonia 
Nitrate  of  potash    . 
Water 

• 

(  from  4-50°  to  +10° 

Sulphate  of  soda     . 
Diluted  nitric  acid  . 

3 

2 

I  from  +50°  to  —3° 

Sulphate  of  soda     . 
Muriate  of  ammonia 
Nitrate  of  potash    . 
Diluted  nitric  acid  . 

6 
4 

2 
4 

1 

Vfrom  +50°  to  —10° 

60° 

Sulphate, of  soda     .     . 
Nitrate  of  ammonia     . 
Diluted  nitric  acid  .     . 

6 
5 

4 

(  from  50°  to  —14° 

64° 

Sulphate  of  soda     .     . 
Muriatic  acid      .     .     . 

8 
5 

:  from +50°  to  0° 

50° 
34° 

Phosphate  of  soda  .     . 
Nitrate  of  ammonia     . 
Diluted  nitric  acid  .     . 

5 
3 
4 

I  from  0°  to  —34° 

FRIGORIFIC  MIXTURES  WITH  ICE. 

Mixtures. 

Parts. 

Thermometer  sinks 

Degree 
of  cold. 

* 
♦ 

Snow  or  pounded  ice 
Common  salt     .     . 

2 
1 

> 

1 
S 

to  —5° 

Snow  or  pounded  ice 
Common  salt      .     . 
Sal  ammoniac    .     . 

5 

2 

1 
24 
10 

5 

5 
12 

5 

5 

'Y 

4 

to  —12° 

Snow  or  pounded  ice 
Common  salt      .    . 
Sal  ammoniac    .     . 
Nitrate  of  potash     . 

> 

to  —18° 

* 
# 

60° 

82° 

Snow  or  pounded  ice 
Common  salt      .     . 
Nitrate  of  ammonia 

to  —25° 

Snow    .     .     .     .     . 

from +32°  to —30° 

Diluted  nitric  acid  . 

Snow 

2 
3 

from +32°  to —50° 

Crys.  muriate  of  lime 

Snow 

3 

4 

from +32°  to— 51° 

83° 
46° 

Potash 

Snow 

3 

2 

;  from  0°  to —46° 

Diluted  nitric  acid  . 

Snow 

1 

2 

from  0°  to —66° 

66° 

Crys.  muriate  of  lime 

Snow 

8 
10 

>  .            

25° 

Diluted  sulphuric  acid 

r^ 

om  —66"  to  —91° 

In  the  ordinary  experiment  of  freezing  mercury  by  a  mixture  of  snow  and  crys- 
tallized chloride  of  calcium,  success  is  seldom  obtained  unless  by  having  two  por- 
tions of  the  mixture,  and  either  cooling  the  materials  for  the  second  by  means  of  the 
first,  or  plunging  the  tube  of  mercury,  when  it  has  exhausted  the  cooling  powers  of 
the  first,  into  the  second  and  freshly-mixed  portion  of  materials. 

There  are  many  cases  in  which  heat  is  evolved  from  solid  bodies 
without  our  being  able  positively  to  ascertain  its  source,  and  where, 


NATURE     OF     SPECIAL      HEA  T. V  APORIZATION.      75 

consequently,  it  may  be  considered  as  having  previously  been  latent. 
Thus,  by  the  friction  of  two  different  bodies  together,  as  when  the 
axle  of  a  carriage  becomes  hot,  or  when,  as  among  savage  nations, 
fire. is  obtained  by  rubbing  two  pieces  of  wood  together.  But  it  is 
rather  a  misuse  of  words  to  say  that  the  heat  evolved  had  previously 
been  latent,  for  the  latent  heat  of  a  body  should  properly  be  consid- 
ered as  that  by  which  the  fluid  condition  is  conferred  upon  it,  and 
hence  a  solid  body  cannot  be  said  to  have  such  latent  heat  at  all. 
It  is  most  likely  that,  as  a  diminution  of  specific  heat  accompanies 
the  increase  of  density  which  occurs  when  oil  of  vitriol  and  water 
are  mixed  together,  so  where,  by  compression,  the  density  of  a  solid 
body  is  increased,  its  specific  heat  may  be  diminished,  and  hence 
sensible  heat  evolved.  Although  our  knowledge  of  this  subject  is 
not  at  all  as  satisfactory  as  its  importance  merits,  it  has  been  ascer- 
tained that,  when  iron  is  violently  compressed,  as  in  boring  cannon 
or  by  repeated  hammering,  its  specific  heat  becomes  much  less,  and 
the  heat  evolved  is  so  considerable  that  the  metal  may  easily  be 
made  red  hot.  It  would  be  well  to  distinguish  between  heat,  cer- 
tainly before  latent,  which  may  thus  be  rendered  sensible,  and  the 
true  latent  heat  which  is  absorbed  during  liquefaction,  and  which 
can  be  only  given  out  again  by  the  reassumption  of  the  solid  form  j 
and  this  might  be  done,  perhaps,  and  its  connexion  with  specific  heat 
made  evident,  by  adopting  the  word  special  heat^  or  heat  peculiar  to 
the  body.  Thus  liquids  and  vapours  only  can  contain  latent  heat ; 
but  every  body  contains  a  quantity  of  special  heat^  equally  insensible 
to  the  thermometer,  but  becoming  manifest  when  the  specific  heat 
is  diminished.  The  special  heat  is  thus  the  heat  which  gives  to  the 
body  the  temperature  which  it  possesses,  and  the  quantity  of  special 
heat  necessary  to  produce  a  rise  of  temperature  measures  the  spe- 
cific heat. 

Many  bodies  undergo,  before  liquefaction,  remarkable  changes  in 
their  molecular  constitution :  thus  iron,  wax,  and  glass  become 
soft  and  pasty,  so  that  different  pieces  may  be  perfectly  united  into 
one  ;  and  it  is,  indeed,  on  this  property  that  the  most  useful  appli- 
cations of  glass  and  iron  in  ordinary  life  depend.  This  has  been 
referred  to  a  certain  quantity  of  latent  heat  having  already  entered 
into  the  body,  and  giving  an  intermediate  condition,  that  of  semiflu- 
idity.  There  is  no  proof  either  for  or  against  this  view,  as  no  exact 
experiments  have  been  made  upon  such  bodies.  In  other  cases, 
where  semifluidity  is  produced,  as  in  lard,  tallow,  &c.,  it  is  plainly 
seen  to  arise  from  the  substance  being  a  mixture  of  two  bodies,  of 
which  one  melts  easily,  and,  being  then  liquid,  forms  with  the  other, 
which  remains  still  solid,  a  kind  of  pulp,  which  gradually  becomes 
less  thick,  according  as  the  temperature  rises,  until  all  is  liquefied 

SECTION  IV. 

OF   VAPORIZATION. 

By  the  application  of  a  higher  temperature  than  that  which  was 
necessary  for  liquefaction,  the  generality  of  fusible  bodies  are  capable 
of  being  converted  into  vapour.  In  this  form  they  resemble,  in  mole- 
cular  constitution,  the  most  permanent  of  the  gases,  and  are  subjected 


76 


LATENT     HEAT     OF     VAPOURS. 


to  precisely  the  same  laws  of  change  of  volume,  for  any  alteration 
of  temperature  or  pressure,  as  atmospheric  air,  as  long  as  the  elastic 
form  is  preserved.  This  passage  from  the  solid  or  liquid  to  the 
gaseous  state  of  aggregation,  may  occur  either  slowly  and  silejitly, 
or  with  violence  and  rapidity  ;  the  hody  may  either  evaporate  or 
boil.  The  evaporation  may  go  on  at  any  temperature,  even  at  the 
lowest ;  but  boiling  commences  only  at  a  certain  temperature,  which 
depends  on  the  nature  of  the  body,  and  upon  the  pressure  to  which 
it  is  subjected.  Each  of  these  modes  of  generating  vapour  will  re- 
quire to  be  specially  examined  ;  but  it  is  necessary  to  attend,  in  the 
first  place,  to  the  phenomenon  which  accompanies  and  may  be  sup- 
posed to  produce  the  change  of  form,  the  absorption  of  the  heat  of 
vaporization ;  for  precisely  as  a  solid  absorbs  heat  in  becoming  liquid, 
so  does  a  liquid,  in  assuming  the  vaporous  condition,  render  heat  la- 
tent, and  even  in  still  greater  quantity. 

If  we  place  upon  a  steady  fire  or  over  a  lamp  a  cup  of  water,  we 
shall  observe  that  its  temperature  rises  until  it  begins  to  boil,  but 
then  remains  perfectly  stationary  until  the  last  drop  of  the  water 
shall  have  been  boiled  away.  If  we  remark  the  time,  we  shall  find 
it  to  be  in  the  following  proportion.  Let  us  suppose  the  temperature 
of  the  water  to  have  been  originally  62°,  and  that  at  the  end  of  six 
minutes  it  began  to  boil,  having  attained  the  temperature  of  212°. 
In  each  minute,  therefore,  there  entered  into  the  water  a  quantity 
of  heat  sufficient  to  raise  its  temperature  ^-^^=^=25°.  Now,  the 
source  of  heat  remaining  perfectly  steady,  it  will  be  found  neces- 
sary to  apply  it  during  40  minutes  to  boil  away  all  the  water  ,•  and 
as  in  each  minute  there  enters  heat  enough  to  raise  the  temperature 
of  the  same  weight  of  water  25°,  the  total  quantity  of  heat  absorbed 
by  the  water  in  being  converted  into  steam  would  have  raised  its 
temperature,  had  it  remained  liquid,  25x40=1000°,  or  just  to  red- 
ness. And  yet  this  becomes  perfectly  latent,  the  temperature  of  the 
vapour  formed,  that  is,  of  the  steam,  being  exactly  212°,  that  of  the 
water  it  is  formed  from. 
By  the  inverse  process  a  corresponding  observation  may  be  made.     Thus,  vvater 

being  boiled  in  a  vessel,  as  in 
the  figure,  the  steam  may  be 
conducted  by  a  tube  into  a  glass 
containing  a  weighed  quantity 
of  cold  water,  the  temperature 
of  which  is  accurately  marked. 
The  steam,  by  condensing  iu 
the  cold  water,  raises  its  tem- 
perature ;  and  when  a  suffi- 
cient rise  has  been  produced, 
the  steam  may  be  shut  off,  and 
the  glass  with  the  warm  water 
weighed  again.  It  is  found  to 
be  heavier  than  before,  from 
the  quantity  of  water  added  to 
it  by  the  condensation  of  the 
steam ;  and  the  quantity  of  heat 
given  out  by  the  steam  in  so 
condensing  may  easily  be  cal- 
culated. Thus :  let  us  suppose  that  there  were  eight  ounces  of  water,  at  60°,  ori- 
ginally used,  and  that,  at  the  termination  of  the  experiment,  there  were  nine  ounces 
at  the  temperature  of  188°.    It  is  then  evident  that  one  ounce  of  steam,  in  conden- 


INCREASE     OF     VOL  U  M  E     IN     VAPORIZATION. 


7-7 


sing,  had  raised  the  temperature  of  the  eight  ounces  128°.  The  temperature  of  one 
ounce  might  have  been,  therefore,  raised  128x8=1024°  :  but  this  was  not  all  la 
tent  heat ;  for  the  steam,  by  merely  condensing,  should  have  formed  liquid  water  at 
212°,  whereas  it  cooled  to  188°.  The  difference,  =24°,  must  be  subtracted  from 
the  1024°  ;  and  thus  the  latent  heat  of  steam  determined  to  be  1000°,  as  it  had  been 
found  by  the  previous  process. 

The  great  quantity  of  heat  thus  contained  in  an  insensible  form  in 
steam  is  very  generally  made  use  of  for  warming  apartments  and 
for  chemical  operations,  in  which  exposure  to  the  direct  action  of  a 
fire,  or  even  to  a  sand  bath,  might  be  injurious.  By  means  of  a 
series  of  pipes,  steam  from  a  boiler,  placed  at  a  distance,  is  brought 
to  cii'culate  through  every  part  of  the  most  extensive  buildings,  and 
condensing  gradually  as  it  passes  along  the  cooling  surfaces,  the 
liquid  water  is  conducted  back  again  to  the  boiler,  there  to  be  recon- 
verted into  steam.  In  large  manufacturing  laboratories,  such  as  those 
of  the  Apothecaries'  Halls  of  Dublin  and  of  London,  there  are  steam 
ranges,  or  series  of  evaporating  pans  and  stills,  set  in  cast-iron  cases, 
within  which  steam  is  introduced,  and  thus  the  most  delicate  vege- 
table preparations,  such  as  extracts  and  inspissated  juices,  prepared 
at  temperatures  which,  being  completely  under  the  control  of  the 
operator,  allows  all  the  freshness  and  active  properties  of  the  plants 
to  be  perfectly  preserved. 

By  means  of  apparatus  similar  in  principle  to  that  in  the  last  figure,  the  latent 
he&ts  of  the  vapours  of  many  fluids  have  been  determined.  It  has  been  found  that 
the  latent  heat  of  equal  weights  of  the  vapours  of  the  following  bodies  would  have 
raised  the  temperature  of  an  equal  weight  of  water  in  condensing : 

Water 1000° 

Alcohol 376° 

Ether 163° 

Oil  of  turpentine 138° 

Nitric  acid 335° 

Tlie  latent  heats  of  bodies,  such  as  vinegar  and  water  of  ammonia,  which  have  no 
definite  chemical  constitution,  but  contain  mixed  water,  do  not  possess  any  value 
or  importance. 

In  changing  from  the  liquid  to  the  gaseous  state,  the  volume  is 
increased  in  a  very  great  degree  ;  the  amount  of  increase,  in  some 
instances,  which  may  be  taken  as  examples,  is  given  in  the  following^ 
table. 


Water  .  .  .  , 
Alchoi  .  .  .  , 
Ether  .  .  .  , 
Oil  of  turpentine 
Mercury     .     .     , 


Spe.  Gra. 

Wafer  = 

1000. 


1000 

907 

715 

867 

13500 


Boiling 
Point. 


Volume 

of  Vapoiir 

at  boiling 

Point. 


212° 
172° 
97° 
315° 
660° 


Volume 
of  Vapour 
at  212°. 


1696 
488 
240 
221 

3395 


1696 
519 
289 
192 

1938 


Specific 

Gravity  of 

Vapour. 


620 
1601  \ 
2583 
4763 
6969 


In  the  first  column  are  the  names  of  the  bodies ;  in  the  second,  theii  specific 
gravities,  water  being  1000 ;  in  the  third,  their  boiling  points ;  in  the  fourth,  the 
number  of  volumes  of  vapour  furnished  by  one  volume  of  each  fluid  at  its  boiUng 
point ;  in  the  fifth,  the  number  of  volumes  of  vapour  reduced  to  a  standard  temper- 
ature, 212°,  which  one  volume  of  fluid  may  produce ;  and  in  the  sixth,  the  specific 
gravity  of  the  vapour,  air  being  1000. 

It  has  been  imagined  that  there  should  exist  some  physical  connexion  between 
the  increase  of  volume  produced  by  the  change  from  the  liquid  to  the  gaseous 
state,  and  the  quantity  of  heat  rendered  latent  during  the  change ;  and  it  is,  in 
fact,  generally  true,  that  those  bodies  which  have  small  latent  heat  expand  least,  as 
oil  of  turpentine  and  ether.    But,  as  yet,  from  the  few  experiments  that  have  been 


78    DETERMINATION    OF    ELASTICITIESOF    VAPOURS- 


made  upon  latent  heats,  with  substances  sufficiently  pure  to  be  taken  as  the  basis 
of  calculation,  nothing  positive  can  be  considered  to  be  known. 

The  passage  from  the  liquid  condition  to  the  state  of  vapour  is 
distinguished  from  the  change  of  a  solid  to  a  fluid,  by  the  impor- 
tant fact  that,  while  liquefaction  is  definitely  produced  at  one  tem- 
perature, and  at  that  alone,  vaporization  occurs  at  all  tempera- 
tures j  and  it  is  only  from  the  influence  of  external  circumstances 
that  the  change  is  accompanied,  at  a  particular  temperature,  by  the 
phenomenon  of  boiling.  The  coldest  water  is  capable  of  forming 
vapour  5  even  ice  evaporates  j  and,  in  order  to  do  so,  it  is  not  neces- 
sary that  it  shall  previously  melt ;  it  is  thus  that  snow  will  gradually 
disappear  from  the  ground,  even  when  shaded  from  the  sun's  rays, 
and  though  the  air  shall  have  continued  below  the  melting  point. 
Other  solid  bodies  also  evaporate  without  previous  melting,  as  cam- 
phor ;  and  arsenic  cannot  be  melted  j  for,  when  heated,  it  is  convert- 
ed at  once  from  the  solid  to  the  vaporous  condition.  The  particles 
of  volatile  bodies  appear  thus,  at  all  temperatures,  to  repel  each 
other  to  a  certain  degree,  and  to  spread  abroad,  in  the  form  of  va- 
pour, until  they  occupy  completely  the  space  in  which  the  body  is 
contained,  and  exercise  a  pressure  which  is  equal  to  the  force  of 
their  mutual  repulsion,  and  which  is  termed  the  elasticity  of  the  va- 
pour. 

The  amount  of  elasticity,  or,  as  it  is  often  called,  tension  of  a  va- 
pour, is  determined  by  very  simple  methods.  Thus,  for  elasticities 
Ph&— — fflL  below  that  of  atmospheric  air,  a  series  of  barom- 
eter tubes  arranged  in  a  stand,  P  P  a  a,  are  to  be 
carefully  filled  and  inverted  in  a  basin  of  mercury, 
c  c,  as  in  the  figure.  One  such  tube,  d  d,  is  to  be 
kept  untouched,  to  measure  the  elasticity  of  the  ex- 
ternal air.  If  a  little  water  be  allowed  to  pass  up 
into  the  next  tube,  and  there  float  upon  the  surface 
of  the  mercury,  it  immediately  forms  vapour,  which 
spreads  through  all  the  empty  space,  and,  pressing 
against  the  upper  surface  of  the  mercurial  column, 
counteracts  a  portion  of  the  pressure  of  the  exter- 
nal air.  The  remaining  pressure  of  the  air  is  able 
to  support,  therefore,  only  a  shorter  column  of  mer- 
cury, and  the  height  of  the  mercury  in  the  tube 
diminishes.  If  into  another  tube  some  alcohol  be 
introduced,  there  is  a  similar,  but  still  greater  de- 
pression of  the  mercurial  column  caused,  and  with 
ether  the  height  of  the  mercurial  column  is  still 
more  diminished.  The  atmospheric  pressure  in 
these  cases  balances  the  shortened  column  of  mer- 
cury added  to  the  elasticity  of  the  vapour,  and  this 
last  is  consequently  measured  by  the  height  of  the 
column  of  mercury  which  it  is  capable  of  replacing,  that  is,  by  the 
space  through  which  the  mercury  has  been  depressed,  which  is 
read  ofi'  by  the  rule  and  index,  r  v  r.  Thus,  if  the  barometer  be  at 
30  inches  and  the  temperature  80°,  the  mercury  will  stand  in  the 
tube  with  watery  vapour  at  29  inches,  in  that  with  alcohol  at  28-1, 
and  in  that  of  ether  at  10  inches.  The  elasticities  of  these  vapours 
are  therefore  at  the  temperature  of  80°. 


DETERMINATION    OF    ELASTICITIES    OF    VAPOURS.    79 

Vapour  of  water 10  inch. 

"      of  alcohol 1-9 

»•      of  ether 200 

In  order  to  ascertain  how  the  elasticity  of  a  vapour  changes  with 
the  temperature,  it  is  only  necessary  to  enclose  the  upper  part  of  the 
tube  in  a  cylindrical  case  containing  water  or  oil  heated  to  the 
necessary  degree.  As  the  heat  increases  the  height  of  the  mercu- 
rial column  will  diminish,  and  at  each  temperature  the  elasticity  is 
so  determined.  The  apparatus  may  be  modified  by  bending  the 
tube  so  as  to  immerse  the  bent  portion  containing  the  vapour  into 
a  globe  of  water  or  oil  to  which  heat  may  be  applied,  but  the  prin- 
ciple remains  the  same.  In  this  way  a  table  of  the  elasticity  of  a 
vapour  at  all  temperatures  below  their  boiling  points  may  be  form- 
ed ',  and  as  there  will  be  frequent  reference  hereafter  to  the  tension 
of  the  vapour  of  water,  the  following  table  is  introduced  for  use 
and  as  an  example : 


Temperature. 

Elasticity. 

Temperature. 

Elasticity. 

32° 

0-200  f; 
0-263  g 
0-375  1 

90° 

1-36  ^ 
1-86   g 

40° 

100° 

50° 

120° 

3  33   53 

55° 

0-443  S. 

140° 

5-74  S 
9-46   I 

60° 

0-524  t, 

160° 

65° 

0-616  1 

180° 

15-15  1 

70° 

0-721  .S 

200° 

23-64  .S 

80° 

1000  .s 

212° 

30-00  S 

When  a  liquid,  in  such  an  apparatus,  is  heated  until  the  vapour 
formed  occupies  all  the  tube  and  expels  the  mercury,  the  elastici- 
ty of  the  vapour  is  equal  to  that  of  the  air,  and  the  liquid  exposed 
to  the  air  boils  j  the  phenomenon  of  boiling  arising  simply  from 
the  fact  that  the  elasticity  of  the  vapour  balances  the  pressure 
of  the  air  while  the  bubble  is  passing  through  the  fluid:  thus, 
suppose  a  vessel  of  water  exposed  to  the  air  at  200°,  and  a  bub 
ble  of  steam  to  form  in  it ;  the  pressure  exercised  by  that  bubble 
being  equal  to  its  tension,  is  equivalent  to  a  column  of  23'64  inches 
of  mercury ;  but  the  external  pressure  being  30  inches,  the  bub- 
ble is  crushed  in  by  a  force  equal  to  the  difference  (6*36  inches 
of  mercury),  and,  consequently,  dispersed.  If  the  water,  however, 
be  heated  to  212°,  the  elasticity  becomes  equal  to  30  inches,  and 
then  the  external  and  internal  pressures  being  equal,  the  bubble 
rises  in  the  liquid  without  injury,  and  maintains  itself  at  the  surface 
until  its  investing  film  of  water  is  ruptured  by  other  causes,  when 
the  vapour  mixes  uniformly  with  the  air. 

It  is  the  bursting  of  the  steam  bubbles  that  are  first  formed  in 
this  manner  that  constitutesthe  simmering  of  a  boiler  or  the  sing- 
ing of  a  kettle  on  the  fire.  The  bottom  of  the  vessel  heats  more 
strongly  the  layer  of  water  in  contact  with  it,  so  that  the  steam  has 
there  a  high  degree  of  elasticity,  and  forms  a  multitude  of  minute 
bubbles  j  when  these  separate  from  the  hot  metal,  they  are  immedi- 
ately burst  in  by  the  greater  external  pressure,  and  the  mass  of 
water  is  thus  thrown  into  a  state  of  exceedingly  rapid  and  uniform 
vibration,  which  fall  upon  the  ear  so  regularly,  in  many  cases,  as  to 
produce  a  musical  and  often  agreeable  tone,  which  may  become 


80  DETER  MINATION  OF   ELASTICITIES    OF   VAPOURS. 


graver  or  more  acute,  according  as  the  bubbles  burst  more  or  less 
rapidly  after  one  another. 

The  elasticity  increases  very  rapidly  with  the  temperature,  as  is 
seen  in  the  table,  where,  in  rising  from  180°  to 
212°,  the  elasticity  is  doubled.  For  high  tem- 
peratures the  rate  of  increase  is  still  more  rapid. 
To  determine  the  elasticity  at  temperatures 
above  the  ordinary  boiling  point,  an  apparatus 
completely  cut  off  from  the  external  air  is  made 
use  of.  In  the  figure  there  is  a  globular  vessel 
of  strong  metal,  a,  into  which  is  introduced  by 
the  stopcock  c/,  the  fluid  to  be  experimented  on, 
as,  for  example,  water.  In  the  aperture  c  is 
fitted  a  thermometer,  the  bulb  of  which  dips 
into  the  fluid  near  the  centre,  and  shows  its  tem- 
perature. A  quantity  of  mercury  being  in  the 
bottom  of  the  vessel,  the  tube  b  dips  under  its 
surface,  and,  rising  to  the  necessary  height,  has 
attached  to  it  the  scale  divided  into  inches  and 
their  parts.  When  the  apparatus  is  heated,  as 
the  vapour  produced  cannot  escape,  all  junc- 
tures being  perfectly  steam-tight,  the  tempera- 
ture rises  continuously  in  place  of  stopping  at 
the  boiling  point,  and  the  vapour  formed  press- 
ing on  the  surface  of  the  remaining  liquid,  and 
by  it  on  the  mercury  underneath,  forces  the. 
mercury  up  the  tube  b  until  the  mercurial  col- 
umn shall  have  attained  such  a  height  as  to  counterbalance  by  its 
weight  the  elasticity  of  the  vapour.  In  these  cases  the  elasticity 
is  generally  reckoned  by  atmospheres,  each  atmosphere  being  equiv- 
alent to  a  mercurial  column  thirty  inches  high.  In  this  manner  the 
vapour  of  water  has  been  found  to  exert  a  pressure  of 


1  atmosphere 

at  212° 

16 

atmosph 

Bres  at  398° 

2  atmospheres 

at  250° 

20 

« 

418° 

3   «   « 

275° 

25 

« 

«    439° 

4   «    « 

294« 

30 

i< 

457° 

6 

320° 

40 

« 

"    486° 

8 

342° 

50 

(( 

510° 

12 

374° 

It  is  necessary,  in  order  to  understand  such  tables,  to  observe 
that  this  great  increase  of  the  elasticity  of  steam,  as  the  tempera- 
ture rises,  results  not  from  the  expansion  of  steam  already  formed, 
but  from  the  constant  addition  of  new  quantities  of  steam  for  every 
variation  of  temperature.  If  a  globe' full  of  steam  at  212°,  but 
containing  no  liquid  water,  were  heated  to  294°,  it  would  tend  to 
expand  precisely  as  air  or  any  other  gas,  and  the  increase  of  elas- 
ticity would  be  only  from  30  to  34  inches,  or  from  1  atmosphere 
to  1\  ;  but  if  the  globe  contain  liquid  water,  there  is  such  an  addi- 
tional quantity  of  vapour  formed  and  compressed  into  the  same 
space,  that  the  elasticity  becomes  equal  to  four  atmospheres,  or  to 
120  inches  of  the  mercurial  column.     Also,  when  the  pressure  on 

vapour  is  made  to  vary,  the  result  deviates  from  the  rule  laid  down 


RELATIONS  OF  VAPOURS  TO  PRESSURE. 


81 


a 


f  ^ 


in  page  20,  for  the  action  of  pressure  upon  gases  ;  for  the  elasticity 
of  a  vapour  cannot  be  really  increased  by  any  increase  of  pressure  : 
it  remains  the  same,  but  a  quantity  of  the  vapour  becomes  liquid, 
and  there  continues  in  the  state  of  vapour  only  as  much  as  occupies 
with  the  same  elasticity  the  diminished  volume  which  the  column 
of  mercury  leaves.     Thus,  if  we  consider  the  bent  ^ 

tube  a  b,  of  which  the  extremity  at  a  is  closed, 
and  the  leg  a  occupied  from  the  dotted  line  c  d 
by  vapour  of  ether  at  its  boiling  point,  and  bal- 
ancing in  the  leg  b  a  column  of  mercury  thirty 
inches  high.  If,  now,  without  allowing  the  tem-  .- 
perature  to  change,  mercury  be  poured  in  at  the 
orifice  of  b  until  it  shall  rise  in  a  up  to  the  line/ 
g,  and  occupy  exactly  one  half  of  that  leg,  the  va- 
pour will  not  be  compressed  into  half  its  volume, 
and,  acquiring  a  double  elasticity,  support  60 
inches  of  mercury  as  a  gas  should  do,  but  one 
half  of  the  ether  will  assume  the  liquid  form,  and 
the  remainder,  occupying  the  remaining  half  of 
the  original  volume,  will  balance  30  inches  of  mer- 
cury precisely  as  it  did  before,  and  the  pressing 
column,  counting  from  the  line/g*,  will  terminate  o 
at  h. 

If,  however,  in  place  of  attempting  to  increase  the  pressure  on  a 
vapour,  we  diminish  it,  then  the  vapour  preserves  its  elastic  form, 
and  its  elasticity  diminishes  in  all  respects  as  if  it  were  a  gas. 

The  specific  gravity  of  a  vapour,  formed  at  any  certain  temperature,  should  be 
proportioned  simply  to  the  elasticity,  if  the  volume  -were  not  altered  by  the  change 
of  temperature,  and  it  should  be  inversely  as  the  volume  if  it  could  all  remain  un- 
condensed ;  but,  in  reality,  the  relation  is  more  complex,  and  may  be  calculated 
upon  the  following  principles.  Thus,  if  we  wish  to  know  the  specific  gravity  of  va- 
pour of  water  having  an  elasticity  expressed  by  742  inches  of  mercury,  and  the 
temperature  150°,  we  proceed  as  follows  :  the  specific  gravity  of  steam  at  30  inches 
and  212°  is  6202  ;  and  hence,  if  the  volume  did  not  change,  the  specific  gravity  of 
the  vapour  at  150°  should  be  620-2 x  ^^6^=1^^'^^  5  but  in  cooling  from  212°  to 
150°,  the  portion  of  steam  which  retains  its  elastic  form  is  compressed  within  a 
smaller  volume,  and  hence  has  its  specific  gravity  increased  in  proportion  to  the 
change,  and  therefore  the  153-39  obtained  above  must  be  increased  in  the  propor- 
tion of  the  volume  at  150°  to  the  volume  at  212°,  or  as  611  :  673,  and  thus  becomes 
169-24.  The  subjoined  table  contains  specific  gravities  for  some  temperatures  cal- 
culated in  that  way,  and  accompanied  by  the  temperatures,  the  elasticities,  and  the 
weight  in  grains  of  100  cubic  inches  of  the  vapour. 


Temperature. 

Elasticity  in 
Inches  of 
Mercury. 

Specific  Gravity. 
Air=1000. 

WeighioflOO 
cubic  Inches. 

32° 

0-200 

5-68 

01361 

50° 

0-375 

10-17 

0-2474 

60° 

0-524 

14-03 

0-3387 

100° 

1-860 

46-36 

1-1028 

150° 

7-420 

169-24 

4-0543 

212° 

30-000 

62020 

14-9600 

There  is  some  reason  to  suspect,  however,  that  vapours  do  not  follow  exactly  the 
theoretic  rules  upon  which  such  tables  are  constructed,  and  which,  in  reality,  apply 
only  to  gaseous  bodies.  Thus,  Despretz  has  found  the  specific  gravity  of  the  va- 
pour of  water  to  be  at  67°  7-72,  while  by  this  calculation  it  should  be  17-26,  air  at 
212°  being  1000 ;  his  results  cannot  be  considered  as  decisive,  although  they  show 
the  necessity  for  an  accurate  re-examination  of  the  subject.    At  very  high  tempera- 


82  PROPERTIES    OF    COMPRESSED    VAPOURS. 

tures,  the  elasticity  does  certainly  not  increase  with  the  specific  gravity  when  the 
volume  remains  constant.  Ether  is  found  to  become  gaseous,  and  to  occupy  only 
twice  the  volume  it  had  when  hquid,  at  the  temperature  of  320°,  and  its  elasticity 
in  that  state  equals  38  atmospheres,  whereas,  by  calculation,  its  elastic  force  should 
be  168  atmospheres.  Alcohol,  enclosed  in  tubes  hermetically  sealed,  is  totally  con- 
verted into  vapour,  occupying  only  three  times  the  volume  of  the  liquid  at  404°,  and 
then  exerts  a  pressure  only  of  129  atmospheres,  while  by  theory  the  pressure  should 
equal  221.  Water,  also,  was  obtained  by  Cagniard  de  la  Tour  gaseous  in  foui 
times  its  hquid  volume  at  773°,  and  should  then,  by  theory,  have  an  elasticity  of 
780  atmospheres,  a  force  far  above  what  the  glass  tube  employed  could  possibly 
have  resisted.  It  would  appear,  therefore,  that  vapours,  so  far  as  the  relation  be- 
tween their  specific  gravity  and  their  elasticity  is  concerned,  do  not  follow  exactly 
the  same  law  as  gases  except  within  certain  limits ;  but  that,  when  the  elasticity  is 
much  smaller  or  much  greater  than  the  atmospheric  pressure,  variations  which  are 
very  remarkable,  though  not  as  yet  well  understood,  present  themselves. 

When  a  vapour,  as,  for  example,  steam,  which  has  been  generated 
in  close  vessels,  and  attained  a  great  elasticity,  is  suddenly  allowed 
to  escape  into  the  air,  its  temperature  is  suddenly  reduced  in  a  re- 
markable degree,  even  independent  of  condensation.  If  the  steam 
had  been  formed  under  a  pressure  of  four  atmospheres,  its  volume 
is  but  one  fourth  of  what  it  should  become  when  free,  and  hence, 
on  escaping,  it  expands  in  that  proportion  ;  under  that  pressure 
its  temperature  had  been  294°,  but  by  the  increase  of  latent  heat 
it  falls  immediately  to  212^  j  there,  however,  the  expansion  does 
not  stop  ;  the  impulse  of  the  particles  of  vapour  carries  them  much 
farther  ;  and  as  the  specific  heat  increases  so  as  nearly  to  be  doubled 
when  the  volume  becomes  doubled,  a  considerable  reduction  of  the 
temperature  below  212°  occurs,  which  is  still  farther  increased  by 
admixture  of  cold  air  which  presses  into  the  rarefied  space  left  by 
the  expansion  of  the  steam.  Hence  it  is  that  steam  escaping  into 
the  air  from  under  considerable  pressure  possesses  much  less  heat- 
ing power  than  steam  arising  from  water  boiling  in  an  open  vessel : 
it  is  much  less  liable  to  scald. 

The  principle  of  the  conversion  of  a  solid  or  liquid  body  into  a 
vapour  at  all  ordinary  temperatures  is  true,  even  where  the  body 
may  be  very  little  volatile.  Thus  the  space  over  the  mercury  in  the 
best  barometers  is  not  truly  empty,  but  contains  a  quantity  of  mer- 
curial vapour,  exercising  a  certain  elasticity,  and,  by  depressing  the 
liquid  column,  making  the  pressure  of  the  external  air  appear  small- 
er than  it  really  is.  It  would  appear,  however,  that  there  are,  for 
some  bodies  at  least,  temperatures  below  which  evaporation  does 
not  go  on  ;  thus  no  mercurial  vapour  can  be  detected  unless  the 
temperature  be  above  40°,  and  oil  of  vitriol  requires  to  be  heated  to 
120°  before  any  vapour  forms  from  it :  it  is  probable,  however,  that 
even  in  these  cases  the  general  principle  holds  good,  and  that  it  is 
only  from  the  minute  quantity  of  vapour  eluding  our  means  of  re- 
search that  the  existence  of  a  limit  to  evaporation  was  believed. 

The  boiling  point  of  a  liquid  being  that  at  which  its  vapour  can 
support  the  external  pressure,  it  is  liable  to  constant  fluctuation  gs 
the  pressure  changes,  and  hence  the  fixing  of  the  temperature  of 
boiling  water  upon  the  thermometer  requires  the  care  and  attention 
already  noticed.  If  the  barometer  stood  at  23'64,  water  would  boil 
at  200°  in  place  of  212°  ;  and  so  close  is  the  connexion  between  the 
pressure  and  boiling  point,  that  the  height  of  any  place  abcre  the 
level  of  the  sea  may  be  determined  by  the  temperature  at  which 


NATURE     OF     THE     BOILING     POINT.  83 

water  boils  there.  Thus,  if,  on  heating  some  water  on  the  summit 
of  a  mountain,  it  be  found  to  boil  at  203^,  we  find,  by  reference  to  a 
table,  that  the  elasticity  of  its  vapour  is  then  25*1  inches,  and  hence 
that  in  the  same  place,  at  the  same  moment,  the  column  of  mercury 
in  a  barometer  should  have  been  at  that  height.  Then,  by  the  or- 
dinary calculation,  the  height  of  the  mountain  may  be  found  with 
as  much  accuracy  as  if  the  barometer  itself  had  been  carried  up.  On 
the  summit  of  Mount  Blanc,  the  highest  point  of  Europe,  water  has 
been  found  to  boil  at  184*°. 

By  reducing,  artificially,  the  amount  of  pressure  upon  a  fluid,  as 
by  placing  the  vessel  containing  it  under  the  receiver  of  an  air-pump 
and  exhausting  the  air,  the  boiling  point  is  lowered  in  a  remarkable 
degree.  If  the  vacuum  were  perfect,  a  fluid  would  boil  even  at  the 
lowest  possible  temperature  j  but  this  is  not  practicable,  as  the  va- 
pour formed  cannot  be  so  perfectly  removed  but  that  it  will  exer 
cise  some  pressure  ;  but,  with  a  good  air-pump,  fluids  may  be  got 
to  boil  145°  below  their  ordinary  boiling  points  j  thus  water  will 
boil  at  67°,  alcohol  at  32°,  ether  at  a  temperature  at  which  quicksil- 
ver would  freeze.  If,  at  the  moment  that  such  a  fluid  is  in  violent 
ebullition,  the  working  of  the  pump  be  stopped,  the  vapour  accumu- 
lates, and,  exercising  on  the  surface  of  the  fluid  an  amount  of  press- 
ure corresponding  to  its  elasticity  at  the  existing  temperature,  rais- 
es the  boiling  point,  and  thus  stops  the  ebullition.  This  fact  may 
be  shown  in  a  very  simple  and  singular  manner,  by  half  filling  a 
flask,  B,  with  water,  and  boiling  the  water  until  all  the  air  in  the 
flask  shall  have  been  expelled,  and  then  care- 
fully closing  the  mouth  of  the  flask,  b,  by  an  air- 
tight cork.  On  removing  the  source  of  heat, 
the  upper  part  of  the  flask,  B,  when  inverted 
as  in  the  figure,  remains  full  of  vapour,  which, 
pressing  upon  the  liquid  water,  arrests  the  ebul- 
lition. If,  then,  a  jet  of  cold  water,  jo,  be  allowed 
to  play  upon  the  flask,  the  vapour  is  condensed, 
and,  a  vacuum  being  thus  produced,  the  water 
begins  to  boil ;  if  a  jet  of  warm  water  be  em- 
ployed, the  vapour  retains  its  elastic  form,  and 
the  ebullition  ceases,  so  that  in  this  apparatus 
the  application  of  cold  may  appear  to  cause, 
and  that  of  heat  to  prevent,  the  water's  boiling. 
The  temperature  at  which  a  liquid  boils  is  thus  totally  dependant 
on  the  amount  of  pressure  to  which  it  is  subjected.  But  the  limits 
within  which  that  pressure  varies  near  the  level  of  the  sea,  in  ordi- 
nary cases,  are  so  small,  that  the  boiling  point  may  be  looked  upon 
as  one  of  the  most  important  characteristic  properties  of  a  volatile 
substance ;  and  from  the  facility  with  which  it  may  be  determined, 
it  is  almost  universally  capable  of  being  applied.  Hence,  in  descri- 
bing such  bodies,  the  boiling  point  will  be  in  all  cases  given;  but, 
for  illustrating  the  present  subject,  a  table  of  the  boiling  points  of 
some  of  the  most  remarkable  liquids  is  subjoined: 


84  ANOMALOUS     PROPERTY    OF     LIQUIDS. 

Muriatic  ether  ....      52°        f        Water 212° 


Sulphuric  ether      ...  96° 

Sulphuret  of  carbon    .    .  116° 

Pyroacetic  spirit    .     ,     .  132° 

Water  of  ammonia     .     .  140° 

Pyroxyhc  spirit      .     .     .  161° 

Alcohol 173° 


Nitric  acid 248° 

Oil  of  turpentine    .     .    .  315° 

Phosphorus        ....  554° 

Sulphur 601° 

Sulphuric  acid   ....  630° 

Mercury 660^ 


The  boiling  point  is  influenced  by  some  other  circumstances  than 
the  atmospheric  pressure  ;  the  nature  of  the  vessel  may  alter  it  sev- 
eral degrees.  Thus,  in  a  glass  or  glazed  porcelain  vessel,  water 
boils,  under  a  pressure  of  30  inches,  not  at  212°,  but  214.°  j  and  in 
graduating  a  thermometer,  it  is  hence  necessary  to  use  a  metallic 
vessel.  This  latter  appears  to  favour  ebullition  by  the  minute  irreg- 
ularities on  its  surface,  affording  a  nucleus  for  the  steam  to  form,  as 
a  crystal  dropped  into  a  saline  solution  facilitates  the  crystallization  ; 
and  if  the  smooth  surface  in  the  glass  vessel  be  removed  in  a  single 
point  by  a  scratch  with  a  diamond,  the  bubbles  of  steam  will  be  seen 
to  form  there  before  the  general  mass  of  liquid  comes  to  boil.  The 
influence  of  roughenfed  or  angular  surfaces  in  thus  favouring  the 
escape  of  steam,  may  be  shown  very  well  by  heating  water  in  a  glass 
flask  to  boiling,  and  then  allowing  it  to  cool  a  little,  so  that  the  boil- 
ing shall  completely  cease ;  if,  then,  a  little  filings  of  copper,  or  a 
platina  wire,  be  dipped  into  the  liquid,  if  the  cooling  had  not  gone 
too  far,  the  boiling  will  immediately  recommence,  the  steam  forming 
at  the  edges  and  angles  of  the  rough  substances  introduced. 

The  temperature  of  the  steam  produced  is  not  affected  by  the 
boiling  point  of  the  liquid.  Thus,  although  by  dissolving  salts,  such 
as  chloride  of  calcium,  in  water,  its  boiling  point  may  be  raised  to 
264°,  the  temperature  of  the  vapour  immediately  over  the  solution 
is  found  to  be  but  212° ;  for,  though  the  temperature  of  a  steam  bub- 
ble which  rises  up  through  such  a  solution  must  be  264°,  yet,  as  its 
elasticity  and  latent  heat  are  proportional  to  that  temperature,  it  ex- 
pands on  mixing  with  the  less  elastic  atmospheric  air,  and  is  cooled 
down  instantly  to  the  ordinary  boiling  point.  The  heat  of  a  water- 
bath  may  thus  be  increased  by  the  addition  of  saline  bodies  ;  but 
the  temperature  of  a  steam-bath  depends  only  on  the  elasticity  of 
the  steam. 

A  curious,  though  only  apparent,  anomaly  in  the  relations  of  liquids 
to  their  boiling  points  consists  in  the  possibility  of  the  vessel  con- 
taining the  liquid  being  heated  even  to  redness  without  the  liquid 
boiling,  though  exposed  only  to  the  ordinary  pressure.  This  may 
easily  be  shown  by  heating  a  platina  crucible  to  redness,  and  drop- 
ping into  it  a  small  quantity  of  water  ;  the  water  remains  on  the  red- 
hot  metal  without  disturbance,  and  appears  scarcely  to  evaporate  ; 
but  if  another  crucible  be  heated  to  300°,  and  the  water  be  poured 
out  of  the  first  into  the  second,  it  instantly  boils,  and  is  dissipated 
in  a  gush  of  vapour.  The  reason  is,  that  in  the  red-hot  crucible  the 
water  is  not  really  in  contact  with  the  metal,  and  hence  the  heat 
passes  to  it  with  extreme  slowness ;  but  the  water  wets  the  colder 
crucible,  and,  absorbing  from  it  all  the  necessary  heat,  is  instantly 
converted  into  steam.  The  cohesive  force  of  the  metal  to  the  water 
being  diminished  considerably,  this  lies  in  a  red-hot  crucible  as  a 
clean  steel  needle  floats  on  water,  or  a  globule  of  mercury  moves 


ARTIFICIAL     COLD     BY     EVAPORATION.  85 

upon  glass,  and  is  not  affected  by  the  heat  until  it  wets  the  vessel, 
just  as  the  needle  does  not  sink  in  the  water  until  it  is  wetted  by  it. 
At  certain  temperatures  all  liquids  manifest  the  same  peculiarity. 

When  a  liquid  evaporates  at  a  temperature  below  its  boiling  point, 
it  still  absorbs  and  renders  latent  a  great  quantity  of  heat,  and,  in- 
deed, more  heat  than  it  would  render  latent  when  converted  into  va- 
pour by  ordinary  boiling.  It  has  been  found,  by  accurate  experi- 
ments with  water,  and  there  is  good  reason  for  supposing  it  to  hold 
also  with  liquids  in  general,  that  no  matter  at  what  temperature  a 
liquid  vaporizes,  it  absorbs  the  same  total  quantity  of  heat.  The 
more  of  this  that  becomes  sensible,  the  less  is  the  portion  which  re- 
mains latent,  the  sum  of  the  latent  and  sensible  heats  of  the  vapour 
being  at  all  temperatures  the  same.     Thus,  with  water  evaporating  at 

32°,  the  latent  heat  is  1180,  the  sum  being  1212 

100°,  "        "         1112,         "        "  1212 

212°,  "         "         1000,         «         "  1212 

300°,  »         "  912,         «         "  1212 

There  is,  therefore,  no  economy  in  evaporating  or  distilling  at  one 
temperature  rather  than  another,  as  the  same  absolute  quantity  of 
heat  is  necessary  for  the  formation  of  the  steam  ;  but,  for  other 
reasons,  the  formation  of  vapours  at  low  temperatures  affords  to  the 
chemist  processes  of  the  greatest  value.  Many  vegetable  substances 
undergo  important  alterations  in  their  chemical  constitution  and  me- 
dicinal properties  if  they  be  exposed  for  a  long  time  even  to  a  heat 
of  212^  ;  and  hence,  in  the  preparation  of  extracts  and  inspissated 
juices  of  plants,  in  pharmacy,  forms  of  apparatus  are  sometimes 
employed,  in  which  the  evaporation  is  carried  on  in  close  vessels 
connected  with  an  air-pump,  and  in  which  a  partial  vacuum,  meas- 
ured by  a  barometer  gauge,  may  be  established.  In  the  manufacture 
of  sugar,  this  principle  of  evaporation  at  low  temperatures,  by  re- 
moval of  the  atmospheric  pressure,  was  the  source  of  great  improve- 
ment, as  the  true  crystallizable  sugar  is  converted  into  the  uncrys- 
tallizable  sugar  (treacle)  with  great  rapidity  at  the  temperature  of 
boiling  sirup,  and  was  hence,  to  a  great  extent,  lost  to  the  manu- 
facturer. By  later  improvements  in  the  mode  of  applying  heat,  the 
necessity  of  evaporating  the  sirup  in  vacuo  has  been,  however, 
completely  obviated. 

The  absorption  of  heat  in  the  conversion  of  a  liquid  into  a  vapour 
at  ordinary  temperatures,  may  become  the  source  of  considerable 
cold  ;  and  it  is,  indeed,  in  this  way  that  the  greatest  cold  yet  gener- 
ated has  been  produced.  The  cold  which  is  felt  when  a  little  ether 
or  spirits  of  wine  is  dropped  on  the  hand,  arises  from  this  fact ;  and 
by  surrounding  the  bulb  of  a  mercurial  thermometer  with  some  loose 
cotton,  and  moistening  it  with  liquid  sulphurous  acid,  the  quicksilver 
in  the  bulb  may  easily  be  frozen.  By  placing  some  ether  in  a  shal- 
low, thin  metallic  cup,  which  rests  in  a  glass  vessel  containing  a 
small  quantity  of  water,  and  producing,  by  the  air-pump,  the  rapid 
vaporization  of  the  ether,  the  water  may  be  so  frozen  that  the  two 
cups  shall  adhere  firmly  together  by  the  intervening  sheet  of  ice. 

Water  may  be  even  frozen  by  its  own  evaporation,  as  in  the  cry- 
ophorus,  which  consists  of  a  long  tube  terminating  in  bulbs  which 
contain  some  water,  and  from  which  the  air  had  been  carefully  ex- 


S6    SYNCHRONOUS     FREEZING     AND     EVAPORATION 


pelled  by  boiling  before  the  apparatus  was  completely  closed.     The 

space  above  the  wa- 


ter remains  then  oc- 
cupied only  by  wa- 
tery vapour.  If  all 
the  water  be  brought 
into  one  bulb,  and 
the  other  bulb  be  im- 
mersed in  a  freezing 
mixture,  the  vapour 
will  condense  there, 
and  new  vapour  be- 
^-'  ing  formed,  a  distil- 
lation will  be  produced  from  the  one  to  the  other  bulb.  The  vapour 
which  forms  in  the  warm  bulb  must  derive  its  latent  heat  from  the 
water  which  remains  behind,  and  this  is  gradually  cooled  to  the 
freezing  point,  and  ultimately  completely  frozen  j  the  latent  heat 
of  about  eight  parts  of  water  being  given  up  to  form  the  latent  heat 
of  one  part  of  vapour  at  32°.  Even  without  the  application  of  arti- 
ficial cold,  water  may  be  frozen  by  its  own  evapo- 
ration. Thus,  if  under  the  receiver  of  an  air-pump 
we  arrange  two  flat  dishes,  the  upper  containing 
water,  the  lower  containing  oil  of  vitriol,  and  then, 
having  removed  the  air,  we  leave  the  apparatus  for 
a  short  time  to  act,  we  shall  find  the  water  in  the 
upper  vessel  converted  into  ice.  Accordingly,  as 
any  portion  of  vapour  forms,  it  is  immediately  ab- 
sorbed by  the  sulphuric  acid,  which  has  a  great  af- 
finity for  water  j  and  the  vapour  being  thus  prevented 
from  collecting,  the  loss  of  heat  by  evaporation  pro- 
ceeds unceasingly,  until  so  much  heat  has  been  re- 
moved that  the  residual  water  is  converted  into  ice. 

In  fluids  more  volatile  than  water,  this  synchronous  freezing  and 
evaporation  may  occur  still  more  simply.  Thus,  if  strong  prussic 
acid  be  allowed  to  form  a  pendant  drop  from  a  glass  rod,  the  drop 
will  become  solid  by  the  evaporation  of  one  portion  of  it,  and  the 
cooling  of  what  remains.  The  remarkable  phenomenon  of  the  so- 
lidification of  carbonic  acid  arises  from  the  same  principle.  A  jet 
of  liquid  carbonic  acid  being  allowed  to  escape  into  the  air,  one 
portion  instantly  flashes  into  the  state  of  gas,  and  absorbs  so  much 
heat  that  the  portion  which  remains  is  converted  into  a  compact 
solid  mass. 

In  warm  climates,  the  evaporation  of  water  is  commonly  employ- 
ed to  moderate  the  sultriness  of  the  air,  by  the  agreeable  cold  and 
freshness  it  produces.  The  Spanish  alcarrazas  are  earthen  vessels, 
so  porous  that  any  liquid  which  is  put  in  them  gradually  filters 
through,  and,  evaporating  from  the  outer  surface,  cools  the  interior 
mass.  In  chemical  operations,  the  same  mode  of  refrigeration  is  in 
constant  use  j  and  when  describing  these  operations,  the  action  of 
this  principle,  in  the  construction  of  the  apparatus  used,  will  be  re- 
ferred to. 

The  conversion  of  a  liquid  into  vapour  at  ordinary  temperatures 


SPONTANEOUS     EVAPORATION.  87 

IS  often  called  spontaneous  evaporation ;  and  in  the  case  of  water, 
from  the  great  extent  to  which  it  becomes  subservient  to  the  econ- 
omy of  nature,  this  process  is  one  of  high  importance.  It  was  for- 
merly supposed  that  the  atmosphere  was  necessary  to  evaporation ; 
and  this  idea  was  strengthened  by  the  fact,  that  by  a  current  of  air 
the  evaporation  is  much  assisted  ;  but  it  is  now  established  that  the 
pressure  of  air  is  really  an  obstacle  to  evaporation,  and  that  a  cur- 
rent is  useful,  not  by  supplying  new  quantities  of  air,  but  by  re- 
moving the  vapour  according  as  it  is  formed,  and  leaving  fresh 
spaces  into  which  it  may  expand.  When  a  liquid  forms  vapour, 
the  quantity  formed  is  determined  only  by  the  space  into  which 
the  vapour  may  spread,  and  by  the  temperature.  It  is  no  matter 
whether  the  space  be  occupied  before  by  other  vapours  or  by  air, 
or  whether  it  be  a  vacuum  ;  the  quantity  of  vapour  which  can  form  in 
it  is  in  all  these  cases  the  same. 

Dalton  was  the  first  who  clearly  showed  that  different  gases  and 
vapours  offer  no  resistance  to  each  other's  elasticity  :  thus,  that  the 
particles  of  watery  vapour  in  the  air  are  not  subjected  to  the  press- 
ure of  the  atmosphere,  but  only  influenced  by  the  pressure  of  the 
particles  of  the  same  kind ;  and  hence,  that  at  32'^,  when  the  elas- 
ticity of  vapour  is  only  0*200  inch,  it  retains  perfectly  its  elastic 
constitution,  though  diffused  through  an  atmosphere,  the  elasticity 
of  which  may  equal  thirty  inches.  If  we  moisten  the  interior  of  a 
bell  glass,  filled  by  air,  with  ether,  alcohol,  sulphuret  of  carbon,  and 
water,  all  mixed  together,  there  will  be  formed  in  the  bell  as  much 
of  the  vapour  of  each  substance  as  if  the  bell  had  been  completely 
empty  of  the  others ;  each  vapour  will  exercise  a  pressure  propor- 
tional to  its  elasticity,  and  by  the  sum  of  all  these  pressures,  the 
pressure  of  the  external  air  will  be  equilibrated.  It  is,  consequent- 
ly, possible  to  produce  the  rapid  evaporation  of  one  fluid,  while  an- 
other beside  it,  or  even  mixed  with  it,  shall  not  evaporate  at  all;  it 
being  only  necessary  to  remove  the  vapour  of  the  one  as  rapidly  as 
it  is  formed,  while  the  portion  of  the  vapour  of  the  second  produ- 
ced in  the  first  instance  shall  remain,  and  prevent  its  farther  change. 
Thus,  by  placing  a  shallow  dish  of  dilute  alcohol  under  the  receiv- 
er of  an  air-pump,  with  a  quantity  of  quicklime,  the  latter  combines 
with  and  absorbs  the  watery  vapour  as  fast  as  formed ;  and  there 
is,  hence,  a  continual  evaporation  of  the  water,  while  the  alcohol, 
after  generating  as  much  vapour  as  once  fills  the  receiver,  is  press- 
ed upon  by  it,  and  cannot  form  any  more.  In  this  manner,  alcohol, 
almost  quite  pure,  though  much  the  more  volatile,  in  the  ordinary 
sense,  may  be  obtained  by  the  evaporation  of  its  solution  in  water, 
as  it  were  to  dryness. 

If  the  liquid  be  in  excess,  the  vapour  possesses  the  elasticity 
belonging  to  its  temperature ;  but  if  there  be  not  liquid  enough  to 
form  so  much  vapour,  the  vapour  formed  then  expands,  so  as  to  oc- 
cupy the  entire  space,  and  its  elasticity  diminishes  in  proportion  to 
the  increase  of  volume  ;  vapours  being  regulated  by  the  same  law 
of  pressure  which  holds  with  gases. 

If,  thus,  a  bell  glass  of  atmospheric  air  be  confined  over  water  at  the  tempera- 
ture of  80°,  a  quantity  of  vapour  diffuses  itself  through  the  air,  and,  as  there  is 
water  in  excess,  the  elasticity  of  that  vapour  will  be  100  inch.  Now  if  we  suppose 
the  elasticity  of  the  air  to  have  been  previously  30  inches,  it  will  become,  by  the 


88  MOIST-BULB     HYGROMETER. 

addition  of  the  vapour,  29,  for  the  vapour  counteracts  one  inch  of  the  external  at- 
mospheric pressure ;  the  air  in  the  bell  glass  will  then  expand  in  the  proportion  of 
30  to  29  ;  or,  what  is  the  same  in  practice,  the  volume  of  the  damp  air  is  the  same 
as  the  volume  which  the  vapour  should  occupy,  if  condensed  in  the  proportion  of  its 
own  elasticity  to  the  atmospheric  pressure,  added  to  the  volume  occupied  by  the 
air  when  dry.  It  is  thus  that  the  volumes  of  gases  collected  over  water  are  cor- 
rected for  the  watery  vapour  that  is  mixed  with  them.  Thus,  in  the  analysis  of  a 
substance  containing  nitrogen,  let  us  suppose  that  854  cubic  inches  of  nitrogen  have 
been  collected  over  water  at  the  temperature  of  63°,  and  the  barometric  pressure 
being  29-35  inches ;  at  that  temperature  the  elasticity  of  vapour  is  058,  and  hence 
that  of  the  dry  air  is  2935 — 0-58=28-77.  The  volumes  whi^h  they  occupy  are  as 
these  numbers,  and  hence  the  854  of  damp  gas  consists  of  •~^x8-54=017  of 
watery  vapour,  and||;||x8-54— 8  37  of  dry  nitrogen. 

This  volume  should  still  be  corrected  for  temperature  and  pressure  before  the 
quantity  of  nitrogen  by  weight  could  be  obtained  from  it. 

Where  the  air  is  not  completely  saturated  with  the  watery  va- 
pour, it  is  not  so  easy  to  determine  the  exact  quantity  of  vapour 
which  it  contains.  One  of  the  best  methods  consists  in  cooling  it 
until  its  volume  is  so  much  diminished  that  the  quantity  of  vapour 
is  sufficient  to  saturate  it,  and  from  the  temperature  at  which  this 
occurs  the  quantity  of  vapour  may  be  calculated.  This  temperature 
is  termed  the  dew  point  of  the  air  or  gas,  because,  if  cooled  in  the 
least  below  that  point,  a  quantity  of  liquid  water  is  deposited  in  the 
form  of  dew  upon  the  neighbouring  cold  bodies.  This  may  be  ea- 
sily done  by  taking  a  tumbler  of  water  somewhat  too  warm,  and 
cooling  it  gradually  by  dissolving  in  it  a  little  mixed  nitre  and  sal 
ammoniac,  until  a  slight  deposition  of  dew  is  perceptible  on  the  ex- 
terior of  the  glass  ;  the  water  is  then  at  the  temperature  of  the  dew 
point.  Another  method  consists  in  observing  the  rapidity  of  evap- 
oration from  the  surface  of  the  bulb  of  a  thermometer  which  is 
covered  Avith  muslin  kept  wet  by  water.  The  thermometer  so  ar- 
ranged is  always  at  a  lower  temperature  than  an  ordinary  thermom- 
eter, from  the  quantity  of  heat  carried  away  by  evaporation,  and 
the  temperature  will  be  lower  in  proportion  to  the  amount  of  evapo- 
ration. In  dry  air,  evaporation  is  quickest ;  in  air  saturated  with 
moisture  evaporation  ceases,  and  in  all  intermediate  degrees  there  is 
a  connexion  between  the  quantity  of  moisture  already  present  in  the 
air  and  the  depression  of  temperature,  which  accompanies  the  forma- 
tion of  as  much  more  as  will  saturate  it.  This  method  is  peculiarly 
of  interest  from  the  means  which  it  afforded  to  Apjohn  of  ascertain- 
ing the  specific  heats  of  the  gases  already  noticed,  and  it  is  easy 
now  to  understand  the  general  principle  upon  which  his  process 
was  established.  If  we  consider  a  certain  space  which  may  be  fill- 
ed by  the  different  gases  in  succession,  and  these  gases  being  dry, 
they  are  made  to  saturate  themselves  with  watery  vapour,  for  the 
formation  of  which  they  themselves  supply  the  heat,  it  will  be  ea- 
sily seen,  that  as  the  quantity  of  heat  to  be  given  out  is  the  same 
for  all,  their  temperatures  will  be  reduced  in  a  degree  inverse  to 
their  specific  heats.  Hydrogen  with  a  high  specific  heat  will  only 
require  to  cool  about  one  third  the  number  of  degrees  necessary  for 
air  or  other  gases.  The  numerical  results  obtained  by  this  process 
have  been  already  given. 

Instruments  for  the  purpose  of  determining  the  quantity  of  the  watery  vapoui 
which  the  atmosphere  contains  are  termed  hygrometers,  and  that  of  Daniell  is  one 
of  the  most  elegant  and  most  useful.     It  is  a  cryophorus,  ah  c,  which  in  place  of 


STEAM    AS     A    MOVING     POWER. 


89 


water  contains  ether,  and  in  one  bulb  of 
which,  h  d,  is  fixed  a  very  delicate  thermom- 
eter. This  bulb  is  made  of  blackened  glass, 
and  the  other  bulb,  a,  is  covered  with  a  httle 
bag  of  muslin.  All  the  ether  having  been 
made  to  pass  into  the  black  glass  bulb,  a  little 
ether  is  poured  on  the  muslin  envelope  of  the 
other.  This,  by  condensing  the  vapour  inside, 
causes  the  ether  to*  distil  from  the  blackened 
bulb,  and  thus  cools  it  and  the  air  in  contact 
with  it,  until  it  anives  at  the  point  of  satura- 
tion, when  a  dew  of  liquid  water  begins  to  be 
deposited,  which  is  at  once  observed  upon  the 
blackened  glass.  The  internal  thermometer 
I  shows  the  temperature  of  the  bulb,  which  is 
the  dew  point,  and  a  thermometer  which  is 
attached  to  the  support  of  the  instrument 
shows  the  temperature  of  the  external  air. 

When  the  dew  point  has  been  thus  deter- 
mined, the  subsequent  calculation  is  very 
simple.  Thus,  if  there  be  air  at  72^,  of 
which  the  dew  point  is  45°,  the  barometric  pressure  being  30  inches,  the  elasticity 
of  steam  at  45°  is  0316  ;  and  as  the  elasticity  diminishes  according  as  the  volume 
increases  from  45°  to  72°,  the  elasticity  of  the  vapour  in  the  air  at  72°  is  030 ;  and 
the  atmospheric  pressure  of  30  inches  is  produced  by  the  dry  atmosphere,  which 
balances  29-70,  and  the  watery  vapour  which  balances  0  30 ;  and  the  respective 
volumes  are  as  these  pressures. 

Gay  Lussac  has  sought  to  establish  a  close  relation  between  the  manner  in  which 
soUd  bodies  dissolve  in  liquids,  and  that  in  which  vapours  diffuse  themselves  through 
space.  Thus,  if  a  sohd  body  dissolved  only  because  the  liquid  diminished  the  co- 
hesion of  its  particles,  the  diminution  of  that  cohesion  in  another  way  should  in- 
crease the  solubihty  very  much :  this,  however,  does  not  occur.  Wlien  paralfine 
dissolves  in  alcohol,  the  solubility  increases  steadily  with  the  temperature,  and  does 
not  change  more  rapidly  at  the  temperature  when  the  paraffine  melts  than  at  any 
other.  This  is  the  case  also  with  many  other  easily  fusible  bodies.  Hence  he  com- 
pares the  diffusion  of  particles  of  the  solid  through  the  liquid  to  the  diffusion  of  par- 
ticles of  vapour  of  water  through  the  air,  which  is  not  affected  by  the  solid  or  liquid 
form  of  the  water,  but  depends  only  on  the^  temperature ;  and  certainly  this  view, 
though  not  applicable  to  all,  or  even  the  majority  of  cases  of  solution,  is  of  much  in- 
terest, as  pointing  out  a  similarity  between  solution  and  vaporization  previously  un- 
noticed, and  which  may  be  applied  to  the  explanation  of  many  anomalous  facts. 

The  employment  of  steam  as  a  moving  power  is  of  so  much  im- 
portance to  science  and  to  the  arts,  that  it  would  be  improper  to 
terminate  a  discussion  of  the  properties  of  vapours  without  any 
allusion  to  the  manner  in  which  it  is  utilized.  The  little  steam  cyl- 
inder of  Wollaston  figured  in  the  margin  contains  all 
that  is  essential  to  the  application  of  steam,  in  princi- 
ple, to  produce  motion.  A  glass  tube,  terminating  be- 
low in  a  bulb,  is  fitted  with  a  little  steam-tight  piston, 
which  slides  up  and  down,  the  rod  passing  through  the 
brass  cap  at  top.  If,  now,  a  little  water  be  placed  in 
the  bulb  and  boiled,  its  steam,  pressing  on  the  bottom 
of  the  piston,  forces  it  up ;  and  when  at  top,  if  the  bulb 
be  dipped  into  cold  water,  the  steam  condenses,  and 
the  pressure  of  the  external  air  forces  the  piston  down 
again.  This  may  be  repeated  any  number  of  times, 
and  is  the  essential  element  of  the  atmospheric  steam 
engine  of  Newcomen.  It  was  in  this  form  when  Watt 
commenced  his  improvements  on  it ;  and  by  applying 
all  the  resources  of  the  exact  knowledge  of  the  properties  of  heat 

M 


90  BOILING    POINTS     OF     CONDENSED     GASES. 

then  first  obtained  by  himself  and  his  illustrious  associate  Black, 
he  converted  it,  though  still  without  changing  its  fundamental  prin- 
ciple, from  the  machine  of  Newcomen,  which  had  been  rejected 
from  practice  for  its  inefficiency  and  expense,  into  the  instrument 
which,  after  the  art  of  printing,  must  be  considered  as  the  most 
powerful  material  agent  of  human  improvement  and  civilization  of 
which  mankind  has  O'ver  obtained  possession. 

The  similarity  of  constitution  of  gases  and  vapours  has  been  already  pointed  out 
on  many  occasions,  and  particularly,  in  page  21,  the  conversion  of  gases  into  liquids 
by  the  application  of  great  pressure  has  been  detailed.  A  liquefied  gas  so  con- 
tained in  a  close  vessel  is  precisely  in  the  condition  of  water  heated  in  a  digester, 
as  in  the  apparatus  figured  in  page  80,  far  above  its  boiling  point,  and  generating 
steam  possessed  of  considerable  tension.  On  this  analogy  has  been  founded  an  in- 
teresting speculation  concerning  the  temperatures  at  which  the  gases  would,  at  or- 
dinary pressures,  assume  their  liquid  form,  that  is,  their  boiling  points  when  hquid, 
thus : 

At  44-5°  the  tension  of  liquid  nitrous  oxide  is  50  atmospheres. 

At  320°  «  "  "  44 

For  12-5°  an  increase  of  tension  of       ...    6  atmospheres. 

Steam  exerts  a  pressure  of  50  atmospheres  at    .    .    .    511-5° 
and  of  44  "  «...    4975° 

For  six  atmospheres  the  difference  is 140°,  or  just  the  same. 

Liquid  carbonic  acid  exerts  a  pressure  of  25  atmos.  at        32°  )  -r,«-         ^   one 

and  of  20     «         "        ^^o  pifFerence,  20° 

The  tension  of  steam  is  25  atmospheres  at      ....  4395°  )  t^-o-  o.n 

20  -  «      .     .     .     .   418-5°  \  Difference,  21° 

Muriatic  acid  exerts,  when  liquid,  a  tension  of  25  atmos.  at      25°  >  js-rr-^^^  „^  „„o 

and  of  20      "       "        30  ^  umerence,  2^ 

Steam  balances  25  atmospheres  at '^39  5°  )  p,.^^^^  ^^  „,g 

20  "  " ^jg.go  ^-L'merence,  ^i 

Ammonia  liquefies  and  exerts  a  pressure  of  65  atmos.  at        50°  )  pjiA-^^^  „„   ,  qo 

and  of  5         "       «        32°  S  ^^nerence,  18 

Steam  exerts  a  pressure  of  65  atmospheres  at     .    .    .  326°     >  rv;flv,__„-_  ^q  eo 
5-0  "  "...    3075°  )  ^'^^^^^^^f  •'■°'" 

It  is  hence  evident  that,  in  every  case,  the  rate  of  increase  of  elasticity  of  these 
gases  with  the  temperature  follows  the  same  law  as  that  of  steam  ;  and  there  is, 
therefore,  good  reason  to  believe  that,  if  the  elasticity  were  diminished  to  one  at- 
mosphere, the  reduction  of  temperature  necessary  to  effect  it  should  be  regulated 
by  the  same  law  as  that  of  watery  vapour ;  the  gases  should  then,  under  the  ordi- 
nary pressure  of  30  inches,  become  liquid,  and  when  liquid,  their  boiling  points 
should  be : 

Nitrous  oxide =  —  252  4°  Fahrenheit. 

Carbonic  acid =  —  2308°  " 

Muriatic  acid =  —  2020°  " 

Ammonia =  —    634°  " 

The  great  increase  of  elasticity  which  these  liquefied  gases  acquire  by  a  chang:e 
of  temperature,  limited  to  a  very  few  degrees,  has  led  to  sanguine  opinions  of  their 
advantages  as  a  source  of  power  in  machines.  No  experiments  at  all  sufficiently 
satisfactory  to  be  decisive  upon  the  question  have  as  yet  been  made. 

There  are  some  other  properties  of  gases  which,  although  closely  connected  with 
,the  subject  now  discussed,  I  shall  postpone,  in  order  to  introduce  them  where  they 
are  found  to  be  of  the  most  practical  importance.  Thus,  the  manner  in  which 
gases  spread  through  each  other,  in  virtue  of  their  diffusive  power,  will  be  descri 
bed  under  the  head  of  Atmospheric  Air,  to  the  proper  constitution  of  vi^hich  this 
law  is  indispensable.  The  relation  of  gases  to  water,  their  solubility  in  that  and 
other  liquids,  and  the  various  modes  of  depriving  them  of  moisture  for  the  purpose 
of  chemical  experiments,  shall  enter  into  the  history  of  the  physical  and  chemical 
properties  of  water. 


CONDUCTIONOFHEAT.  91 

SECTION  V. 

OF    THE    TRANSMISSION    OF    HEAT   THROUGH   BODIES. 

It  is  a  matter  of  every-day  experience,  that  heat  may  be  propagated 
from  one  part  of  a  body  to  another,  and  also  that  this  propagation 
takes  place  in  unequal  degrees  with  different  bodies.  Thus,  if  one 
extremity  of  a  poker  be  heated  to  bright  redness,  the  other  will  be- 
come so  hot  as  to  be  intolerable  to  the  hand  j  while,  if  a  stick  of 
the  same  length  be  inserted  in  the  fire,  the  heated  extremity  may  be 
completely  burned  off,  without  the  farther  extremity  having  its  tem- 
perature raised  in  any  remarkable  degree.  The  extremity  of  a  glass 
rod  may  be  melted  by  the  flame  of  a  blowpipe,  though  held  in  the 
fingers  scarcely  an  inch  from  the  flame  :  but  we  shall  find  it  difficult 
to  melt  the  extremity  of  a  silver  wire,  from  the  heat  spreading  it- 
self generally  through  its  mass,  and  elevating  the  temperature  of 
its  entire  length  almost  to  the  same  degree.  Bodies  which  act  like 
silver  are  said  to  conduct  heat  well,  and  are  termed  conductors. 
Bodies  which  intercept  it,  like  wood  or  glass,  are  termed  non-con- 
ductors. It  is  only  a  difference  of  degree,  for  there  is  no  body 
which  prevents  totally  the  passage  of  heat  across  its  mass. 

The  propagation  of  heat  through  a  body,  in  virtue  of  its  conduct- 
ing power,  is  supposed  to  take  place  from  particle  to  particle,  pre- 
cisely as,  when  we  apply  a  heated  to  a  cold  ball  of  iron,  the  latter 
becomes  warmed  at  its  point  of  contact.  If,  in  place  of  using  balls 
of  iron,  cubical  masses  were  employed,  touching  by  their  surfaces, 
the  communication  of  heat  would  be  much  more  rapid,  from  the 
greater  number  of  points  at  which  transmission  could  take  place. 
In  the  interior  of  a  body  we  should  expect,  therefore,  to  find  the 
degree  of  approximation  of  the  particles  to  have  some  influence  on 
the  rapidity  of  transmission,  that  is,  on  the  conducting  power,  or,  in 
other  words,  that  the  power  of  conducting  heat  should  have  some 
relation  to  the  density  and  the  cohesion  of  each  body. 

Many  series  of  experiments  have  been  made  to  determine  the  con- 
ducting power  of  different  bodies.  Such  experiments  may  be  ar- 
ranged in  a  variety  of  ways.  Thus,  if  a  number  of  similar  rods,  of 
different  substances,  be  coated  to  a  certain  distance  from  one  ex- 
tremity with  wax,  and  then  heat  be  applied  to  the  other  extremity, 
the  wax  will  melt  according  as  the  temperature  of  each  rod  rises, 
from  the  transmission  of  the  heat  along  it ,  and  the  length  of  the 
coating  melted  at  the  end  of  a  certain  time  will  be  a  measure  of  its 
conducting  power.  Another  mode  consists  in  forming  the  sub- 
stances to  be  tried  into  disks,  and,  having  placed  a  small  morsel  of 
phosphorus  upon  each,  warming  all  equally  by  laying  them  on  a 
heated  surface.  The  phosphorus  inflames  first  upon  the  disk  which 
transmits  most  readily  the  heat,  and  on  the  other  disks  in  the  order 
of  the  conducting  power  of  their  substance.  But  such  experiments 
are  only  useful  in  giving  the  order  of  conducting  power  in  a  gen- 
eral way,  and  are  inapplicable  to  exact  purposes. 

The  best  results  are  those  which  have  been  obtained  by  Despretz, 
whose  method  was  the  following.  All  the  bars  used  in  his  experi- 
ments were  square  prisms,  and  were  all  covered  with  the  same  black 


92   RELATIVE     CONDUCTING     POWER     OF     SOLIDS. 


varnish,  in  order  that  the  loss  of  heat  from  their  surface  might  be 
exactly  similar.  At  every  four  inches  of  their  length  was  a  hole 
bored  to  half  the  depth  of  the  bar,  which  was  filled  with  oil  or  mer- 
cury, into  which  the  bulb  of  a  delicate  thermometer  dipped,  so  as 
at  every  instant  to  show  the  temperature  of  the  bar  at  this  series  of 
points.  By  means  of  a  lamp  applied  to  one  extremity  of  the  bar, 
it  was  strongly  heated,  and  the  steadiness  of  the  heat  secured  by 
finding  the  temperature  of  the  thermometer  nearest  the  lamp  to  be 
stationary  for  six  hours,  the  usual  time  of  an  experiment.  The 
temperature  of  the  air  of  the  room,  which  should  scarcely  at  all 
vary  during  that  time,  is  known  by  a  thermometer. 

After  the  bar  has  been  heated  for  two  or  three  hours,  each  ther 
mometer  arrives  at  a  temperature  which  thenceforth  continues  the 
same  as  long  as  the  source  of  heat  is  kept  up.  This  temperature 
depends  on  the  difference  between  the  quantity  of  heat  that  is  prop- 
agated along  the  bar  from  the  lamp,  and  the  quantity  which  is  lost 
by  cooling.  The  excess  of  the  temperatures  of  the  thermometers 
attached  to  the  bar  above  the  temperature  of  the  room,  forms,  there- 
fore, a  series,  the  ratio  of  which  depends  upon  the  conducting  pow- 
er of  the  bar  in  a  manner  which,  though  not  simply  proportional, 
is  easily  deduced  from  it  by  calculation.  By  these  principles,  of 
which  the  theory  was  given  by  the  celebrated  Fourier,  Despretz  has 
deduced,  from  his  experiments,  the  following  conducting  powers, 
gold  being  assumed  as  the  standard  for  comparison. 


Gold 1000 

Silver 973 

Copper 898 

Platinum 381 

Iron 374 

Zinc 363 


Tin 304 

Lead 180 

Marble 23  G 

Porcelain 12-3 

Fire  clay 114 


Although  this  series  presents,  when  compared  with  the  specific 
gravities,  or  other  physical  properties  of  these  bodies,  very  great 
diversity,  yet  it  is  remarkable  that  the  more  expansible  and  more 
fusible  metals,  tin,  lead,  and  zinc,  are  those  which  conduct  heat 
worst.  The  position  of  platina  is,  however,  quite  anomalous,  and 
must  prevent  any  attempt  at  generalization. 

The  difference  of  the  conducting  power  of  solid  bodies  is  of  daily 
utility  in  ordinary  life,  as  well  as  in  chemical  operations.  It  is  thus 
that  substances  of  exactly  the  same  temperature  may  produce  quite 
opposite  sensations  to  the  hand.  If  we  grasp  in  one  hand  a  piece 
of  metal,  and  in  the  other  a  piece  of  wood,  both  at  180^,  the  hand 
will  be  reddened  and  blistered  by  the  former,  but  the  latter  will  feel 
only  moderately  warm.  If  the  metal  and  wood  be  both  cooled  to 
32^,  the  former  will  feel  intensely  cold,  but  the  latter  scarcely  at  all 
so.  In  the  first  case,  the  metal  gives  out  its  heat  to  the  hand,  and 
in  the  second,  abstracts  it  from  the  hand  so  rapidly  that  the  nerves 
and  circulation  become  acutely  sensible  of  the  change;  but  with 
the  wood,  from  its  low  conducting  J)ower,  the  flow  of  heat  takes 
place  so  gradually  in  each  direction  as  almost  to  escape  notice. 
The  brickwork  of  a  fireplace  or  of  a  furnace  is  for  the  purpose  of 
keeping  the  heat  generated  by  combustion  from  spreading  to  the 
surrounding  bodies,  and  so  being  lost.     It  woi  Id  be  difficult  to  light 


CONDUCTING     POWER     OF     LIQUID  S. 


93 


a  fire  in  a  massive  metallic  grate,  for  the  heat  would  be  so  rapidly 
carried  off  by  its  conducting  power,  that  the  fuel,  if  not  well  lighted 
before  being  introduced,  would  be  cooled  down  and  extinguished. 

Liquids  conduct  heat  but  very  slowly ;  so  slowly,  that  they  were 
long  considered  to  be  true  non-conductors.  It  is  now  satisfactorily 
proved,  however,  that  they  do  conduct ;  and  although  no  accurate 
numbers  have  been  obtained,  their  power  appears  to  be  generally  as 
their  density ;  mercury  being  the  best  conductor,  and  alcohol  and 
ether  being  the  worst.  This  low  conducting  power  may  easily  be 
demonstrated  by  experiment.  Thus,  if  in  ajar  of  water  an  air  ther 
mometer  be  inverted,  so  that  its  bulb  shall  be  very 
near  the  surface,  and  the  cup  containing  ether  be  laid 
floating  on  the  water,  as  in  the  figure,  the  ether  may 
be  set  on  fire,  and  allowed  to  burn  for  a  considerable 
time  before  any  action  on  the  thermometer  becomes 
sensible,  and  even  then  the  heat  appears  to  have 
travelled  rather  by  the  solid  material  of  the  glass 
than  by  the  water.  If  a  little  water  be  frozen  in  the 
bottom  of  a  narrow  tube,  and  a  solid  adherent  piece 
of  ice  being  so  obtained,  if  more  water  be  poured  in 
so  as  to  cover  the  ice  to  the  depth  of  a  few  inches, 
on  inclining  the  tube,  and  applying  the  flame  of  a 
lamp  to  the  water  near  the  surface,  it  may  be  kept  boiling  violently, 
and  for  a  long  time,  before  the  ice  begins  to  liquefy,  and  even  then 
it  is  by  the  glass  material  of  the  tube  that  the  heat  is  conveyed. 

Notwithstanding  such  facts,  it  is  still  well  known  that  heat  may 
be  communicated  through  large  quantities  of  fluid,  so  that  the  mass 
shall  be  rapidly  and  uniformly  heated.  It  occurs,  then,  not  by  con- 
duction, but  by  diffusion  ;  and  the  source  of  heat  cannot  be  applied 
indifferently  to  any  surface  of  the  fluid,  as  it  might  be  to  a  solid 
body,  but  must  be  applied  underneath.  When  any  portion  of  a 
liquid  is  heated,  it  expands,  and,  becoming  specifically  lighter,  as- 
cends in  the  mass,  and  is  replaced  by  the  colder  and  heavier  por- 
tions, which,  being  in  their  turn  heated,  ascend  also,  and 
thus  generate  a  circulating  current  of  ascending  warm, 
and  descending  cold  liquid,  as  in  the  figure,  by  which 
every  particle  of  the  liquid  is  brought  in  succession  into 
contact  with  the  source  of  heat,  and  the  resulting  tem- 
perature quickly  and  uniformly  gained. 

In  the  case  of  water,  and  such  liquids  as  have  a  point 
of  maximum  density,  this  communication  of  heat,  by  as- 
cending and  descending  currents,  occurs  in  the  inverse 
order  below  that  point.  Thus,  to  warm  water  which  is 
below  SQ'S"^,  the  heat  should  be  applied  above,  or  to  cool 
it  farther  the  heat  should  be  abstracted  below.  On  this 
property  depends  the  preservation  of  the  lakes  and  rivers 
of  these  countries  from  total  and  eternal  congelation. 
When  the  mass  of  water  becomes  cooled  to  39-5°,  the  su- 
perficial layer  becoming  lighter  as  it  cools  more,  prevents, 
by  its  non-conducting  power,  the  farther  abstraction  of 
heat  from  the  deeper  portions ;  but  when  the  warm  air  of 
spring  plays  on  it,  the  heat  is  rapidly  diffused  from  above  down- 
ward, until  the  temperature  of  the  entire  mass  is  raised  to  39-5°. 


ti 


94      COMMUNICATION     OF     HEAT     BY     RADIATION. 

In  their  mode  of  communicating  heat,  gases  resemble  liquids. 
Their  true  conducting  power  is  quite  insensible,  but  by  the  currents 
which  are  produced  by  the  ascent  of  warm  and  the  descent  of  cold 
particles,  they  abstract  and  communicate  heat  with  great  rapidity. 
The  difference  is  easily  felt  by  holding  the  hand  first  at  the  side 
and  then  over  the  flame  of  a  candle,  the  distance  being  the  same. 
In  the  latter  case  the  great  increase  of  heat  arises  from  the  ascend- 
ing current  of  heated  air,  which  does  not  affect  the  hand  when  at 
the  side. 

The  non-conducting  power  of  gases  is  practically  of  great  impor- 
tance. The  different  kinds  of  clothing  owe  their  warmth  to  the  fact 
that  they  prevent  the  heat  of  the  body  from  escaping  ;  this  they  ef- 
fect not  so  much  by  the  power  of  their  proper  solid  substance,  as 
by  being  of  a  loose  and  spongy  texture,  they  imprison  in  their  pores 
a  quantity  of  air,  which,  not  being  able  to  form  those  continual  cur- 
rents, acts  as  a  non-conductor.  The  more  loose  and  spongy,  there- 
fore, the  tissue  of  a  cloth  may  be,  the  more  air  does  it  confine  and 
the  warmer  it  is.  This  is  fully  supported  by  the  experiments  of 
Rumford,  who,  having  heated  to  the  same  degree  a  thermometer 
imbedded  in  the  materials  of  which  clothing  is  generally  made, 
found  that  it  cooled  through  135°  with 


Air                   in     576'' 

Raw  silk        in    1284' 

Fine  lint            "     1032" 

Beaver's  fur    "     1296' 

Cotton  wool      "     1046'' 

Eider  down     "     1305' 

Sheep's  wool    "     1118" 

Hare's  fur       "     1315' 

When  these  bodies  are  tightly  compressed,  so  as  to  diminish  the 
quantity  of  air  confined  within  their  tissue,  the  power  of  retaining 
warmth  diminishes  in  the  same  degree. 

On  standing  before  a  fire,  the  influence  of  the  heat  is  felt  even 
at  a  considerable  distance,  although  the  air  is,  as  has  been  just  stated, 
so  bad  a  conductor  that  the  warmth  cannot  be  ascribed  to  direct 
transmission  through  its  mass  ;  and  since  a  current  of  air  is  passing 
to  the  fire  in  order  to  supply  its  conduction  and  produce  the  draught 
of  the  chimney,  no  heat  can  arrive  at  the  body  by  the  current  from 
the  fire.  Also,  if  a  heated  iron  ball  be  suspended  in  a  room,  it 
propagates  heat  in  all  directions,  although  the  current  of  air  which, 
so  far  as  has  been  yet  described,  alone  can  convey  any  great  quan- 
tity of  heat,  is  directed  only  upward.  Heat  is  therefore  propagated 
by  a  third  mode,  distinct  from  diffusion  and  from  combustion;  and 
the  heated  body  being  supposed  to  emit  actual  quantities  of  heat  in 
straight  lines  or  rays  from  every  point  of  its  surface,  this  mode  is 
termed  radiation. 

Radiation  is  remarkably  distinct  from  conduction  and  diffusion 
in  not  requiring  for  its  existence  any  material  medium.  On  the 
contrary,  the  existence  of  any  coherent  substance  in  their  path  is 
an  obstacle  to  the  transmission  of  the  rays  of  heat,  and  hence  in 
most  solids  and  liquids  there  is  little  heat  transmitted  by  radiation, 
unless  we  look  upon  conduction  as  a  kind  of  radiation  from  particle 
to  particle  in  the  interior  of  the  mass,  and  it  is  only  with  gases  that 
radiation  is  equal  to  what  takes  place  in  empty  space.  A  heated 
body  throws  off  rays  of  heat  precisely  as  a  luminous  body  throws 
off  rays  of  light ;  and  in  every  detail  of  physical  constitution  that 


PROPERTIES     OF     RADIANT     HEAT. 


95 


has  yet  been  discussed,  there  exists  a  perfect  similarity  between 
heat  and  light  in  these  radiant  forms. 

Different  bodies  radiate  heat  with  different  powers,  which  appear 
to  depend  more  upon  the  mechanical  nature  of  the  surface  than 
upon  the  internal  constitution  of  the  body.  When  any  substance  is 
interposed  in  the  path  of  the  rays  of  heat,  these  are  either  reflected, 
or  are  absorbed,  or  they  pass  through  the  body  without  loss.  In 
general,  all  these  efiects  are  in  part  produced ;  that  is  to  say,  one 
portion  of  the  incident  rays  will  be  transmitted,  another  portion  re- 
flected, and  a  third  will  disappear  by  being  absorbed.  There  are 
thus  in  relation  to  radiant  heat  four  qualities,  which  various  sub- 
stances possess  in  different  degrees,  the  radiating,  the  absorbing,  the 
reflecting,  and  the  transmitting  power. 

The  rays  of  heat  may,  like  those  of  light,  be  concentrated  by  re- 
flection or  refraction.  By  the  former  mode,  that  originally  used  by 
Prevost  and  by  Leslie,  the  properties  of  radiant  heat  may  be  de- 
monstrated in  a  simple  manner. 

The  form  of  apparatus  generally  employed  for  demonstrative  ex- 
periments on  radiant 
heat  consists  of  re- 
flecting mirrors  of  pol- 
ished silvered  copper, 
of  a  paraboloid  form, 
A  B  ;  the  property  of 
this  figure  bein^  that 
rays  emanating  from 
the  focus  of  one  mir- 
ror are  reflected  from 
it  in  parallel  directions,  and  falling  thus  parallel  upon  the  other,  are 
brought  to  convergence  in  its  focus.  In  this  manner  the  heat  ra- 
diating from  a  body  may  be  concentrated  upon  a  single  point,  and 
all  its  properties  determined  with  great  precision.  Thus,  a  hot  iron 
ball  may  be  placed  at  a  distance  of  a  few  feet  from  a  bit  of  phos- 
phorus for  any  length  of  time  without  affecting  it ;  but  if  the  hot 
ball  be  placed  in  the  focus  of  one  mirror,  C,  and  the  phosphorus  in 
the  focus  of  the  other,  D,  this  immediately  begins  to  melt,  and  after 
a  moment  bursts  into  flame.  If  the  hand  be 
held  in  the  focus,  it  feels  hot ;  but,  on  moving 
it  much  nearer  to  the  source  of  heat,  the  iron 
bail,  it  feels  cooled.  It  is  thus  not  by  the  di- 
rect conduction  of  the  air,  or  by  diffusion  of 
warm  currents,  that  the  effects  are  caused, 
but  from  the  radiation  of  heat  in  a  form  which, 
like  light,  admits  of  being  reflected  from  pol- 
ished surfaces,  and  concentrated  upon  a  focus, 
and  which  will  be  found  to  follow  the  analogy 
of  light  through  all  its  branches. 

If  a  thermometer  be  placed  in  the  focus  of 
the  mirror  opposite  the  heated  ball,  it  imme- 
diately indicates  the  rise  of  temperature,  and 
may  serve  to  measure  it.     But  it  is  only  the  ^^n^^' 
air  thermometer  which  is  delicate  enough  for 


96 


OF     THE     RADIATING,     ABSORBING, 


such  experiments,  and  it  is  specially  for  this  use  that  the  differen- 
tial air  thermometer  is  constructed.  One  bulb  being  placed  ^n  the 
focus,  the  difference  of  temperature  between  the  two  bulbs  is  in- 
stantly shown ;  and  it  is  thus  also  proved  that  the  rise  of  tempera- 
ture is  local,  that  it  is  confined  to  the  point  where  the  rays  of  heat 
are  brought  to  meet,  for  the  instrument  is  insensible  to  every  gen- 
eral change  of  temperature,  no  matter  how  extensive. 

By  means  of  this  apparatus,  the  radiating  and  absorbing,  as  well 
as  the  reflecting  and  transmitting  powers  of  bodies  may  be  exam- 
ined.    The  radiating  power  may  be  conveniently  exhibited  by  filling 

a  tin  cube,  a,  with  boiling 
water,  and  applying  to  the 
surfaces  of  the  cube  the  bod- 
ies which  are  to  be  exam- 
ined. Thus,  one  side  being 
left  brightly  polished,  an- 
other dimmed  by  being  rub- 
bed with  sand  paper,  a  third 
covered  by  paper,  and  the 
fourth  being  blacked  by  the 
smoke  from  a  candle,  each 
side,  on  being  turned  towards  the  mirror  c,  gives  out  a  quantity  of 
heat  proportional  to  its  radiating  power,  and  this  being  reflected 
and  brought  to  bear  upon  the  thermometer  in  the  focus,  is  measured 
by  its  indication.  Leslie  thus  found  the  radiating  power  of  the 
following  surfaces  to  be  relatively, 


Lampblack 100 

Writing  paper 98 

Crown  glass    .....  90 

Ice 85 

Red  lead 80 


Plumbago 75 

Tarnished  lead     ....  45 

Clean  lead 19 

Polished  iron 15 

Other  bright  metals  ...  12 


It  is  here  evident  that  the  radiating  power  is  quite  independent  of  the  colour  of 
the  body,  and  that,  in  all  cases,  those  bodies  with  bright  metallic  surfaces  radiate 
least,  the  radiating  power  of  lead  being  doubled  by  simply  tarnishing  its  surface. 
It  has  been  rendered  probable,  however,  by  recent  observation,  that  it  is  not  the 
degree  of  polishing  of  the  surface  which  influences  the  radiating  power,  so  much  as 
the  closeness  and  density  of  the  exceedingly  thin  surface  layer,  on  which  the  quan- 
tity of  radiant  heat  depends.  In  the  process  of  polishing,  the  surface  of  a  metallic 
plate,  particularly  if  it  be  rolled,  is  very  much  compressed,  and  in  this  state  radiates 
in  the  lowest  possible  degree ;  but  if,  by  rubbing  with  sand-paper,  that  dense  film  of 
compressed  metal  be  removed,  the  softer  material  underneath  radiates  with  nearly 
double  the  power.  If  a  plate  of  silver  be  cast  without  being  subjected  to  any  press- 
ure, the  surface,  although  perfectly  bright,  radiates  with  a  power  of  22 ;  but  if  it  be 
dimmed  by  rubbing  with  sand-paper,  the  compression,  even  though  so  slight,  di- 
minishes the  radiating  power  to  12.  Substances  which  are  highly  elastic,  as  ivory, 
or  very  hard,  as  agate,  radiate  in  the  same  degree,  no  matter  what  may  be  the 
rough  or  smooth  condition  of  the  surface. 

That  the  texture  of  the  surface  should  influence  the  radiating  power  is  easily 
comprehended,  when  we  know  that  it  is  not  from  the  external  surface,  but  from  a 
little  depth  below  it,  that  radiation  actually  takes  place.  If  radiation  were  truly 
from  the  surface,  every  point  of  it  emitting  rays  in  all  directions  equally  intense, 
there  should  occur  inequalities  in  the  temperature  of  the  surrounding  bodies  of  the 
most  remarkable  and  intolerable  kind.  Thus,  let  us  suppose  two  surfaces  at  right 
angles  radiating  heat,  as,  for  instance,  two  surfaces  of  a  red-hot  poker.  A  body  A, 
at  a  certain  distance  from  the  angle,  should  have  its  temperature  raised  much 
more  than  a  body,  B  or  C,  directly  opposite  either  side,  for  it  should  receive  the  rays 
A  M  and  A  M'  equally  intense,  while  the  bodies  B  and  C  should  receive  from  the 


AND     REFLECTING     POWERS     OF     BODIES.  97 

same  points  only  the  rays  B  M  or  C  M'.  But  the  rays 
emanating  not  from  the  surface  at  M  or  M',  but  from  N'  and 
N,  at  some  depth  below,  the  oblique  ray  N  A  has  to  pass 
tlK-ough  so  much  a  thicker  stratum  of  solid  matter  from  N 
to  P  than  the  direct  ray  from  N  to  M,  that  the  conjoint 
action  of  the  two  does  no  more  than  enable  the  sur- 
rounding bodies  to  attain  an  equable  temperature.  Bodies 
obliquely  exposed  to  a  flat  radiating  surface  receive  less 
heat ;  not  that  a  smaller  number  of  rays  impinge  upon  them, 
but  that  a  greater  proportion  of  heat  is  lost  in  escaping 
from  below  the  surface  of  the  body. 

Th-e  radiating  powers  of  bodies  are  the  foundation  of  numeroua 
applications  in  the  arts.  Those  bodies  which  radiate  least  cool 
slowest  5  and  hence,  if  it  be  required  to  keep  any  material  hot  for  a 
considerable  time,  it  should  be  enclosed  in  a  vessel  with  a  bright 
metallic  surface,  that  being  the  kind  which  retards  most  the  escape 
of  heat.  If,  on  the  contrary,  the  object  be  to  diffuse  heat,  the  best 
radiating  surface  should  be  made  use  of.  It  is  thus  that  the  tubes 
by  which  heated  air,  or  water,  or  steam  is  supplied  to  buildings,  for 
the  purposes  of  warmth,  should  be  bright  and  polished  until  they 
arrive  at  the  precise  locality  where  the  heat  is  to  be  given  out,  but 
should  there  be  painted  with  whitelead  or  lampblack,  the  surfaces  by 
which  the  heat  is  most  rapidly  given  out. 

If  two  tin  vessels,  precisely  similar  in  form,  but  one  being  painted 
and  the  other  polished,  be  filled  with  warm  water  and  placed  in  a  cold 
room,  that  which  is  painted  will  cool  more  rapidly  than  the  other,  in 
consequence  of  its  greater  power  of  radiation.  If  the  two  vessels, 
when  cold,  be  placed  opposite  a  steady  fire,  the  temperature  of  the 
water  in  that  which  is  painted  will  be  observed  to  rise  more  rapidly 
than  that  of  the  other  j  it  will  absorb  the  heat  of  the  fire,  precisely 
as  it  had  given  out  the  heat  of  the  water,  with  most  rapidity.  The 
bodies,  therefore,  that  radiate  best,  absorb  heat,  likewise,  with  greater 
power,  and  those  which,  when  hot,  cool  most  slowly,  are  those  also 
which  have  least  tendency  to  receive  radiant  heat. 

The  absorbing  and  radiating  power  may  even  be  proved  to  be  exactly  proper 
tioned  to  one  another  by  the  following  experiment.  A  large  diflTerential  thermom- 
eter is  arranged,  whose  bulbs  are  chambers  of  considerable  size,  presenting  large 
and  equal  plane  surfaces  on  the  sides  that  are  towards  each  other.  Of  these,  one 
is  polished  and  the  other  coated.  Midway  between  them  is  placed  a  canister  hav- 
ing equal  plane  surfaces,  facing  each  of  the  former  respectively,  and  one  polished, 
the  other  coated  with  the  same  pigment  as  before.  This  canister  is  filled  with  hot 
water,  and  is  capable  of  turning  on  a  vertical  axis  ;  thus  the  coated  surface  of  the 
canister  can  be  turned  to  the  coated  bulb  or  to  the  polished ;  in  the  former  case,  a 
great  effect  is  produced  upon  the  coated  bulb,  and  a  very  small  effect  upon  the 
plain  ;  in  the  second  case,  the  better  radiating  surface  is  directed  to  the  worse  ab- 
sorbing one,  and  the  worse  radiating  to  the  best  absorbing,  and  the  hquid  in  the  tube 
remains  perfectly  stationary,  estabhshing  thereby  the  exact  equality  of  the  absorb- 
ing and  radiating  powers. 

Although  colour  is  without  influence  on  the  radiating  power,  it  yet 
appears  to  influence  the  absorbing  power  in  a  remarkable  degree. 
If  pieces  of  cloth  of  various  colours  be  laid  upon  snow,  and  exposed 
to  the  direct  solar  rays,  that  which  is  black  will,  by  absorbing  more 
heat,  melt  the  snow  away  from  under  it,  and  sink  deepest.  White 
will  sink  least,  and  the  others  in  the  order  of  their  depth  of  colour. 
It  is,  therefore,  v/ith  reason  that  dark-coloured  cloths  are  preferred 
for  winter  use,  and  light  colours  for  summer.     It  is,  however,  to  be 

N 


98  TRANSMISSION     OF     HEAT. 

noticed,  that  it  is  only  upon  the  absorption  of  those  rays  of  heat 
which  accompany  rays  of  light  that  colour  has  this  power. 

The  great  difference  of  *ibsorbing  power  of  a  blackened  and  of  a 
metallic  surface  may  easily  be  shown,  by  coating  one  bulb  of  a  dif- 
ferential thermometer  with  silver  leaf  and  blackening  the  other. 
W  hen,  with  the  same  source  of  heat,  the  rays  are  received  upon  the 
silvered  bulb,  scarcely  any  rise  of  temperature  can  be  observed  ;  but 
when  the  blackened  bulb  is  placed  in  the  focus,  the  rise  is  much 
more  than  would  have  occurred  with  the  thermometer  in  its  ordinary 
condition  of  the  bulb  with  a  glass  surface. 

The  mirrors  which  are  used  in  those  experiments  do  not  become 
sensibly  heated  until  after  a  long  time  ;  they  absorb  but  very  little 
heat :  but  if  the  surface  of  the  mirror  be  smeared  with  glue,  it  loses 
to  a  great  degree  its  power  of  reflecting ;  and  having  thus  obtained 
an  absorbing  and  radiating  power,  it  very  soon  becomes  warm.  If 
it  be  coated  with  lampblack,  its  reflecting  power  vanishes,  and  its 
surface  becomes  highly  absorbent.  The  reflecting  property  is  there- 
fore possessed  by  the  surfaces  of  bodies  in  the  inverse  degree  to  the 
absorbing  and  radiating  powers,  and  hence  the  best  absorbers  are 
those  which  reflect  least. 

The  heat  which  is  naturally  associated  with  light  in  the  sun's  rays  < 
is  capable  of  being  so  concentrated  by  reflection,  that  in  the  focus 
of  a  burning  mirror,  results  equal  to  those  of  the  most  intense  arti- 
ficial heat  may  be  produced.  The  heat  of  the  sun's  rays  may  also  be 
concentrated  by  refraction,  the  heat  accompanying  the  rays  of  light 
in  their  passage  across  lenses  ;  hence  the  use  of  the  burning  glass* 
But  when  we  thus  come  to  discuss  the  property  possessed  by  bodies 
of  transmitting  heat  through  their  substance,  it  becomes  necessary 
to  look  farther  to  the  source  and  intimate  structure  of  the  heat.  For 
the  results  which  have  as  yet  been  described,  we  are  indebted  al- 
most exclusively  to  Leslie,  but  the  power  of  transmitting  heat  could 
only  have  led  to  the  important  consequences  deduced  from  it  by 
Forbes  and  Melloni  more  recently,  when  the  advance  of  other  sci- 
ences had  placed  at  the  disposal  of  the  experimenter  measures  of 
temperature  infinitely  more  sensible  than  any  form  of  thermometer 
formerly  in  use.  ' 

It  is  by  means  of  the  thermo-multiplier  and  galvanometer  that  the  effects  of  the 
transmission  of  heat  require  to  be  observed. 

The  apparatus  employed  by  Melloni  was,  in  its  general  arrangement,  such  as  is 
represented  in  the  subjoined  figure. 

On  a  steady  table  there  rests  a  frame  M  M,  along  the  middle  of  which  a  slip  R  R 
IS  cut,  by  which  the  various  stands  and  supports  may  be  moved  back  and  forward, 
so  as  to  vary  their  distances  from  each  other.  On  the  stand  S  is  placed  the  source 
of  heat ;  in  the  figure  it  is  a  coil  of  platina  wire  ignited  by  a  spirit  lamp  ;  but  the 
flame  may  be  surrounded  by  a  cylinder  of  blackened  copper,  or  it  may  be  a  vessel 
of  boiling  water,  or  an  argand  or  Locatelli  lamp.  The  rays  proceeding  from  it  are 
received  by  the  thermo-multiplier  P,  from  which  the  wires  F  F  convey  the  electri- 
city generated  to  the  galvanometer  G,  which  for  steadiness  is  placed  at  a  distance, 
and  on  brackets  secured  against  a  wall.  These  parts,  P  and  G,  will  be  represented 
in  full  in  the  chapter  on  electricity.  If  it  be  required  to  study  the  action  of  a  plate 
of  any  substance  upon  the  rays  of  heat,  the  screen  E  is  interposed,  having  an  aper 
ture  0,  somewhat  smaller  than  the  plate  to  be  employed.  This  last  is  then  sup- 
ported immediately  behind  the  aperture  by  means  of  the  little  frame  S',  so  that  no 
heat  can  reach  the  ttiermo-multiplier  unless  after  having  passed  through  it.  As  it 
is  of  great  importance  to  have  the  end  of  P  farthest  from  the  lamp  uninfluenced  by 
any  disturbing  causes,  the  screen  E"  is  placed  immediately  behind  it,  to  protect  it 


TRANSMISSION     OF     HEAT. 


99 


trom  irregular  radiation  and  from  currents ;  and  as  the  action  of  the  heat  upon  the 
pile  must  be  limited  to  the  actual  time  of  the  experiment,  the  double  scl:^en  E'  is 
interposed  immediately  next  the  lamp,  and,  being  provided  with  a  hinge,  is  raised 
or  lowered  at  the  moment  when  the  rays  of  heat  are  to  be  allowed  to  pass  or  are 
to  be  intercepted. 

The  orifice  of  the  thermo-multiplier  is  occasionally  fitted  with  a  conical  tube  of 
plated  brass,  for  the  purpose  of  collecting  the  rays  of  heat  in  greater  number  ;  birt 
that  is  not  often  wanted. 

The  reflecting  power  of  bodies  has  been  exactly  determined  by 
Buflfto  be  as  follows.  Of  100  rays  incident  at  an  angle  of  60°  from 
the  perpendicular,  there  are  reflected,  by 

Polished  gold 76 

"       silver 62 

"       brass 62 

Brass  without  polish 52 

Polished  brass  varnished 41 

Glass  plate  blackened  on  back 12 

Looking-glass  .     , 20 

Metal  plate  blackened 6 

The  power  of  a  body  to  transmit  heat  is  termed  transcahscence^ 
and  of  intercepting  heat  intranscahscence.  These  properties  are  to- 
tally independent  of  the  power  of  transmitting  light,  as  will  be  at 
once  seen  from  the  following  table.  Of  100  rays  proceeding  from 
tbfl  flame  of  an  argand  lamp,  there  are  transmitted  by 


Rock  salt      .     .     .     . 

colourless 

92 

Glass  coloured     . 

yellow 

22 

Calc  spar      .... 

do. 

62 

Do.    .    .    . 

blue 

21 

Smoke  topaz      ,     .     . 

brown 

57 

Sulphuric  ether    . 

colourless 

21 

Plate  glass    .    .     .     . 

colourless 

40 

Gypsum      .     .     . 

do. 

20 

White  agate      ,    .     . 

do. 

35 

Tourmaline 

green 

18 

Glass  coloured  .    .    . 

violet 

34 

Opaque  glass 

. 

black 

16 

Do.  .     .     .     .    . 

red 

33 

Citric  acid  . 

. 

colourless 

15 

Chromate  of  potash    . 

orange 

33 

Alcohol  .     . 

do. 

15 

jBorax  ...... 

colourless 

28 

Alum      .    . 

do. 

12 

1  Glass  coloured  .     .     . 

green 

23 

Water    .     . 

do.    ^ 

11 

Rock  salt  is  thus  the  most  tran  scale  scent  substance  that  has  been 


100 


PERMEABILITY     OF     BODIES     TO     HEAT. 


found.  Glass  arrests  more  than  one  half  of  all  the  heat  which  it  re- 
ceives, while  colourless  and  transparent  alum,  and  the  most  limpid 
water,  arrest  more  of  the  heat  which  they  receive  than  the  deepest 
coloured  glasses,  or  topaz,  or  quartz,  so  brown  as  to  be  quite 
opaque. 

But  not  merely  do  different  bodies  act  differently  on  rays  pro- 
ceeding from  the  same  source,  but  the  same  body  may  allow  the 
heat  from  one  source  to  pass  freely  through  its  substance,  and  inter- 
cept partially  or  completely  the  heat  radiating  from  another.  Thus 
using,  in  his  experiments,  the  heat  emanating  from  five  kinds  of 
source,  first,  the  argand  lamp  ;  second,  the  lamp  of  Locatelli,  which 
is  remarkable  for  the  steadiness  of  its  flame  ;  third,  a  red-hot  spiral 
of  platina  wire ;  fourth,  a  blackened  copper  plate  heated  to  734°  ; 
and,  fifth,  a  blackened  copper  plate  heated  to  212^  by  boiling  water, 
Melloni  found  the  heat  arising  from  these  sources  to  be  transmitted 
m  the  following  proportion  per  cent.  ;  the  results  with  the  argand 
lamp,  having  been  given  in  the  last  table,  are  here  omitted. 


Substance. 

Locatelli 
Lamp. 

Ignited 
Hlalina. 

,a% 

a?2TI^ 

100 

Free  radiation    . 

100 

100 

100 

Rock  salt  .     .     . 

92 

92 

92 

92 

Fluor  spar      .     . 

78 

69 

42 

33 

Calc  spar  .     .     . 

39 

28 

6 

0 

Plate  glass     .     . 

39 

24 

6 

0 

Agate   .     .     .     . 

23 

11 

2 

0 

Gypsum    .     .     . 

14 

5 

0 

0 

Alum    .... 

9 

2 

0 

0 

Ice 

6 

0 

0 

0 

Rock  salt  is  thus  not  only  the  most  transcalescent  body,  but  it  is 
that  which  alone  is  equally  transcalescent  to  heat  of  all  tempera- 
tures. The  rays  of  heat  evidently  acquire  a  greater  power  of  trans- 
missibility  as  the  temperature  of  the  source  increases,  and  hence 
glass  arrests  scarcely  any  portion  of  the  direct  solar  heat,  while 
from  the  argand  lamp  it  intercepts  47  j  from  Locatelli's  lamp,  61 ; 
from  ignited  platina,  72 ;  from  copper  at  734°,  94 ;  and  from  cop- 
per at  212°,  100  per  cent.  The  action  of  these  media  upon  radi- 
ant heat  consists  not  merely  in  stopping  a  certain  portion  of  it,  but 
in  separating  it  into  two  portions,  physically  distinct,  of  which  one 
is  capable  of  transmission,  while  the  other  is  absorbed.  Hence  a 
second  plate,  of  the  same  kind  of  substance,  exerts  but  a  very  slight 
action  upon  the  heat  which  has  already  passed  through  the  first. 
Thus,  though  a  plate  of  alum  allows  only  9  in  100  of  the  direct  rays 
of  the  lamp  to  pass,  yet  it  admits  of  the  passage  of  90  in  100  of 
rays  which  have  already  passed  through  a  plate  of  the  same  sub- 
stance ;  and  calc  spar,  which  transmits  only  yVo  ^^  the  direct  heat, 
transmits  91  of  that  which  had  passed  through  alum,  and  89  of  that 
which  had  passed  through  gypsum.  On  the  other  hand,  a  green 
tourmaline,  which  transmitted  18  out  of  100  rays  directly  incident 
upon  it,  intercepts  //„  of  those  which  had  previously  passed  through 
alum,  but  gives  passage  to  jW  of  radiant  heat  which  had  passed 
through  black  glass. 

The  nature  of  the  physical  distinction  between  the  intercepted 
and  the  transmitted  portions  of  the  heat  is  to  be  found  in  the  differ- 


ANALOGY     OF     HEAT     TO     COLOURED     LIGHT.     101 

ent  refrangibility  of  the  rays  of  heat  emanating  from  sources  of  va 
rious  temperatures.  If  the  rays  of  heat  emanating  from  a  lamp  be 
incident  upon  a  rock-salt  prism,  they  will  undergo  refraction,  sub- 
ject to  the  same  law  of  the  sines  as  in  the  case  of  ordinary  light, 
and  there  will  be  obtained  a  band  or  spectrum  of  rays  from  the 
lamp ;  the  most  refrangible  will  coincide  with  about  the  middle  of 
the  luminous  spectrum,  while  the  least  refrangible  will  extend  far 
beyond  the  limits  of  the  least  refrangible  rays  of  light.  The  mean 
refrangibility  of  heat  is  therefore  less  than  that  of  white  light,  and 
the  length  of  its  undulation,  if  that  theory  be  adopted,  longer  in 
proportion. 

If,  now,  the  heat  spectrum  so  obtained  be  examined  by  means  of 
the  media  which  have  been  already  noticed,  the  explanation  of  the 
peculiarities  in  their  action  will  be  at  once  observed.  Rock  salt  al- 
lows the  rays  of  all  degrees  of  refrangibility  to  permeate  its  mass ; 
it  is  to  heat  what  perfectly  colourless  glass  is  to  white  light ;  it  acts 
equally  on  all  portions  of  it.  Alum  stops  all  but  the  very  least  re- 
frangible rays ;  it  is  to  heat  what  ruby-coloured  glass  is  to  light, 
which  allows  only  the  rays  of  the  least  refrangible  extremity  of  the 
spectrum  to  pass  through.  Glass,  gypsum,  and  such  bodies  as  give 
passage  to  the  rays  of  least  and  of  mean  refrangibility,  resemble 
those  orange-coloured  glasses  which  exclude  the  blue  and  violet 
rays  of  light,  but  admit  the  others. 

After  long  search,  Melloni  at  last  found  that  by  coating  with  soot 
the  surface  of  a  plate  of  rock  salt,  it  became  to  heat  what  blue  glass 
is  to  light ;  it  excluded  the  rays  of  inferior  refrangibility  ;  and  when 
a  plate  so  prepared  was  combined  with  a  plate  of  alum,  all  heat  was 
intercepted,  precisely  as  when,  by  laying  a  plate  of  blue  and  a  plate 
of  orange  glass  together,  perfect  opacity  is  produced,  the  one  ab- 
sorbing the  portion  of  light  which  alone  the  other  is  capable  of 
transmitting. 

The  rays  of  heat  derived  from  sources  of  different  temperatures 
are  thus  analogous  to  the  rays  of  light  of  different  colours.  The 
higher  the  temperature  of  the  source,  the  more  does  it  resemble  red 
light ;  the  lower  its  temperature,  the  greater  is  its  analogy  with  the 
violet  rays.  Hence  alum  absorbs  all  the  heat  from  boiling  water, 
but  gives  passage  to  that  from  the  argand  lamp ;  but  alum  is  like  a 
glass  so  deeply  coloured  red  that  it  is  almost  opaque,  and  trans- 
mits only  a  small  portion  even  of  its  own  coloured  light  that  may 
fall  upon  it. 

When  a  ray  of  heat  is  incident  upon  a  doubly-refracting  substance,  it  follows 
precisely  the  same  law  as  light,  and  is  refracted  doubly.  In  this  case,  also,  the 
rays  after  emergence  are  found  to  be  polarized  in  planes  perpendicular  to  each 
other  ;  and  all  those  consequences  of  the  mutual  action  of  polarized  rays  which  give 
rise  to  such  magnificent  phenomena  of  colours  in  the  case  of  light,  must  occur  with 
lieat,  and  be  made  sensible  if  our  organs  or  our  instruments  were  of  a  construc- 
tion suitable  for  their  appreciation.  As  yet,  however,  the  fact  which  alone  remains 
wanting  towards  a  physical  theory  of  heat  has  not  been  observed — that  of  interfe- 
rence ;  up  to  the  present  time,  the  actual  production  of  cold  by  the  combined  action 
of  two  rays  of  heat  has  not  been  seen  ;  but  the  closeness  of  the  analogy,  which  in 
this  case  alone  requires  additional  observation  between  light  and  heat,  is  so  remark- 
a!)le,  that  we  can  have  little  hesitation  in  referring  these  agents,  in  their  radiant 
form,  to  the  same  kind  of  physical  arrangement. 

There  is  no  difficulty  in  conceiving  radiant  heat  to  consist  in  vibr^li<*n«  -»f  the 
same  ethereal  medium  which  produces  light,  and  in  considering  that  Ih-,  dJ3-»vence 


102       RELATIONS     BETWEEN     HEAT     AND     LIGHT. 

between  heat  and  light  should  be  m  the  magnitude  of  the  vibrations,  and  the  conse- 
quent refrangibility  of  their  rays.  On  the  contrary,  it  is  not  reasonable  to  sup- 
pose, that  while  we  are  conscious  of  the  waves  in  air,  although  they  may  vary  in 
length  from  32  feet  to  ^  of  an  inch,  the  limits  of  our  sensibihty  to  the  ethereal 
waves  should  be  so  narrow  that  the  shortest  (violet)  is  to  the  longest  (red)  as  60  to 
38 ;  it  is  more  consonant  to  our  idea  of  the  various  and  beautiful  uses  to  which 
every  object  of  creation  is  made  subservient,  to  believe  that,  while  the  waves  with- 
m  these  limits  produce  upon  the  eye  the  sensation  of  coloured  light,  another  range 
of  lengths,  greater  than  those  of  light,  should  give  to  our  organs  the  sensation  of  ra- 
diant heat ;  and  that  a  third  order  of  vibration,  still  shorter,  and  more  refrangible 
even  than  violet  light,  is  capable  of  acting  upon  the  elementary  constituents  of  bod- 
ies, and  constitute  the  chemical  rays.  The  coexistence  of  these  three  kinds  of  rays 
in  solar  light  is  an  argument  remarkably  in  favour  of  this  view  ;  for  we  can  weU 
imagine  that,  by  whatever  means  the  sun  communicates  to  the  ethweal  expanse 
the  vibrations  of  various  lengths  which  constitute  the  rays  of  light,  that  vibrations 
of  other  magnitudes,  greater  or  less,  should  be  at  the  same  time  produced  ;  and 
thus  the  light,  which  exhibits  to  us  the  beauty  of  the  external  world,  be  accompa- 
nied by  the  heating  power  which  animates  all  living  nature,  and  without  which  the 
universe  would  be  a  tenantless  and  barren  void. 

These  arguments,  however  natural,  and  in  appearance  sound,  are  met  by  facts 
which,  if  not  positive  against  light  and  heat  differing  only  in  the  length  of  the 
waves  by  which  they  are  produced,  are  at  least  of  so  much  importance  as  to  de- 
serve attentive  study.  If  it  were  so,  then  the  heating  rays  of  the  spectrum  should 
be  thrown  always  below  the  coloured  space,  being  less  refrangible ;  and  it  is  found 
that,  with  a  flint  glass  prism,  the  greatest  heat  is  produced  outside  the  visible  con- 
fines of  the  spectrum  at  the  limit  of  the  red  light.  This  is,  however,  only  accident- 
al, from  the  nature  of  the  prism  ;  for  if  a  prism  of  crown  glass  be  employed,  the 
rays  of  heat  are  collected  in  the  middle  of  the  red  space :  with  a  prism  of  sulphuric 
acid,  in  the  orange ;  and  by  a  prism  of  oil  of  turpentine  or  water,  they  may  be  col- 
lected into  the  centre  of  the  yellow  light. 

The  rays  of  heat,  therefore,  although  generally  less  refrangible  than  those  of 
light,  are  still  not  necessarily,  or  even  always  so.  There  is  distributed  over  the  en- 
tire visible  spectrum  a  heating  spectrum,  which  has  its  pecuhar  point  of  greatest 
energy,  and  which  may  be  refracted  more  or  less  quite  independently  of  the  lumi- 
nous space,  and  may  be  brought  to  overlap  it  at  either  end,  or  to  lie  evenly  upon  it. 
The  ethereal  medium,  if  it  be  the  means  of  transmitting  radiant  heat,  must  be  ca- 
pable of  two  distinct  methods  of  vibration,  by  which  rays  of  equal  refrangibilities, 
but  totally  different  properties,  may  be  produced. 

The  physical  independence  of  solar  light  and  heat  was  beautiful- 
ly shown  by  Melloni,  who,  using  quartz  and  black  mica,  perfectly 
opaque,  upon  the  one  hand,  and  rock  salt  made  perfectly  opaque  by 
soot  upon  the  other,  obtained  radiant  heat  of  all  refrangibilities  to- 
tally free  from  light ;  and  on  the  other  hand,  by  combining  a  plate  of 
alum  with  a  glass  coloured  green  by  oxide  of  copper,  he  obtained  a 
brilliant  beam  of  light,  which,  when  concentrated  by  a  lens  upon  the 
most  delicate  thermoscope  he  couid  apply,  exhibited  no  trace  of  any 
heating  power  whatsoever. 

An  interesting  property  of  radiant  heat,  and  one  which  shows  the  remarkable 
distinction  between  it  and  light  ia  a  very  evident  manner,  is,  that  the  heat  may 
change  its  degree  of  refrangibility ;  and  hence,  if  it  be  vibrations,  one  wave  may 
break  it  up  into  several,  or  several  smaller  waves  may  unite  to  form  one.  The 
light  of  the  aun,  dep/ived  of  all  the  more  refrangible  rays  by  passage  through  a 
plate  of  alum,  may  be  received  on  a  blackened  surface,  the  temperature  of  which 
will  be  thus  elevated,  and  which,  in  turn,  will  become  a  source  of  radiant  heat. 
But  the  heat  so  radiated  is  found  to  have  totally  changed  its  properties ;  it  can  no 
longer  pass  through  alum ;  it  has  passed  from  the  state  of  heat  of  the  lowest  to  the 
stat^  of  heat  of  the  highest  refrangibility.  In  like  manner,  if  the  most  refrangible 
rays  emanating  from  a  source  at  212°  be  concentrated  by  a  rock-salt  lens,  and 
brought  to  act  on  a  small  surface,  they  may  raise  the  temperature  of  this  surface 
above  212°,  and  radiate  from  thence  in  a  less  refrangible  condition  than  before. 
The  parallel  case  to  this  has  never  been  found  with  hght.  Red  light  has  never 
ihaiiged  into  blue,  nor  violet  into  orange  ;  and  there  must  be  in  the  physical  theory 


EQUILIBRIUM     OF     TEMPERATURE.  103 

ol  radiant  heat  some  general  principle  of  so  high  an  order,  that  the  physical  optics 
of  the  present  day  is  but  a  particular  case  of  it. 

This  change  of  radiant  heat  from  one  degree  of  refrangibility  to  another  occurs 
m  nature  very  often,  and  is  the  source  of  some  remarkable  phenomena.  Thus  the 
heat  of  the  sun's  rays,  being  of  low  refrangibility  from  their  intensely-heated  source, 
is  transmitted  easily  by  jce  or  snow,  and  hence  a  layer  of  snow  upon  a  field,  ex- 
posed even  to  the  powerful  action  of  the  sun,  is  but  slowly  melted ;  if,  however,  a 
dark-coloured  object,  as  a  branch  of  a  tree,  be  laid  upon  the  surface,  it  absorbs  the 
solar  heat,  and  becoming  a  source  of  radiation  of  heat  of  great  refrangibility,  which 
the  snow  absorbs  completely,  this  is  melted  under  the  stick,  which  sinks  and 
gradually  disappears  beneath  the  surface.  The  earlier  melting  of  snow  upon  the- 
branches  and  round  the  stems  of  plants,  which  was  supposed  to  demonstrate  a 
kind  of  natural  warmth  belonging  to  the  Uving  vegetable,  arises  from  this  naerely 
physical  conversion. 

From  this  results  also  the  influence  of  colour  on  the  power  of  bodies  to  absorb 
the  heat  of  the  sun  or  of  a  fire  ;  the  strips  of  coloured  cloth  (page  97)  melted  the 
snov^  beneath  them,  not  merely  because  they  absorbed  more  heat  in  proportion  to 
the  depth  of  colour,  but  because  they  in  that  proportion  possessed  the  property  of 
changing  the  heat,  which  would  be  transmitted  into  the  heat  which  would  be  ab- 
sorbed by  the  snow  on  which  they  rested. 

The  construction  of  a  theory  of  heat  would  be,  even  were  an  undulatory  hypoth- 
esis adopted  for  its  radiant  form,  involved  in  difficulties  which  may  require  many 
years  of  research  to  render  them  even  clearly  understood.  The  relation  betw^een 
radiation  and  conduction ;  the  connexion  between  specific  and  latent  heat ;  the 
laws  of  cohesive  force  against  which  heat  acts  in  causing  the  expansion  of  a  body, 
will  all  require  to  be  comprehended  within  the  folds  of  whatever  principle  shall 
hereafter  be  made  the  basis  of  thermotics.  But  it  is  no  disrespect  to  the  illustrious 
names  that  have  been  connected  with  speculations  on  this  subject,  to  conclude,  that 
Jione  of  the  views  brought  forward  appear  positi^ve  or  clear  enough  to  be  described 
in  a  work  of  an  elementary  nature  like  the  present. 

SECTION  VI. 

OF  THE  COOLING  OF  BODIES. 

Bodies  at  an  elevated  temperature  are  capable  of  giving  out  the 
heat  which  they  contain  by  every  method  by  which,  when  cold,  they 
become  heated  at  the  expense  of  the  surrounding  warmer  bodies. 
Cooling  may  occur,  therefore,  by  contact  or  by  i^adiation.  The  rapid- 
ity of  cooling  by  the  immediate  contact  of  the  hotter  with  the  colder 
body  depends  on  the  degree  of  intimacy  of  the  contact,  and  on  the 
conducting  powers  of  the  bodies.  Thus  solids,  which  merely  touch 
at  a  few  points,  communicate  their  relative  temperatures  but  very 
slowly,  while  with  liquids  or  gases  which  may  mix  completely  with 
each  other,  the  establishment  of  a  uniform  temperature  is  almost 
instantaneous.  The  colder  body  becomes  heated  to  the  original 
temperature  of  the  hotter  only  when  there  is  a  continual  supply  of 
heat  to  maintain  that  temperature,  as  in  a  furnace  j  in  other  cases 
the  hotter  body  cools  in  proportion  as  the  colder  becomes  warm,  and 
the  resulting  temperature  depends  on  the  specific  h»at  of  each,  as  has 
been  described,  page  62.  In  determining,  therefore,  the  temperature 
of  a  body  by  a  thermometer,  it  must  not  be  forgotten  that  the  ther- 
mometer, in  becoming  hot,  cools  the  body,  so  that,  unless  there  be  a 
continuous  source  of  heat,  the  true  temperature  of  a  body  is  never 
given  by  the  instrument.  Where  the  substances,  being  solid,  can 
only  come  into  external  contact,  the  rapidity  with  which  heat  passes 
from  one  to  the  other  depends  upon  their  conducting  power  ;  thus, 
a  cold  brick  may  be  laid  upon  a  heated  brick  for  a  considerable  time 
without  much  heat  changing  place,  but  a  plate  of  red-hot  iron  laid 


104         THEORY  OF  DEW  AND  FROST. 

upon  a  plate  of  cold  iron,  abandons  its  excess  of  temperature  so 
rapidly,  that  a  mean  temperature  is  attained  by  both  in  a  very  short 
time. 

The  cooling  of  bodies  by  radiation  is  governed  by  the  principle 
that  all  bodies  in  nature  are  in  a  continual  state  of  interchange  of 
heat  j  no  matter  how  hot  or  how  cold  a  body  may  be,  it  is  constantly 
giving  out  radiant  heat  to  other  bodies,  and  receiving  in  exchange, 
and  absorbing  the  heat  which  radiates  from  them.     The  quantity  of 
heat  thus  radiated  depends  on  the  temperature  of  the  bodyj  the 
higher  this  is,  the  greater  quantity  of  heat  is  thrown  off;  the  lower 
the  temperature,  the  less  heat  does  a  body  radiate  in  a  certain  time. 
Hence,  if  we  conceive  a  ball  heated  to  redness,  and  suspended  in  the 
centre  of  a  number  of  similar  but  colder  balls,  each  will  radiate  and 
absorb,  but  the  hotter  ball  will  give  out  more  than  it  can  gain  iif  re- 
turn, and  will  hence  cool,  while  the  surrounding  colder  bodies,  ab- 
sorbing more  of  the  radiant  heat  than  they  return,  will  have  their 
temperature  raised.     Every  body  in  nature,  therefore,  no  matter  how 
its  temperature  may,  by  peculiar  or  local  means,  be  elevated  or  de- 
pressed, tends  ultimately  to  an  equilibrium  with  all  the  neighbouring 
bodies ;  and  hence,  the  instant  we  remove  a  substance  from  our  fur- 
naces or  freezing  mixtures,  it  begins  to  cool  or  to  become  less  cold. 
This  principle  explains,  in  a  very  perfect  manner,  a  singular  but  in- 
structive experiment  which  may  be  made  with  the  concave  mirror 
apparatus  described,  page  95.*     In  the  ordinary  form,  the  thermom- 
eter and  the  heated  ball  tend,  by  radiation,  to  assume  a  common 
temperature,  and  the  thermometer,  being  the  colder  body,  becomes 
heated  ;  but  if,  in  place  of  the  heated  iron  ball,  a  mass  of  ice  be  sub- 
stituted, the  temperature  of  the  thermometer  in  the  focus  of  the  op- 
posite mirror  immediately  sinks  below  that  of  the  surrounding  air. 
The  explanation  consists  simply  in  the  fact  that  the  thermometer 
is  now  the  hotter  body,  and  hence,  giving  out  to  the  ice  more  heat 
than  the  ice  gives  back,  has  its  temperature  reduced.     At  first  this 
effect  appeared  to  demonstrate  the  existence  of  rays  of  cold,  which 
were  reflected,  radiated,  and  absorbed  like  rays  of  heat. 

In  this  principle  of  the  uniformity  of  temperature  being  sustained 
by  the  equivalent  radiation  and  absorption  of  the  bodies  at  the  sur- 
face of  the  earth,  we  find  the  solution  of  many  interesting  natural 
phenomena.  The  production  of  dew  and  frost  are  to  be  thus  ac- 
counted for.  In  the  absence  of  the  sun,  the  surface  of  the  earth 
losing  by  radiation  a  great  quantity  of  heat,  would  have  its  temper- 
ature considerably  lowered,  were  it  not  that  the  canopy  of  clouds 
which  generally  lies  above  it  radiate  in  return,  and  thus  maintains  the 
temperature  almost  the  same.  If,  then,  the  clouds  be  absent,  all  the 
heat  radiated  by  the  earth  is  lost  in  the  planetary  spaces,  and  the 
temperature  of  its  surface  brought  many  degrees  below  that  of  tlie 
atmosphere.  The  stratum  of  air  whichlies  in  contact  with  the  sur- 
face of  the  ground  is  then  cooled  by  contact,  and  a  portion  of  the 
watery  vapour  which  it  had  possessed  in  its  elastic  form  is  depos- 
ited as  liquid  water.  If  the  temperature  of  the  air  be  itself  low, 
and  the  night  very  clear,  the  cooling  may  proceed  so  far  that  the 
drops  of  dew  at  the  moment  of  their  deposition  shall  be  frozen,  and 
thus  form  frost.     The  truth  of  this  explanation  is  demonstrated  by 


CENTRAL  HEAT  OF  THE  EARTH.        105 

the  fact  that  it  is  only  on  the  surface  of  good  radiators,  and  during 
clear  starlit  nights,  that  dew  or  frost  is  found.  If  a  plate  of  pol- 
ished metal  be  laid  on  the  centre  of  a  rough  board,  and  exposed  to 
the  air  of  a  frosty  night,  the  rough  surface  will  be  found  in  the 
morning  covered  with  copious  frost,  but  on  the  bright  metal  no  trace 
will  be  deposited.  It  is  thus  that,  by  lightly  covering  a  thin  layer  of 
water  with  straw  to  increase  the  radiating  power,  a  sheet  of  ice  may 
be  obtained  in  a  single  night  between  the  tropics,  where  the  actual 
temperature  of  the  air  may  have  continued  far  above  the  freezing 
point.  That  the  cooling  effect  is  produced  by  the  loss  of  heat  in 
its  radiant  form,  and  not  by  the  contact  or  diffusion  of  the  particles 
of  the  air,  may  be  proved  by  the  interposition  of  a  screen  of  any 
substance  which  intercepts  the  passage  of  radiant  heat,  when  the  de- 
position of  dew  or  frost  instantly  ceases,  and  the  surface  cools  no 
more.  Thus  plants  are  protected  by  mats  from  the  frost  of  spring 
and  autumn,  and  thus  the  screen  of  snow,  which  covers  the  surface 
in  the  depth  of  winter,  prevents  the  loss  of  heat  from  the  soil  below, 
and  favours  the  vegetation  of  the  seed. 

The  rapidity  of  cooling  depends  upon  the  difference  of  tempera- 
ture of  the  radiating  bodies,  but  it  is  not  proportional  to  this  differ- 
ence except  within  a  very  narrow  range  of  temperature.  Newton, 
having  experimented  only  within  that  limit,  announced  that  law  as 
general  j  but  the  establishment  of  the  true  law  is  due  to  Petit  and 
Dulong.  It  is,  that  the  rapidity  with  which  a  body  cools,  for  a  con- 
stant excess  of  temperature,  increases  in  a  geometrical  proportion, 
of  which  the  ratio  is  1'161,  when  the  temperatures  increase  in  an 
arithmetical  proportion.  Bodies  at  moderately  high  temperatures 
cool,  therefore,  much  more  rapidly  than  they  should  do  by  New- 
ton's law. 

The  heat,  by  means  of  which  we  produce  a  rise  of  temperature,  or  any  other  of 
the  effects  which  have  been  described,  may  be  derived  from  any  one  of  a  variety  of 
sources.  To  the  earth  at  large  the  sun  is  the  source  of  warmth  ;  and  by  his  vary- 
ing position  in  the  heavens,  by  which  his  rays  strike  upon  the  surface  with  different 
inchnations,  and,  passing  through  the  different  thicknesses  of  atmosphere,  undergo 
absorption  to  a  variable  amount,  the  change  of  seasons  as  to  temperature  is  pro- 
duced ;  and  the  alternation  of  vital  activity  and  torpor  which  characterizes  the  ve- 
getable world,  and  a  great  portion  of  the  animal  creation,  is  occasioned.  Although 
at  the  surface  the  temperature  of  the  earth  is  solely  dependant  upon  the  radiating 
power  of  the  sun,  yet  it  is  found  that  it  contains  within  itself  a  source  of  heat,  which, 
in  ages  excessively  remote,  must  have  retained  the  general  mass  of  all  constituents 
of  the  mineral  globe  in  igneous  liquefaction.  In  fact,  if  we  dig  below  the  surface 
of  the  earth,  we  arrive,  at  a  depth  of  about  forty  feet,  at  a  layer  of  which  the  tem- 
perature is  in  winter  and  in  summer  exactly  the  same.  It  is  termed  the  stratum  of 
invariable  temperature,  and  is  in  general  of  the  mean  temperature  of  the  place  ;  that 
is,  the  temperature  of  the  surface  falls  in  winter  as  much  below  that  of  the  invari- 
able stratum,  as  in  summer  it  is  raised  above  it  by  the  excessive  action  of  the  solar 
rays.  The  heat  of  the  sun,  falling  upon  the  surface,  is  transmitted  inward  in  virtue 
of  the  conducting  power  of  the  ground  ;  and  thus,  each  summer,  a  thin  layer  of  ele- 
vated temperature  moves  inward,  those  of  successive  summers  being  separated 
from  each  other  by  the  intervening  colder  shell,  which  marks  the  period  of  dimin- 
ished heat  in  winter,  until  they  mix  and  confound  themselves  in  the  layer  of  con- 
stant temperature,  below  which  the  influence  of  the  sun  is  felt  no  more.  But,  on 
descending  beyond  this  depth,  the  temperature  steadily  increases,  and,  although 
subject  to  irregularities  consequent  on  the  different  conducting  powers  of  the  rocks 
of  different  countries,  the  augmentation  is  in  general  about  one  degree  for  every 
forty-two  feet,  or  about  120°  for  every  mile.  At  a  depth  of  two  miles,  therefore, 
water  could  not  exist  as  a  liquid,  unless  from  the  great  pressure  to  which  it  would 

o 


106  PROPERTIES     OF     ELECTRICITY. 

be  subjected:  at  four  miles'  depth  tin  and  bismuth  would  naturally  be  liijuid";  ana 
at  five  miles,  lead.  At  a  depth  of  thirty  miles  the  temperature  would  be  so  high  as 
10  melt  iron  ;  and  still  more  easily,  almost  without  exception,  the  rocks,  which  con- 
stitute the  solid  earth  which  we  inhabit.  The  central  heat,  therefore,  although  in- 
sensible at  the  surface,  is  still,  there  is  every  reason  to  believe,  in  violent  activity 
at  a  small  depth  below  :  we  hve  upon  a  pellicle  of  sohd  crystalline  rocks,  with  which 
the  melted  mass  has  become  skinned  over,  and  which  extends  but  to  y|^^  of  the 
distance  to  the  centre.  Hence  we  can  well  imagine,  that  in  many  places  where 
orifices  or  cracks  in  this  sohd  crust  might  form,  violent  manifestations  of  the  inter- 
nal fire  should  be  produced,  and  the  magnificent  phenomena  of  volcanoes  and 
earthquakes  should  thus  arise. 

For  artificial  purposes,  the  source  of  heat  is  generally  chemical  combination. 
The  details  of  this  mode  of  generating  heat  will  require  to  be  carefully  and  minutely 
considfered  hereafter,  under  the  heads  of  Combustion,  and  the  Relations  of  Heat  to 
Chemical  Affinity.  By  mechanical  causes,  as  percussion  and  friction,  heat  may 
also  be  set  free ;  but  such  cases  arise  from  a  change  in  the  specific  heat  of  the 
bodies  before  and  after  the  mechanical  action  ;  and  hence,  although  once  considered 
as  influencing  our  ideas  of  the  nature  of  heat,  do  not  now  require  special  notice.  A 
very  interesting  source  of  heat  consists  in  the  respiration  of  certain  kinds  of  animals, 
and  constitutes  an  important  branch  of  chemical  physiology,  which  shall  be  dis- 
cussed in  its  proper  place :  and,  finally,  one  of  the  most  remarkable  sources  of  heat 
is  to  be  found  in  the  properties  of  electricity,  in  its  various  forms  ;  and  to  the  de 
scription  of  this  interesting  and  important  agent  we  shall  now  proceed. 


CHAPTER  IV. 

OF    ELECTEICITY  CONSIDERED    AS    CHARACTERIZING    CHEMICAL  SUBSTANCES. 

Among  the  various  forces  which  concur  to  the  production  of  nat- 
ural phenomena,  there  are  few  whose  agencies  are  more  remarkable 
or  more  general  than  those  of  electricity ;  and  so  intimately  does  it 
appear  to  be  connected  with  chemical  action,  becoming  sensible  in 
all  cases  of  union  or  decomposition,  and  being  even  developed  in 
a  degree  proportional  to  their  amount,  that  the  most  eminent  phi- 
losophers have  not  hesitated  to  consider  electrical  and  chemical 
agencies  as  being,  if  not  identical,  at  least  intimately  connected  with 
each  other. 

It  is  not  the  object  of  this  work  to  enter  into  the  minute  description  of  electrical 
phenomena,  nor  to  attempt  the  detailed  discussion  of  their  causes ;  as  for  a  complete 
examination  of  the  subject,  it  must  be  considered  as  one,  and  certainly  not  one  of 
the  least  extensive  branches  of  natural  philosophy  ;  it  is  only  with  regard  to  the  in 
fluence  which  electricity  exercises  in  the  operations  and  the  theory  of  chemistry, 
and  the  means  which  the  electrical  properties  of  bodies  afford  for  their  recognition, 
that  it  requires  notice  here  ;  and  hence,  although  it  is  necessary  to  describe  the  pe- 
culiar origin  and  characters  of  each  form  which  electricity  assumes,  yet  that  shall 
be  accomplished  within  the  shortest  limits  that  are  consistent  with  the  importance 
of  this  branch  of  science.  In  the  present  chapter  the  subject  will  be  studied  in  its 
general  history,  and  considered  as  affording  useful  characteristics  of  substances,  the 
properties  of  which  we  have  to  learn  ;  and  in  a  future  place  the  influence  which  it 
exercises  upon  chemical  affinity,  and  the  opinions  which  have  been  advanced  con- 
cerning its  relation  to  purely  chemical  forces,  shall  be  carefully  discussed. 

Of  the  true  nature  of  electricity  nothing  is  positively  known  ; 
whether  it  be  a  mere  property  of  matter  like  attraction  or  cohesion,  a 
mere  force  acting  independently  of  all  interposed  material,  or  wheth- 
er, like  light,  it  consists  in  the  undulations  of  an  ethereal  medium  fill- 


NATURE     OF     ELECTRICITY.  107 

ing  space,  cannot  be  determined.  Indeed,  the  ordinary  views  of  its 
nature  consist  in  supposing  the  existence  of  one  or  of  two  fluids  of 
electricity,  of  exceeding  tenuity  and  of  perfect  elasticity  j  and  that, 
according  as  ordinary  bodies  were  supposed  to  contain  more  or  less 
of  these  fluids  of  electricity,  they  acquired  or  lost  the  properties  of 
electrical  excitation.  Of  these  opinions  it  is  exceedingly  diflicult 
vO  say  which  is  the  more  reasonable  or  more  consonant  to  experi- 
mental truth,  so  far  as  the  explanation  of  phenomena  is  concerned  ; 
but  no  positive  evidence  has  ever  been  obtained  of  the  existence  of 
such  an  electric  fluid  :  it  has  never  been  found  capable  of  being  sep- 
arated from  the  ordinary  particles  of  matter,  of  which  it  appears 
always  as  an  additional  property  assumed  under  peculiar  circumstan- 
ces, and  not  as  a  superadded  constituent.  I  consequently  incline  to 
the  idea  that,  in  the  phenomena  of  electricity,  we  have  exhibited 
only  the  results  of  new  mechanical  conditions  of  the  ordinary  par- 
ticles of  matter,  produced  by  the  action  of  forces  which  may  be  called 
into  play  in  a  variety  of  ways,  and  which  may  be  either  totally  new 
forces  which  are  first  generated  at  the  time,  or  modifications  of  the 
forces  of  gravity  and  cohesion  which  exist  already.  But,  although 
such  may  be  the  true  condition  of  the  electric  properties  of  bodies, 
yet  such  views  are  far  too  abstract  and  indefinite  to  be  as  yet  carried 
out  into  the  detailed  explanation  of  experiments;  and  hence,  in  the 
present  chapter,  I  shall  adopt  the  language  of  that  view,  which  has 
been  so  long  in  use  as  to  have  become  incorporated  with  science, 
and  speak  of  an  electric  fluid  uniting  with  or  separating  from  ordi- 
nary bodies,  without  being  considered  as  at  all  believing  in  its  actual 
existence. 

This  electric  fluid,  whether  it  be  looked  upon  as  of  one  or  of  two 
kinds,  may,  like  air  or  water,  be  examined  in  a  state  of  rest  or  in 
motion ;  and  the  science  of  electricity  may  be  thus  divided  into 
electrodynamics  and  electrostatics.  The  electricity  generated  by 
friction,  or  by  change  of  state  of  aggregation,  is  ranked  under  the 
latter  head ;  while  the  effects  of  electricity  in  motion  are  found  to 
include  the  phenomena  of  magnetism,  of  galvanism,  and  their  rela- 
tions to  each  other,  electro-magnetism  and  magneto-electricity,  and 
also  those  of  the  electricity  produced  by  a  change  of  temperature  in 
bodies.  Under  these  heads,  therefore,  the  subject  will  be  treated  of 
at  present. 

SECTION  I. 

OF    STATICAL    ELECTRICITY. 

Electricity,  in  its  statical  condition,  may  be  evolved  in  various 
ways,  of  which  one  of  the  most  remarkable,  and  that  most  commonly 
employed,  is  friction.  If  a  piece  of  silk,  or  a  handkerchief,  warm 
and  dry,  be  rubbed  briskly  against  the  surface  of  a  dry  glass  rod,  a 
peculiar  odour  will  become  manifest ;  and  in  the  dark,  the  surface 
of  the  glass  rod  will  appear  covered  with  a  peculiar  phosphores- 
cent glow.  If  the  rod  be  brought  near  the  cheek,  a  sensation  as  if 
a  spider's  web  had  been  drawn  across  the  face  will  be  felt ;  and  on 
approaching  to  the  rod,  as  in  the  figure,  any  very  light  bodies,  as  a 
silk  thread,  a  feather,  balls  of  elder  pith,  or  little  bits  of  paper,  they 


108        ELECTRICITY    PRODUCED     BY    FRICTION. 

will  suddenly  spring  towards  the  rod,  and  be- 
come attached  to  it  for  a  moment ;  after 
which  they  will  spring  from  it,  and  fall  away 
with  equal  power,  assuming  the  positions  of 
I  the  dotted  lines.  The  rod  which  has  acquired 
\  these  properties  is  said  to  have  been  electri- 
k  fied  by  friction  with  the  silk  handkerchief  j  it 
has  become  excited,  and  the  phenomena  pro- 
duced are  known  j  the  phosphorescent  appear- 
ance, as  the  electrical  light  j  the  motion  to 
and  from  the  rod  by  the  light  bodies,  as  elec- 
trical attraction  and  repulsion  ;  in  which  also,  acting  on  the  minute 
down  of  the  cheek,  the  sensation  above  described  has  its  source. 
It  is  not  alone  by  rubbing  together  silk  and  glass  that  these  phenom- 
ena may  be  produced ;  two  pieces  of  silk,  by  their  mutual  friction, 
become  electric  also,  particularly  if  they  be  of  different  colours ; 
thus,  on  laying  flat  together  slips  of  black  and  of  white  riband,  and 
drawing  them  smartly  through  the  fingers,  each  will  attract  the 
feathers  or  pith  balls ;  and  being  both  light  bodies,  they  will  also 
attract  each  other.  A  piece  of  sealing-wax,  or  any  other  resinous 
body,  when  rubbed  with  flannel  or  a  woollen  cloth,  becomes  similar- 
ly excited.  Sulphur  and  amber,  in  which  last,  indeed,  the  property 
was  first  discovered,  and  from  the  Greek  name  of  which,  7]XeKTpov^ 
the  science  electricity  has  its  name,  assume  this  excited  state  with 
remarkable  facility  and  power. 

It  is  not  every  substance  which  may  be  thus  electrified  by  fric- 
tion, and  even  the  same  substance  may  often  become  incapable  of 
being  excited ;  thus,  if  the  silk  or  flannel  be  not  completely  dry, 
if  the  glass  rod  be  damp,  no  elebtric  properties  can  be  conferred 
upon  them.  But  it  matters  not  how  much  care  we  use  in  drying  a 
metallic  surface  which  rests  upon  the  ground,  or  which  we  support 
by  the  hand,  it  cannot  be  electrically  excited  by  any  amount  of  fric- 
tion. Such  a  body  is  termed  a  non-electric  ;  dry  glass,  resin,  sul- 
phur, silk,  &c.,  being  called  electrics.  Excitation  may  therefore  be 
produced  by  rubbing  together  two  electrics,  but  by  the  friction  of 
non-electrics  no  electrical  effects  can  be  observed.  This  distinction 
is,  however,  not  real ;  it  arises  from  the  construction  of  the  appara- 
tus 5  for  if,  in  place  of  resting  the  metallic  rod  or  plate  upon  the 
ground,  or  grasping  it  in  the  hand,  we  support  it  on  a  piece  of  seal- 
ing-wax, or  hold  it  by  a  glass  or  resinous  handle,  it  becomes,  when 
rubbed  with  the  silk,  as  highly  electrified  as  any  of  the  electrics ; 
and  in  this  way,  by  suitable  arrangement  of  supports,  all  bodies  in 
nature  may  be  made  to  assume  electric  properties  by  friction. 

To  account  for  this  diversity  of  character,  bodies  are  supposed  to 
retain  the  electric  fluid  upon  their  surface  with  different  degrees  of 
power,  according  to  their  nature.  When  by  friction  electricity  has 
been  accumulated  upon  the  surface  of  a  glass  rod,  it  being  a  highly 
elastic  fluid,  its  particles  repel  each  other,  and  tend,  consequently, 
to  escape  from  the  limited  space  which  it  occupies,  precisely  as  air 
tends  to  escape  from  a  vessel  into  which  it  has  been  powerfully 
condensed.  Glass,  resin,  sulphur,  amber,  silk,  flannel,  and  such 
bodies,  do  not  allow  of  such  escape  of  the  electricity,  and  it  is  hence 


RELATIVE     CONDUCTING     POWERS.  109 

retained  in  its  elastic  form  upon  their  surface,  and  produces  all  the 
effects  of  excitation.  They  are  electrics  because  they  are  non-con- 
ductors of  electricity.  But  such  is  the  molecular  constitution  of  the 
metals,  that  they  allow  of  the  escape  of  all  that  is  set  free  upon 
their  surface,  unless  its  passage  away  to  other  bodies  is  intercepted 
by  the  interposition  of  some  non-conducting  substance.  A  metal 
is  thus  a  non-electric  because  it  is  a  conductor  of  electricity ;  and 
when,  by  supporting  it  upon  a  non-conductor,  we  oblige  it  to  retain 
its  charge  of  electricity,  it  is  said  to  be  insulated.  Ice  is  a  non-con- 
ductor of  electricity,  and  by  rubbing  a  stick  of  ice  it  becomes  ex- 
cited ;  but  it  must  not  melt  upon  the  surface,  for  liquid  water,  al- 
though inferior  to  the  metals  in  conducting  power,  is  yet  so  excel- 
lent a  conductor,  that  it  allows  the  electricity  which  we  might  de- 
velop to  pass  totally  away.  Hence  the  necessity  of  drying  care- 
fully the  substances  which  are,  by  their  friction,  to  produce  the 
electricity,  and  also  the  reason  that  insulating  bodies  must  be  kept 
free  from  damp ;  for  if  the  thinnest  layer  of  moisture  be  deposited 
upon  their  surface,  the  electricity  will  instantly  escape  by  the  path 
so  opened  for  it. 

The  conducting  powers  of  bodies  have  as  yet  been  scarcely  as- 
certained with  accuracy  enough  to  justify  their  being  expressed  in 
numbers,  at  least  for  the  non-metallic  bodies.  The  general  order 
appears  to  be,  commencing  with  the  best  insulators  or  worst  con- 
ductors : 

Strong  acids. 
Fused  saline  bodies. 
Charcoal. 
Metals. 

The  worst  metallic  conductor  is  many  thousand  times  better  than 
water,  and  by  the  following  method  an  idea  of  their  relative  power 
may  be  formed.  A  wire,  across  which  an  electric  discharge  is  passed, 
becomes  heated  in  proportion  to  the  resistance  offered  to  the  motion 
of  the  electricity,  and  therefore  the  rise  of  temperature  is  inversely 
proportional  to  the  conducting  power.  By  such  experiments  Harris 
found  that,  with 


Dry  air. 

Glass. 

Shell-lac. 

Spermaceti. 

Resins. 

Damp  organic  bodies 

Oil  of  turpentine. 

Damp  air. 

Sulphur. 

Water. 

Silver       .     .    . 

The  Heat 
evolved. 

.     .     .     6    .    .    . 

The  conduct 
JDg  Power. 

.     ...  120 

Copper     .     .     . 
Gold    .     .     .     . 

.     .     .     6     .     .     . 
.     .     .     9     ,     .     . 

,     ...  120 
.     ...     80 

Zinc    .     .    .     . 

.     .     .  18     .     .     . 

.     ...     40 

Platinum      .    . 
Iron     .... 

.     .     .  30    .     .     . 
.     .     .  30    .     .     . 

.     ...     24 
....     24 

Tin      .     .     .     . 

.     .     .  36    .     .     . 

....     20 

Lead   .    .    .    . 

.     .     .  72    .     .     . 

.     ...     12 

These  numbers  are  merely  comparative,  and  can  only  be  looked 
upon  as  approximations. 

The  difference  of  the  conducting  power  explains  the  fact  that, 
when  we  excite  by  friction  the  surface  of  a  glass  plate  or  rod,  it  is 
only  at  the  points  actually  rubbed  that  electricity  at  first  appears, 
and  it  requires  considerable  time  to  creep  over  the  other  portions ; 
but  on  exciting  an  insulated  metallic  rod  or  plate,  no  matter  how  ex- 


110  DISTRIBUTION     OF     ELECTRICITY. 

tensive  or  how  long,  the  electricity,  when  evolved  by  friction  at  a 
single  spot,  appears  uniformly  distributed  over  the  entire.  Hence, 
also,  a  spark  may  be  obtained  by  electricity  passing  instantly  along 
a  great  extent  of  metal  surface,  but  is  interrupted  by  a  narrow  inter- 
val filled  by  any  non-conducting  matter. 

The  rapidity  with  which  the  electric  impulse  is  propagated  has 
been  examined  by  Wheatstone  in  a  very  ingenious  manner,  the  de- 
tails of  which  could  not  be  well  introduced  here,  but  which  enabled 
him  to  determine  an  interval  of  the  xs  2V¥o-  ^^  ^  second  ;  he  found 
that  the  impulse  of  the  shock  of  a  Leyden  jar  is  transmitted  from 
each  end  of  an  interposed  wire,  and  arrives  latest  at  the  centre,  so 
far  appearing  favourable  to  the  idea  of  the  existence  of  two  fluids 
rather  than  of  only  one,  and  that  the  velocity  of  transmission  of  this 
impulse  is  greater  than  that  with  which  light  passes  through  the 
planetary  space,  that  is,  at  the  rate  of  more  than  195,000  miles  in  a 
second  of  time. 

The  electricity,  when  thus  evolved,  accumulates  upon  the  surface 
of  the  body,  not  penetrating  to  any  appreciable  depth,  but  forming  a 
layer  of  fluid,  which  by  its  elasticity,  and  hence  expansive  power, 
tends  constantly  to  break  away  and  pass  to  other  bodies  which 
are  not  excited.  It  thus  passing  through  air  produces  the  electric 
spark,  and  is  accompanied  by  a  snapping  report.  The  tendency  to 
escape  under  the  form  of  the  spark  depends  upon  the  thickness  of 
the  layer  of  electricity,  and  is  accurately  proportional  to  its  square  ; 
so  that  if  we  excite  a  brass  ball  with  double  or  treble  the  quantity 
of  electricity,  the  force  of  the  electricity  to  pass  away  will  be  quad- 
rupled, or  increased  ninefold.  Hence  it  requires  exceedingly  good 
insulation  to  retain  electricity  of  great  intensity. 


These  principles  may  be  easily  demonstrated  by  means  of  the  appa- 
ratus in  the  figure.  A  is  a  hollow  sphere  of  some  conducting  sub- 
stance, and  B  B  are  hemispheres  of  gilt  paper  or  thin  metallic  foil, 
which,  when  closed  upon  the  globe,  cover  its  surface  accurately. 
They  are  provided  with  insulating  handles,  C  C.  The  hemispheres 
being  placed  on  the  globe,  if  the  whole  be  excited  by  friction  or  by  a 
spark  from  the  machine,  the  electricity  will  be  found  uniformly  diffu- 
sed over  the  whole  external  surface ;  and  if  the  hemispheres  be  sud- 
denly removed  by  means  of  the  handles,  the  globe  A  will  remain  total- 
ly deprived  of  its  electricity,  which  will  be  found  all  collected  on  the 
surfaces  of  B  and  B  ;  but  it  will  be  no  longer  uniformly  spread  j  its 
intensity  will  be  found  much  greater  on  and  near  the  edges  of  the 
hemispheres,  and  towards  the  centres  of  the  surfaces  the  signs  of 
excitation  will  be  extremely  feeble. 

The  form  of  a  body  has  a  remarkable  influence  upon  the  manner 
in  which  the  electricity  is  distributed  upon  its  surface.  In  a  sphere 
the  layer  is  everywhere  of  equal  thickness,  but  in  an  elongated  body 


OPPOSITE     CONDITIONS     OF     EXCITATION,       111 

it  accumulates  more  at  the  extremities  of  the  longest  axis.  Hence 
on  a  wire  or  a  needle,  the  electricity  is  accumulated  almost  exclu- 
sively on  the  ends  ;  and  even  though  the  total  quantity  of  electricity 
may  not  be  large,  it  is  there  so  thickly  heaped  that  it  breaks  off  and 
rapidly  escapes.  Hence  electrical  apparatus  should  be  completely 
smooth  except  where  a  point  or  projection  is  intentionally  attached, 
and  many  remarkable  experiments  are  founded  upon  the  escape  of 
electricity  from  points.  Electricity  is  not  merely  prevented  from 
accumulating  upon  a  pointed  body  itself,  but  it  cannot  collect,  upon 
any  surface  near  it,  the  point  abstracting  the  electricity.  Thus,  a 
point  held  near  to  the  excited  glass  tube  used  in  the  experiments 
first  described  may  prevent  the  attraction  of  the  light  bodies,  which 
demonstrates  its  excited  state,  by  concentrating  all  the  action  upon 
itself.  The  detailed  theory  of  this  power  of  points  to  dissipate  their 
own  electricity  and  to  absorb  that  of  other  bodies,  will  be  hereafter 
fully  noticed  ;  at  present  it  is  sufficient  to  refer  it  to  the  thickness 
and  high  elasticity  of  the  layer  of  electric  fluid  which  forms  upon 
them. 

It  has  been  already  stated  that,  when  two  slips  of  silk  riband  are 
excited  by  rubbing  against  each  other,  the  electricity  appeared  to  be 
equally  evolved  upon  each.  This  occurs  in  all  cases  of  excitation 
by  means  of  friction.  Thus,  when  silk  and  glass  are  rubbed  together, 
the  silk  acquires  as  much  electricity  as  the  glass,  but  by  the  silk 
being  held  in  the  hand,  the  electricity  escapes  by  the  dampness  which 
is  always  present,  and  is  lost.  If,  however,  the  silk  be  insulated ; 
if  a  disk  of  dry  wood  covered  with  some  folds  of  silk  be  held  upon 
an  insulating  handle,  and  rubbed  against  a  similar  disk  of  glass,  then 
the  same  phenomena  are  produced  in  an  equal  degree  by  both.  The 
attraction  and  repulsion  of  light  bodies,  the  odour  and  the  phospho- 
rescence belong  to  both,  and  thus  in  every  case  where  bodies  are 
rubbed  together,  the  excitation  is  completely  mutual.  There  is, 
however,  a  profound  and  curious  difference  between  the  two  condi- 
tions :  separately  they  attract  and  repel  other  bodies  exactly  in  the 
same  way;  together  they  produce  neither  attraction  nor  repulsion: 
separately  they  may  manifest  the  most  remarkable  evidence  of  ten- 
sion, giving  sparks  and  shocks ;  but  when  combined,  all  signs  of  free 
electricity  are  lost,  and  the  body  on  which  they  are  collected  appears 
as  destitute  of  excitation  as  if  the  power  had  never  been  called  into 
existence.  The  states  of  the  two  bodies  are  therefore  so  far  op- 
posed that  they  may  interfere  ;  and  as  from  the  action  of  two  lights 
there  may  be  produced  total  darkness,  so  from  the  coalition  of  the 
excitation  of  the  two  bodies  which  had  been  rubbed  together,  abso- 
lute indifference  may  result. 

This  neutralizing  power  of  the  excitation  of  each  body  for  that  of  the  other  may 
be  shown  by  very  simple  means.  If  a  feather  be  suspended  by  a  silken  string,  and 
upon  the  one  side  there  be  presented  to  it  the  disk  of  glass,  and  upon  the  other  the 
disk  of  silk,  which  had  been  rubbed  together,  it  may  be  brought  to  remain,  by  man- 
aging the  distance,  perfectly  at  rest.  If  there  be  the  glass  alone,  it  instantly  at- 
tracts the  feather ;  the  silk  alone  acts  in  the  same  way ;  but  no  matter  how  strong 
the  power  of  each  may  be,  when  at  equal  distances  the  feather  remains  indifferent 
to  both.  In  order,  however,  to  obtain  perfect  demonstration  of  this  principle,  it  is 
useful  to  examine  it  by  means  of  more  exact  instruments  than  the  feather  or  other 
Light  bodies,  which  hitherto  have  been  sufficient,  and  for  this  purpose  the  gold-leaf 
4cctroscope  is  best  adapted  :  deferring  the  description  of  its  principle  to  another 


112      ELECTRICAL     ATTRACTIONS     AND     REPULSIONS. 

place,  I  shall  here  only  notice  its  construction  and  the  indications  which  it  gives 
^»  A  glass  jar,  A,  is  closed  at  the  top  by  a  metallic  (brass)  plate, 

^^^^^  B,  to  which  are  attached  below,  by  a  wire,  two  slips  of  gold  leaf, 

lying,  when  unexcited,  flat  on  one  another,  and  reaching  below 
the  middle  of  the  jar.  The  jar  rests  on  a  wooden  or  metal  foot, 
with  which  are  connected  two  slips  of  tin  foil,  applied  to  the  in- 
side of  the  glass,  and  rising  so  far  that  the  gold  leaves,  on  open- 
ing out,  may  come  into  contact  with  them.  When  this  occurs 
there  is  evidently  a  free  conducting  medium  from  the  upper  me- 
tallic plate  to  the  ground  ;  but,  except  when  the  gold  leaves  touch 
the  slips  of  tin  foil,  the  cap  and  leaves  are  perfectly  insulated, 
if  the  instrument  be  kept  dry.  When  this  electroscope  is  brought  near  to  an  exci- 
ted body,  the  gold  leaves  diverge,  and  remain  so,  in  the  position  of  the  figure,  as 
long  as  the  excited  body  be  kept  near.  But  if  the  instrument  be  not  touched,  the 
leaves  collapse  on  its  removal,  and  all  remains  indifferent,  as  it  had  been  before. 
By  the  divergence  of  the  gold  leaves,  therefore,  the  existence  of  free  electricity  act- 
ing on  the  electroscope  is  made  known. 

No  matter  what  may  be  the  nature  of  the  excited  body  acting  on  this  instrument, 
it  gives  the  same  indication  of  its  presence,  but  when  exposed  to  the  action  of  the 
two  bodies  which  had  been  rubbed  together,  the  gold  leaves  remain  quiescent.  If 
-they  be  made  to  separate  by  the  influence  of  the  glass,  and  the  excited  silk  be  then 
slowly  approximated,  the  divergence  gradually  diminishes,  until  at  last  the  leaves 
lie  close  together.  If  the  silk  be  then  brought  still  nearer,  there  is  a  new  divergence, 
but  it  is  due  to  the  excess  of  power  of  the  silk  after  the  neutralization  of  the  glass. 
On  removing  either  of  the  excited  bodies  when  the  instrument  is  in  the  neutrahzed 
condition,  the  leaves  diverge,  from  that  remaining  being  free  to  act.  Not  merely 
is  the  excitation  assumed  by  the  two  bodies  immediately  rubbed  together,  of  these 
opposite  kinds,  but  it  may  be  shown  that  this  peculiar  power  may  exist  in  the  con- 
ditions of  two  bodies  rubbed  by  a  third,  as  if  a  glass  be  rubbed  with  silk,  and  an  in- 
sulated metal  rod  be  likewise  excited  by  rubbing  with  silk,  the  glass  and  metal  rod 
assume  electricities  which  destroy  each  other,  or  the  silk  is  related  to  the  metal  as 
the  glass  had  been  to  the  silk.  Bodies  rubbed  by  different  other  substances  are  also 
so  circumstanced ;  if  a  stick  of  sealing-wax  be  rubbed  by  flannel,  it  will  assume  op- 
posite excitation  to  that  of  glass  when  rubbed  with  silk,  and  would  counteract  its 
influence ;  and,  consequently,  the  condition  of  the  flannel  in  the  one  case,  and  the 
silk  in  the  other,  would  be  opposite  also.  This  assumption  of  opposite  states  of  ex- 
citation may  be  caused  by  trifling  mechanical  conditions  :  thus,  if  smooth  glass  and 
muffed  glass  be  both  rubbed  with  silk,  they  become  oppositely  electrified  ;  and  two 
pieces  of  silk,  which  differ  markedly  in  colour,  neutralize  each  other  when  electrified 
by  their  mutual  friction.  The  peculiar  characters  of  these  two  forms  of  excitation 
extend,  however,  much  farther  than  the  principle  of  mutual  destruction.  If  we  hang 
by  a  dry  silk  thread,  varnished  with  shell-lac  in  order  to  render  it  a  better  insulator, 
a  little  cylinder  of  gilt  paper,  and  bring  near  it  an  excited  body,  the  cylinder  is  at- 
tracted, and  moves  towards  the  body  until  it  touches,  when  it  is  immediately  and 
forcibly  repelled.  It  has  by  contact  participated  in  the  state  of  excitation  of  the 
body,  and,  when  that  is  so,  they  mutually  repel  each  other.  In  all  cases,  bodies 
which  are  in  the  same  electrical  condition  repel  each  other ;  and  it  is  thus  that  the 
gold  leaves  of  the  electroscope  become  an  index  of  any  electricity  which  may  be 
present ;  for  as  both  slips  of  leaf  are  necessarily  excited  in  the  same  way,  they  repel 
each  other,  and,  consequently,  they  diverge. 

If,  now,  the  insulated  gilt  paper  cyhnder  which  has  been,  as  above  described,  re- 
pelled by  the  glass  rod,  after  having  shared  its  electricity,  be  brought  near  the  silk 
against  which  the  glass  rod  had  been  rubbed,  or  to  any  body  which  is  in  the  same 
state  of  excitation  as  the  silk,  attraction  will  ensue,  and  this  will  be  found  more 
iwwerful  than  if  the  body  had  previously  been  neutral.  If  two  such  gilt  paper  cyl- 
inders be  touched,  both  vi'ith  the  glass  rod  or  both  with  the  silken  disk,  they  will 
repel  each  other ;  but  if  one  be  touched  with  the  glass  and  the  other  by  the  silk, 
they  will  attract  each  other,  and  move  until  they  touch,  when  the  states  of  excita- 
tion neutralize  each  other,  and  they  become  inactive. 

When  bodies  are  rubbed  together,  therefore,  they  become  elec- 
tric, and  with  such  properties,  that  while  each  when  separate  gives 
signs  of  powerful  excitation,  together  they  destroy  each  other's 
power.    Bodies  when  thus  oppositely  electrified  attract  each  other  j 


LAW  OF  ELECTRICAL  ATTRACTIONS. 


113 


bodies  which  are  excited  in^  the  same  manner  repel  each  other ; 
and  these  attractions  and  repulsions  arise  from  the  exertion  of  a 
force  which,  like  that  of  gravitation,  diminishes  in  intensity  ac- 
cording as  the  square  of  the  distance  between  the  bodies  becomes 
greater. 

This  law,  which  is  of  the  greatest  importance  for  the  theory  of  electricity,  was 
discovered  by  Coulomb  by  means  of  the  torsion  electrometer.  The  gold-leaf  appara- 
tus, though  ex;ceedingly  sensible  as  a  test  of  the  presence  of  free  electricity,  is  yet 
not  susceptible  of  being  used  to  measure  its  amount.  It  is  an  electroscope,  but  not 
an  electrometer.  The  torsion  balance  of  Coulomb  consists  of  a 
glass  drum,  a,  on  the  centre  of  which  rises  a  glass  tube,  b,  to  the 
height  of  one  or  two  feet.  From  the  top  of  this  tube  is  hung,  by 
a  fine  thread  of  glass  or  of  cocoon  silk,  a  very  light  wooden  beam, 
c,  to  which  is  attached  at  one  end  a  ball  of  dry  elder  pith,  and  at 
the  other  a  piece  of  gilt  paper,  which  serves  as  a  counterpoise, 
and  by  its  surface  prevents  irregular  motions  of  the  beam.  The 
pith  ball  is  usually  gilt,  to  give  it  a  more  uniform  surface.  In  ^^^ 
the  top  of  the  drum  there  is  an  aperture,  by  means  of  which  a 
second  gilt  pith  ball,  d,  may  be  introduced,  and  made  to  touch 
that  of  the  balance  ;  and  around  the  centre  of  the  drum  is  fixed 
a  scale  of  degrees,  by  which  the  angular  distance  to  which  the 
balls  separate  after  repulsion  may  be  measured.  Now  let  us 
suppose  that,  by  touching  the  second,  or,  as  it  is  called,  the  car- 
rying ball,  to  an  excited  body,  we  charge  it  with  electricity,  and, 
having  inserted  it  in  the  aperture,  it  touches  the  ball  of  the  bal- 
ance, which  is  immediately  repelled :  in  moving  away,  this  twists 
the  thread  by  which  it  is  suspended,  and  the  amount  of  the  twisting  which  is  ne- 
cessary in  the  opposite  direction  to  bring  it  back  again,  ^d  maintain  it  at  a  certain 
distance,  measures  the  force  of  repulsion  the  balls  then  exercise.  This  measure- 
ment is  effected  by  the  glass  or  silken  thread  being  attached,  not  to  the  tube,  but  to 
a  stem  carrying  an  index,  which  shows,  on  a  graduated  circle,  the  number  of  de- 
gi-ees  through  which  the  thread  is  twisted ;  and  as  the  thread  is  exceedingly  long 
in  proportion  to  its  thickness,  and  its  elasticity  almost  exact,  the  force  of  torsion  is 
taken  as  proportional  to  the  angle  through  which  the  index  moves. 

By  this  instrument,  into  the  detail  of  experiments  with  which  it  would  be  improper 
here  to  enter.  Coulomb  established  the  fundamental  law  of  electrical  attraction  and 
repulsion  ;  and  it  has  been  found,  that  from  this  law  all  the  results  of  the  distribu- 
tion of  electricity  on  bodies,  its  accumulation  on  and  escape  from  points,  that  have 
been  noticed,  might  be  deduced. 

The  fundamental  principles  of  electrical  excitation,  the  distribution  of  electricity 
on  bodies,  and  the  manner  in  which  the  electric  states  of  the  excited  bodies  are  re- 
lated to  each  other,  having  been  thus  described,  I  shall  pass  to  the  explanation  of 
the  general  principles  under  which  those  phenomena  and  laws  have  been  arranged, 
and  a  knowledge  of  which  we  shall  find  necessary  to  our  future  progress.  I  shall 
lay  aside  all  consideration  of  the  more  abstract  theories  of  electricity,  which  refer 
it'to  mere  molecular  disturbance  or  to  vibrations,  and  consider  only  those  views 
which  suppose  the  existence,  in  the  one  case,  of  two  electric  fluids,  the  theory  of 
Dufay,  and,  on  the  other,  that  of  a  single  fluid,  the  theory  of  Franklin. 

Theory  of  two  Fluids. — It  is  assumed  that  there  exist  in  nature  two 
kinds  of  electricity,  each  a  highly  elastic  fluid,  whose  particles  repel 
each  other  according  to  the  law  of  the  inverse  square,  while  they 
attract  the  particles  of  matter,  and  also  attract  each  other,  accord- 
ing to  the  same  law :  that  every  body  in  nature  contains  usually 
an  exactly  equal  quantity  of  each  fluid  ;  that  bodies  then  are  in  their 
ordinary  state ;  and  hence,  manifesting  no  unusual  properties,  we 
look  upon  them  as  being  quiescent :  but  if  a  body  contains  more 
of  one  fluid  than  of  another,  it  comes  into  an  extraordinary  state, 
and,  acquiring  new  properties,  we  say.  that  it  has  become  excited. 

Upon  this  view,  the  phenomena  of  electricity  are  capable  of  very 
simple  explanation.     When  two  bodies  are  rubbed  togethd^,  the  re- 


114  THEORIES     OF     ELECTRICITY. 

suit  is,  that  one  electric  fluid  accumulates  in  excess  upon  the  olie, 
and  the  other  upon  the  other  body.  They  are  thus  both  brought 
into  a  state  of  excitation  ;  and  as  the  excess  of  the  one  fluid  musi 
be  exactly  equal  to  that  of  the  other,  the  excitation  of  both  is  equal, 
and,  being  opposite,  must  neutralize  each  other  when  they  are 
brought  to  reunite.  Of  these  electricities,  that  which  passes  to 
glass  when  it  is  rubbed  with  silk  is  termed,  in  the  language  of  Du- 
fay,  vitreous  electricity,  and  that  which  accumulates  on  resin  when 
rubbed  with  flannel  is  called  resinous.  There  are  few  bodies  which 
may  not  assume  vitreous,  or  resinous  excitation,  according  to  the 
substance  by  which  the  friction  is  produced,  and  hence  these  names 
are  liable  to  some  objection,  and  are  not  much  employed. 

Since  the  electric  fluids  and  matter  attract  each  other,  the  bodies 
upon  which  the  electricities  become  free  appear  to  attract  or  repel 
each  other  according  as  they  are  invested  by  the  same  or  opposite 
fluids,  in  consequence  of  the  necessity  of  accompanying  these  flu- 
ids in  their  action  on  each  other.  Hence  the  electric  attractions 
and  repulsions  which  manifest  themselves  in  all  cases  of  excitation, 
and  hence  the  bodies  return  to  their  indiflMerent  condition  as  soon 
as  the  excess  of  electricity  they  contain  is  neutralized.  It  was  for 
a  long  time  supposed  that  the  atmosphere,  by  its  mechanical  press- 
ure, assisted  in  retaining  the  free  electricities  upon  the  surface  of 
the  excited  bodies  ;  but  this  is  not  the  case.  The  air  acts  as  an  in- 
sulator of  the  excited^body,  without  which  no  accumulation  of  free 
electricity  could  occur  ;  but  the  mechanical  pressure  of  the  air  may 
be  removed  without  affecting  the  electrical  conditions. 

Theory  of  one  Fluid. — In  the  hypothesis  of  Franklin  there  is  as- 
sumed to  exist  but  one  electric  fluid,  of  which,  in  its  ordinary  state, 
every  substance  contains  a  certain  quantity.  This  fluid  is  consid- 
ered to  be  highly  elastic,  to  repel  its  own  particles  with  a  force 
varying  as  the  inverse  square  of  the  distance,  and  to  attract  the  par- 
ticles of  matter  according  to  the  same  law.  A  substance  with  its 
proper  share  of  electricity  is  therefore  in  its  indifferent  condition, 
possessing  no  properties  beyond  what  we  ordinarily  attribute  to  it. 
But  when  two  such  bodies  are  rubbed  together,  a  quantity  of  elec- 
tricity abandons  one  and  collects  upon  the  other,  and  thus  both  are 
brought  into  an  abnormal  state,  and  assume  the  unusual  properties 
which  constitute  excitation.  The  excitation  is  equal,  for  the  one 
has  gained  precisely  what  the  other  lost ;  and  by  recombination 
they  destroy  each  other's  action,  for  they  are  brought  to  their  ori- 
ginal ordinary  state.  The  excitation  being  produced,  according  to 
this  view,  by  one  body  having  electricity  in  excess,  while  that  of 
the  other  is  deficient,  one  is  said  to  be  plus  and  the  other  minus 
electrified ;  or,  more  generally,  the  one  to  be  positively^  the  other 
negatively  excited,  and  the  signs  -f-  and  —  are  often  used  as  abbre- 
viations for  these  words. 

The  particles  of  the  electric  fluid  being  mutually  repulsive,  and  at- 
tracting those  of  matter,  it  is  natural  that  two  bodies  having  elec- 
tricity in  excess  shall  mutually  repel,  and  that  a  body  having  an 
excess  of  electricity  shall  attract  one  having  an  excess  of  matter. 
Bodies  both  -\-  therefore  repel,  a  +  and  a  —  body  attract  each  other. 
But,  to  ^explain  the  mutual  repulsion  of  bodies  both  in  the  negative 


ELECTRICAL     MACHINES. 


115 


condition,  an  assumption  is  required  which  at  first  sight  appears  to 
militate  considerably  against  our  reason  j  for  as  it  is  matter  which 
is  in  excess  in  that  condition,  Ave  must  consider  that  the  particles 
of  matter  mutually  repel  each  other,  according  to  precisely  the  same 
law,  as  it  is  demonstrated  by  the  whole  construction  of  the  universe, 
that  the  particles  of  matter  mutually  attract  each  other.  There  is 
not,  however,  any  real  contradiction  in  these  principles  ;  the  law  of 
gravitation  applies  to  matter  in  its  ordinary  state,  in  which  it  con- 
tains its  natural  quantity  of  electricity  j  and  it  affords  no  grounds 
for  supposing  that,  if  matter  were  deprived  of  that  natural  electri- 
city, it  would  continue  to  attract.  There  is,  consequently,  nothing 
illegitimate  in  that  assumption  ;  and  the  theory  of  a  single  fluid  may 
be  as  easily  and  successfully  applied  to  the  explanation  of  phenom- 
ena as  that  of  the  two  fluids  before  described. 

Already,  indeed,  considerable  progress  has  been  made  towards  a  theory  of  elec- 
tricity upon  this  idea.  In  order  to  account  for  the  ordinary  molecular  constitution 
of  matter,  it  is  necessary  to  suppose  that  the  forces  which  act  upon  its  particles 
may  change  from  attractive  to  repulsive,  and  again  from  repulsive  to  attractive,  ac- 
cording as  the  distance  between  the  particles  is  made  to  vary ;  and  Mosotti  has 
shown  that  it  is  only  necessary  to  assume  that  the  mutual  repulsion  of  matter, 
wlien  destitute  of  electricity,  is  inferior  to  its  attraction  for  electricity,  and  to  the 
mutual  repulsion  of  the  electricity  itself,  and  the  law  of  gravitation  becomes  a  neces- 
sary consequence  of  the  conditions  under  which  alone  electrical  equilibrium  can  be 
established. 

Such  are  the  theories  of  electricity  that  have  hitherto  met  with  most  general  ac- 
ceptation. In  the  succeeding  portions  of  this  work,  I  shall  adopt  the  language  of 
the  theory  of  the  two  fluids,  except  that  I  shall  use  the  words  positive  and  negative 
fluids  in  place  of  vitreous  and  resinous  ;  but  I  do  so  merely  from  convenience,  and. 
seek  not  to  connect  the  idea  of  a  fluid  in  any  way  more  intimately  with  the  true 
causes  of  the  electrical  properties  of  bodies. 

Before  passing  to  the  description  of  the  phenomena,  and  the  dis- 
cussion of  the  principles  of  electricity  which  yet  remain,  it  is  ne- 
cessary to  notice  the  construction  of  some  electrical  apparatus,  which 
is  employed  in  all  ca- 
ses where  it  is  desira- 
ble to  operate  upon 
this  agent  in  a  state 
of  high  intensity  and 
power.  Of  these  the 
most  important  is  the 
electrical  machine. 

The  machine  is  in 
principle  only  a  mod- 
ification of  the  glass 
tube  which,  by  fric- 
tion with  a  piece  of 
silk,  evolved  the  elec- 
tricity in  the  first  ex- 
periments described. 
It  consists  of  a  glass 
having  such  a  form 
as  to  expose  a  great 
extent  of  surface,  and 
generally  being  used 
in  the  shape  of  a  cyl- 


116 


ELECTRIJAL     MACHINES. 


inder,  A,  or  of  a  plate.  There  are  hence  the  cylinder  and  the  plate 
machines.  To  produce  the  friction,  an  elastic  rubber,  B,  is  covered 
with  silk,  and  made  to  press  against  the  surface  of  the  glass  accord- 
ing as  the  plate  or  cylinder  is  turned  round  by  means  of  the  handle. 
The  rubber  being  generally  insulated,  the  electricity  evolved  upon 
it  is  at  once  collected,  and  may  be  transferred  along  conductors,  or 
drawn  as  sparks  from  the  knob  of  brass  attached  to  it  at  the  back. 
The  electricity  which  is  diftused  upon  the  glass  passes  from  its  sur- 
face to  that  of  a  brass  cylin- 
der, termed  the  prime  con- 
ductor, C,  being  collected  by 
means  of  a  series  of  pointed 
wires,  which  graze  the  sur- 
face of  the  cylinder  accord- 
ing as  it  is  turned  round.  The 
prime  conductor  is  also  insu- 
lated ;  and  in  the  case  of  a 
cylinder  machine,  the  glass 
itself  is  often  supported  upon 
insulating  pillars,  by  which 
the  loss  of  electricity  is  pre- 
vented. To  increase  the  en- 
ergy of  the  machine,  the  silk 
of  the  rubber  is  generally 
smeared  over  with  a  mixture 
of  grease  and  an  amalgam  of 
tin  and  zinc,  and  a  silken 
apron  extends  from  the  rubber  half  over  the  cylinder  or  plate  to  con- 
duct the  electricity  to  the  points,  and  prevent  its  being  carried  away 
by  the  air. 

Although  I  shall  have  occasion,  when  we  have  examined  the  rel- 
ative action  of  excited  bodies  and  conductors  somewhat  better,  to 
notice  the  true  theory  of  the  prime  conductor,  yet  for  the  present  it 
may  be  considered  as  simply,  from  its  proximity,  collecting  the  free 
electricity  on  its  points  from  the  surface  of  the  glass  cylinder  or  plate, 
and  by  thus  accumulating  it  upon  a  confined  surface,  enabling  the 
experimenter  to  apply  it  or  carry  it  to  other  bodies  at  his  pleasure. 
When  the  machine  is  worked,  the  two  portions  of  electricity  become 
developed,  as  in  the  rubbing  of  the  tube  and  handkerchief,  upon  the 
silk  and  glass  ;  and  if  all  be  insulated,  they  attract  each  other  so  in- 
tensely that  they  break  through  the  intervening  air,  and  recombine 
across  the  surface  of  the  cylinder,  or  round  the  edges  of  the  plate, 
presenting  the  appearance  of  a  brilliant  spark,  and  accompanied  by 
a  snapping  noise  and  a  peculiar  phosphorescent  odour.  To  prevent 
this  recombination,  which  would,  of  course,  render  accumulation  up- 
on the  prime  conductor  impossible,  the  rubber,  when  the  machine  is 
required  for  active  work,  is  connected  with  the  ground  by  a  wire 
or  chain,  through  which  the  electricity  which  forms  upon  the  silk 
makes  its  escape  ;  and  as  new  quantities  are  then  liberated  at  each 
moment,  those  passing  from  the  glass  to  the  prime  conductor,  by 
the  projecting  points  with  which  it  is  always  furnished,  collect  upon 
it,  and,  acquiring  a  high  degree  of  tension,  pass  under  the  form  of 
sparks  to  any  conducting  body  which  may  be  brought  near. 


PHENOMENA     OF     THE     ELECTRICAL     MACHINE.    117 

By  means  of  a  machine  of  such  construction,  the  opposing  prop- 
erties of  the  electricities  of  the  bodies  rubbed  together  may  be  sim- 
ply and  completely  shown. 

The  degree  of  excitation  of  the  prime  conductor  is  generally, 
though  not  very  accurately,  shown  by  means  of  the  quad- 
rant electrometer.  This  consists  of  a  stem  of  brass,  which 
rests  in  a  socket  in  the  prime  conductor,  or,  when  not  in 
use,  in  a  wooden  foot,  as  in  the  figure.  To  this  is  attached 
an  ivory  semicircular  scale,  of  which  a  portion  is  graduated, 
from  whence  the  name ;  on  an  axis  at  the  centre  of  the 
ivory  scale  there  is  hung,  by  a  light  arm  of  whalebone,  a 
pith  ball,  which,  when  the  apparatus  is  unexcited,  lies  in 
contact  with  the  brass  stem,  and  thus  assumes  the  same  elec- 
trical condition  with  it  when  the  instrument  is  placed  on  the 
prime  conductor  and  the  machine  worked.  The  stem  and  the  pith 
ball  then  repel  each  other,  and  the  ball  being  consequently  set  in  mo- 
tion by  the  united  repulsion,  its  radius  moves  through  an  angular 
space  on  the  graduated  scale,  which  serves  in  rough  experiments  as 
an  index  of  the  intensity  of  the  excitation.  Now  if,  when  this  instru- 
ment is  fixed  on  the  prime  conductor,  the  latter  be  connected  with 
the  insulated  rubber  by  a  chain  or  wire,  no  matter  how  vigorously 
the  machine  may  be  worked,  no  signs  of  excitation  can  be  produced  ; 
the  electricity  collected  from  the  glass  by  the  prime  conductor 
passing  along  the  chain  or  wire  to  unite  with  that  which  is  devel- 
oped on  the  rubber,  and  the  two  being  evolved  in  equal  quantities, 
complete  neutralization  is  produced.  That  bodies  similarly  electri- 
fied repel  each  other,  is  shown  by  the  principle  of  this  instrument, 
as  its  indications  of  free  electricity  depend  upon  the  stem  and  ball 
being  both  excited  in  the  same  way,  and  the  repulsion  being  the 
same,  whether  it  be  fixed  upon  the  rubber  or  the  prime  conductor. 

To  prove  on  a  large  scale,  by  means  of  the  machine,  that  the  op- 
posite electricities  attract  each  other,  it  is  only  necessary  to  place 
in  connexion  with  the  conductor  on  each  side  a  metallic  wire,  to 
which  is  hung,  by  a  wetted  thread,  a  ball  of  pith,  or  a  cylinder  of 
gilt  paper.  When  the  machine  is  turned,  the  balls  attract  each  oth 
er  across  the  cylinder,  and  touching,  interchange  the  electricities 
by  which  they  are  excited,  and  thus  the  fluids,  separated  by  the 
friction,  are  continually  recomposed,  being  brought  together  by 
their  mutual  attractions.  If  to  each  wire  there  be  hung  two  such 
balls,  those  of  each  side  will  be  seen  to  repel  each  other,  while 
they  move  towards  those  oppositely  excited.  Numerous  experi- 
ments of  an  amusing  kind,  which  it  Avould  be  foreign  to  my  purpose 
to  introduce,  are  founded  on  these  principles. 

There  have  been  now  noticed  four  methods  by  which  bodies  may 
be  electrically  excited.  1st,  hy  friction^  which  is,  indeed,  the  only 
true  direct  excitation.  2d,  by  contact ;  as  when  an  insulated 
brass  disk  excited  by  friction  is  touched  to  another,  also  insulated 
and  neutral,  a  spark  passes  between  them  at  the  moment  previous 
to  actual  contact,  and  the  first  is  found  to  have  divided  its  electri- 
city with  the  second  in  proportion  to  its  surface.  In  this  case  the 
two  bodies,  after  contact,  are  in  the  same  state  of  excitation.  3d. 
as  where  the  prime  conductor,  which  is  neither  itself  rubbed,  nor 


118  EXCITATION     BY     INDUCTION. 

does  it  touch  the  cylinder  of  the  machine,  yet  gathers  from  it  the 
electricity  which  is  evolved  thereon,  and  allows  it  to  be  transferred, 
under  the  form  of  the  spark,  to  other  bodies  ;  and,  finally,  all  the 
attractions  and  repulsions  which  have  been  observed  indicate  a  pow- 
er of  action  and  excitation  even  at  considerable  distances  ;  and  this 
mode,  which  results  from  the  attraction  and  repulsion  of  the  elec- 
tric fluids  for  each  other,  is,  when  examined,  found  really  to  com- 
prehend the  second  and  third  modes  of  excitation,  by  contact  and 
by  gathering  with  points.  There  are,  therefore,  truly,  only  two 
means  of  excitation,  this  at  a  distance,  which  is  termed  induction^ 
and  that  hj  friction. 

It  is  not  difficult  to  understand  how  bodies  come  to  be  excited  by 
induction.     Let  us  consider  the  insulated  cylinders,  B  C,  as  being 

neutral,  and  having 
their  natural  electri- 
cities combined,  and 
distributed  uniform- 
ly over  their  surface. 
^^^If  a  globe,  A,  exci- 
*^      ted,   say  with   posi- 
tive electricity.,  be  brought  near,  it  will  attract  the  opposite  electri- 
city of  B  to  the  end  which  is  nearest  it,  and  repel  the  electricity 
of  the  same  name  to  the  farthest  extremity  ;  both  electricities  of 
B  will  thus  become  free,  and  B  will  be  excited  by  the  influence  of 
the  electricity  of  the  body,  A,  at  a  distance  ;  and  the  condition  of 
B  is  characterized  by  its  two  extremities  being  in  opposite  states, 
and  hence,  at  a  certain  point  between  them,  perfect  neutrality  re- 
maining.    The  positively  excited  end  of  B  influencing  C  in  a  cor- 
responding way,  brings  it  also  into  an  excited  state,  and  this  com- 
munication of  action  would  go  on  through  any  number  of  bodies, 
the  force  set  free  being  regulated  by  the  law  of  the  inverse  square 
of  the  distance  from  the  original  disturbing  cause  at  A.     As  long 
as  A  remains  in  its  place,  the  state  of  electrical  excitation  is  kept 
up ;  if  A  be  totally  removed,  the  natural  electricities  of  each  body 
recombine,  and  all  become  neutral ;  if  A  be  brought  very  close  to 
,B,  or  B  to  C,  the  attractions  between  the  opposite  electricities  be- 
come so  great  that  they  unite  across  the  intervening  space  of  air, 
and  a  spark  passes.     The  bodies  are  then  found  to  be  in  the  same 
state,  and  the  communication  by  contact,  or  the  excitation  which 
occurs,  is  shown  to  be  only  the  termination  of  the  inductive  action. 
For  suppose  that  A  had  10  parts  of  +  electricity,  and  that,  by  in- 
duction, it  set  free  5  of  the  —  and  5  of  the  -\-  fluid  on  the  surface 
of  the  body  B  ;  then,  when  the  spark  had  passed,  the  — 5  destroy- 
ing 4-5  of  the  body  A,  the  two  bodies  should  remain  each  with 
-}-5,  and  thus  the  results  of  contact  described  already  should  be 
produced. 

The  distance  at  which  the  combination  of  the  electricities  of  the 
inducing  and  the  induced  body  may  occur,  depends  upon  the  inten- 
sity of  the  fluids  collected  on  the  parts  of  the  surface  nearest  to 
each  other  ;  and  hence,  when  there  is  on  the  body  a  point  on  which 
the  great  proportion  of  the  liberated  fluid,  as  has  been  already  de- 
scribed, becomes  accumulated,  the  fluid  escapes  from  thence  before 


THEORY  OF   THE   GOLD  LEAF  ELECTROSCOPE.  119 

it  is  in  sufficient  mass  to  break  its  way  under  the  form  of  a  spark, 
and  thus  the  permanent  and  similar  excitation  of  the  body  silently 
occurs.  This  is  the  true  theory  of  what  has  hitherto  been  de- 
scribed as  the  power  of  points  to  gather  and  to  disperse  the  elec- 
tric fluid.  If  a  pointed  body  be  excited  by  friction,  it  induces  an 
opposite  state  in  the  particles  of  air  by  which  it  is  surrounded,  and 
communicates  to  them,  with  great  rapidity,  the  charge  which  it  had 
received.  The  prime  conductor  of  the  machine,  being  insulated, 
has  its  electricities  separated  by  the  inductive  action  of  the  excited 
glass  cylinder  or  plate  ;  the  negative  electricity  collected  on  the 
points  turned  towards  the  glass  escapes  from  thence,  and  unites 
with  the  positive  fluid  which  had  been  set  loose  by  friction,  and 
proportional  quantities  of  the  positive  fluid  of  the  prime  conductor 
being  left  free  upon  its  surface,  it  serves  the  same  purpose  as  a 
source  of  electricity  as  if  it  had  come  directly  from  the  glass.  A 
point  placed  on  the  prime  conductor  prevents  the  accumulation  of 
the  electricity,  because  it  gives  the  -j-  to  the  air  as  fast  as  the  oth- 
er points  give  the  —  to  the  glass  ;  a  point  held  near  the  prime  con- 
ductor also  prevents  its  excitation,  by  giving  to  it  by  induction  — 
electricity  as  fast  as  it  obtains  -j-  electricity  from  the  glass  of  the 
machine. 

In  all  these  cases  of  induction  where  the  electricities  attract  and 
repel  each  other,  the  bodies  on  which  the  electricities  are  collected 
will  accompany  them  in  their  motions  if  they  be  not  too  heavy. 
Hence  all  the  singular  motions  of  bodies,  when  excited,  are  ex- 
plained upon  this  principle.  The  variety  of  dancing  figures,  ring- 
ing bells,  revolving  wheels,  afli-ighted  heads,  and  so  on,  that  are  ex- 
hibited in  popular  lectures  on  this  subject,  will  serve  to  practise  the 
ingenuity  of  the  student  in  tracing  out  their  theory  in  the  detail, 
with  which  it  would  be  quite  improper  to  occupy  this  work. 

The  theory  of  the  Bennet's  gold  leaf  electrometer,  with  which  some  of  the  most 
important  principles  of  statical  electricity  are  demonstrated,  must  not,  however,  be 
omitted.  When  an  excited  rod  is  brought  over  the  electroscope,  it  separates  the 
electricities  of  the  metallic  portions  of  the  instrument,  attracting  the  opposite  to  the 
upper  surface  of  the  cap,  and  repelling  that  of  the  same  name  into  the  gold  leaves, 
which,  being  thus  excited  with  the  same  electricity,  repel  each  other,  and  hence 
diverge.  If  the  exciting  body  be  -4-,  it  is  the  -{-  fluid  by  which  the  instrument  ap- 
pears affected  ;  if  it  be  — ,  the  leaves  diverge  from  the  presence  of  —  electricity. 
Hence  if,  when  it  is  under  the  influence  of  a  glass  rod  rubbed  with  silk,  a  stick  of 
seahng-wax  which  had  been  rubbed  with  flannel  be  brought  near,  the  divergence 
diminishes,  until  at  last  the  leaves  collapse  completely,  the  resin  having  driven  down 
as  much  negative  electricity  as  there  had  been  positive  brought  into  action  by  the 
glass,  and  hence  the  gold  leaves  coming  into  their  natural  and  indifferent  condition. 
That  it  is  by  this  inductive  process  that  the  gold  leaves  act,  may  be  thus  shown.  If 
the  cap  of  the  electroscope  be  rubbed  with  a  dry  silk  handkerchief,  it  becomes  excited, 
and  the  leaves  diverge  with  negative  electricity ;  if  then  an  excited  glass  rod  be 
brought  near,  the  divergence  is  neutralized,  showing  that  positive  electricity  had  been 
sent  down  by  the  glass  ;  but  if  an  excited  resinous  body  be  approached,  the  diver- 
gence increases,  indicating  the  superaddition  of  electricity  of  the  same  aame  from 
the  inducing  power  of  the  resin. 

If,  as  in  the  figure  (page  118),  the  cylinder  C  be  connected  with  the  ground  by 
means  of  a  wire  or  a  wetted  thread,  D,  the  positive  electricity  passes  from  that  body 
through  the  wire  into  the  earth,  where,  from  the  enormous  surface  of  the  globe,  it 
may  be  looked  upon  as  lost,  and  the  surface  of  C  is  altogether  in  a  state  of  negative 
excitation.  If,  now,  the  exciting  body  A  be  taken  away,  the  quantity  of  positive  fluid 
returns  along  the  wire,  and  brings  the  body  C  into  its  neutral  state  ;  but  if  before  the 
body  A  be  taken  away,  the  conducting  communication  with  the  ground  be  cut  off  by 


120  CONSTRUCTION     OF     THE    LEYDEN    JAR. 

the  removal  of  the  wire  or  thread,  the  body  C  cannot  get  its  positive  electricity  back, 
and  hence  remains  in  a  state  of  negative  excitation.  In  this  manner  a  substance 
may,  by  induction,  be  made  to  receive  a  permanent  charge.  This  is  often  useful  in 
experiments  with  the  electroscope,  and  the  manipulation  to  charge  it  permanently  is 
as  follows  :  If  it  be  desired  to  charge  it  positively,  an  excited  stick  of  resin  is  held 
near,  and  the  cap  of  the  electroscope  is  touched  with  the  finger.  The  negative  elec- 
tricity then  escapes  by  the  hand  into  the  ground,  and  the  positive  electricity,  accu- 
mulating over  the  cap  and  leaves,  these  last  diverge.  On  then  removing  the  finger, 
the  leaves  are  insulated ;  and  when  the  stick  of  resin  is  taken  away,  the  permanent 
charge  remains.  To  charge  with  negative  electricity,  an  excited  glass  rod  is  to  be 
used  ;  and  it  will  be  recollected,  that  where  the  charge  of  the  leaves  is  temporary, 
its  electricity  is  the  same  as  that  of  the  exciting  body  ;  but  where  the  charge  is  per- 
manent, the  electricity  is  of  an  opposite  kind. 

After  the  exciting  body,  in  the  latter  instance,  has  been  withdrawn,  the  divergence 
of  the  gold  leaves  becomes  much  greater  than  it  had  been  before.  This  arises  from 
the  charge  being  increased  by  its  action  on  the  surrounding  bodies,  particularly  on 
the  glass  by  which  the  leaves  are  enclosed.  By  taking  advantage  of  the  increase 
of  charge,  by  secondary  inductive  action,  various  forms  of  the  electroscope  have  been 
contrived  for  rendering  it  more  sensible,  and  are  described  in  special  treatises  on 
electricity  under  the  name  of  DouUcrs  and  Condensers.  As  they  do  not  add  anything 
to  our  knowledge  of  principles,  and  have  no  peculiar  chemical  relations,  I  shall  not 
enter  on  their  farther  consideration. 

One  of  the  most  interesting  instruments  in  statical  electricity, 
founded  on  the  principle  of  induction,  is  the  Ley  den  Jai\  so  called 
from  the  city  where  its  construction  was  discovered. 
It  consists  of  a  glass  hottle,  which  is  coated  inside  and 
outside,  to  a  small  distance  from  the  top,  with  tin  foil, 
and  has  fitted  to  the  orifice  a  wooden  or  cork  stopper, 
through  which  passes  a  stout  wire,  touching  at  the  bot- 
tom the  internal  coating,  and  terminated  outside  by  a 
metallic  knob.  When  this  jar  is  insulated,  and  the  knob 
>is  touched  to  the  prime  conductor  of  the  machine,  and 
!;^-=^  the  handle  turned,  the  positive  electricity  passes  to  the 
internal  coating  of  the  jar,  and  excites  it  to  an  equally  powerful  de- 
gree. This,  then,  reacting  by  induction  upon  the  electricities  of  the 
external  coating,  separates  them,  attracting  the  negative  to  the  side 
next  the  glass,  repelling  the  positive  to  the  outer  side.  The  posi- 
tion becomes,  therefore,  -|-  —  +  j  and  when  the  +  fluid  inside 
makes  up  by  its  greater  quantity  for  the  thickness  of  the  ^ass  by 
which  it  is  separated  from  the  —  fluid,  no  more  can  enter  into  the 
jar.  In  this  case  the  inside  of  the  jar  may  be  considered  as  being 
merely  an  extension  of  the  prime  conductor  j  and  the  electricities 
of  the  external  coating,  although  separated  from  each  other,  are 
only  in  the  quantities  which  had  been  always  present.  But  if  the 
external  coating  be  connected  with  the  ground,  the  +  fluid,  being 
repelled  by  that  inside,  passes  away,  and  another  quantity,  entering 
from  the  prime  conductor  into  the  jar,  decomposes  a  new  quantity 
of  the  natural  fluids  of  the  external  coating,  of  which  also  the  posi- 
tive escapes  and  the  negative  remains  behind,  held  by  the  attraction 
across  the  glass  to  the  positive  fluid  inside.  New  quantities  of  pos- 
itive electricity  entering  continually  from  the  machine,  the  accu- 
mulation of  negative  electricity  on  the  outer  coating  proceeds,  un- 
til the  tendency  of  the  two  to  combine  is  so  intense  as  to  break 
their  way  across  the  glass,  cracking  the  jar,  or  to  creep  over  the 
mouth  from  the  edge  of  one  coating  to  that  of  the  other,  and  thus 
the  jar  discharges  itself.     To  discharge  a  jar  in  which  the  elec- 


ELECTROPHORUS     OF    VOLT  A.  121 

tricities  are  so  accumulated,  it  is  only  necessary  to  connect  by  a 
wire  the  internal  and  external  coatings  ;  when  the  extremities  of 
the  wire,  which  are  generally  terminated  by  brass  balls,  approach, 
a  large  brilliant  spark  passes,  accompanied  by  a  loud  report,  and  the 
jar  returns  to  its  original  neutral  state. 

By  thus  collecting  great  quantities  of  electricity  in  large  jars  or 
in  sets  of  jars  (electrical  batteries),  the  most  beautiful  and  remark- 
able phenomena  of  electrical  force  may  be  exhibited. 

The  principle  of  the  construction  of  the  Leyden  jar  may  be  ex- 
perimentally demonstrated  as  follows:  First,  it  has  been  already 
explained  that  the  jar,  when  insulated,  is  incapable  of  receiving  any 
other  charge  from  the  machine  than  what  its  internal  coating  obtains 
by  forming  part  of  the  surface  of  the  prime  conductor  ;  the  principle 
of  induction  requiring,  in  order  that  one  electricity  may  accumu- 
late upon  its  outer  surface,  the  other  shall  be  dissipated  on  the  ground. 
Second,  a  light  body  placed  between  two  balls,  connected,  one  with 
the  internal,  and  one  with  the  external  coating,  is  alternately  attract- 
ed and  repelled  by  each,  and  thus  the  accumulation  on  the  two 
coatings  is  shown  to  be  of  opposite  kinds.  Third,  the  quantity  of 
electricity  which  passes  from  the  external  coating  may  be  shown 
to  be  equal  to  that  which  passes  into  the  internal  coating  from  the 
machine,  by  insulating  the  jar,  and  applying  the  knob  of  a  second 
jar  which  is  not  insulated  to  its  outer  surface ;  this  second  jar  will 
be  found  charged  to  the  same  degree  as  the  first,  and  the  inner  and 
outer  coatings  will  be  respectively  in  the  same  state. 

Statical  electricity,  thus  accumulated  in  the  Leyden  jar,  is  capa- 
ble of  giving  violent  shocks  to  the  animal  frame,  of  evolving  light 
and  heat,  and  producing  also  powerful  mechanical  effects. 

An  instrument  founded  on  the  principle  of  induction,  and  which 
is  of  frequent  use  in  chemical  experiments,  when  an  electric  spark 
of  moderate  power  is  required,  is  the  electrophorus  of  Volta.  It  con- 
sists of  a  flat  cake  of  resin,  &,  which  is  generally  spread  on  a  circu- 
lar board  of  eight  or  ten  inches  diameter.  There  is  laid  on  this 
another  circular  plate,  a,  somewhat  smaller,  and  which  may  be  either 
of  brass  or  tinned  iron,  with  the  edges  turned  up  over  a  thick  wire, 
so  as  to  round  it,  or  a  board  covered  with  tin  foil.  To  this  upper 
plate  is  attached  an  insulating  handle  of  glass,  c,  and  from  its  edge 
projects  a  wire  terminated  by  a  knob.  The  resin- 
ous plate,  being  warmed,  is  to  be  strongly  excited 
by  friction  with  a  warm  flannel  cloth  or  a  cat's 
skin,  and  then  the  upper  plate  is  to  be  laid  on  it,  and 
is  touched  with  the  finger.  The  negative  electricity  j 
of  this  passes,  then,  into  the  ground,  and  the  positive 
accumulates  on  the  surface  next  the  resin,  of  which 
it,  by  induction,  increases  the  negative  charge.  This  new  portion 
of  negative  fluid  decomposes  a  new  quantity  of  the  electricities  of 
the  upper  plate,  which  again  reacts,  and  thus  the  plates  are  mutually 
brought  into  a  state  of  very  intense  excitement.  ^If,  then,  the  finger 
be  removed,  the  upper  plate  is  insulated,  and  its  charge  of  positive 
electricity  retained  upon  it ;  and  on  applying  the  knob  of  the  wire 
to  any  conductor  or  to  the  knuckle,  a  strong  spark  may  be  obtain- 
ed from  it  3  the  instrument  may  be  repeatedly  charged  and  dischar- 


122  TRANSMISSION     BY     INDUCTION. 

ged  in  a  few  minutes,  and  retains  its  charge  better  than  the  electrify- 
ing machine. 

This  inductive  action  of  electricity  would  at  first  appear  to  be 
exercised  at  a  distance,  altogether  independent  of  the  interposed 
substances,  and  to  produce  the  motions  to  which  it  gives  rise,  as 
gravity  causes  the  revolutions  of  the  planets  and  their  satellites, 
without  the  existence  of  any  interposed  medium  5  but  a  more  exact 
■  examination  shows  that  this  is  not  the  case.  The  substances  inter 
posed  in  the  path  of  the  inductive  action  are  necessary  to  its  trans- 
mission, and  modify,  by  their  nature,  its  direction  and  amount ;  and 
it  is,  indeed,  only  from  molecule  to  molecule  of  any  substance,  gas- 
eous or  solid,  that  the  decomposition  of  the  natural  electricities  can 
take  place. 

This  may  be  beautifully  shown  by  plunging  in  a  vessel  of  oil  of 
turpentine,  which  is  an  excellent  fluid  insulator,  two  brass  balls,  of 
which  one  is  in  connexion  with  the  electrical  machine,  and  the 
other  with  the  ground.     On  turning  the  machine,  the  latter  be- 
comes excited  by  induction.     If,  now,  a  number  of  short  shreds  of 
sewing  silk  be  mixed  with  the  oil  of  turpentine,  the  mechanism  of 
the  inductive  action  is  shown  by  each  little  bit  of  silk  acting  like 
the  bodies  B  and  C  in  the  figure  (p.  118)  j  and  attaching  themselves 
mutually  by  their  extremities,  they  transmit  the  electricity  of  the 
machine,  by  a  series  of  decompositions,  to  the  ball  which  is  con- 
nected with  the  ground.     If  the  excitation  be  very  violent,  the  at- 
tractions and  repulsions  become  too  strong  to  be  regularly  trans- 
mitted; and  this  induction  is  accompanied  by  a  powerful  current 
of  the  particles  of  the  oil  from  the  first  ball  to  the  second.     The 
particles  immediately  in  contact  with  the  directly  excited  ball  ac- 
quire its  state,  and,  being  repelled,  immediately  pass  off'  to  that  which 
has  obtained,  by  induction,  the  opposite  condition,  and  there  become 
neutralized.     Now  what  here  occurs  with  the  oil  of  turpentine  takes 
place  in  ordinary  induction  with  the  air  ;  every  molecule  of  it  inter- 
posed between  the  solid  bodies  becomes  itself  subjected  to  the  in- 
ductive action,  and  forms  a  chain  of  alternate  positive  and  negative 
poles,  by  which  the  efi^ect  may  be  transmitted  to  any  distance.     If 
t'he  excitation  be  very  great,  the  neutralization  may  occur  with  vi- 
olence and  rapidity,  and  generate  currents,  as  in  the  oil  of  turpen- 
tine.    It  is  these  currents  which,  being  produced  by  the  repulsion 
of  the  particles  of  air  from  excited  points,  are  rendered  sensible  in 
the  effect  termed  the  electrical  aura,  and  are  shown  by  the  experi- 
ments of  revolving  flies.     A  still  more  violent  and  rapid  recomposi- 
tion  of  the  electricities  of  the  air  molecules,  which  had  been  sep- 
arated by  induction,  gives  the  electric  spark  in  its  various  forms, 
such  as  the  star,  the  brush,  &c.,  according  to  the  manner  in  which 
it  is  received  and  generated. 

That  the  excitation  by  induction  of  a  body  at  a  distance  is  efl^ect- 
ed  in  this  manner,  from  particle  to  particle  of  the  interposed  sub- 
stance, is  beautifully  shown  in  the  results  obtained  by  Faraday  con- 
cerning the  influence  of  the  nature  of  the  medium  on  the  amount 
of  inductive  charge  transmitted.  The  instrument,  which  he  has 
termed  a.n  inductometer,  consists  of  a  hollow  sphere  of  brass,  a  a  b, 
and  a  sphere  of  smaller  size,  A,  also  of  brass,  which  is  placed  exact- 


SPECIFIC     INDUCTIVE     CAPACITY. 


123 


ly  concentric  with  it.  The  interval  between 
these,  0  o,  may  be  occupied  by  any  substance, 
as  air,  or  glass,  or  sulphur  ;  and  then  the  central 
sphere  being  insulated  from  the  outer  by  the 
shell-lac  column  b,  and  having  been  excited  from 
+he  machine  through  the  ball  and  wire  B,  the 
uter  one  is  uninsulated,  and  the  whole  becomes 
a  Leyden  jar,  in  which  the  material  may  be  va- 
ried at  the  will  of  the  experimenter.  By  means 
of  the  tube  and  stopcock  /  J,  the  air  in  o  o  may 
be  removed,  and  any  other  gas  substituted  for  it.  ^j 
The  outer  sphere  opens  at  b  in  two,  so  that 
melted  sulphur  or  shell-lac  may  be  poured  in  to 
form  the  inductive  medium. 

When  the  internal  sphere  is  excited  always 
to  the  same  degree,  the  charge  of  the  external 
coating  should  be  the  same,  no  matter  what 
might  be  the  nature  of  the  intervening  substance, 
if  the  action  took  place  simply  at  a  distance,  after 
the  manner  of  gravitation.  But  this  is  not  the 
case.  With  the  same  internal  charge,  the  exci- 
tation of  the  external  sphere  was  found  to  be, 
that  with  air  being  100,  with  shell-lac  150,  with 
flint  glass  176,  and  with  sulphur  224.  In  these  cases,  therefore, 
the  molecular  excitation  was  transmitted  in  proportion  to  these 
numbers,  which  express,  therefore,  the  degree  of  excitation  that  a 
common  amount  of  inductive  influence  is  able  to  produce  in  masses 
of  these  bodies.  All  gases,  no  matter  how  different  in  chemical 
properties  and  constitution,  even  though  the  temperature  and  press- 
ure do  not  remain  the  same,  possessed  the  same  specific  inductive 
capacity  as  air. 

This  principle  is  farther  shown  in  an  interesting  manner  by  the 
fact  that  the  induction  is  not  exercised  only  in  ^ 

the  straight  line  connecting  the  solid  inducing  @ 

and  induced  bodies,  but  that  at  every  intervening  @ 

point  there  is  a  lateral  action  exercised  by  the      ©@  @ 

interposed  molecules  of  air,  which  may  be  them-  a\  W 

selves    considered    centres    of  inductive   force.      V  / 

Thus,  if  a  cylinder,  a,  of  shell-lac  be  excited  by- 
friction,  and  a  brass  hemisphere.  A,  placed  on  top 
of  it,  the  intensity  of  the  induced  electricity  will 


be  found  to  depend  not  merely  on  the  distance  d 
from  the  excited  source  and  the  nature  of  the 
interposed  material,  but  to  be  more  energetic 
in  certain  positions  in  the  air,  as  when  the  car- 
rier ball  of  Coulomb's  torsion  electrometer  was 
placed  at  o,  than  when  it  was  lower  or  higher  at 
n  or  p. 

Faraday  has  been  led  by  his  experiments  to  conclude  that  the 
difference  between  conducting  and  non-conducting  bodies  is,  that 
the  former  assume  with  exceeding  rapidity,  under  an  inductive  in- 
fluence, this  condition  of  molecular  excitation,  and  hence  appear  to 


124    OTHER    CAUSES    OF     STATICAL     EXCITATION. 

allow  the  electricity  to  pass  actually  and  instantly  through  their 
substance,  whereas,  in  reality,  it  is  only  that  the  separation  and  re- 
composition  of  the  electricities  of  the  chain  of  molecules  has  been 
so  accomplished.  They  lose  also  this  condition  as  soon  as  the  ex- 
citing cause  has  been  removed,  whereas  non-conductors,  when  their 
particles  have  acquired  electrical  excitation,  remain  in  that  state  of 
tension  for  a  certain  time.  Thus,  if  the  internal  and  external  coat- 
ings of  a  Leyden  jar  were  connected  by  a  metallic  wire,  the  induct- 
ive action  would  be  propagated  immediately  across  it  j  but  the  in- 
stant that  the  source  of  the  excitation  was  removed,  the  electrici- 
ties of  the  two  coatings  would  recombine,  from  the  facility  with 
which  the  molecules  of  the  wire  can  assume  the  inverse  condition. 
But  with  an  interposed  plate  of  glass  the  result  is  different ;  the  in- 
ductive action  is  propagated  equally,  but  more  slowly ;  and  that  it 
is  the  particles  of  the  glass  that  really  produce  the  charge  by  their 
excitation,  is  demonstrated  by  the  fact  that  the  metallic  coatings 
may  be  removed,  and  yet  the  accumulated  electricities  be  not  dis- 
turbed ;  the  tin  foil  serving  only  to  discharge  at  the  same  moment 
every  particle  of  the  glass,  as  if  a  wire  had  been  individually  applied 
to  each.  That  the  induction  has  acted  on  the  substance  of  the 
glass  explains  also  the  peculiarity  of  what  is  called  the  secondary 
or  residual  charge.  When  the  particles  at  the  surface  have  been 
discharged,  they  are  acted  on  by  the  deeper  molecules  which  are 
still  excited,  and  hence  acquire  a  second  inductive  charge  ;  and  with 
thick  glass,  and  particularly  with  bodies  which  do  not  insulate  quite 
so  well  as  glass,  there  may  be  even  a  third  or  a  fourth  charge  of 
this  kind. 

Conduction  is  therefore  only  the  highest,  most  intense,  and  most 
rapid  form  of  induction ;  and  it  appears  from  Faraday's  investiga- 
tions that  the  permanent  excitation  of  an  electrified  body  has  its 
origin  also  in  the  inductive  influence  of  the  bodies  that  are  around. 

The  source  of  the  electricity  evolved  by  the  electrical  machine 
cannot  be  considered  as  being  positively  known.  Wollaston  in- 
stituted a  series  of  experiments,  by  which  it  appeared  to  be  demon- 
strated that  there  was  no  electricity  evolved  except  where  chemical 
combination  took  place,  and  the  superior  power  given  to  the  ma- 
chine by  the  amalgam  of  tin  and  zinc  being  spread  upon  the  rubber 
was  supposed  to  verify  this  idea.  These  experiments  of  Wollaston 
have  been  latterly  repeated  with  great  care  by  Peltier,  and  with 
different  results ;  he  found  that  the  electricity  evolved  was  propor- 
tional only  to  the  amount  of  friction,  and  was  the  same  under  va 
rious  circumstances  of  liability  to  the  presence  or  absence  of  chem 
ical  action  of  the  materials  rubbed.  It  is  therefore  likely  that,  at 
least,  the  electricity  of  the  machine  may  be  generated  by  the  sim- 
ple molecular  derangement  and  vibration  which  friction  necessarily 
produces  ;  and  this  view  is  very  much  supported  by  the  undeniable 
fact,  that  by  other  agencies  purely  molecular,  where  no  trace  of 
chemical  action  can  be  pretended,  the  same  form  of  statical  elec- 
tricity may  be  produced. 

In  almost  all  cases  where  the  particles  of  bodies  are  suddenly  and  violently  dis- 
arranged, the  separated  surfaces  are  found  to  be  electrically  excited  ;  for  instance, 
if  a  piece  of  mica  be  torn  into  thin  leaves,  these  are  powerfully  electric.  In  many 
mineral  substances  a  change  of  temperature  causes  a  manifestation  of  electrical 


ATMOSPHERIC     ELECTRICITY.  ^    125 

polarity  in  a  very  remarkable  degree ;  thus,  if  a  long  prism  of  tourmaline  be  heater?, 
one  extremity  becomes  positive  and  the  other  negative  ;  when  the  temperature  at- 
tains its  highest  point  and  becomes  stationary,  all  symptoms  of  electricity  disappear, 
but  on  cooling  they  return ;  in  the  inverse  order,  however,  the  end  which  had 
been  positive  becoming  negative,  and  so  on.  In  this  case  it  appears  as  if  the  par- 
ticles, in  the  internal  motion  which  the  expanding  force  of  heat  produces  in  them, 
acquired  the  same  condition  of  polarity  as  they  would  have  done  by  an  external 
friction.  If  the  expansive  effect  of  heat  and  the  consequent  change  of  position 
among  the  particles  of  the  tourmaline  had  been  the  same  throughout,  there  would 
have  been  no  reason  for  electrical  disturbance;  but  this  mineral,  and  some  others 
which  likewise  become  electric  on  being  heated,  as  boracite,  are  exceptions  to  the 
general  law  of  crystalline  symmetry,  and  in  other  respects,  as  with  regard  to  light, 
indicate  a  kind  of  structure  which  is  very  complex  and  peculiar.  In  such  cases,  an 
internal  friction  by  the  action  of  expansion  on  the  unsymmetrically  situated  mole- 
cules of  the  crystal  is  the  origin  of  the  electrical  excitation. 

The  source  of  statical  electricity,  which  is  of  the  greatest  importance  in  nature 
from  the  universahty  of  its  action,  is  that  of  change  of  state  of  aggregation.  When 
any  body  passes  from  the  liquid  to  the  solid,  or  from  the  liquid  to  the  vaporous  con 
dition,  or  in  the  reverse  order,  from  being  solid  or  being  gaseous  becomes  liquid,  dis- 
turbance of  the  previous  electrical  equilibrium  results.  Thus,  if  a  little  melted  sul- 
phur be  poured  into  a  glass,  or  if  melted  tallow  or  resin  be  poured  out  on  a  me- 
tallic plate,  the  bodies  after  sohdification  will  be  found  excited.  If  a  cup  of  watei 
be  placed  on  the  plate  of  the  electroscope,  and  a  red-hot  ball  of  metal,  or  even  a 
red-hot  cinder,  be  dropped  into  it,  the  gold  leaves  immediately  diverge  by  the  influ- 
ence of  the  negative  excitement  which  is  assumed  by  the  water  which  remains, 
and  which  communicates  itself  to  the  metallic  cup  and  to  the  instrument ;  if  the 
gush  of  vapour  had  been  allowed  to  impinge  on  the  plate  of  another  instrument^  it 
would  have  shown  excitation  by  positive  electricity.  This  last  is  one  of  the  mj»st 
abundant  sources  of  electricity ;  for  as  at  all  ordinary  temperatures  evaporation 
takes  place  from  the  surface  of  all  the  water  of  the  globe,  and  the  vapour  produced, 
carrying  with  it  the  prodigious  quantity  of  positive  electricity  which  is  thus  set  free, 
mixes  with  the  air,  our  atmosphere  is  almost  continually  in  an  electrical  condition, 
generally  positive,  but  at  some  times,  from  interfering  causes,  negative.  The  great 
body  of  vapour,  when  condensed  by  the  more  elevated  and  colder  regions  of  the 
air,  collects  into  the  peculiar  condition  which  constitutes  a  mass  of  cloud,  and 
therein  is  thus  concentrated  all  the  electricity  evolved  by  evaporation  at  the  sur- 
face. The  clouds  are,  therefore,  intensely  electric  ;  and  when  attracted  by  indue 
tion  to  each  other,  or  to  some  prominent  object  on  the  earth,  as  a  mountain-peak 
or  an  elevated  building,  the  discharge  and  neutralization  of  the  electricities  take 
place  with  the  brilliancy  and  destructive  agency  of  the  lightning,  while  the  report, 
re-echoed  from  the  surfaces  of  the  remaining  clouds,  or  by  the  sides  of  the  adja- 
cent mountains,  produces  the  effect  upon  the  ear  of  the  continuous  rattle  of  the 
thunder. 

There  is  no  doubt,  however,  but  that  in  many  cases  of  chemical  combination 
and  decomposition  electricity  in  its  statical  form  may  be  evolved  ;  thus  Pouillet 
proved  decisively,  that  when  charcoal  is  burned,  the  carbonic  acid  which  passes  ofT 
is  in  a  state  of  positive  excitement,  and  the  residual  mass  of  charcoal  becomes  neg- 
atively charged.  When  hydrogen  burns  in  air,  the  vapour  of  water  carries  off  the 
positive  electricity,  while  the  negative  fluid  distributes  itself  on  the  hydrogen  re- 
maining, and  the  vessel  from  which  it  issues.  There  is  thus,  in  the  combustion 
of  our  ordinary  fuel,  a  vast  source  of  the  electricity  of  our  atmosphere,  in  addition 
to  that  evolved  by  water  in  evaporating ;  and  it  has  been  found  that  the  evaporation 
of  a  saline  solution,  as  sea- water,  produces  a  much  greater  degree  of  excitement 
than  when  the  water  is  completely  pure,  owing,  perhaps,  to  the  destruction  of  the 
condition  in  which  the  salt  and  water  had  been  united.  The  evolution  of  statical 
electricity  occurs,  also,  when  the  chemical  action  is  of  a  much  more  complex  and 
obscure  kind ;  thus,  in  the  growth  of  a  seedling  plant,  the  carbonic  acid  which  it 
evolves  is  in  a  positively  excited  state,  and  the  substance  in  which  the  seed  is  im- 
bedded becomes  negative.  It  would  appear,  however,  that  frequently  electricity 
that  had  been  imagined  to  arise  from  the  chemical  relation  of  the  bodies  brought 
into  contact,  arose  from  their  merely  mechanical  action  on  each  other ;  thus  the 
electricities  produced  by  sifting  lime  and  oxalic  acid  together  on  the  plate  of  the 
electrometer  are  produced. 

The  mere  contact  of  bodies  has  been  supposed  sufficient  to  evolve  electricity  upon 


126  DYNAMICAL     ELECTRICITY. 

their  surface.  The  trace  of  excitation  in  such  experiments  is  so  small,  and  dimin- 
ishes so  much  in  proportion  as  care  is  taken  to  avoid  friction  and  other  causes, 
that  we  may  consider  contact  as  being  in  itself  without  power. 

The  remarkable  characteristic  of  statical  electricity  developed  by  any  of  these 
methods,  is  the  amazing  energy  of  its  action  on  bad  conductors,  and  on  the  best 
conductors  if  their  substance  be  not  of  sufficient  mass  to  give  it  free  passage  from 
one  point  to  another  ;  while  it  is  only  with  difficulty  that  we  can  obtain,  by  means 
of  it,  the  slightest  chemical  decomposition.  In  the  language  of  the  theory  of  elec- 
trical fluids,  the  electricity  is  developed  in  exceedingly  small  quantities  by  friction 
or  change  of  aggregation,  and  hence  can  perform  but  feebly  such  offices  as  chemi- 
cal decomposition,  which  depend  on  the  quantity  that  passes  in  a  given  time ;  but 
this  small  quantity  is  gifted  with  immense  tension ;  the  few  molecules  which  be- 
come polarized  are  so  to  an  intense  degree,  and  the  attractive  and  repulsive  forces 
which  they  exert  are  then  sufficient  to  cause  the  greatest  mechanical  effects 

SECTION  II. 
OF   DYNAMICAL   ELECTRICITY. 

The  sources  from  which  electricity  is  derived  in  a  continually 
circulating  form,  so  that  its  properties  shall  result  from  its  uninter- 
rupted motion,  must  necessarily  consist  in  arrangements  from  which 
all  insulating  substances  are  to  be  carefully  excluded.  In  statical 
electricity,  the  connexion,  by  a  conducting  medium,  of  the  opposite 
extremities  of  an  inductively  excited  body,  caused  all  electrical  in- 
dications instantly  to  disappear,  while  that  kind  of  connexion  is  ab- 
solutely necessary  to  the  continuous  flowing  of  the  electricity  which 
constitutes  its  dynamical  condition  ;  and  when  the  conducting  circle 
is  broken  by  the  intervention  of  the  smallest  portion  of  insulating 
matter,  either  all  electrical  excitation  ceases,  or  at  most  a  feeble 
trace  of  it  remains,  with  the  properties  which  characterize  its  stat- 
ical condition. 

1st.  Electricity  thus  circulating  through  conductors  is  found 
naturally  existing  in  those  substances  which  thereby  possess  mag- 
netic properties.  There  is  every  reason  to  believe  that  the  native 
loadstone,  as  well  as  all  our  artificial  steel  and  iron  magnets,  are 
closed  circles  of  dynamical  electricity,  set  in  motion  by  forces 
which  depend  on  the  chemical  and  mechanical  constitution  of  these 
bodies.  2d.  When  any  closed  conducting  circuit  is  at  the  same 
time  unequal  in  mechanical  constitution  and  in  temperature,  so  that 
the  current  may  pass  more  easily  through  one  point  than  another, 
such  a  current  is  generated,  flowing  from  the  portion  where  the  ob- 
stacle is  greatest  to  that  part  where  it  is  least.  3d.  When  sub- 
stances capable  of  mutual  chemical  combination  or  decomposition 
act  on  one  another,  there  is  a  current  of  electricity  produced.  In 
the  case  of  simple  union  or  double  decomposition,  the  circle  is  in- 
ternally closed,  like  that  of  a  steel  magnet ;  but  where  there  is  sim- 
ple decomposition  or  replacement,  the  current  may  be  directed 
through  any  kind  of  circuit ;  and  thus  constituting  the  most  impor- 
tant branch  of  dynamical  electricity,  is  called  Galvanism  or  Voltaism, 
from  the  names  of  its  most  illustrious  investigators. 

4th.  By  means  of  organized  structures,  of  which  it  is  only  lately, 
by  the  researches  of  Matteucci,  that  the  true  nature  and  functions 
have  become  known,  certain  fishes  possess  the  power  of  transmit- 
ting a  current  of  electricity  across  even  imperfect  conductors,  and 
employ,  instinctively,  the  efl^ect  of  this  current  upon  the  living 
frame  of  smaller  animals  in  order  to  obtain  them  for  food.     The 


GALVANIC     ELECTRICITY.  127 

identity  of  the  electricity  from  this  animal  origin,  with  the  fluid  of 
the  other  dynamic  sources,  has  been  completely  proved,  particular 
ly  by  Faraday  j  and  as  the  question  of  the  anatomical  structure  of 
the  electric  organ,  and  of  the  peculiar  part  of  the  brain  from  which 
the  electric  nerves  arise,  interests  the  physiologist  rather  than  the 
chemist,  I  shall  merely  state  that  the  current  so  obtained  possesses 
all  the  properties  ihat  will  be  described  as  characterizing  galvanic 
electricity  of  very  high  tension,  and  allude  no  farther  to  it. 

To  the  chemist,  the  electricity  of  the  Galvanic  or  Voltaic  battery 
is  the  most  interesting  of  all  the  forms  which  this  agent  may  as- 
sume, from  the  intimate  relation  which  exists  between  it  and  the 
force  by  which  the  elements  of  bodies  are  bound  together  in  chem- 
ical combination.  To  it,  therefore,  I  shall  especially  direct  atten- 
tion, and  consider  the  remaining  sources  only  so  far  as  the  electri- 
city which  they  yield  may  differ  from  it.  I  shall  endeavour,  also, 
to  consider  it  only  as  characterizing  bodies  by  their  properties  of 
exciting  the  current,  or  of  conducting  it  when  excited,  deferring 
the  important  topic  of  the  action  of  the  current  upon  compound 
bodies  until  the  nature  of  chemical  affinities  has  been  described. 

Galvanic  Electricity, — The  manner  in  which  this  form  of  excita- 
tion occurs  may  be  very  simply  shown.  If  a  slip  of  perfectly  pure 
zinc  be  partly  immersed  in  a  cup  of  dilute  muriatic  acid, 
this  last  remains  totally  without  action  on  it,  and  there 
is  no  appearance  of  electrical  disturbance  5  but  if  a  slip 
of  copper  be  introduced,  which  touches  the  zinc  at  C, 
out  of  the  liquid,  active  decomposition  of  the  muriatic 
acid  begins,  the  chlorine  combining  with,  and  dissolving 
the  metallic  zinc,  and  the  hydrogen  making  its  appearance  under  the 
form  of  minute  bubbles  on  the  surface  of  the  copper.  At  the  same 
moment  a  remarkable  state  of  electrical  excitation  is  produced,  in 
which  the  zinc  resembles  a  body  to  which  negative  electricity,  in  a 
state  of  exceedingly  low  tension,  is  uninterruptedly  supplied,  while 
an  equal  quantity  of  the  positive  fluid  flows  along  the  copper,  and 
these,  uniting  at  the  point  of  contact,  produce  the  effects  which  are 
spoken  of  as  those  of  the  electric  current,  the  passage  of  which  may 
be  rendered  evident  in  a  great  variety  of  ways. 

The  precise  manner  in  which  the  electrical  excitement  is  here 
produced,  may  be  explained  sufficiently  well  without  involving  any 
consideration  of  the  theory  of  chemical  decomposition,  which  at 
the  present  moment  would  require  a  knowledge  of  principles  that 
have  not  been  as  yet  described.  We  may  suppose,  simply,  that  the 
chemical  relations  of  the  zinc  and  muriatic  acid  are  such,  that  when 
placed  in  contact  they  mutually  induce  on  each  other  a  development 
of  electricity :  that  part  of  the  zinc  which  is  immersed  becoming  -}-, 
and  that  out  of  the  acid  — ,  while  the  molecules  of  the  acid  near  the 
zinc  become  - — ,  and  the  general  mass  of  the  fluid  obtains  -\-  excita- 
tion ;  the  +  electricity  of  the  zinc  being,  however,  balanced  between 
the  fluids  of  its  own  mass  and  of  the  acid,  and  the  —  fluid  of  the 
acid  being  in  equilibrium  between  the  +  fluids  of  the  zinc  and  of 
its  own  particles,  it  results  that  this  condition  of  induced  excitation 
may  remain  for  any  length  of  time  without  increasing  or  diminishing 
in  intensity,  the  apparptus  being  in  the  condition  of  a  very  feebly 
charged  Leyden  jar :  and  on  applying  the  slip  of  copper  by  which 


tk 


128 


SIMPLE     GALVANIC     CIRCLES. 


the  excited  surfaces,  the  zinc  and  acid,  are  placed  in  communication, 
the  negative  electricity  of  the  zinc  unites  with  the  positive  of  the 
copper,  whether  by  direct  translation  or  by  inductive  action,  and  the 
positive  electricity  of  the  liquid  unites  with  the  negative  of  the  cop- 
per to  produce  neutralization  j  at  the  same  time  the  +  of  the  zinc 
and  the  —  of  the  acid  combine.  As,  on  the  theory  of  Franklin,  the 
single  electric  fluid  is  supposed  to  pass  from  the 
body  which  is  positively  to  the  body  which  is  neg 
atively  excited,  it  is  usual  to  imagine  this  exchange 
of  electricities  to  take  place  by  a  current,  which  in 
this  case,  as  shown  by  the  arrows  in  the  figure,  is 
from  the  copper  to  the  zinc  at  the  superior  junction, 
but  from  the  zinc  to  the  copper  in  the  acid  under- 
neath. At  every  moment,  according  as  the  neutral 
ization  of  the  electricities  is  effected,  the  system  is 
competent  to  generate  new  quantities,  and  hence  the 
analogy  of  the  weakly-charged  Leyden  jar,  noticed  above,  does  not 
completely  hold  ;  for,  to  be  accurate,  it  would  require  the  jar  to  pos- 
sess a  power  of  charging  itself  as  rapidly  as  it  could  be  discharged 
The  passage  of  the  current  is  accompanied  by  the  solution  of  tho 
zinc  and  the  liberation  of  the  hydrogen.  This  hydrogen  accompa 
nies  the  positively  electrified  molecules  of  the  acid  across  the  fluid, 
«ind  is  discharged  under  the  form  of  gas  upon  the  surface  of  the 
copper  plate. 

The  essential  elements  of  an  arrangement  by  which  a  current  of 
electricity  may  be  produced  are,  therefore,  first,  two  bodies,  one 
simple  and  one  compound,  which  act  chemically  upon  one  another 
in  such  a  way  as  that  the  simple  element  shall  be  substituted  for  a 
constituent  of  the  other,  which  shall  be  expelled  ;  and,  second,  a 
conducting  substance,  which  is  indifferent  in  a  chemical  point  of 
view,  and  only  furnishes  a  route  for  the  fluids  of  the 
actual  elements  to  recombine  continually  with  each 
other.  In  the  example  given  just  now,  this  conduct- 
or was  a  slip  of  copper  ;  but  it  may  be  of  any  form,  or 
almost  any  substance  5  thus,  as  in  the  figure,  a  wire 
may  be  soldered  to  the  end  of  each  slip,  and  on  bring- 
ing these  wires  into  contact  at  X,  the  current  passes 
precisely  as  if  the  contact  of  Z  with  C  had  been  direct. 
Such  an  arrangement  is  termed  a  simple  circle. 
It  is  not  even  necessary  that  the  conductor  should  be  solid  or  me- 
tallic ;  it  is,  indeed,  only  for  convenience  that  the  ordinary  conduct- 
ing plates  and  wires  are  metallic.  Thus,  in  the  figure, 
A  Z  W,  a  plate  of  zinc  is  in  contact  on  the  one  side  witk 
muriatic  acid,  A,  and  on  the  other  with  water,  W,  to 
which  a  better  conducting  power  has  been  given  by  dis- 
solving in  it  a  little  common  salt.  The  current  is  then  es- 
tablished, being  from  the  conductor  to  the  zinc,  and  from 
the  zinc  to  the  acid,  precisely  as  in  the  former  instances. 
The  passage  of  the  current  under  these  various  circumstances 
may  be  shown,  and  also  that,  for  its  origin  and  transfer,  metallic 
communication  between  the  plates  Z  and  C  is  not  necessary,  by 
a  very  simple  experiment.     If  the  slip  of  zinc  be  bent,  as  in  B,  and 


f 

Z 

^ 

A. 

GALVANIC     AND     CHEMICAL     ACTION. 


129 


n. 


f^^\ 


\l 


a  bit  of  paper  moistened  with  iodide  of  potassium  be  laid 
upon  it,  and  the  wire  from  A  be  then  brought  to  touch  the  k 
upper  surface  of  the  moistened  paper,  the  current  passes  in  A 
the  direction  of  the  arrow,  and  iodine  is  evolved  at  the 
point  of  contact  of  the  wire.  If  the  surface  of  the  paper 
next  the  zinc  plate,  B,  be  examined,  it  will  be  found  to  be 
alkaline,  from  free  potash.  Thus  the  chemical  action  of 
the  current,  which  will  hereafter  assume  so  important  a 
position,  may  here  be  simply  used  as  a  test  of  its  having 
passed. 

The  direction  of  the  current  depends  upon  the  nature  of  the  chem- 
ical action  which  is  produced  at  the  period  of  its  passage,  and  on 
this  principle  is  founded  one  of  the  most  cogent  and  reasonable  ar- 
guments in  favour  of  the  idea  that  the  current  is  produced  by  the 
chemical  decomposition,  and  not  by  the  contact  of  the  metals,  as 
has  been  maintained.  Thus,  if  a  slip  of  iron  and  a  plate  of  copper 
be  immersed  in  muriatic  acid,  the  action  is  altogether  on  the  iron, 
and  the  current  passes  from  the  copper  to  the  iron  at  the  point  of 
contact.  But  if  the  metals  be  immersed  in  a  strong  solution  of  am- 
monia, which  acts  upon  the  copper,  but  not  upon  the  iron,  the  cur- 
rent is  produced  in  the  reverse  direction.  If  persulphuret  of  lime, 
dissolved  in  water,  be  used  as  the  exciting  fluid  with  iron  and  cop- 
per, the  current  is  from  the  copper  to  the  iron  through  the  fluid ; 
but  on  using  zinc  and  copper  with  the  same  fluid,  the  direction  of 
the  current  is  reversed;  in  the  first  case  the  copper,  and  in  the  last 
the  zinc,  is  acted  on:  with  acid  solutions  the  copper  would  have  es- 
caped action,  and  the  current  would  be  in  both  cases  from  the  iron 
or  zinc  to  it,  through  the  liquid. 

It  thus  appears  that  the  relation  between  the  current  and  the 
chemical  action  is  of  the  most  intimate  nature  possible  ;  the  one,  as 
Faraday  and  others  have  decisively  shown,  cannot  exist  in  such  ar- 
rangements without  the  other,  and  the  nature  and  tendencies  of  one 
determine  the  power  and  the  direction  of  the  other  ;  for  the  quantity 
of  electricity  which  is  set  in  motion  in  such  an  arrangement  depends 
strictly  on  the  amount  of  chemical  decomposition  which  occurs  in 
the  liquid  element,  and  is  simply  proportional  to  it. 

It  is  usual  to  arrange  the  various  bodies  in  a  list  with  relation  to  a  fluid,  in  which, 
if  they  be  immersed  and  brought  to  touch  outside,  a  current  is  generated  from  that 
of  the  two  metals  which  stands  highest  in  the  scale  to  that  which  is  below ;  tlie 
current  through  the  fluid  is,  of  course,  in  the  opposite  direction.  The  metals  ar- 
range themselves,  however,  very  differently  with  different  fluids,  according  to  their 
liability  to  chemical  action  from  them,  as  may  be  seen  in  the  following  table  • 


Dilute  Nitric 

Strong  Nitric 

Muriatic   Acid. 

Soiuiinn  of 

Yellow  Hydrosul- 

Acid. 

Acid. 

Caustic  Potash. 

phuret  of  Hotassiuii:. 

Platinum. 

Platinum. 

Platinum. 

Platinum. 

Platinum. 

Silver. 

Nickel. 

Antimony. 

Silver. 

Iron. 

Copper. 

Silver. 

Silver. 

Nickel. 

Nickel. 

Antimony. 

Antimony. 

Nickel. 

Copper. 

Bismuth. 

Bismuth. 

Copper. 

Bismuth. 

Iron. 

Antimony. 

Nickel. 

Bismuth. 

Copper. 

Bismuth. 

Lead. 

Iron. 

Iron. 

Iron. 

Lead. 

Silver. 

Tin. 

Tin. 

Lead. 

Antimony. 

Tin. 

Lead. 

Lead. 

Tin. 

Cadmium. 

Cadmium. 

Cadmium. 

Zinc. 

Cadmium. 

Tin. 

Copper. 

Zinc. 

Cadmium. 

Zinc. 

Zinc. 

Zinc. 

R 


130        PRINCIPLE     OF     ELECTROTYPE     COPYING. 

At  the  head  of  each  column  is  placed  the  name  of  the  exciting  fluid ;  on  taking 
any  two  of  the  metals  of  the  list  beneath,  and  making  them  the  solid  elements  of 
the  circle,  the  current  is,  at  the  point  of  contact,  from  the  upper  to  the  lower,  and 
is  more  powerful  in  proportion  as  the  metals  are  farther  separated  from  one  another 
in  the  list ;  thus,  with  dilute  nitric  acid  and  with  solution  of  caustic  potash,  the 
most  powerful  current  is,  after  platinum,  by  silver  and  zinc ;  with  muriatic  acid  by 
antimony  and  zinc,  and  with  persulphuret  of  potassium  with  iron  and  zinc. 

If  the  metals  in  contact  with  the  exciting  hquid  be  such  as  that  one  is  totally 
without  chemical  action  on  it,  it  serves  only  as  a  means  of  mechanically  transmit- 
ting the  inductive  force,  and  the  current  is  simply  due  and  is  proportional  to  the 
electricity  evolved  by  the  action  of  the  acid  on  the  other.  But  if  both  metals  be 
such  that  either  would  act  upon  the  acid  if  by  itself,  and  thus  produce  excitation, 
as  when  zinc  and  copper  are  placed  in  dilute  nitric  acid,  then  the  molecules  of  acid 
are  submitted  to  two  polarizing  forces  in  opposite  directions,  which,  if  equal,  would 
exactly  neutralize ;  but  in  practice  they  are  not  equal,  and  a  current  is  produced 
proportional  to  their  difference.  Hence,  the  more  nearly  the  metals  resemble  each 
other  in  their  chemical  relations  to  a  given  liquid,  the  weaker  is  the  current  they 
produce  ;  but,  though  acting  similarly  to  one  hquid,  they  may  be  oppositely  related 
to  another,  with  which,  therefore,  they  become  a  source  of  powerful  excitation. 
Thus  copper  and  zinc,  being  both  acted  on  violently  by  sulphuret  of  potassium, 
generate  but  a  feeble  cun-ent,  wtiile  with  dilute  acids,  which  act  very  differently 
on  each,  the  current  is  very  powerful ;  and  thus  platinum,  which  is  inattackable  by 
ahnost  all  liquids,  forms  the  best  possible  element  in  every  instance. 

The  metal  which  is  used  as  the  conducting  medium  conducts  by  having  its  natu- 
ral polarity  inverted  ;  and  hence,  in  place  of  a  disposition  to  combine  with  the  oxy- 
gen or  chlorine  of  the  liquid,  it  would,  if  already  combined,  abandon  it ;  hence  this 
metal  remains  clean  and  bright.  On  this  principle  was  founded  the  mode  of  protect- 
ing the  copper  sheathing  of  ships,  by  attaching  small  portions  of  iron  of  about  j^ 
of  the  surface ;  the  chlorine  of  the  salt  in  the  sea-water  being  thus  transferred  to 
the  iron,  and  the  copper,  in  place  of  becoming  covered  with  the  green  rust  of 
oxychloride  of  copper,  remaining  completely  bright.  This  process  succeeded  in 
practice  somewhat  too  well ;  for  the  negative  elements  of  the  sea-water  being 
transferred  to  the  iron,  the  positive  bases  present,  lime  and  magnesia,  were  depos- 
ited upon  the  copper,  and  thus  affording  points  of  adhesion  for  marine  plants  and 
shell-fish,  caused  the  bottoms  of  the  vessels  to  become  so  foul  as  materially  to  in- 
jure their  saihng  powers.  The  process  at  present  so  extensively  employed,  of  fix- 
ing a  layer  of  zinc  upon  iron  surfaces,  acts  in  protecting  them  from  rust  in  the 
same  manner. 

This  transfer  of  the  elemeitts  of  the  exciting  liquids  has  become  recently,  in  the 
hands  of  Spencer,  the  basis  of  one  of  the  most  beautiful  and  important  of  the  ap- 
plications of  science  to  the  arts.  If  one  of  the  exciting  liquids  be  a  solution  of  sul- 
phate of  copper,  as  in  Daniell's  battery  (page  136),  the  metallic  copper  which  sep- 
arates is  deposited  upon  the  surface  of  the  plate  to  which  the  current  passes  in  the 
liquid,  and  there  is  formed  a  layer  of  metal,  which  may  be  obtained,  by  slow  and 
long-continued  action,  as  dense  and  homogeneous  as  the  best  hammered  copper. 
Any  prominences  or  depressions,  even  a  scratch  of  a  pin,  drawn  on  the  plate  on 
which  the  deposite  forms,  are  accurately  represented  on  its  internal  surface :  and  ii 
IS  only  necessary  to  use  as  the  negative  metallic  element  a  medal  in  relievo  or  in- 
tagho,  to  reproduce,  with  an  accuracy  equalling  the  powers  of  the  most  finished 
hand  or  machine,  the  finest  w^orks  of  art.  This  principle  has  been  shown  by  Mr. 
Spencer  to  be  applicable  to  the  copying  of  all  varieties  of  designs,  and  may  be  looked 
upon  as  the  most  important  means  of  facilitating  the  possession  of  works  of  art, 
and  thus  elevating  public  taste,  that  has  been  made  since  the  discovery  of  the  method 
of  transferring  engravings  to  any  number  of  steel  plates. 

The  electricity  which  is  evolved  by  the  chemical  action  of  such 
simple  circles  is  remarkably  different  in  its  characters  from  that 
form  which  has  been  described  as  its  statical  condition.  Although 
present  in  much  greater  quantity  than  can  be  developed  by  friction 
with  the  most  powerful  machines,  yet,  from  its  state  of  continued 
recombination,  it  cannot  acquire  intensity ;  it  hence  can  pass  only 
through  good  conductors  ;  pure  water,  which,  from  the  facility  with 
which  it  allows  of  the  passage  of  machine  electricity^  proves  the 


COMPOUND  VOLTAIC  CIRCLE 


131 


great  source  of  failure  and  uncertainty  in  our  experiments,  inter- 
cepts almost  completely  the  current  from  a  simple  circle,  and  the 
wires  which  are  used  to  effect  communication  may  be  touched  with 
the  fingers  without  any  tendency  to  lateral  shock  becoming  evi 
dent  j  and  yet  the  disproportion  in  quantity  between  the  fluid,  which 
bursts  through  the  strongest  insulating  bonds  of  our  apparatus,  or 
breaks  from  the  clouds,  devastating  forests,  as  the  lightning,  and 
that  which  passes  silently  across  the  wires  of  the  voltaic  circle,  is 
such  as  almost  to  surpass  belief.  By  actual  experiment,  the  im- 
mersion of  two  wires,  one  of  platina  and  the  other  of  zinc,  each 
0*06  inch  in  thickness,  to  a  depth  of  five  eighths  of  an  inch,  in  di- 
lute sulphuric  acid  for  three  seconds,  gave  as  much  electricity  as 
could  be  generated  by  thirty  turns  of  the  most  powerful  machine 
of  the  Royal  Institution.  Indeed,  Faraday  has  shown  that,  in  the 
current  which  passes  during  the  decomposition  of  a  grain  of  water, 
there  is  contained  more  electricity  than  in  the  brightest  flash  of 
lightning. 

If  the  metallic  elements  of  a  simple  circle  be  connected,  not  di- 
rectly by  metallic  contact  or  by  a  wire,  but  by  means  of  one  or  more 
other  similar  simple  circles,  interposed  in  the  course  of  the  current  o 
its  electricity,  it  is  not  at  all  interfered  with,  but  the  quantity  of  elec- 
tricity which  circulates  is  precisely  equal  to  what  is  generated  by 
the  chemical  action  Avhich  takes  place  in  each  cell.  For,  consider- 
ing the  circle  of  four  cells,  represented  in  the  figure,  consisting  of 


copper  and  zinc  plates,  acted  upon  by  muriatic  acid,  the  copper  of 
each  cell  discharges  its  positive  electricity  upon  the  negative  fluid 
of  the  zinc  in  the  adjoining  cell,  and  hence  there  is  neutralization 
of  effect  at  the  points  a,  6,  and  c,  and  it  is  only  the  amount  of  elec- 
tricity liberated  upon  the  copper  and  zinc  plates  in  the  terminal 
cells  that  passes  along  the  wires,  and,  recombining  at  d,  produces 
the  phenomenon  of  the  current ;  but  this  is  the  same  quantity  as 
should  be  evolved  by  any  one  of  these  simple  cells  by  itself,  and 
hence  the  remarkable  result,  which  has  been  fully  demonstrated  by 
experiment,  that  no  matter  how  we  may  increase  the  number  of  the 
elements  of  a  galvanic  circle,  the  quantity  of  electricity  passing  in 
the  current  is  equal  only  to  that  evolved  by  a  single  cell.  If  the 
chemical  action  be  not  of  the  same  energy  ip.  all  the  cells,  there 
passes  little  more  electricity  than  what  is  generated  where  the  de- 
composition is  least  active  ;  for,  as  the  excess  would  have  to  pen- 
etrate through  the  liquid  conductor  in  all  the  cells,  the  obstacle  af- 
forded to  its  progress  is  so  great  that  it  is  almost  totally  absorbed. 
Although  the  increase  in  number  of  the  elements  ojf  the  galvanic 


182    RELATION     OF     INTENSITY     AND     QUANTITY. 


circuit  is  inefficient  towards  augmenting  the  quantity  of  electricity 
which  passes,  yet  it  changes  the  character  of  the  current  in  a  very 
remarkable  degree,  and  confers  upon  the  fluid  an  intensity  which, 
in  a  simple  circle  no  matter  of  what  magnitude,  it  never  can  possess. 
It  has  been  seen,  that  by  the  state  of  mutual  excitation  into  which  the 
zinc  and  acid  are  thrown  before  the  circuit  is  compileted,  the  inten- 
sity of  the  evolved  fluids  is  limited  to  that  which  will 
not  suffice  to  enable  the  excited  particles  of  acid  to  dis- 
charge themselves  upon  the  oppositely  excited  particles 
of  zinc  j  for  if  this  discharge  occurred,  all  should  be 
brought  back  to  the  neutral  condition.  Now,  if  there  be 
interposed  a  second  cell,  containing  an  equal  quantity  of 
the  same  liquid  as  the  first,  its  particles  must  be  brought  into  an 
equally  excited  state  before  discharge  can  occur ;  and  as  the  elec- 
tricity has  then  to  pass  through  a  bad  conductor  of  double  the 
length,  it  will  require  much  greater  intensity  to  penetrate  it.  The 
process,  in  virtue  of  which,  therefore,  the  electric  equilibrium  is  in 
the  first  instance  disturbed,  continues,  even  before  contact  is  made, 
until  the  intensity  accumulated  is  sufficient  to  propel  the  current 
across  the  interposed  retarding  liquid,  and  is  hence  proportional 
to  the  number  of  cells,  or,  as  it  is  usually  stated,  to  the  number  of 
pairs  of  plates.  The  peculiar  character  of  intensity  may  be  suppo- 
sed to  arise,  also,  from  the  electricity  generated  by  the  outside 
plates  obtaining  additional  velocity,  in  passing  across  the  intermedi- 
ate cells,  in  each  of  which  it  meets  an  equal  quantity  of  fluid  moving 
in  the  same  direction,  and  Wiose  motion  it  absorbs,  restoring  them 
to  rest,  and  being  thereby  hurried  itself  onward  in  proportion. 

1^6  intensity  of  the  electricity  which  is  thus  excited  is  very  slight,  even  where 
the  number  of  combinations  is  considerable ;  thus,  it  requires  a  series  of  at  least 
300  pairs  of  plates,  four  inches  square,  immersed  in  dilute  sulphuric  acid,  to  cause  a 
sensible  divergence  of  the  gold  leaves  of  the  most  delicate  electroscope.  It  is  only 
where  the  arrangement  involves  some  thousands  of  couples  that  electricity  is 
evolved  of  sufficient  tension  to  produce  a  spark  across  a  non-conductor,  such  as  that 
given  by  the  electrical  machine,  or  to  cause  any  of  those  attractive  and  repulsive 
motions  by  which  the  feeblest  form  of  statical  electricity  is  recognised  ;  to  obtain 
these  effects  also,  the  circuit  must  be  broken,  for  even  with  the  most  powerful  com- 
binations the  current  of  electricity  is  without  any  action  of  intensity.  Where,  how- 
ever, by  means  of  a  sufficient  number  of  elements,  intensity  has  been  given,  the 
quantity  of  electricity  which  accumulates,  and  the  quantity  of  chemical  action  from 
which  it  has  its  origin,  are  exceedingly  minute.  This  is  exemplified  in  the  dry  piles 
of  Zamboni,  the  form  in  which  electricity  may  be  considered  as  connecting  its  purely 
dynamical  and  properly  statical  conditions.  The  pile  of  Zamboni  contains  no  ap- 
parent liquid  element ;  it  consists  of  disks  of  gilt  paper,  and  of  exceedingly  thin  zinc 
foil,  laid  alternately  over  one  another,  to  the  number  of  from  five  to  tvventy  thousand, 

care  being  taken  to  turn  all  the  gilt  surfaces 
the  same  way.  These  are  enclosed  in  a  glass 
tube,  and  terminated  at  each  end  by  a  brass 
cap  with  a  pressure  screw.  The  paper  con- 
taining in  its  pores,  when  not  artificially  dried, 
a  small  quantity  of  water,  this  gradually  acts 
upon  the  zinc,  and  electricity  is  evolved,  which, 
from  the  great  obstacle  presented  to  its  recom 
bination  through  the  disks  internally,  and  by 
the  atmospheric  air  outside,  attains  a  degree 
of  intensity  so  high  that  it  acts  decidedly  upon 
the  electroscope,  as  shown  in  the  figure,  and 
is  amusingly  applied  to  produce  various  at- 
tractive and  repulsive  motions,  such  as  ringing 


volta's   theory    of    contact.  133 

bell->,  (Si-o. ;  for  there  being  a  continual  source  of  electricity  in  the  action  of  the 
moisture  of  the  paper  on  the  zinc,  these  phenomena  may  continue  manifested  for 
years  without  diminution. 

Such  a  dry  pile,  when  insulated,  shows  opposite  electrical  excitation  at  the  two 
extremities,  these  being,  however,  of  equal  force,  and  hence  producing  neutrality 
when  combined.  If,  therefore,  the  two  ends  of  a  dry  pile  be  connected  by  a  wire, 
the  electricities  which  had  accumulated  recombine,  and  the  pile  becomes  inert,  and 
requires  a  certain  time  before  it  can  recover  a  charge  equal  to  that  which  it  had 
lost.  When  the  pile  is  examined  at  a  distance  from  its  ends,  the  excitation  is  found 
to  be  less  powerful,  until  at  the  centre  it  is  exactly  neutral.  This  arises  from  the 
action  at  each  point  being  the  resultant  of  the  opposing  actions  of  the  two  extrem- 
ities, and  vanishing  at  the  centre  where  these  last  are  equal,  precisely  as  there  ex- 
ists a  neutral  place  upon  the  surface  of  any  body  inductively  excited  by  ordinary 
electricity.  If  the  pile  be  held  in  the  hand  by  one  extremity,  the  electricity  of^that 
end  is  dissipated,  and  the  other  end  becomes  capable  of  acting  more  powerfully 
upon  the  electroscope,  from  the  opposing  influence  being  removed. 

No  principle  has  ever  been  discovered  in  science  more  rich  in  consequences  than 
this  of  the  increase  of  tension  given  to  electricity  in  motion  by  the  connexion  of  a 
number  of  simple  galvanic  circles.  Hence,  deservedly,  the  instrument  so  formed 
has  obtained  the  name  of  the  Voltaic  pile.  It  has  enriched  chemistry  with  a  crowd 
of  important  substances  discovered  by  its  means,  and  has  led,  by  its  results,  to  the 
suggestion  of  the  most  plausible  theory  of  chemical  combination  that  has  been  as  yet 
proposed.  In  physical  science  it  became  the  origin  of  all  subsequent  improvement 
in  the  domain  of  electricity,  for  without  its  agency  it  is  hard  to  see  how  the  steps 
which  followed  could  have  been  made. 

The  form  in  which  the  Voltaic  pile  was  first  constructed  was  sim- 
ilar to  that  of  the  dry  pile  noticed  above.  The  disks  were  of  zinc 
and  silver  or  copper.  The  fluid  conductor,  which  was  rendered 
more  capable  of  acting  on  the  zinc  by  the  addition  to  it  of  some 
acid  or  of  common  salt,  was  imbibed  in  disks  of  common  cloth, 
which  were  interposed  between  every  pair  of  metallic  disks.  There 
were  thus,  copper-zinc,  acid,  copper-zinc,  acid,  copper-zinc,  and  so 
on  to  an  indefinite  extent.  It  is  a  peculiarity  of  this  instrument, 
which,  as  it  extends  to  many  forms  of  it  even  now  in  use,  and  afiects 
our  chemical  nomenclature  remarkably,  it  is  necessary  to  notice, 
that  the  current  in  the  connecting  wires  appears  to  be  in  a  direction 
opposite  to  that  described  in  the  battery  of  cells  of  page  131 ;  for 
the  outer  copper  plate  at  the  one  end,  and  the  outer  zinc  plate  at 
the  other,  having  no  communication  with  the  exciting  acid,  trans- 
mit the  current  merely  as  portions  of  the  attached  wires,  and  hence 
the  direction  of  the  current  is  in  appearance  from  the  zinc  to  the 
copper  end,  while  it  is  properly  the  copper  from  which  the  positive 
fluid  emanates,  and  it  is  the  negative  which  arises  from  the  zinc. 
This  diversity  had  its  origin  in  the  circumstance  that  the  theory  of 
the  pile  maintained  by  Volta,  and  even  at  the  present  moment  sup- 
ported by  some  illustrious  men,  ascribed  the  origin  of  the  electri- 
city not  to  the  action  of  the  acid  upon  the  zinc,  but  to  the  contact 
of  the  zinc  with  the  copper  ;  the  point  ^vhere  the  metals  touched 
being  supposed  to  be  a  continual  source  of  positive  electricity  to 
the  copper.  It  was  even  attempted  to  prove  this  by  soldering  to- 
gether plates  of  zinc  and  copper,  and  testing  their  electrical  condi- 
tion by  the  gold-leaf  condenser,  which  was  supposed  to  indicate  a 
permanent  state  of  excitation,  independent  of  all  fluid  or  chemically 
acting  media.  It  has  been  fully  proved,  however,  that,  according 
as  such  contact  experiments  are  made  with  increased  care,  the  re- 
sults become  less  evident  in  favour  of  that  theory.  Such  trials  tend 
to  show  the  evolution  of  minute  traces  of  statical  electricity,  where- 


134      VARIOUS    FORMS     OF     GALVANIC     BATTERIES. 


as  the  simple  galvanic  circle  is  characterized  by  the  great  quantity 
of  electricity  it  may  yield,  and  by  its  total  want  of  statical  intensity. 
Even,  therefore,  if  it  were  proved,  which  it  is  not,  that  the  mere 
contact  of  bodies  evolved  electricity  affecting  the  gold-leaf  electro- 
scope,  it  would  be  as  far  from  accounting  for  the  totally  different 
kind  of  electrical  excitement  by  which  the  galvanic  battery  is  cre- 
ated, as  it  would  be  from  giving  a  true  or  satisfactory  theory  of  the 
cause  of  magnetism. 

But  the  pretended  excitation  by  contact,  or  the  electromotor  force, 
as  it  was  termed  by  Volta,  must  be  carefully  distinguished  from  the 
capability  of  inductive  excitement,  which  bodies  capable  of  chemi- 
cal action,  as  a  slip  of  zinc  and  muriatic  acid,  mutually  confer  upon 
each  other. 

This  last  arises  from  the  possible  substitution  of  the  zinc  for  the 
hydrogen  of  the  acid,  which  does  occur  as  soon  as  the  interchange 
of  the  electricities  allows  of  the  transfer  of  elements  j  for  on  the 
first  immersion  of  the  zinc,  the  equilibrium  of  the  chlorine  and  hy- 
drogen, which  had  previously  been  totally  engaged  with  each  other, 
is  interrupted,  and  that  of  the  particles  of  the  zinc,  which  had  be- 
fore been  all  circumstanced  alike,  is  disturbed  by  some  of  them  be- 
ing nearer  the  acting  muriatic  acid  than  the  others,  and  thus  the  in- 
duced condition  of  both  arises.  On  this  positive  and  necessary 
principle,  the  theory  of  the  simple  and  compound  circles  already 
described  has  been  given ;  and  although  it  will  require  to  be  again 
noticed  in  describing  the  phenomena  of  decomposition  which  ac- 
company the  passage  of  the  current,  yet,  for  the  only  purpose  which 
we  here  require,  of  studying  the  manner  in  which  the  current  of 
electricity  of  the  battery  has  its  rise,  the  peculiar  and  important  in- 
fluence exercised  by  the  chemical  reaction  among  the  elements  of 
which  it  consists  has  been  sufficiently  described. 

It  is  now  necessary  to  notice  more  in  detail  the  construction  of 

some  of  the  more  usual  forms  of 
the  Voltaic  or  Galvanic  battery. 
The  first  improvement  on  the  pile 
of  Volta  consisted  in  placing  it 
horizontally  in  a  wooden  trough, 
and  replacing  by  cells  containing 
dilute  acid  the  moistened  disks  of  cloth  employed  by  the  original 
inventor.      It  being  difficult  to  cleanse  the  surfaces  of  the  plates, 

which  in  that  form  were  per- 
manently cemented  into  the 
trough,  this  was  made  of  delft- 
ware  divided  into  cells,  and  the 
plates,  being  soldered  together 
by  projecting  bands  at  the  top, 
were  hung  upon  a  rod,  as  in  the 
figure,  so  that,  when  wante'd, 
they  may  be  immersed  with 
great  rapidity,  and  withdrawn 
as  easily  from  the  liquid  when 
the  battery  is  not  wanted.  The 
power  of  such  troughs  is  in- 


INTERFERING     ACTION     OF     COMMON     ZINC.       135 

creased  by  one  half  when  the  copper  slip  is  doubled  over  so  as  to 
oppose  both  surfaces  of  the  zinc.  Batteries  intended  rather  for  in- 
tensity than  for  quantity,  and  which  consequently  consist  of  a  great 
number  of  plates  of  moderate  dimensions,  are  generally  employed 
on  this  last  construction :  each  delftware  trough  holding  ten  pairs  of 
plates,  and  any  number  of  troughs  that  may  be  required  being  rap- 
idly and  easily  arranged  together.  When  a  current  of  electricity 
of  great  quantity,  but  not  of  intensity,  is  required,  it  is  usual  to  em- 
ploy a  few,  or  even  only  one  pair  of  plates  of  considerable  size.  Thus, 
a  sheet  of  copper  and  a  sheet  of  zinc,  each  of  from  80  to  120  square 
feet  of  surface,  being  kept  separated  by  ropes  of  horsehair,  have 
been  rolled  up  together  and  immersed  into  a  large  tub  of  acid,  form- 
ing thus  a  simple  circle,  giving  a  current  so  feeble  in  intensity  as  to 
pass  with  difficulty  through  a  short  column  of  distilled  water,  and  to 
be  quite  insensible  to  the  feeling,  but  which  fused  down  into  globules 
the  most  refractory  metals,  and  gave  with  charcoal  points  a  light  of 
brilliancy  insupportable  to  the  eye.  The  copper  plate  may  be  very 
conveniently  made  to  act  as  the  cell  containing  the  acid :  cylindric^ 
batteries  of  moderate  size  are  very  frequently  so  constructed. 

I  have  supposed,  in  the  description  of  the  nature  of  simple  and 
compound  Voltaic  circles,  that  the  zinc  employed  was  completely 
pure,  in  which  state,  when  first  immersed  in  the  acid,  there  is  no  chem- 
ical action,  but  only  the  preparatory  inductive  state  produced,  the 
decomposition  of  the  acid  by  the  zinc  commencing  only  when  the 
circuit  is  completed.  But  such  pure  zinc  is  too  expensive  for  ordinary 
use,  and  the  commercial  zinc  contains  always  traces  of  impurities, 
particularly  iron,  from  which  it  acquires  a  power  of  generating  a 
multitude  of  little  secondary  currents  across  the  fluid,  and  thus  pre- 
venting to  a  great  extent  the  formation  of  the  proper  current.  For 
suppose  that  there  is  on  the  centre  of  a  plate  of  zinc  a  little  piece  of 
iron  or  of  copper,  this  serves  to  return  to  the  zinc  from  the  acid  the 
positive  electricity,  which  had  passed  away  from  it  precisely  as  if 
it  had  been  a  copper  wire,  which  touched  the  acid  with  the  one  end, 
and  the  zinc  plate  with  the  other.  Such  a  plate  is  therefore  occu- 
pied almost  solely  with  its  own  self-contained  currents,  and  scarcely 
assists  in  generating  the  electricity  which  is  brought  into  play  in  the 
battery  at  large.  To  this  cause  must  be  assigned  the  property  which 
ordinary  zinc  possesses  of  dissolving  readily  in  an  acid,  and  of  evolv- 
ing hydrogen  upon  its  own  surface.  It  evolves  the  hydrogen  upon 
those  points  of  its  surface  on  which  foreign  metals  being  deposited, 
serve  to  complete  its  circuits.  This  injurious  property  of  ordinary 
zinc  is  remedied  by  coating  the  surface  of  the  plate  with  mercury, 
or,  as  it  is  termed,  amalgamating  it.  By  this  means  the  whole  sur- 
face of  the  metal  is  brought  into  the  same  state,  and  must  hence  act 
in  the  same  manner  on  the  acid.  Any  secondary  current  which 
might  arise  could  therefore  find  no  means  of  discharge,  and  such 
zinc  is  not  acted  on  until  the  circuit  is  completed,  and  then  all  hy- 
drogen is  carried  by  the  excited  molecules  of  acid  to  the  copper 
plate,  and  there  evolved  as  gas. 

To  amalgamate  the  zinc  plates  of  a  battery,  a  quantity  of  mercury 
is  to  be  laid  in  a  flat  dish,  sufficient  to  cover  the  bottom  ;  moderately 
dilute  nitric  acid,  to  which  a  small  quantity  of  nitrate  of  mercury 


136 


FORMS  OF  CONSTANT  BATTERIES. 


has  been  added,  is  to  be  then  poured  on  the  mercury,  so  deep  that 
the  zinc  plate,  when  floating  on  the  mercury,  shall  be  covered  by 
the  acid.  Before  immersing  the  zinc  plate,  it  should  be,  if  not  new, 
cleaned  as  well  as  possible  with  sand-paper  from  adhering  dirt,  and 
then  it  combines  with  the  mercury  very  rapidly,  so  as  to  form  a  sur- 
face which,  by  rubbing  with  a  little  flannel,  may  be  rendered  com- 
pletely uniform.  The  zinc  should  not  be  too  highly  mercurialized, 
for  then  it  becomes  extremely  brittle,  and  requires  considerable  care 
in  using  it.  The  power  of  a  battery  may  often  be  quadrupled  by 
this  method.  A  source  of  great  inconvenience  in  the  ordinary  bat- 
teries arises  from  the  hydrogen  acting  on  the  oxide  of  zinc  which 
is  dissolved,  and  reducing  it  to  the  metallic  state,  when  it  is  carried, 
with  the  remaining  hydrogen,  to  the  copper  plate,  and  deposited  upon 
it.  In  this  way  there  is  gradually  formed  a  second  zinc  surface 
opposite  to  the  proper  zinc  plate,  and  which,  tending  to  transmit  a 
current  in  the  reversed  direction,  neutralizes  a  certain  proportion  of 
the  power  of  the  circle,  and  may  even  destroy  it  altogether.  Hence 
an  ordinary  battery  is  most  active  when  first  brought  into  play,  and 
diminishes  very  rapidly  in  power  until,  after  the  lapse  of  some  hours, 
even  though  the  acid  be  not  saturated,  its  action  ceases. 

This  disadvantage  has  been  beautifully  removed  by  the  principle 
of  absorbing  the  hydrogen  by  means  of  a  solution  of  sulphate  of 
copper,  which  it  decomposes,  and  precipitates  upon  the  surface  of 
the  copper  plate  a  layer  of  clean,  new,  metallic  copper,  in  the  best 
possible  condition  for  supporting  the  action  of  the  battery.  The 
simplest  arrangement  of  this  kind  is  that  of  Mullins ;  the  mechani- 
cal construction  is  most  perfect  in  Daniell's  constant  battery.  Mul- 
lins' battery  consists  of  a  delftware  trough,  D,  in 
jC^JL  which  the  cylindrical  zinc  plate  B,  of  nearly  the 
same  diameter,  is  placed,  and  inside  of  which,  again, 
is  the  copper  cylinder  A,  which  is  close,  and  acts 
only  by  its  external  surface  j  round  the  upper  edge 
of  the  copper  cylinder  C  is  tied  a  bladder,  into  vvhich 
fluid  may  be  introduced  by  means  of  a  row  of  ap- 
ertures in  the  rim  to  which  the  bladder  is  attached. 
A  solution  of  sulphate  of  copper  is  poured  into  the 
bladder,  and  its  state  of  concentration  is  kept  up  by 
heaping  some  coarsely-pounded  crystals  on  the  top  of  the  copper 
cylinder.  Into  the  trough  in  contact  with  the 
zinc  is  then  poured  dilute  sulphuric  acid.  When 
the  action  commences,  the  hydrogen  is  transfer- 
r-fi  red  through  the  membrane,  and,  meeting  there 
the  solution  of  sulphate  of  copper,  is  absorbed 
in  the  production  of  metallic  copper.  The  cop- 
per cylinder  never  wears  nor  dirties.  The  metal 
is  all  recovered  from  the  sulphate  of  copper, 
and  the  only  thing  necessary  is  that  the  plates 
of  zinc  shall  be  renewed  from  time  to  time. 
Daniell's  battery  has  the  advantage  that  the  cop- 
per is  outside,  and  hence  is  capable,  with  ex- 
posure of  the  same  surface  of  zinc,  of  producing 
a  much  more  pow^erful  current.     The  cell  con- 


CONSTANT     BATTERIES,  137 

sists  of  a  copper  cylinder,  a,  c,  near  the  top  of  which  is  attached 
a  perforated  platp,  P,  on  which,  when  the  cell  has  been  filled  with 
the  solution  of  sulphate  of  copper,  a  quantity  of  crystals  are  laid, 
to  be  dissolved  according  as  they  are  required.  A  solid  zinc  rod, 
ffi,  supported  at  the  top  of  the  copper  cylinder  by  a  wooden  cross- 
piece,  is  contained  in  a  membranous  bag,  formed  of  the  gullet  of  an 
ox,  g,  A,  and  into  this  is  poured  the  dilute  acid,  which  consists  of 
one  part  of  oil  of  vitriol  and  eight  parts  of  water.  Any  number  of 
these  cells  may  be  arranged  together  so  as  to  give  a  battery,  which, 
if  all  the  coppers  be  connected  upon  the  one  hand,  and  all  the  zinc 
rods  upon  the  other,  will  evolve  large  quantities  of  electricity  of 
low  tension  ;  but  when  the  copper  and  zinc  elements  are  alternately 
connected  with  each  other,  the  tension  of  the  electricity  evolved  is 
much  increased,  though  at  the  expense  of  the  quantity  generated. 

The  great  advantage  of  such  batteries  is  the  perfect  uniformity 
of  their  action,  by  which  they  deserve  fully  the  name  applied  by 
Daniell  to  his  construction,  of  the  constant  battery ;  with  such  an 
instrument,  the  conditions  of  the  current  may  remain  for  days  per- 
fectly unaltered ;  and  thus  the  laws  of  action  of  the  current  have 
been  determined,  particularly  in  its  chemical  relations,  with  com- 
plete success,  and  views  of  the  analogies  between  affinity  and  elec- 
tricity, equally  novel  and  important,  which  will  be  discussed  in  an- 
other place,  have  been  arrived  at  by  its  means. 

Latterly,  the  membranous  bags,  originally  used  by  Daniell  and 
others  as  the  diaphragm  between  the  acid  solution  and  that  of  the 
sulphate  of  copper,  have  been  with  great  advantage  replaced  by 
porous  cells  of  biscuit-ware,  such  as  is  represented  in  the  figure  by 

Some  forms  of  battery  have  recently  been  proposed,  in  which, 
under  a  small  compass,  very  great  power  is  obtained,  by,  1st,  bring- 
ing the  plates  very  near  each  other  j  2d,  selecting  solid  elements, 
which  difier  as  much  as  possible  in  their  chemical  relations ;  and, 
3d,  using  as  the  exciting  fluids  those  of  the  most  intense  action, 
and  of  the  highest  conducting  power.  In  this  way,  the  most  pow- 
erful Voltaic  combination  that  has  been  yet  made  is  that  of  Mr. 
Groves.  Plates  of  zinc  and  platina  are  separated  by  diaphragms  of 
porous  earthenware,  the  zinc  being  acted  upon  by  dilute  sulphuric 
acid  mixed  with  some  nitric  acid,  and  the  platina  being  in  contact 
with  tolerably  strong  nitric  acid.  The  hydrogen  evolved  by  the 
zinc  is  completely  absorbed  by  the  nitric  acid  on  which  it  acts, 
forming  nitrous  acid  which  remains  dissolved  ;  and  the  metals,  being 
those  most  opposite  in  their  electrical  relations,  give  the  most  pow- 
erful current  possible. 

The  conducting  powers  of  various  bodies  for  this  form  of  electri- 
city has  been  determined  with  great  care  by  Pouillet,  whose  results 
are,  that  the  relative  conducting  powers  of  the  various  metals  are 
expressed  by  the  following  numbers  : 

Palladium 
Silver    .     , 
Gold     .     . 
Copper 
Platina 
Bismuth    . 


5791 

Brass  from .    . 

.     .      900 

5152 

to     .     . 

.      200 

3975 

Cast  steel  from 

.      800 

3838 

to     .     . 

.      500 

855 

Iron  .... 

.      600 

384 

Mercury      .    . 

.       100 

138  RELATIVE     CONDUCTING     POWERS. 

He  ascertained,  also,  the  relative  conducting  powers  of  the  saline 
solutions  usually  contained  in  the  cells  of  the  Galvanic  battery  j 
and  it  appears  that  the  conducting  power  of  platina  is  two  million 
and  a  half  times  that  of  a  saturated  solution  of  sulphate  of  copper, 
and  hence  that  of  copper  is  sixteen  million  times  as  great.  The 
conducting  power  of  the  saturated  solution  of  the  sulphate  of  cop- 
per being  taken  as  10-000,  he  found  that  of 

a  saturated  solution  of  sulphate  of  zinc  to  be  .    4*170 

distilled  water 0-025 

distilled  water  with  ^o¥oo  of  nitric  acid      .     .     0-150 

The  great  retardation  which  occurs  when  the  current  has  to  pass 
through  any  considerable  length  of  liquid,  will  now  be  easily  under- 
stood. Pure  water  may  be  considered,  with  feeble  circles,  as  an 
absolute  non-conductor  ;  and  even  with  the  most  powerful  combi- 
nations that  have  been  yet  made,  the  current  is  unable  to  force  its 
way  through  the  smallest  measurable  interval  of  air.  It  was  not 
long  ago  believed  that,  even  with  simple  circles,  a  spark  indicating 
the  passage  of  a  current  was  seen  on  making  contact,  and  hence 
that  the  electricity  had  passed  before  the  metals  had  touched,  and, 
consequently,  that  the  chemical  action  should  be  alone  considered 
as  the  source  of  the  electricity.  It  is,  however,  now  acknowledged, 
that  no  spark  can  pass  until  the  wires  have  touched  and  are  again 
separated,  and  the  passage  of  the  electricity  is  then  accomplished, 
not  by  the  action  of  the  excited  molecules  of  air,  as  occurs  with  the 
machine,  but  by  the  violent  inductive  polarization  of  the  particles  of 
the  terminal  conductors,  which  are  torn  off  and  pass  from  one  pole 
to  the  other. 

When  the  current  of  electricity  is  retarded  by  means  of  an  in- 
sufficient conducting  medium,  the  centre  of  the  conductor  becomes 
hot,  and  thus  the  most  brilliant  effects  of  heat  and  light  may  be  pro- 
duced ;  even  the  most  refractory  metals,  as  gold  and  platina,  being, 
when  in  thin  foil  or  wire,  dissipated  actually  in  smoke.  By  termi- 
nal points  of  well-burned  charcoal,  this  phenomenon  is  beautifully 
produced,  the  ignition  being  totally  independent  of  combustion,  for 
it  takes  place  in  vacuo  or  in  carbonic  acid  gas  ;  and  when  the  points 
are  separated  from  one  another  to  a  certain  distance,  the  interval 
becomes  occupied  by  a  splendid  arch  of  light,  formed  by  the  induc- 
tively excited  particles  of  charcoal,  which,  in  a  state  of  intense  ig- 
nition, abandon  the  positive  to  attach  themselves  to  the  negative 
extremity  of  the  conductor. 

The  action  of  galvanic  electricity  upon  the  animal  frame  does  not 
properly  fall  within  the  scope  of  the  present  work,  but  in  termina- 
ting the  subject,  the  mode  in  which  the 
first  view  of  this  important  science  was 
obtained  may  with  propriety  be  noticed. 
Galvani  was  professor  of  anatomy  at  Bo- 
logna, and,  while  preparing  frogs  for 
some  physiological  experiments,  he  hap- 
^Wl    Wl^^  pened  to  touch,  by  one  extremity  of  a 

metallic  wire,  the  lumbar  nerves  which 
still  remained  attached  to  the  spine,  while 


G  A  L  V  A  N  I  S  M. T  HERMO-ELECTRICITY.  139 

the  Other  extremity  of  the  wire  was  in  contact  with  the  muscles  of 
the  leg  j  these  last  were  instantly  thrown  into  strong  convulsions. 
To  perform  this  experiment  with  success,  the  legs  of  the  frog  are 
to  be  left  attached  to  the  spine  by  the  crural  nerves  alone,  and  then 
a  copper  wire  and  a  zinc  wire  being  either  twisted  or  soldered  to- 
gether at  one  end,  the  nerves  are  to  be  touched  with  one  wire, 
while  the  other  is  to  be  applied  to  the  muscles  of  the  leg. 

Galvani  erred  in  the  explanation  of  this  remarkable  effect  j  he  look- 
ed upon  the  body  as  being  in  the  stat*  of  a  charged  Leyden  jar,  of 
which  the  nerves  and  muscles  were  the  external  and  internal  coat- 
ings, and  that,  on  connecting  these  by  the  conducting  wire,  the  elec- 
tricities recombined,  and  the  passage  renewed  for  the  instant  the 
phenomena  of  life.  Volta  pointed  out,  however,  that,  in  order  to 
produce  full  effect,  the  presence  of  two  metals  in  the  conductor  was 
required,  and  he  ascribed  the  origin  of  the  electricity  not  to  the 
body,  but  to  the  contact  of  the  two  metals,  and  supposed  the  con- 
vulsive motions  to  be  merely  the  indication  of  the  passage  of  the 
current  across  the  body  of  the  frog.  This  view  has  also  been  since 
modified  by  ascribing  the  electricity  to  minute  traces  of  chemical 
action  on  the  wires ;  but  it  was  so  fruitful  in  results,  of  which  the 
construction  of  the  Voltaic  pile  is  the  most  remarkable,  that  Volta 
is,  with  justice,  looked  upon  as  the  true  originator  of  this  branch  of 
electricity  as  a  science,  although  it  was  Galvani  who  observed  the 
first  fact  belonging  to  it. 

The  frog  so  prepared  is  a  most  delicate  test  of  the  passage  of  a 
Galvanic  current ;  it  is  truly  a  galvanoscope,  corresponding  to  the 
gold-leaf  electroscope  for  ordinary  electricity  ;  but  it  does  not  meas- 
ure the  quantity  or  intensity  of  the  electricity  which  passes.  As 
yet  we  have  no  exact  measure  of  the  intensity  of  Galvanic  electri- 
city ;  but  that  its  quantity  may  be  exactly  determined,  two  of  its 
properties  may  be  applied:  the  first  consists  in  determining  the 
quantity  of  a  given  chemical  substance,  as  water,  which  the  current 
can  decompose  in  a  certain  time,  for  the  quantity  decomposed  is 
proportional  to  the  quantity  of  electricity  which  passes  ;  the  second 
consists  in  observing  the  degree  to  which  the  current  is  able  to  de- 
flect the  magnetic  needle  from  its  natural  position  of  north  and 
south,  for  the  angle  of  deflection  is  connected  with  the  quantity  of 
electricity  in  the  current  by  a  very  simple  law;  we  are  not  yet  in  a 
position  to  understand  fully  the  theory  either  of  the  chemical  or 
the  magnetic  galvanometer,  and  hence  I  merely  indicate,  for  the 
present,  their  existence  and  their  names. 

Thermo-electricity. — If  heat  be  applied  to  a  wire,  uniform  in  tex- 
ture and  thickness,  bent  into  a  ring,  there  is  no  disturbance  of  elec- 
trical equilibrium ;  but  if  any  obstacle  to  the  transmission  of  the 
heat,  such  as  a  knot  or  a  coil  in  the  wire,  exist,  a  cur- 
rent will  be  established,  of  which  the  direction  will  be 
from  the  point  of  the  circuit  to  which  the  heat  is  applied 
towards  the  point  where  the  retarding  cause  exists.  If 
in  place  of  merely  causing  an  artificial  obstacle  on  a 
uniform  wire,  two  metals,  a  b,  be  selected,  which  differ 
in  conducting  power,  and  the  point  at  which  they  touch 
one  another,  c,  be  kept  at  a  different  temperature  from 
the  rest,  a  current  is  also  produced  from  the  latter  point  towards 


140  THERMO-ELECTRIC     CURRENTS. 

the  metal  which  is  the  worst  conductor.  The  more  unlike  the  met- 
als are  in  molecular  constitution,  and  the  greater  the  difference  be- 
tween their  conducting  powers,  the  more  energetic  is  the  current. 
The  best  combinations  are  therefore  of  a  crystalline  and  a  non- 
crystalline metal,  or  of  two  metals  which  crystallize  in  different  sys- 
tems. Bismuth  and  antimony,  which  are  the  worst  conductors  of 
the  metals,  are  also  among  the  most  crystalline  ;  and  while  bismuth 
crystallizes  in  cubes,  the  form  of  antimony  is  a  rhombohedron  j  these 
metals,  therefore,  combine  ajl  the  essential  qualities  for  generating 
a  current  when  unequally  heated,  and  they  are,  consequently,  the 
most  powerful  sources  of  thermo-electricity  that  have  been  found. 
The  results  obtained  with  other  metals  will  be  understood  by  wri- 
ting them  down  in  the  following  order,  any  two  of  them  being 
capable  of  forming  a  current  when  their  junctions  are  unequally 
heated,  the  current  being  from  the  metal  highest  to  that  which  is 
lowest  in  the  list,  and  the  power  of  the  current  being  greater  in 
proportion  to  the  distance  between  the  metals  in  the  following  or- 
der :  bismuth,  platinum,  lead,  tin,  copper  or  silver,  zinc,  iron,  anti- 
mony. The  molecular  texture  would  appear  from  this  list  to  have 
more  influence  on  the  production  of  the  current  than  the  mere  dif- 
ference of  conducting  power. 

The  intensity  of  the  thermo-electric  current  so  excited  is  exceed- 
ingly small ',  it  is  only  capable  of  passing  through  very  good  con- 
ductors, and  it  requires  the  combination  of  a  number  of  exciting 
couples  to  give  sufficient  tension  to  enable  it  to  produce  a  spark,  or 
to  show  any  signs  of  chemical  influence.  It  then,  however,  agrees 
in  all  respects  with  the  electricity  of  the  Galvanic  battery  when  in 
an  excessively  feeble  state  of  tension,  and  it  resembles  remarkably 
the  hydro-electric  current,  in  being  able  to  reproduce  at  a  distance 
the  circumstances  in  which  it  originates ;  for  precisely  as  a  current 
passes  through  a  combination  of  antimony  and  bismuth  when  its 
junctions  are  at  unequal  temperatures,  so,  when  a  similar  current 
from  any  other  source  is  passed  through  the  metallic  couple,  a  change 
of  temperature  is  produced  at  the  place  where  the  two  unite  ',  if  the 
current  pass  from  the  bismuth  to  the  antimony,  the  junction  becomes 
heated  j  but  if  the  electricity  pass  in  the  opposite  direction,  the  junc- 
tion is  cooled  to  a  remarkable  degree,  so  that,  if  a  little  hole  be 
bored  where  the  metals  touch,  and  a  drop  of  water  be  laid  therein, 
it  is  frozen  after  a  few  moments.  This  result,  which  was  first  ob- 
tained by  Peltier,  and  has  been  confirmed  by  Bottger,  is  one  of  the 
most  remarkable  proofs  of  connexion  between  the  physical  sources 
of  temperature  and  electrical  equilibrium  that  has  been  as  yet  dis- 
covered, and  may  influence  our  theories  of  the  nature  of  heat  in  no 
inconsiderable  degree. 

The  principle  of  strengthening  the  thermo-electric  current,  by 

combining  together  the  action  of  a 
number  of  metallic  couples,  is  due  to 
Nobili.  If  we  consider  a  number  of 
bars  of  antimony  and  bismuth,  a  i, 
soldered  together  alternately  at  their 
ends,  so  that  every  alternate  soldering 
shall  be  in  the  same  plane,  and  the 
extremities  of  the  terminal  bars  be 


CONSTRUCTION     OF     THE     THERM  OSCOPE.         141 

connected  by  a  wire,  on  applying  heat  to  the  alternate  solderings, 
a  current  is  generated  at  each,  which,  being  all  in  the  same  direc- 
tion, travel  together  through  the  system,  and  thus  increase  its  en- 
ergy in  proportion  to  the  number  of  combinations.  The  important 
distinction  between  this  and  the  combination  of  elements  in  the 
Voltaic  pile  is,  that  in  the  latter  the  increase  of  number  affects  only 
the  tension  of  the  current,  but  leaves  the  quantity  the  same  as  the 
single  couple  ;  but  in  the  thermo-electric  pile,  although  the  intensity 
is  increased,  yet  the  quantity  which  passes  in  the  current  is  aug- 
mented also. 

It  is  this  principle  which  has  been  applied  by  Nobili  to  the  con- 
struction of  the  thermo-multiplier  or  thermo-electroscope  used  by 
Melloni  and  Forbes  in  their  researches  on  radiant  heat,  of  which  a 
sketch  has  been  given  in  the  last  chapter.  The  thermoscope  con- 
sists of  fifty  small  bars  of  bismuth  and  antimony,  placed  parallel  be- 
side one  another,  and  forming  a  single  prismatic  bundle,  F,  F',  about 
1^  inch  long  and  f  inch  square  in  section.  The  two  terminal  faces 
are  blackened.  The  bars  of  bismuth,  which  are  arranged  alternately 
with  those  of  antimony,  are  soldered  at  their  extremities,  and  sep- 
arated all  through  their  length  by  an  insulating  substance.     To  the 

CnflC 


first  and  last  bars  are  attached  copper  wires,  which  terminate  in  the 
pins  C  C,  of  the  same  metal,  passing  across  a  piece  of  ivory  fixed 
on  the  ring  A  A.  The  space  between  the  interior  of  this  ring  and 
the  elements  of  the  pile  is  filled  by  insulating  material.  The  free  ex- 
tremities of  the  two  wires  are  put  in  communication  with  the  ter- 
minal wires  of  a  magnetic  galvanometer,  the  needle  of  which  indi- 
cates by  its  motions  when  the  temperature  of  the  anterior  surface 
of  the  thermo-electric  pile  is  raised  or  lowered,  in  comparison  to  that 
of  the  posterior  surface.     (See  P  in  figure,  page  99.) 

By  means  of  a  jointed  support,  the  axis  of  the  pile  may  be  turned 
in  any  direction  that  may  be  wished  ;  and  to  protect  its  surface  from 
lateral  radiation,  the  metallic  tubes  B  B,  brilliant  externally  and  black 
ened  on  the  inside,  are  attached  to  the  extremities  of  the  ring  A  A. 

If  by  changing  through  one  degree  the  temperature  of  a  single 
soldering,  a  current  of  a  certain  power  be  obtained,  there  should  be 
with  fifty  solderings  a  current  fifty  times  as  strong,  or  an  equal 
current  when  the  temperature  of  the  solderings  varies  through  one 
fiftieth  of  a  degree.  It  has  been  ascertained  that  instruments  of 
this  kind  may  be  made  to  indicate  a  variation  of  temperature  of  3  ^Vo- 
of  a  degree  on  Fahrenheit's  scale. 

The  electricity  which  is  thus  evolved  by  change  of  temperature 
in  conducting  bodies,  although  so  feeble  in  quantity  and  intensity 
as  to  be  utterly  devoid  of  those  brilliant  qualities  which  attach  much 
popularity  to  the  phenomena  of  Galvanism  and  of  machine  electri- 
city, has  thus  been  found  the  means  of  assigning  the  true  laws  of 
some  of  the  most  interesting  and  important  branches  of  the  ph^ical 
Bciences  j  and  it  will  be  hereafter  seen  that  thermo-electric  currents, 


142 


RELATIONS    OF    THERMO-ELECTRIC    CURRENTS. 


excited  in  the  superficial  stratum  of  the  globe  by  the  inequality  of 
temperature  which  arises  from  the  action  of  the  sun,  may  generate 
not  only  the  magnetic  properties  on  which  are  founded  the  com- 
mercial intercourse  of  civilized  nations,  but,  by  influencing  the  affin- 
itary  powers  of  the  elementary  constituents  of  our  planet,  may  have 
been  the  agent  in  silently,  but  effectively,  regulating  the  constitution 
of  inorganic  nature. 

[From  the  extensive  employment  of  thermo-electric  currents  as  measures  of  tem- 
perature, it  is  desirable  to  understand  their  habitudes.  Dr.  Draper  has  shown  that 
equal  quantities  of  heat  do  not  set  in  motion  equal  quantities  of  electricity ;  with 
certain  combinations  of  metals  the  proportion  increases,  and  with  others  decreases. 
For  this  reason,  temperatures  estimated  in  this  way  must  always  undergo  correc- 
tion, as  the  following  table  shows  : 


M  5 

£5" 


Mercurial  thermometer  . 

Copper  and  iron    .     .  . 

Silver  and  palladium 

^  ^    Iron  and  palladium    .  . 

S  :^  I  Platina  and  copper    .  . 

S -2     Iron  and  silver       .     .  . 

H  6  I  Iron  and  platina     .     .  . 


Water  boils. 

Mercury  boils. 

212 

662 

202 

257 

235 

880 

211 

539 

244 

1030 

170 

279 

212 

829 

We  therefore  infer,  that  in  these  six  systems  of  metals,  the  developments  of  electii- 
city  do  not  increase  proportionally  with  the  temperatures,  but  in  some  with  greater 
rapidity,  and  in  others  with  less. 

The  tension  of  these  currents  undergoes  a  slight  increase  with  increase  of  tem- 
perature :  a  phenomenon  due  to  the  increased  resistance  to  conduction  of  metals 
when  their  temperature  rises.  In  hydro-electric  pairs,  the  quantity  of  electricity 
evolved  depends  on  the  surface  of  the  plates ;  but  in  thermo-electric  arrangements, 
the  quantity  of  electricity  is  independent  of  the  amount  of  heated  surface,  a  mere 
point  being  just  as  efficacious  as  an  indefinitely  extended  surface.  And  in  a  com- 
pound series  of  many  pairs,  the  quantity  of  electricity  evolved  is  directly  proportional 
to  the  number  of  pairs. 

Thermo-electric  currents  traverse  metallic  masses  only  on  account  of  differences 
of  temperature  existing  at  different  points.  When  a  current  flowing  from  the  poles 
of  a  battery  is  made  to  traverse  a  wide  metallic  sheet,  the  whole  of  it  does  not 

pass  in  a  straight  line  from  one  pole  to 
the  other,  but  diffuses  itself  through  the 
metal,  diverging  from  one  pole  and  con- 
verging to  the  other.  For  these  reasons, 
there  are  certain  forms  of  construction 
which  give  thermo-electric  arrangements 
peculiar  advantages.  For  example,  the  sur- 
faces united  by  soldering  must  not  be  too 
massive.  Let  a,  fig.  1,  be  a  bar  of  anti- 
mony, and  h  a  bar  of  bismuth  ;  let  them  be 
soldered  together  along  the  line  c  d,  and  at 
the  point  d  let  the  temperature  be  raised, 
a  current  is  immediately  excited ;  but  this 
does  not  pass  round  the  bars  a  b,  inasmuch  as  it  finds  a  shorter  and  readier  chan- 
nel through  the  metals  between  c  and  d,  circulating,  therefore,  as  indicated  by  the 
arrows.  Nor  will  the  whole  current  pass  round  the  bars  until  the  temperature  of 
the  soldered  surface  has  become  uniform. 

An  obvious  improvement  on  such  a  combination  is  shown  in  fig.  2,  which  con- 
sists of  the  former  arrangement  cut  out  along  the  dotted  lines  ;  here  the  whole  cur- 
rent, as  soon  as  it  exists,  is  forced  to  pass  along  the  bars.  And  because  the  mass 
of  metal  has  been  diminished  along  the  hne  of  junction,  such  a  pair  will  change  its 
temperature  very  quickly. 

One  of  the  very  best  forms  for  a  thermo-electric  couple  is  given  in  fig.  3,  where  a 
is  a  semi-cylindrical  bar  of  antimony,  b  one  of  bismuth,  united  together  by  the  oppo- 
site ^rners  of  a  lozenge-shaped  piece  of  copper,  c.  From  its  exposing  so  much 
surface,  the  copper  becomes  hot  and  cold  with  the  greatest  promptitude  ;  and  from 
its  good  conducting  power,  it  may  be  made  very  thin  without  injury  to  the  current.] 


MAGNETIC    PROPERTIES     OF     IRON     AND    STEEL.     143 


Magnetic  Electricity. — The  properties  which  are  now  known  as 
magnetic  were  first  recognised  in  a  peculiar  ore  of  iron,  found  in 
the  vicinity  of  the  town  Magnesia,  in  Asia  Minor,  from  which  the 
names  of  the  substance  and  of  the  science  have  been  derived.  The 
native  magnetic  ore  or  loadstone  consists  of  iron  and  oxygen.  This 
mineral,  although  quite  ineft  with  regard  to  all  other  bodies,  attracts 
iron  and  steel  with  great  power ;  and  the  pieces  of  iron  and  steel, 
while  in  contact  with  the  loadstone,  participate  in  its  powers,  and 
are  capable  of  attracting  other  pieces  to  themselves.  Iron  and  steel, 
though  both  attracted  by  the  magnet,  differ  remarkably  in  the  fact 
that  iron,  although  magnetic  while  in  contact  with  the  loadstone, 
loses  all  its  properties  when  it  is  removed;  while  steel,  which  is  at 
first  attracted  with  inferior  power,  when  it  has  become  magnetic  by 
contact  with  that  mineral,  retains  that  condition  after  separation, 
and  thus  becomes  a  permanent  artificial  magnet.  A  steel  magnet 
thus  formed  may  in  its  turn  be  used  in  place  of  a  loadstone  to  form 
others  j  and  almost  all  the  magnets  we  employ  in  experiments  have 
thus  obtained  their  power,  as  native  loadstone  is  not  found  in  suf- 
ficient quantity,  or  sufficiently  intense  in  action,  for  our  purposes. 
The  steel  bars  which  are  magnetized  are  generally  straight,  but  often 
also  bent  in  the  centre,  so  that  the  halves  are  nearly  parallel,  and 
are  then  called  horseshoe  magnets. 

When  a  magnetic  bar  is  dusted  over  with  iron  filings,  it  will  be 
found  that  the  filings  attach  themselves  to 

the  extremities  of  the  bar,  and  scarcely  at  ^  I  f^^ 

all  to  the  centre ;  the  magnetic  power  is  '^^gppw-*'A^'-t^'i*'JJi^^iJl|Nf^ 
thus  seen  to  exist  only  near  the  ends  of  the  bar.  Each  filing  being 
itself  for  the  time  a  magnet,  attracts  others,  so  that  they  form  strings, 
which  arrange  themselves,  according  to  definite  laws,  in  an  order 
which  is  termed  the  magnetic  curves,  and  from  the  disposition  of 
these  curves  it  is  evident  that  the  action  of  the  magnet  emanates 
from  a  single  point,  P,  near  each 
extremity;  these  points  being  the 
centres  of  action  of  the  magnet, 
are  termed  iX?,  poles.  Thus,  in  the 
figure,  the  bar  being  a  magnet,  the 
points  P  and  P  are  the  poles,  and 
the  directions  of  attractive  force 
are  indicated  by  the  diverging 
lines,  which,  uniting  on  the  inner 
side,  form  the  magnetic  curves. 

The  utility  of  the  magnet  in  navigation  is  well  known  ;  it  arises 
from  the  poles  of  the  magnet  being  attracted  by  the  earth  in  such  a 
way,  that,  when  free  to  move,  the  magnet  rests  in  a  direction  nearly 
north  and  south ;  the  pole  of  the  magnet  which  is  turned  to  the 
north  is  termed  the  north  pole,  the  other  the  south  pole.  If  two 
magnets  be  brought  into  the  neighbourhood  of  one  another,  they  do 
not  attract  indifferently,  as  either  would  attract  a  mass  of  iron  ;  but 
the  north  pole  of  one  magnet  attracts  the  south  pole  of  the  other, 
and  is  attracted  by  it,  while  the  north  poles  of  the  two,  or  the  south 
poles,  if  brought  near  each  other,  repel  as  powerfully.  In  magnets, 
therefore,  poles  of  the  same  name  repel,  and  poles  of  opposite  names 


144  INTIMATE     STRUCTURE     OF     MAGNETS. 

attract,  a  condition  precisely  similar  to  that  which  holds  between  the 
electricities  evolved  by  friction.  In  magnetism,  also,  the  attractions 
and  repulsions  follow  the  law  of  the  inverse  square  of  the  distance, 
and  thus  complete  the  superficial  analogy  which  led  astray  for  so 
many  years  the  investigators  of  this  branch  of  science. 

The  action  of  the  earth  upon  magnets  at  its  surface  can  only  be  explained  by 
supposing  the  earth  itself  to  possess  magnetic  properties.  The  northern  portions 
of  the  earth  attract  the  north  pole  of  a  magnet,  and  must  therefore  possess  south- 
ern polarity ;  the  southern  portions  of  the  earth  attracting  the  south  pole  of  the 
magnet,  must  possess  northern  polarity.  The  action  of  the  earth  cannot  be  ex- 
plained, however,  by  supposing  it  to  be  a  simple  magnet  with  a  pole  at  each  ex- 
tremity. It  possesses  at  least  two  centres  of  force  or  poles  in  the  north,  one  in 
Siberia  and  one  in  North  America,  while  the  exact  distribution  of  the  centres  of 
magnetic  force  in  the  southern  hemisphere  has  not  been  yet  made  out,  These  cen- 
tres themselves  are,  however,  not  fixed ;  the  needle  is  continually  changing  in  di- 
rection ;  at  present  it  points  to  24i°  west  of  north ;  but  in  the  year  1664  it  pointed 
to  the  north,  and  it  had  previously  pointed  in  an  easterly  direction,  towards  which 
it  is  now  returning. 

Prior  to  the  discovery,  by  Ampere,  of  the  true  nature  of  magnetic 
phenomena,  a  theory  similar  for  the  most  part  to  that  of  the  two 
electrical  fluids  was  maintained;  two  magnetisms  were  supposed  to 
exist,  the  particles  of  the  same  fluid  repelling  each  other,  but  the 
particles  of  one  fluid  attracting  those  of  the  other.  The  assumption 
of  magnetic  properties  by  a  piece  of  iron  or  steel  in  contact  with  a 
magnet  became,  therefore,  a  phenomenon  of  induction  similar  to 
that  described  under  th|j  head  of  statical  electricity,  the  constitution 
of  iron  being  such  that  the  fluids  recombined  on  the  disturbing  cause 
being  removed ;  the  constitution  of  steel,  on  the  contrary,  prevent- 
ing their  reunion.  There  existed,  however,  one  great  difference 
between  a  magnetic  bar  and  a  body  excited  by  induction  with  ma- 

^ C B      chine  electricity.     If  the  bar  A,  C,  B,  excited 

C 1 )    by  induction,  and  of  which  the  portion  A  is 

/\  jjj  /\     positive,  and  B  negative,  the  middle  C  being 

neutral,  be  cut  in  two  at  C,  the  portions  A 

1     j ^     and  B  retain  their  peculiar  states,  one  posi- 

tive  and  the  other  negative.  But  if  the  mag- 
netic bar  A,  C,  B  be  broken  across  at  the 
neutral  portion  C,  then  each  half  becomes 


k 


^^3[^':;  a  perfect  magnet  of  half  the  strength  of  the 
'■'/?i?\v  ^  entire  j  the  points  C   and  C,  which  had 


■•sjM^vjJC-'-  teen  neutral,  acquire  magnetic  power  ',  and 
if  these  portions  be  again  broken,  each  frag- 
ment is  a  perfect  magnet.  Magnetism  be- 
longs, in  this  way,  to  the  inmost  particles  of  the  body,  and  in  the 
general  mass  each  magnetic  molecule  is  still  active  and  independ- 
ent ;  a  magnet  resembles,  therefore,  an  exceedingly  bad  conductor, 
which  has  been  inductively  excited  by  common  electricity,  and  the 
particles  of  which  retain  for  an  indefinite  length  of  time  their  state 
of  polar  excitation. 

In  order  to  understand  the  real  nature  of  magnetic  action,  we 
must  free  ourselves,  however,  from  all  these  analogies  to  machine 
electricity,  no  matter  how  well  grounded  they  may  appear  to  be 
when  superficially  examined.  The  electricity  of  the  magnet  is 
constantly  circulating,  and  it  possesses  so  little   tension   that  it 


MAGNETIC     QUALITIES    OF     GALVANIC     CURRENT.    145 


Fig.  3. 


Fig.  4. 


never  leaves  the  magnetic  element,  or  molecule  of  iron  or  steel,  in 
which  it  has  its  origin ;  in  fact,  every  current  of  electricity  possess- 
es magnetic  properties,  and  simulates  the  action  of  a  magnet  situ- 
ated transversely  to  it.  Thus,  if  a  needle  be  held  transversely  on  a 
wire  carrying  an  electric  current,  it  becomes  magnetic  precisely  as 
if  it  had  been  laid  parallel  to  a  magnet ;  and  by  bending  the  wire 
round  so  as  to  form  a  coil,  the  magnetism  which  it  confers  being 
increased  in  proportion  to  the  number  of  turns,  may  be  rendered  so 
intense  as  to  surpass  that  of  the  most 
powerful  steel  magnets  that  are  made. 
In  fig.  1  a  small  coil  is  represented,  by 
which  magnetism  is  conferred  upon  the 
bar  of  steel  inside.  And 
in  fig.  2,  a  large  horse- 
shoe of  soft  iron,  by  being  covered  by  a  helix  of  many 
hundred  turns,  may  become  able  to  raise  a  weight  of 
some  hundreds  of  pounds  by  the  magnetism  it  ac- 
quires. 

The  coil  of  wire  carrying  the  current  may  be 
shown,  also,  to  possess  magnetic  properties  by  its 
attractive  and  repulsive  action  on  a  magnet.  A  coil 
as  in  fig.  3,  suspended  so  as 
to  be  able  to  move  freely,  is 
attracted  and  repelled  by  the 
poles  of  a  magnet  precisely 
as  if  it  also  had  a  magnetic 
pole  at  each  end.  A  flat  coil,  as  in  fig.  4, 
is  also  found  to  be  magnetic,  the  poles  be- 
ing indefinitely  near  each  other  at  the  cen- 
tre of  the  coil.  A  beautiful  form  of  the  ex- 
Fig.  5.  periment  consists  ,...■>., 
in  a  long  wire,  ^^^^^ 
which  is  made  into  a  close  coil,  and  connect- 
ed at  the  ends  with  a  pair  of  little  plates  of 
zinc  and  copper,  as  in  fig.  5.  On  placing  this 
system,  buoyed  by  a  piece  of  cork,  in  a  dish 
of  acidulated  water,  it  settles  itself  at  right 
angles  to  the  direction  of  the  magnetic  nee- 
dle, and  behaves  in  all  respects  like  a  mag- 
net situated  in  the  centre  of  the  coil,  and 
perpendicular  to  its  plane. 

It  is  now  necessary  to  examine  into  the 
relation  which  the  direction  of  the  current 
bears  to  the  poles  of  the  magnets  which  it  forms,  or  which  might 
represent  its  action.  If  A  B  be  a  wire  in  which  a  current  ^ 
is  descending,  as  marked  by  the  arrow,  and  a  needle,  N  S, 
is  placed  transverse  to  it,  the  right-hand  end  of  the  needle 
^  becomes  the  north,  and  left-hand  end  of  the  nee- 
zqii  die  the  south  pole  ;  if  the  direction  of  the  current  ^^ 
^  ^  be  reversed,  the  north  pole  is  formed  at  the  left.  In  a 
circular  current,  the  position  of  the  pole  may  be,  conse- 
quentljr,  easily  seen;  the  current  A  B,  which  descends  in  front 

T 


lA 


B 


KS 


146    MAGNETIC    ACTION    OF    A    GALVANIC    CURRENT. 

of,  and  ascends  behind  the  needle,  produces  in  the  bar,  N  S,  a 
northern  polarity  to  the  right,  and  a  southern  to  the  left ;  the  ac- 
tion of  magnetic  currents  upon  each  other  supplies  the  explana- 
tion of  these  phenomena.  If  two  wires  carrying  Galvanic  currents 
be  brought  near  each  other,  there  is  attraction  or  repulsion,  accord- 
ing to  the  direction  of  the  currents ;  if  the  two  currents  be  in  the 
same  direction,  the  wires  attract  j  if  in  opposite  directions,  the  wires 
^  m  repel  each  other.  The  cause  is  evident  on  inspecting 
^'^  the  figure :  the  upper  wires  being  arrows  which  carry 
^2S  currents  in  the  same  direction,  they  act  on  each  other, 
as  should  a  pair  of  magnets  placed  transverse  to  their 
direction  j  the  ends  of  the  magnets  which  are  juxtaposed 
have  opposite  polarities,  and  attract ;  while  in  the  lower 
arrows,  where  the  currents  are  in  opposite  directions, 
the  effect  is  the  same  as  would  result  from  the  magnets 
of  which  the  contiguous  poles  are  of  the  same  name,  and  hence  re- 
pulsion. 

A  wire  carrying  an  electric  current  being  thus  a  magnet,  it  acts 
upon  permanent  magnets,  attracting  or  repelling,  according  to  its 
position,  and  generally,  from  the  combination  of  the  two  forces, 
generating  very  complex  and  singular  motions.  These  actions 
have  been  so  minutely  and  so  extensively  studied  as  to  constitute 
a  distinct  branch  of  this  department,  termed  electro-magnetism  ;  but 
being  unimportant  in  detail  except  in  physical  relations,  I  shall 
only  notice  the  experiments  by  which  CErsted  first  created  this 
branch  of  science,  and  which  have  ultimately  led  to  one  of  the  best 
measures  of  electricity,  the  multiplying  galvanometer. 

If  a  Galvanic  current  be  passed  over  a  magnet  in  the  direction  of 

the  arrow  in  the  figure,  and  the 
needle  be  movable  on  its  centre, 
it  endeavours  to  assume  a  position 
such  as  will  bring  it  parallel,  and 
with  opposite  poles  presented  to 
the  magnet  which  the  wire  repre- 
sents J  and  hence,  in  the  figure,  the 
motion  would  be  to  bring  the  south 
pole  above  the  plane  of  the  paper,  and  to  depress  the  north  pole 
below  it,  until  the  needle  had  assumed  a  position  perpendicular  to 
the  conducting  wire.  )f  the  current  had  been  in  the  opposite  di- 
rection, the  action  would  have  been  reversed,  and  the  north  pole 
would  have  been  turned  up  from  the  paper  j  but  if  the  current  be 
reversed  at  the  same  time  that  it  is  brought  under  the  needle,  as  in 
the  figure,  it  causes  a  deflection  similar  to  that  of  the  superior  por- 
tion, and  hence  the  angle  through  which  the  needle  moves  is  much 
increased.  If  the  needle  were  affected  only  by  the  current  passing 
over  or  under  it,  its  ultimate  position  would  be,  in  all  cases,  at  right 
angles  to  the  current ;  but  as  the  magnetic  action  of  the  earth  tends 
constantly  to  bring  it  back  to  its  direction  of  north  and  south,  the 
position  which  it  ultimately  assumes  is  the  resultant  of  the  two 
forces. 

The  deflection  of  the  needle  being  thus  an  indication  of  the  pas- 
sage of  an  electric  current  through  the  wire,  it  is  desirable  in  prac 


)i 


ASTATIC     COMBINATIONS    OF     MAGNETS.  147 

tice  to  give  the  power  of  the  current  as  much  eifect  as  possible, 
and  at  the  same  time  to  diminish  as  much  as  can  he  done  the  action 
of  the  terrestrial  magnetism.  The  first  is  effected  easily  by  increas- 
mg  to  the  desired  degree  the  number  of  turns  which  the  wire  makes 
round  the  needle ;  for  the  total  effect,  as  will  easily  be  understood 
from  the  description  of  the  figure  above,  is  proportional  to  the  num- 
ber of  coils  5  but  the  diminution  of  the  effect  of  the  earth  upon  the 
needle  requires  some  more  care.  If  the  needle  be  made  but  feebly 
magnetic,  the  power  of  the  current  to  turn  it  diminishes  just  as 
much  as  the  power  of  the  earth  to  prevent  its  turning,  and  there  is 
hence  nothing  gained  j  but  the  object  is  effected  by  using  a  combi- 
nation of  two,  three,  or  four  powerful  needles,  so  arranged  that 
with  regard  to  the  earth  they  are  made  to  represent  one  very  feeble* 
needle.  Thus,  in  the  figure,  the  three  magnets  N  and  S,  being 
suspended  with  their  opposite  poles  next  one 
another,  act  on  each  other  so  powerfully  that. 


Du 


the  remote  and  weaker  opposing  action  of  the     j^^ 
earth  becomes  almost  insensible.     A  current 


C  = 


air 


& 


3]sr 


passing  in  the  direction  of  the  arrows,  C,  E,      g, 

D,  will  tend  to  depress  the  north  poles  of  the 
upper  and  lower,  and  the  south  pole  of  the  middle  needle  below  the 
plane  of  the  paper ;  and  when  it  passes  under  the  middle  needle, 
its  action  upon  it  will  be  the  same,  since  its  direction  is  reversed. 
The  amount  of  deflection  of  such  a  system  of  needles  will  still  be 
regulated  by  residual  terrestrial  influence ;  but  as  this  may  be  ren- 
dered as  small  as  may  be  wished,  the  delicacy  of  the  apparatus  may 
be  increased  without  limit.  It  is  not  desirable  that  the  system  of 
needles  should  be  completely  astatic,  that  is,  indifferent  to  the  earth, 
for  then  the  degree  of  deflection  by  a  given  current  would  be  af- 
fected by  trivial  and  accidental  causes ;  but  by  leaving  a  small  resi- 
due of  terrestrial  magnetic  efiect,  the  current  acts  against  this,  and 
thus  produces  a  deflection  subject  to  an  assignable  law,  by  which 
the  strength  of  the  current  may  be  determined.  Within  a  certain 
limit,  about  30^,  the  angle  of  deflection  is  proportional  to  the  quan- 
tity of  electricity  flowing  along  the  wire,  but  beyond  that  it  follows 
a  more  complicated  law,  which,  as  involving  mathematical  relations, 
I  shall  not  admit  here.  To  obtain  a  greater  degree  of  delicacy  and 
uniformity  of  action,  the  system  of  needles  is  in  all  good  instruments 
hung  by  a  thread  of  glass  or  of  silk,  like  the  beam  of  Coulomb's 
balance  (page  113).  The  deflecting  force  then  acts  against  the  force 
of  torsion,  and  the  resistance  to  be  overcome  is  reduced  to  its  sim- 
plest possible  conditions. 

The  galvanometer,  such  as,  with  the  thermo-pile,  constitutes  the 
thermo-multiplier,  is  represented  in  section  and  in  perspective  in 
the  following  figures  ;  the  same  letters  apply  to  both.  A,  B,  C  is  the 
frame  around  which  the  copper  wire  is  coiled,  the  ends  T  of  which 
terminate  in  the  metallic  tubes  F,  F'.  This  frame  is  fixed  on  a  hor- 
izontal plate  D,  E,  which  can  turn  in  its  own  plane  around  its  cen- 
tre by  means  of  a  toothed  wheel  and  endless  screw,  which  are  put 
in  motion  by  the  button  G.  Q,  M,  N  is  the  support  of  the  astatic 
system  of  two  magnetic  needles,  suspended  to  a  thread  of  cocoon 
silk  V,  L.     R,  S  is  the  glass  cylinder,  secured  by  brass  rings  P,  S, 


148       CONSTRUCTION     OF     THE     GALVANOMETER. 


Y,  Z,  which  covers  the  apparatus,  and  rests  on  the  base  K,  I.  A 
graduated  semicircle,  accurately  divided,  is  drawn  upon  the  card, 
and  by  means  of  the  supporting  screws,  and  the  movement  of  the 
frame  A,  B,  C,  the  upper  needle  is  brought  to  be  exactly  parallel  to 
the  coils,  and  to  point  to  the  commencement  of  the  scale,  being 
regulated  in  its  height  by  means  of  the  screw  X,  with  which  the 
silk  thread  is  in  connexion. 

Where  the  current  to  be  measured  by  the  galvanometer  is  deri- 
ved from  a  thermo-electric  combination,  it  is  necessary  that  the 
wire  should  be  much  thicker  than  for  a  similar  current  from  a  hydro- 
electric source,  as  the  low  intensity  of  the  fluid  thrown  into  motion 
by  heat  might  cause  false  indications  of  its  quantity,  unless  an  am- 
ple path  were  opened  through  the  best  conductors  for  it ;  the  num- 
ber of  coils  for  a  thermo-electric  galvanometer  should  also,  for  the 
same  reason,  be  as  few  as  possible.  It  is,  therefore,  not  usual  to 
employ  the  same  instrument  for  these  two  kinds  of  researches. 
The  position  of  the  galvanometer  in  employing  the  thermo-electric 
pile  in  the  researches  on  radiant  heat,  has  been  described,  page  98, 
and  its  use  in  measuring  the  quantity  of  electricity  flowing  from 
galvanic  sources,  which  has  been  already  partly  noticed,  will  be  far- 
ther described  in  a  future  place. 

The  passage  of  an  electric  current  in  the  vicinity  of  any  substance 
capable  of  assuming  magnetic  properties  is  thus,  by  what  has  pass- 
ed, shown  to  be  suflicient  for  their  excitation,  and  conversely  if  a 
magnet,  whether  permanent  or  temporarily  produced,  be  brought 
near  a  substance  through  which  an  electric  current  may  circulate, 
a  current  is  immediately  formed,  the  direction  of  which  is  always 
the  same  as  that  of  a  pre-existing  current,  which  would  have  con- 
ferred on  the  magnet  the  properties  which  it  actually  has.  In  like 
manner,  one  current  may  generate  another  in  a  closed  conductor 
near  it,  precisely  as  one  magnet  may  produce  another,  or  that  a 
body  statically  excited  may  induce  the  electric  condition  on  the 


bodies  in  its  neighbourhood ;  but  such  peculiar  infiu^ces  are  too 
removed  from  the  proper  domain  of  chemistry  to  justify  any  detail- 
ed description  of  them. 

In  concluding  this  section  of  the  subject  of  electricity,  it  is,  however,  important 
to  prevent  its  being  supposed  that,  by  the  omission  of  such  considerations,  they  are 
to  be  considered  as  of  inferior  interest  in  the  phenomena  of  nature.  It  is  so  much 
the  reverse,,  that  perhaps  one  of  the  most  active  sources  of  the  electricity  which 
we  shall  find  to  play  a  most  important  part  in  chemical  combination,  is  derived  from 
the  induction  of  the  magnetic  influence  of  the  earth  itself :  for  the  earth  being  ren- 
dered magnetic  by  means  of  the  thermo-electric  currents  which  circulate  around 
it  spirally  from  the  equator  to  the  poles,  it  is  sufficient  to  bend  a  bit  of  copper  wire 
into  a  ring,  and  whirl  it  round  the  finger  in  the  plane  of  the  magnetic  equator,  to 
obtain  a  current  through  the  wire.  A  disk  of  copper  revolving  in  this  plane  is  a 
source  of  electricity  derived  from  the  inductive  influence  of  the  earth,  differing,  in- 
deed, amazingly  from  the  brilliant  excitation  of  the  thunder-cloud,  but  surpassing 
it  far  in  real  power  of  effect,  and  in  the  quantity  of  the  electric  fluid  actually  brought 
into  play.  We  arrive  here,  indeed,  at  the  extreme  modification  of  this  active  and 
omnipresent  force  :  we  found  it  in  the  commencement,  though  existing  in  exceed- 
ingly small  quantity,  preservable  only  by  the  very  best  insulating  means,  and  mani- 
festing its  tendency  to  escape  by  the  attractions,  the  flashes,  the  mechanical  vio- 
lence which  characterize  machine  electricity ;  while,  in  the  form  of  magnetism,  or 
of  a  magneto- electric  current,  though  present  in  a  quantity  many  millions  of  times 
greater,  it  flows  uniformly,  and  almost  insensibly,  along  the  perfect  conductors 
through  which  alone  it  is  competent  to  pass,  and  it  requires  particular  care  to  suc- 
ceed in  demonstrating  its  heating,  its  luminous,  or  its  mechanical  effects  ;  but  we 
recognise  in  it,  nevertheless,  the  untiring  agent  by  which  the  inorganic  superstruc- 
ture of  the  habitable  glob*  has  been  produced,  by  which  the  depositories  of  the  most 
important  metals  in  the  clefts  of  rocks  have  been  accumulated,  and  which  being 
thus  the  safeguard  of  navigation,  the  source  of  all  metallurgic  industry,  becomes  not 
less  important  to  the  civilization  of  mankind  at  large,  than  it  is  found,  from  its  par- 
amount influence  on  chemical  affinity,  its  power  to  separate  those  elements  most 
intimately  joined,  and  to  effect  the  union  of  those  which  appear  most  adverse  to 
mutual  combination,  as  well  as  the  facility  with  which  its  principles  may  be  applied 
to  the  explanation  of  the  laws  of  chemical  phenomena,  to  be  available  in  the  hands 
of  the  philosopher  for  the  advancement  of  science. 

To  the  chemist,  therefore,  the  most  useful  property  of  electricity  is  the  power 
which  it  possesses  of  modifying,  annulling,  or  superseding  chemical  affinity.  I  have 
liitherto  avoided  as  much  as  possible  involving  any  ideas  of  chemical  decomposition 
in  the  account  of  electricity  just  given,  restricting  myself  to  narrate  such  circum- 
stances as  might  serve  for  the  recognition  of  bodies  by  means  of  their  electrical 
properties,  independent  of  their  chemical  constitution.  But  the  question  whether 
electrical  influence  and  affinity  are  identical,  or  what  are  their  exact  relations, 
and  the  discussion  of  the  theory  of  electro-chemical  combination,  still  remain,  and 
will  be  examined  when,  first,  the  nature  of  affinity  and  the  distinction  between  it 
and  the  action  of  cohesive  force  have  been  described,  and  the  general  system  of  nom 
eaclature  by  which  chemical  substances  are  designated  has  been  briefly  noticed 


CHAPTER  V. 

OF    CHEMICAL    NOMENCLATURE. 


The  general  properties  and  laws  of  the  physical  agents,  cohesion, 
light,  heat,  and  electricity,  having  been  now  described  so  far  as  was 
necessary,  that  we  may  avail  ourselves  of  those  properties  in  char- 
acterizing the  substances,  elementary  or  compound,  whose  more  pe- 
culiarly chemical  relations  we  shall  now  proceed  to  study,  it  is  ne- 


150 


PRINCIPLES  OF  NOMENCLATURE. 


cessary  to  prefix  to  the  description  of  the  forces  by  wliich  chemical 
union  is  effected,  and  of  the  laws  by  which  it  is  controlled,  a  short 
statement  of  the  principles  upon  which  the  names  of  the  substances 
to  which  there  will  be  frequent  occasion  to  refer  have  been  con- 
structed. 

There  are  at  present  known  fifty-five  substances  which  the  chemist 
has  not  been  as  yet  able  to  separate  into  other  elements.  These  are 
distinguished  by  the  following  names : 


Oxygen, 

0. 

Potassium, 

K. 

Arsenic, 

As. 

Hydrogen, 

H. 

Sodium, 

Na. 

Antimony, 

Sb. 

Nitrogen, 

N. 

Lithium, 

Li. 

Tungsten, 

W. 

Carbon, 

C. 

Barium, 

Ba. 

Molybdenum, 

Mo. 

Boron, 

B. 

Strontium, 

Sr. 

Tantalum, 

Ta. 

Silicon, 

Si. 

Calcium, 

Ca. 

Chromium, 

Cr. 

Sulphur, 

s. 

Magnesium, 

Mg. 

Vanadium, 

V. 

Selenium, 

Se. 

Aluminum, 

Al. 

Uranium, 

U. 

Phosphorus, 

P. 

Glucinum, 

G. 

Gold, 

Au. 

Chlorine, 

CI. 

Zirconium, 

Zr. 

Iridium, 

Ir. 

Iodine, 

I. 

Thorium, 

Th. 

Osmium, 

Os. 

Bromine, 

Br. 

Yttrium, 

Y.' 

Platinum, 

PI. 

Fluorine, 

F. 

Cerium, 

Ce. 

Tin, 

Sn. 

Tellurium, 

Te. 

Lanthanum, 

Ln. 

Lead, 

Pb. 

Mercury, 

Hg. 

Manganese, 

Mn. 

Bismuth, 

Bi. 

Zinc, 

Zn. 

Iron, 

Fe. 

Silver, 

Ag. 

Cadmium, 

Cd. 

Copper, 

Cu. 

Palladium, 

Pd. 

Cobalt, 

Co. 

Titanium, 

Ti. 

Rhodium, 

R. 

Nickel, 

Ni. 

By  the  combination  of  these  bodies  among  each  other,  the  various 
substances  which  exist  in  nature  are  produced. 

These  simple  bodies  have  been  divided,  from  the  earliest  days  of 
accurate  chemistry,  into  two  classes,  the  metallic  and  the  non-me- 
tallic elements.  The  first  thirteen  in  the  list  are  non-metallic  ;  the 
remaining  bodies  are  metallic.  It  is  found,  however,  that  this  di- 
vision is  only  popularly  correct ;  no  matter  how  we  may  define  a 
metal,  we  cannot  avoid  breaking  through  connexions  of  the  most  in- 
timate and  important  kind  if  we  endeavour  to  retain  the  class  of 
metals  as  one  founded  on  really  existing  chemical  principles.  Thus, 
in  density  and  lustre,  arsenic  and  tellurium  are  indubitably  metals ; 
and  yet,  if  we  class  these  bodies  with  copper  or  lead,  we  break  through 
all  laws  of  chemical  analogy,  for  in  their  combinations  they  assim 
ilate  themselves  most  perfectly,  one  to  sulphur,  and  the  other  to 
phosphorus.  In  selenium,  also,  the  metallic  characters  are  so  feebly 
marked,  that  even  did  we  not  know  that  by  its  properties  it  must  be 
classed  with  sulphur,  we  could  not  place  it  as  a  metal  without  great 
doubt. 

In  describing  the  simple  bodies,  I  shall  retain  as  a  division  the 
chemistry  of  the  metals,  for  the  classification,  like  all  those  which 
have  been  long  in  extensive  use,  has  in  some  respects  much  utility 
and  truth;  but  in  cases  where  the  study  of  certain  bodies  will  be  fa- 
cilitated by  departing  from  it,  I  shall  not  hesitate  to  do  so.  In  order 
to  avoid  confusion  subsequently,  I  shall  here  describe,  as  succinctly 
as  possible,  the  nomenclature  which  has  been  adopted  in  chemistry ; 
for  in  a  science  where  the  multiplicity  of  objects  to,  be  noticed  is 
so  great,  it  is  of  the  highest  importance  that  the  principles  upou 


NOMENCLATURE     OF     LAVOISIER    AND    GUYTON.    151 

which  the  names  of  these  objects  are  founded  should  be  clearly- 
understood. 

In  all  conditions  of  science,  the  nomenclature  has  been  regulated 
by  the  prevalent  theoretical  ideas  of  the  time,  and  it  is  probably  vain 
to  look  for  a  system  of  names  which  shall  tell  what  the  bodies  really 
are,  and  not  pretend  to  tell  more  ;  for  that  would  suppose  that  we 
knew  what  the  bodies  are,  whereas,  in  the  most  perfect  state  of 
science,  we  only  know  what  we  believe  them  to  be.  Thus,  at  a  time 
when,  by  a  mal-application  to  chemistry  of  the  analogy  of  the  human 
body  and  its  soul,  all  bodies  were  looked  upon  as  having  a  volatile 
and  a  fixed,  an  active  and  an  inert  element,  the  names  of  spirit  of 
wine,  spirit  of  hartshorn,  and  spirit  of  salt  were  invented ;  at  a  later 
period,  when  the  theory  of  phlogiston  prevailed  in  the  minds  of 
chemists,  the  spirit  of  salt  became  dephlogisticated  marine  acid ; 
when  the  important  functions  of  oxygen  were  pointed  out  by  Lavoi- 
sier, the  name  was  in  his  theory  changed  to  oxymuriatic  acid  ;  and, 
finally,  when  the  present  view  was  introduced  by  Davy,  the  name 
hydrochloric  acid  became  the  most  correct.  The  cause  of  this  is, 
that  in  a  good  system  of  chemical  nomenclature,  we  require  two  con- 
ditions which  it  is  very  difficult  to  successfully  combine ;  that  the 
name  shall  not  only  tell  us  that  the  substance  is  an  independent  sub- 
stance, but  that  it  shall  give  to  us  an  idea  of  its  most  important  chem- 
ical character,  its  composition ;  thus  the  name  prussic  acid  is  less 
strictly  scientific  than  that  of  hydrocyanic  acid,  which  shows  us  that 
its  elements  are  hydrogen  and  cyanogen ;  and  iron  pyrites  gives  a 
less  perfect  picture  of  the  body  it  describes  than  the  words  bisulphuret 
of  iron.  The  necessity  for  indicating  by  the  chemical  name  of  a 
body  its  chemical  composition,  is  thus  what  renders  chemical  nom- 
enclature at  once  so  variable  and  so  complex,  but  it  is  also  that  which 
alone  enables  us  to  connect  distinct  ideas  with  our  words. 

The  benefit  conferred  upon  chemistry  by  the  nomenclature  intro- 
duced by  Lavoisier  and  Guyton  was  scarcely  inferior  in  its  impor- 
tance to  the  accurate  ideas  of  combination  in  which  it  had  its  origin. 
The  removal  of  the  unconnected  and  unfounded  names,  which  had 
been  invented  by  the  older  chemists,  and  the  invention  of  the  idea 
that  every  name  of  a  compound  body  should  express  its  composition, 
involved  the  increase  of  accuracy  in  the  minds  of  those  chemists  by 
whom  science  was  subsequently  to  be  prosecuted,  which  may  be 
looked  upon  as  the  most  fertile  source  of  the  discoveries  made  up 
to  the  present  day. 

The  names  most  employed  in  chemistry  are  acid^  base,  and  salt. 
The  word  acid  signifying  originally  sour,  was  applied  to  all  bodies 
which  tasted  like  vinegar.  The  word  base  signifies  any  substance 
which,  uniting  with  an  acid,  forms  a  compound,  of  which  it  is  the 
basis  or  foundation ;  and  the  compound  formed  by  their  union,  being 
generally  similar  to  common  salt  in  superficial  characters,  is  termed 
a  salt.  Thus,  oil  of  vitriol  tasting,  when  mixed  with  water,  sour,  is 
an  acid ;  soda  is  a  base,  and,  when  combined,  they  form  the  well- 
known  salt  called  after  Glauber,  who  discovered  it.  Such  are  the 
names  of  those  classes  of  bodies,  the  discovery  of  which  dates  from 
a  remote  period. 

Acting  on  the  principle  that,  in  naming  a  simple  substance,  the 


152     SIMPLE     BODIES     AND     PRIMARY     COMPOUNDS. 

name  should  be  derived  from  its  most  characteristic  property,  La- 
voisier formed  the  word  "  oxygen"  from  o^vg^  acid,  and  yevvao),  I 
generate,  to  signify  the  important  substance,  the  functions  of  which 
he  was  the  first  to  show,  and  which  he  imagined  to  have  the  peculiar 
property  of  forming  acids.  In  like  manner,  he  constructed  the  word 
"hydrogen"  from  vdcop,  water,  and  yevvaio^to  express  its  most  im- 
portant property,  of  being  an  element  of  water.  This  principle  can, 
however,  seldom  be  rigidly  acted  on  j  for  example,  oxygen  is  as 
much  a  water  former  as  hydrogen  ;  and  the  name  of  oxygen  itself  is 
not  without  objection,  as  the  pre-eminence  as  acid  former,  which 
Lavoisier  imagined  it  to  possess,  has  been  latterly  overthrown.  In 
the  case  of  simple  bodies,  names  derived  from  quite  arbitrary  sources, 
as  tellurium  from  tellus^  the  earth ;  selenium  from  a7}?i7jV7],  the  moon ; 
vanadium  and  thorium  from  Vanadis  and  Thor,  deities  of  Scandi- 
navian mythology  ;  chlorine  from  x^<^pog,  yellowish  green  (its  col- 
our) ;  and  similarly  iodine  from  loetdrjg  (like  a  violet),  have  a  great 
superiority  over  those  which,  by  attempting  to  teach  more  when 
first  invented,  have  the  disadvantage  of  teaching  falsely  at  a  future 
period. 

The  simple  bodies,  combining  with  each  other,  form  compound 
bodies  of  the  first  order,  or  binary  compounds.  The  names  of  those 
binary  compounds  which  contain  oxygen  are  of  two  kinds,  according 
as  the  compound  possesses  acid  properties  or  not  j  if  it  be  an  acid, 
the  word  acid  is  added  to  that  of  the  other  body  to  which  the  ter- 
mination ic  is  joined.  Thus  the  acid  compound  of  sulphur  and 
oxygen  is  sulphuric  acid ;  the  acid  compound  of  phosphorus  and 
oxygen  is  phosphoric  acid.  It  frequently  happens  that  the  same 
body  forms  with  oxygen  two  acids,  in  which  case,  that  containing 
most  oxygen  retains  the  terminal  zc,  while  that  in  which  there  is 
least  oxygen  ends  in  ous.  Thus  there  is  sulphurous  acid^  and  phos- 
phorous acidj  consisting  of  sulphur  united  with  less  oxygen  than 
could  form  the  sulphuric  or  the  phosphoric  acids.  Many  bodies  form, 
however,  with  oxygen  more  than  two  acids,  and  in  this  case  a 
new  principle  of  nomenclature  has  been  introduced:  the  words 
?;7ro,  hypo,  and  vnepj  hyper,  under  and  over,  are  prefixed  to  the  de- 
grees terminating  as  before  stated.  Thus  there  is  an  acid  of  sul- 
phur containing  less  oxygen  than  the  sulphurous  acid,  and  it  is  call- 
ed hypo-sulphurous  acid  ;  and  also  an  acid  containing  more  oxygen 
than  the  sulphurous,  but  less  than  the  sulphuric  acid  :  this  might  be 
called  either  hyper-sulphurous  or  hypo-sulphuric  acid  ;  the  latter  name 
has  been  universally  adopted.  Chlorine  forms,  with  oxygen,  four 
acids,  which  are  the  hypo-chlorous  acid,  chlorous  acid,  chloric  acid, 
and  hyper-chloric  acid,  or,  as  it  is  often  called,  substituting  the  short- 
er Latin  per  for  the  Greek  virep,  perchloric  acid. 

In  cases  where  the  compound  formed  with  oxygen  is  not  an  acid, 
it  is  termed  2iXi  oxide  of  the  substance  with  which  the  oxygen  is  uni- 
ted. Thus  oxide  of  lead,  oxide  of  iron,  oxide  of  copper,  are  re- 
spectively the  compounds  of  oxygen  with  lead,  with  iron,  and  with 
copper.  In  many  cases,  where  oxygen  unites  with  bodies  in  more 
than  one  proportion,  one  compound  may  be  an  acid,  and  the  other 
not.  Thus  manganese, uniting  with  oxygen,gives  manganic  acid  and 
permanganic  acid,  but  in  a  lower  degree  of  oxidation  it  forms  several 


VARIOUS     CLASSES     OF     PRIMARY     COMPOUNDS.    153 

oxides  of  manganese.  For  as  a  substance  uniting  with  oxygen  may- 
form  many  acids,  so  may  it  form  many  oxides  also  3  and  in  such 
cases  it  becomes  necessary  to  distinguish  them  from  one  another. 
This  is  done  by  the  adoption  of  the  Greek  words  nporog,  devrepog, 
TpLTog  (first,  second,  third),  prefixed  to  the  word  oxide.  Thus  we 
say  protoxide  of  lead,  deutoxide  of  lead,  tritoxide  of  iron ;  the  ox- 
ide which  contains  most  oxygen  is  often  called  the  peroxide,  and  that 
which  contains  least  the  suboxide,  as  peroxide  of  manganese,  suboxide  of 
copper.  The  word  sesqui  (one  and  a  half)  is  also  used  for  oxides  in- 
termediate between  protoxides  and  deutoxides,  but  the  nomenclature 
then  involves  numerical  proportions,  which  will  require  to  be  de- 
scribed herafter. 

Some  other  simple  non-metallic  bodies,  in  combining  with  the  met- 
als, form  compounds,  of  which  the  names  are  constructed  on  the  same 
plan  as  those  of  the  metallic  oxides.     Thus, 


Chlorine  forms  Chlorides. 
Iodine  "      Iodides. 


Bromine  forms  Bromides. 
Fluorine      "      Fluorides. 


The  compounds  of  sulphur  with  the  metals  having  been  popularly 
named  before  Lavoisier's  time,  and  it  being  desirable  to  retain,  as 
much  as  possible,  the  names  already  in  common  use,  a  different 
form  of  termination  is  adopted  for  that  body  and  some  others. 
Thus, 


Sulphur     gives  Sulphurets. 
Selenium      "      Seleniurets. 
Tellurium    "      Tellurets. 
Carbon         "      Carburets. 


Nitrogen,   gives  Nitrurets. 
Phosphorus    "     Phosphurets 
Arsenic  "     Arseniurets. 


To  distinguish  between  the  different  sulphurets  or  chlorides,  &c., 
of  the  same  metal,  the  Greek'prefixes  are  adopted,  as  in  the  case  of 
oxides.  We  have  thus  proto-chloride  and  dcuto- chloride  of  manga- 
nese ;  also  perchlorides  and  subchlorides.  The  Latin  bis  is  often 
substituted  for  the  Greek  deuto,  as  the  bichloride  of  tin  in  place  of 
the  deuto-chloride.  Among  Continental  chemists,  names  which 
should  be  translated  chloruret  in  place  of  chloride,  and  sulphide  in 
place  of  sulphuret,  are  frequently  employed  ;  but  as  these  are  found- 
ed on  certain  theoretical  ideas  that  have  not  yet  been  discussed,  the 
propriety  of  adopting  such  additional  terminations  cannot  be  con- 
sidered until  we  have  proceeded  farther. 

Where  two  non-metallic  bodies  are  united,  it  is  a  question  how 
the  name  of  the  compound  should  be  formed.  Thus,  in  a  compound 
of  chlorine  and  phosphorus,  should  it  be  called  chloride  of  phos- 
phorus or  phosphuret  of  chlorine  1  This  is  decided  by  referring  to 
the  classification  of  the  simple  bodies  which  will  be  hereafter  given, 
and  which  is  founded  on  a  view  of  all  their  chemical  properties  taken 
together.  Whichever  element  stands  highest  in  the  scale  gives 
the  characteristic  name  to  the  compound  body.  Thus  chlorine  is 
above  phosphorus,  and  we  say  chloride  of  phosphorus.  Iodine  is  also 
above  phosphorus,  and  we  say  iodide  of  phosphorus  ;  but  iodine  is 
below  chlorine,  and  we  hence  call  the  compound  which  they  form 
chloride  of  iodine. 

The  combination  of  the  metals  with  each  other,  except  in  some 

U 


154     NAMES  OF  SECONDARY  COMPOUNDS. 

peculiar  instances,  are  termed  alloys.  Thus  we  say  brass  is  an  alloy 
of  copper  and  zinc  \  fusible  metal  is  an  alloy  of  bismuth,  tin,  and 
lead.  Where  one  metal  is  mercury,  the  alloy  is  termed  an  amalgam 
of  the  other  metal ;  thus,  an  amalgam  of  silver  is  an  alloy  of  mercury 
and  silver  ;  an  amalgam  of  tin  is  an  alloy  of  mercury  and  tin.  Arse- 
nic and  tellurium  are  so  far  removed  from  the  metals  by  their 
chemical  characters,  that  their  compounds  with  the  proper  metals 
have  the  peculiar  termination  in  uret. 

By  the  union  of  two  primary  compounds  there  is  formed  a  sec- 
(mdary  compound.  These  secondary  compounds  are  generally  termed 
saks.  The  word  salt  is,  however,  applied  to  numerous  classes  of 
primary  compounds.  Thus,  the  metallic  iodides,  chlorides,  bromides, 
and  fluorides  are  recognised  as  salts.  It  is  now  also  a  debated  ques- 
tion whether  the  bodies  formed  by  the  direct  union  of  an  acid  and 
an  oxide  are  really  primary  or  secondary  compounds ;  but  I  shall 
now  describe  only  the  ordinary  nomenclature  of  those  bodies,  post- 
poning the  discussion  of  their  intimate  constitution  to  another  place. 
When  an  acid  and  a  metallic  oxide,  both  primary  compounds,  com- 
bine to  form  a  secondary  compound  or  a  salt,  the  specific  name  of 
the  salt  is  that  of  the  base,  without  any  change  \  we  thus  say  a  salt 
of  soda^  a  salt  of  oxide  of  copper  ;  the  generic  name  is  taken  from  the 
acid,  the  word  acid  being  omitted,  and  the  final  ic  being  changed  into 
ate,  or  the  final  ous  into  ite.  There  is  thus  formed  from  sulphuric 
acid  and  soda  sulphate  of  soda.  From  nitric  acid  and  oxide  of  lead, 
nitrate  of  oxide  of  lead:  From  sulphurous  acid  and  potash,  sulphite 
of  potash.  From  hypochlorous  acid  and  lime,  hypochlorite  of  lime. 
Where  the  salt  contains  an  oxide  of  one  of  the  common  metals,  it 
is  usual  to  suppress  the  words  of  oxide  in  its  name,  and  thus  to  say 
sulphate  of  copper  in  place  of  sulphate  of  oxide  of  copper ;  nitrate 
of  lead  in  place  of  nitrate  of  oxide  of  lead.  The  strict  correctness 
of  language  is  thus  sacrificed  ;  but  if  the  idea  of  the  composition  of 
the  salt  be  held  clearly  in  the  mind,  the  abbreviation  is  not  injuri- 
ous ;  this  mode  of  naming  salts  is  so  universal,  that  breaking  in  on 
it  might  be  productive  of  more  injury  than  allowing  it  to  remain  j  I 
shall  therefore  say,  for  example,  nitrate  of  lead,  understanding,  how- 
ever, that  the  nitric  acid  is  combined  not  with  lead,  but  with  oxide 
of  lead. 

It  frequently  happens  that  a  metal  forming  with  oxygen  two  ox- 
ides, will  form  with  acids  a  class  of  salts  for  each  oxide.  In  this 
case  the  words  proto,  deuto,  sesqui,  or  per,  by  which  the  oxides  are 
distinguished  from  each  other,  are  prefixed  to  the  generic  name  of 
the  salt.  We  thus  say  proto-sulphate  of  iron,  persulphate  of  iron  ', 
indicating  that  there  is  in  one  salt  the  protoxide,  and  in  the  other 
the  peroxide  of  iron.  We  have  sesqui-sulphate  of  manganese,  and 
deuto-sulphate  of  platinum.  The  relative  quantity  of  acid  and  base 
being  liable  to  variation,  there  are  acid  salts  with  an  excess  of  acid, 
and  basic  salts  with  an  excess  of  base.  In  such  case,  the  proportion 
of  acid  is  marked  by  the  Latin  bi,  ter,  &c.,  as  bisulphate  of  potash,  and 
the  proportion  of  base  where  it  is  in  excess  by  the  Greek  dtg,  rpic^ 
&CC.,  as  di-sulphate  of  zinc,  tri-sulphate  of  mercury  ;  or  still  iDctter 
by  the  words  bi-basic,  tri-basic,  &c.,  to  indicate  the  quantity  of  base ; 
there  is  thus  tribasic-sulphate  of  mercury,  quadribasic-sulphate  of 
copper,  and  so  on. 


TERNARY  AND  QUATERNARY  COMPOUNDS.   155 

Th«re  are  many  other  kinds  of  secondary  compounds  than  the  salts 
just  noticed.  Thus  water  enters  into  numerous  compounds,  which 
are  called  hydrates.  This  water  may  act  in  very  many  different  ca- 
pacities, and  its  nomenclature  must  be  varied  accordingly,  as  will 
be  seen  under  its  proper  head ;  but  where  we  wish  to  indicate  that 
a  body  contains  water,  without  determining  more  nearly  the  specific 
function  of  the  water,  we  describe  the  body  as  being  hydrated. 

Oxides  and  chlorides  combine  together  to  form  secondary  com- 
pounds, which  are  called  oxychlorides,  as  the  oxychlorides  of  mercury^ 
the  oxychloride  of  lead.  Oxides  and  sulphurets  combining  form  oxy 
sulphurets,  as  oxysulphuret  of  antimony.  Chlorides  and  sulphurets 
form  by  their  union  chloro-sulphurets^  as  chloro-sulphuret  of  mercury. 

When  two  chlorides  combine,  the  compound  is  termed  a  double 
chloride^  or  a  chloride  of  the  metals  ;  as  the  chloride  of  gold  and  sodi- 
um, the  chloride  of  copper  and  potassium.  In  the  same  way  there  are 
double  iodides  and  double  bromides.  But  where  two  sulphurets  unite, 
the  nomenclature  has  received  an  important  change. 

Berzelius  has  proved  that,  in  very  numerous  cases,  where  a  body 
forms  an  acid  with  oxygen,  which  acid  uniting  with  a  metallic  oxide 
forms  a  salt,  that  body,  uniting  also  with  sulphur,  gives  a  sulphur 
acid,  which,  uniting  with  a  sulphuret  of  a  basic  metal  (a  sulphur 
base),  forms  what  he  terms  a  sulphur  salt.  Thus  double  sulphurets 
are  salts,  consisting  of  a  sulphur  acid  united  to  a  sulphur  base 
Hence,  as  arsenic  combining  with  oxygen  forms  arsenious  acid,  so, 
uniting  with  sulphur,  it  produces  sulpho-arsenious  acid,  which,  uniting 
with  sulphuret  of  lead,  forms  sulpharsenite  of  lead,  precisely  as  the 
oxygen  acid,  uniting  with  oxide  of  lead,  produces  what  should  be 
called  oxyarsenite  of  lead.  The  prefix  oxy  is,  however,  not  usedj 
the  ordinary  salts  are  supposed  to  contain  the  oxygen  acid,  and  it 
is  only  where  a  salt  does  not  contain  an  oxygen  acid  that  an  addi- 
tional word  is  necessary  to  point  out  what  sort  of  acid  it  does  con- 
tain. Tellurium  and  selenium  act  like  sulphur  ;  there  are  tellurium 
acids  and  tellurium  bases,  selenium  acids  and  selenium  bases,  and  hence, 
in  place  of  calling  the  compound  of  seleniuret  of  antimony  and  se- 
leniuret  of  sodium  a  double  seleniuret,  it  is  called  the  selenio-sti- 
biate  of  sodium. 

An  attempt  was  made  to  assimilate  the  nomenclature  of  the  chlorine  and  iodine 
bodies  to  that  of  the  oxygen  and  sulphur  compounds  ;  thus,  to  call  chloride  of  mer- 
cury a  chlorine  acid,  and  chloride  of  sodium  a  chlorine  base,  and  the  compound 
which  they  form  a  chlorine  salt,  chlorohy  drargyrate  of  sodium.  This  idea,  howev- 
er, has  not  been  received  into  science ;  for,  indeed,  now  the  direction  of  the  ideas 
most  popular  am.ong  chemists  points  precisely  contrary,  and  in  place  of  assimilating 
the  double  chlorides  to  ordinary  oxygen  salts,  there  is  a  general  tendency  to  class 
the  ordinary  salts  along  with  the  simple  chlorides. 

Ternary  compounds  are  formed  by  the  union  of  two  secondary  com- 
pounds. Thus  dry  alum  is  a  compound  of  sulphate  of  potash  and  sul- 
phate of  alumina.  Compounds  of  this  order  seldom  exist  in  more 
than  one  proportion.  Alum  combining  with  water  to  produce  the 
crystallized  alum,  generates  a  quaternary  compound;  and  even  more 
complicated  stages  may  be  attained  ;  but  they  are  so  rare,  and  of  so 
little  scientific  importance,  that  they  do  not  require  notice  here. 

In  organic  chemistry,  the  principles  of  nomenclature  are  for  the 
most  part  identical  with  those  now  stated ;  where  deviations  occur, 
they  will  be  noticed  under  their  proper  heads.     The  progress  of  sci 


156  SYMBOLICAL     NOMENCLATURE. 

ence  has,  however,  introduced  remarkable  changes  in  the  mode  ot 
representing  the  constitution  of  bodies,  particularly  by  means  of  the 
symbolical  nomenclature  now  universally  adopted  after  Berzelius. 

In  the  list  of  the  simple  bodies  in  page  150,  the  name  of  each 
substance  is  accompanied  by  its  symbol,  which  is  generally  the  in- 
itial letter  of  its  Latin  name  ;  and  in  cases  where  the  name  of  more 
than  one  body  begins  with  the  same  letter,  they  are  distinguished 
by  adding  to  the  symbols  of  all  the  bodies  but  one  a  second  letter 
in  smaller  type,  which  may  be  the  second  letter  of  the  word,  or 
whatever  letter  will  best  serve  to  characterize  the  name. 

If  there  be  but  one  non-metallic  substance  in  the  group,  it  is  gen- 
erally selected  to  be  denoted  by  the  single  letter,  as  C.  and  P.  for 
.carbon  and  phosphorus,  while  the  metals  whose  symbols  have  the 
same  letter  are  denoted  by  Ca.,  Co.,  Cd.,  Ce.,  and  PL,  Ph.,  Pd.  Where 
there  are  more  than  one  non-metallic  body  commencing  with  the 
same  letter,  it  is  a  matter  of  indifference  which  is  designated  by 
the  one  or  by  the  two,  but  the  single  letter  is  generally  attached  to 
the  body  which  is  of  most  importance  in  chemical  phenomena. 
Thus  S.  is  sulphur,  while  Si.  and  Se.  denote  silicon  and  selenium 
respectively. 

The  symbols  of  compound  bodies  are  constructed  by  grouping  to- 
gether the  symbols  of  their  constituents;  thus  Pb.O.  represents  a 
compound  of  oxygen  and  lead ;  C.H.N.O.  a  compound  of  carbon, 
hydrogen,  nitrogen,  and  oxygen.  The  algebraic  sign  of  addition  is 
frequently  used  to  connect  symbols,  as  Cl.-f-S.,  chloride  of  sulphur  ; 
I  H-K.,  iodide  of  potassium.  But  I  shall  use  that  sign  only  where  I 
wish  to  express  that  the  bodies  so  connected  are  united  by  an  infe- 
rior degree  of  affinity ;  thus  Cl.Ca.  is  chloride  of  calcium  dry,  but 
when  crystallized  it  becomes  Cl.Ca.+6H.O.,  in  which  the  -f-  sign  is 
used  to  show  that  the  water  is  united  with  the  Ca.  CI.  by  a  power 
distinct  from,  and  inferior  to,  that  which  retains  Ca.  and  CI.  in  com- 
bination. Water  thus  combined  is  often  represented  by  the  symbol 
Aq.,  for  water  is  capable  of  acting  in  a  variety  of  ways  in  combina- 
tion, and,  as  will  be  shown  when  we  come  to  speak  of  the  chemical 
relations  of  water,  it  requires  to  be  expressed  sometimes  as  H.O.  and 
sometimes  as  Aq. 

But  that  which  requires  special  notice  in  speaking  of  symbolical 
nomenclature  is,  that  it  involves  essentially  the  idea  of  numerical 
relations.  Thus  the  symbols  Pb.  or  Cu.  do  not  call  up  to  the  mind 
of  the  chemist  the  simple  ideas  of  lead  or  copper,  but  of  a  quantity 
of  lead  and  of  a  quantity  of  copper,  in  the  proportion  of  103*6  and 
31*7,  which  is  termed  an  equivalent  of  each.  Thus,  also,  the  sym- 
bol Pb.O.  signifies  not  merely  a  compound  of  lead  and  oxygen,  but. 
specially  a  compound  of  an  equivalent  of  lead  and  an  equivalent 
of  oxygen,  in  the  proportion  by  weight  of  103-6  of  lead  and  8*0  of 
oxygen.  It  is  thus  that  the  symbol  Pb.Oj,  or  Pb.-f  20.,  which  rep- 
resents also  a  compound  of  lead  with  oxygen,  shows  to  the  chemist 
that  this  second  body  contains  to  the  same  103'6  of  lead  twice  as 
much,  or  16-0  of  oxygen,  as  had  existed  in  the  former.  Pb.O.  is 
therefore  protoxide,  and  Pb.Oi  is  the  peroxide  of  lead. 

The  details  of  the  application  of  those  symbols  involve  thus  the 
numerical  laws  of  constitution,  which  have  yet  to  be  described  ,*  and 


NATURE     OF     CHEMICAL     AFFINITY.  157 

hence  it  is  unnecessary  to  develop  their  arrangement  farther  at 
present.  It  was  necessary  to  allude  so  far  to  them  when  speaking 
of  nomenclature,  as  I  may  have  occasion  to  introduce  some  of  them 
in  a  general  way  in  the  next  chapter. 


CHAPTER  VI. 

OF   CHEMICAL  AFFINITY,  AND   ITS  RELATIONS    TO    HEAT,  TO    LIGHT,  AND  TO 

COHESION. 

The  peculiar  power  by  which  we  suppose  chemical  phenomena  to 
be  produced,  is  specially  distinguished  from  cohesion,  and  from  aU 
other  forces  in  nature,  by  exerting  in  the  different  kinds  of  element- 
ary or  compound  substances  various  degrees  of  energy  j  and  by  its 
capability  of  acting  upon  certain  bodies  exclusively,  and  in  prefer- 
ence to  acting  upon  others,  which,  so  far  as  physical  circumstances 
go,  appear  equally  exposed  to  its  effects.  Thus,  if  to  some  liquid 
muriatic  acid  there  be  added  a  mixture  of  lime  and  magnesia,  the 
lime  will  all  dissolve  in  the  acid  before  any  trace  of  the  magnesia 
will  be  taken  up.  If  a  slip  of  iron  be  placed  in  a  cup  of  nitric  acid, 
a  large  quantity  of  deep  red  fumes  is  immediately  expelled  from 
the  acid,  with  an  appearance  of  boiling  or  effervescence ;  and  the 
iron  disappears,  being  taken  up  by  the  liquid  in  place  of  the  sub- 
stances which  had  been  expelled.  If  a  slip  of  copper  be  dipped  in 
the  acid,  the  same  effect  is  produced ;  but  if  the  iron  and  copper  be 
left  together  in  the  acid,  no  action  takes  place  upon  the  copper  until 
the  iron  shall  have  been  totally  dissolved.  The  muriatic  acid,  there- 
fore, presented  equally  to  lime  and  magnesia,  combines  with  the 
lime  in  preference,  and  the  nitric  acid  takes  up  copper,  giving  off, 
to  make  room  for  it,  a  quantity  of  gaseous  elements  (nitrous  acid 
fumes)  it  had  previously  contained ;  but  it  will  take  iron  in  prefer- 
ence to  copper,  if  the  two  be  presented  to  it  at  the  same  time. 
Chemical  affinity  is  therefore  elective  ;  it  chooses  among  a  variety 
of  bodies  which  it  will  act  upon,  and  is  thus  different  from  cohesion 
or  gravity,  which  will  act  upon  all  bodies  equally  exposed  to  their 
influence  at  the  same  time. 

In  the  example  of  the  metal  and  nitric  acid,  there  is  involved  a 
second  phenomenon,  which,  equally  with  elective  affinity,  is  char- 
acteristic of  chemical  force.  It  is  decomposition.  The  copper  can- 
not dissolve  in  the  nitric  acid  without  the  expulsion  of  another  sub- 
stance. By  a  simpler  example,  the  decomposition  may  be  rendered 
more  evident.  Sulphuret  of  hydrogen  consists  of  sulphur  and  hy- 
drogen ;  if  it  be  brought  into  contact  with  iodine,  the  iodine  expels 
the  sulphur  and  takes  the  hydrogen ;  the  sulphuret  of  hydrogen  is 
decomposed,  and  a  new  body,  iodide  of  hydrogen,  is  formed.  Here 
the  hydrogen  chose  between  iodine  and  sulphur,  and  preferred  the 
former  :  the  greater  affinity  for  the  iodine  caused  the  decomposition. 
Hydrogen  has,  however,  a  still  more  decided  tendency  to  combine 


158     PRINCIPLES     OF     ELECTIVE     DECOMPOSITION, 

with  chlorine ;  and  if  chlorine  be  brought  into  contact  with  iodide 
of  hydrogen,  the  iodine  is  in  its  turn  expelled,  and  chloride  of  hy- 
drogen formed.  Here  is  a  series  of  decompositions  depending  on 
the  relative  power  of  the  affinities  of  chlorine,  iodine,  and  sulphur 
for  the  one  body,  hydrogen.  Thus,  by  the  elective  affinity  of  an 
uncombined  body,  choosing  among  a  variety  of  other  bodies  all 
equally  uncombined,  there  is  produced  a  new  combination,  contain- 
ing that  for  which  its  affinity  was  strongest.  But  when  an  uncom- 
bined body  is  put  in  contact  with  two  substances  already  united,  it 
tends  to  separate  them,  to  combine  with  one  and  to  set  the  other 
free. 

If  we  could  combine  any  one  body,  as  hydrogen,  for  example, 
with  every  other  of  the  simple  substances,  we  might,  by  such  ex- 
periments as  those  described  with  the  sulphuret  of  hydrogen,  iodine, 
and  chlorine,  obtain  an  idea  of  the  exact  order  of  intensity  of  the 
affinity  of  each  of  them  for  hydrogen,  and  could  easily  represent, 
under  a  tabular  form,  such  an  idea.  This  has  accordingly  been  tried, 
and  was,  indeed,  the  result  of  the  first  sound  ideas  of  the  nature  of 
chemical  affinity  which  were  obtained.  It  was  not  done  completely 
in  any  case,  for  even  at  present  our  knowledge  is  not  sufficient  to 
enable  us  to  form  a  series,  including  all  the  simple  bodies.  It  was 
particularly  in  the  chemistry  of  the  salts  that  the  benefit  of  this 
principle  was  found,  and  it  was  to  explain  and  predict  the  result  of 
the  decomposition  of  salts  that  tables  of  the  elective  affinity  were 
constructed. 

It  has  been  stated  that,  if  lime  and  magnesia  be  placed  together 
in  contact  with  muriatic  acid,  the  acid  will  dissolve  all  the  lime  be- 
fore it  acts  upon  the  magnesia  j  the  affinity  of  lime  for  muriatic  acid 
is  therefore  greater  than  that  of  magnesia  for  the  same  acid,  and 
hence,  if  to  a  solution  of  magnesia  there  be  lime  added,  the  mag- 
nesia will  be  expelled  and  the  lime  will  take  its  place.  If  to  the 
lime  solution  of  soda  be  added,  the  lime  will  separate,  and  soda  may 
be  in  turn  expelled  by  potash.  On  the  other  hand,  there  are  many 
metallic  oxides  which  enjoy  a  still  more  feeble  affinity  than  magne- 
sia ;  thus,  if  to  a  solution  containing  oxide  of  iron,  magnesia  be 
added,  the  oxide  of  iron  is  thrown  down  and  the  magnesia  taken  in 
its  place.  In  this  manner  may  be  arranged  a  series  of  compounds, 
consisting  of  different  bases,  in  union  with  the  same  acid  j  and  by 
observing  the  order  of  decomposition  by  each  other,  a  view  of  the 
relative  affinities  which  they  exercise  may  be  fovmed.  If,  also,  a 
series  of  acids  be  combined  with  the  same  base,  a  similar  view  of 
their  relative  affinities  may  be  drawn  up.  Thus,  when  a  solution 
oi  potash  is  exposed  to  the  air,  it  absorbs  carbonic  acid,  for  which, 
therefore,  the  potash  has  an  affinity  of  a  certain  energy  j  on  adding 
acetic  acid,  the  carbonic  acid  is  expelled,  and  acetate  of  potash 
formed ;  on  adding  nitric  acid,  the  acetic  acid  is  expelled  from  it, 
and  nitrate  of  potash  formed  ;  and  from  this,  by  means  of  sulphuric 
acid,  the  nitric  acid  may  be  recovered,  the  potash  remaining  in  the 
state  of  sulphate. 

The  results  so  described  may  be  exhibited  as  follows,  by  writing 
in  a  column  the  names  of  the  different  acids,  in  the  order  of  their 
affinities  for  a  certain  base  (soda),  which  is  placed  at  top.     Similarly 


ORDER    OF     ELECTIVE    DECOMPOSITION.  159 

in  a  column,  at  the  top  of  which  is  placed  the  name  of  a  given  acid, 
the  various  bases  in  the  order  of  their  affinities  may  be  written. 
Thus: 


Soda. 
Sulphuric  acid. 
Nitric  acid. 
Muriatic  acid. 
Acetic  acid. 
Carbonic  acid. 


Muriatic  Acid. 

Potash. 

Soda. 

Lime. 

Magnesia. 

Oxide  of  iron. 


For  the  simple  bodies  similar  lists  might  be  constructed  :  thus,  in 
the  same  way  as  the  series  of  affinities  for  hydrogen  already  noticed, 
a  table  of  affinites  of  the  diffisrent  metals  for  oxygen  may  be  drawn 
up  from  observation.  If  to  a  solution  of  nitrate  of  silver,  in  which 
the  silver  is  combined  with  oxygen,  a  globule  of  mercury  be  placed, 
it  dissolves,  and  the  silver  is  set  free.  By  dipping  into  the  solution 
of  nitrate  of  mercury  a  slip  of  copper,  the  mercury  is  thrown  down, 
and  the  copper  takes  its  place.  From  the  nitrate  of  copper  the 
metal  may  be  thrown  down  by  lead,  and  the  lead  again  precipitated 
by  a  plate  of  zinc.  The  affinities  of  the  simple  bodies  for  each  other 
may  be  therefore  expressed,  taking  hydrogen  and  oxygen  as  illus 
trations,  by  the  following  columns : 


Hydrogen. 
Chlorine. 
Iodine. 
Sulphur. 


Oxygen. 
Zinc. 
Lead. 
Copper. 
Mercury. 
Silver. 


m  which  any  one  body  in  the  list  may  expel  all  below  it  from  com- 
bination, and  will  itself  be  expelled  by  every  body  below  which  it 
stands. 

Such  is  simple  elective  affinity ;  but  it  often  manifests  itself  in  a 
more  complex  form,  as  when  it  acts  among  a  greater  number  of 
bodies  than  three ;  and  by  the  mutual  action  of  two  compound  bod- 
ies, two  new  ones  may  be  formed.  Thus,  when  nitrate  of  lime  is 
decomposed  by  potash,  there  is  simple  decomposition,  and  the  lime 
is  set  free  ;  but  if,  in  place  of  pure  potash,  we  employ  carbonate  of 
potash,  the  result  is  the  formation  of  carbonate  of  lime  5  for  when 
the  potash  leaves  the  carbonic  acid  to  go  to  the  nitric  acid,  and 
the  nitric  acid  leaves  the  lime  to  go  to  the  potash,  the  carbonic 
acid  and  the  lime,  finding  themselves  in  presence  of  one  another, 
unite,  and  precipitate  as  carbonate  of  lime.  The  nature  of  the  de- 
composition may  be  more  clearly  shown  from  the  figure : 

i  Nitric  acid.     Potash.  > 

(  Lime.  Carbonic  acid.  3 

The  bodies  existing  before  mixture  being  composed  of  those  writ- 
ten above  one  another,  and  those  formed  by  decomposition  consist- 
ing of  those  which  are  in  the  same  horizontal  line. 

This  action  is  termed  double  decomposition.  In  the  example  just 
stated,  the  diffisrence  between  it  and  simple  decomposition  may 


s 


160  DOUBLE     DECOMPOSITION. 

appear  to  have  been  accidental,  the  potash  acting  precisely  as  if  it 
had  been  free,  and  the  lime  and  carbonic  acid  uniting  only  because 
they  came  into  contact,  without  any  other  ties,  and  hence  com- 
bined together  J  but  the  peculiarity  of  double  decomposition  is, 
that  by  means  of  it  reactions  may  occur  which  could  not  have 
been  produced  by  simple  affinity,  and  which,  on  the  contrary,  ap- 
pear to  have  been  produced  in  opposition  to  it.  Thus,  ammonia 
cannot  decompose  nitrate  of  lime  ;  on  the  contrary,  lime  will  take 
nitric  acid  from  ammonia ;  and  yet,  if  we  mix  a  solution  of  nitrate 
of  lime  and  carbonate  of  ammonia,  they  decompose  each  other, 
and,  by  double  elective  affinity,  there  are  formed  nitrate  of  ammo- 
nia and  carbonate  of  lime.  As  in  the  former  diagram,  the  com- 
pounds, before  and  after  mixture,  are  found  arranged  in  the  hori- 
zontal and  vertical  lines  of  the  diagram : 

Nitric  acid.     Ammonia. 
Lime.  Carbonic  acid. 

In  fact,  m  order  to  understand  the  cause  of  such  double  decompo- 
sition, we  must  take  into  account  not  merely  the  affinity  of  the 
ammonia  for  the  nitric  acid,  but  that  of  the  lime  for  the  carbonic 
acid.  Thus,  if  the  affinity  of  lime  for  nitric  acid  be  represented 
by  80,  and  that  of  ammonia  for  nitric  acid  be  represented  by  70, 
the  lime  will  be  the  stronger,  and  can,  when  by  itself,  expel  ammo- 
nia ;  but  if  the  carbonic  acid  intervene,  and  the  affinity  of  lime  for 
carbonic  acid  be  50,  and  of  ammonia  for  the  same  acid  be  30,  then 
decomposition  must  occur ;  for  the  forces  preventing  decomposi- 
tion are  the  affinities  of  nitric  acid  for  lime,  and  of  carbonic  acid 
for  ammonia;  that  is,  80+30  =  110;  while  those  tending  to  cause 
decomposition  are  the  affinities  of  nitric  acid  for  ammonia,  and  of 
carbonic  acid  for  lime,  =70 -|- 50  =  120  ;  the  latter  are  the  more 
powerful,  and  the  constituents  of  the  two  salts  consequently  ex- 
change places.  The  former  affinities  are  termed  the  quiescent,  the 
latter  the  divellent  affinities ;  and  whenever  the  sum  of  the  divel- 
lent  is  greater  than  that  of  the  quiescent  affinities,  decomposition 
must  occur. 

Thus  the  simple  affinity  of  hydrogen  for  sulphur  is  much  greater  than  that  of 
mercury  for  sulphur,  and  the  affinity  of  mercury  for  chlorine  is  much  greater  than 
its  affinity  for  sulphur ;  and  yet,  on  bringing  chloride  of  mercury  into  contact  with 
sulphuret  of  hydrogen,  complete  decomposition  ensues,  chloride  of  hydrogen  and 
sulphuret  of  mercury  being  produced.  In  this  case,  the  affinity  of  mercury  for 
chlorine  being  20,  and  for  sulphur  being  10;  the  affinity  of  hydrogen  being  for  sul- 
phur 15,  and  for  chlorine  30,  the  result  may  be  shown  as  follows  : 

30 


««{SX^:    f^hurh* 


10 

the  force  producing  decomposition  being  30-|-10=40,  and  greater  than  those, 
204-15=35,  which  tend  to  keep  the  elements  as  they  were. 

Such  are  the  results  of  chemical  affinity  manifesting  itself  in  its 
simple  and  in  its  more  complex  form ;  hence  there  would  appear 
to  be  nothing  more  easy  than  to  determine  the  scale  of  affinities, 
and  to  construct  a  series  of  tables  in  which  all  existing  substances 


CAUSES     WHICH     INFLUENCE     AFFINITY.  161 

should  tind  tneh  place,  and  all  possible  cases  of  chemical  decompo 
sition  might  be  loretold  with  the  same  accuracy  as  the  law  of  grav- 
itation allows  the  disturbing  effects  of  a  new  planet  to  be  calculated  ; 
but,  unlortunateiy  tor  tiie  simplicity  of  expression  which  the  laws  of 
chemical  aifinity  would  thus  assume,  new  and  unexpected  compli- 
cations arise,  and  embarrasjs  all  cur  explanations  ;  thus,  if  we  take 
muriatic  acid,  and  form  a  table  oi  the  affinities  of  bases  for  it,  we 
«hail  find  that  it  is  as  given  m  Jyo.  i,  aud  constructing  for  sulphuric 
iccid  an  independent  column,  we  sh&Jl  liW  it  to  be  as  in  No.  2. 

No.  1. — Muriatic  Acid.  "No.  2. — Sulphuric  Acid. 

Oxide  of  silver.  Barytes. 

Potash.  Strontia. 

Soda.  Potash. 

Barytes.  Soda. 

Strontia.  Lime. 

Lime.  Magnesia. 

Magnesia.  Oxide  of  silver. 

Here  the  order  is  quite  reversed,  for  oxide  of  silver,  the  strong- 
est base  in  one  column,  is  the  weakest  in  the  other  j  and  barytes 
and  strontia,  which  manifest  the  most  intense  affinity  for  sulphuric 
dcid,  are  found  but  midway  among  the  bases  arranged  in  order  of 
strength  for  muriatic  acid.  Which  column  must  be  taken  as  repre* 
senting  the  true  order  of  affinities'?  What  principle  is  there  by 
which  these  conflicting  testimonies  of  experiments  may  be  brought 
to  correspond  1  The  answer  is,  that  neither  table  is  exclusively 
correct  j  that  these  lists,  although  showing  the  order  of  decomposi- 
tion, and  thus  exhibiting  to  the  eye,  most  usefully,  the  result  of  a 
great  number  of  experiments,  must  not  be  supposed  as  strictly  show- 
ing to  us  the  order  of  the  affinities  of  these  bodies,  unless  we  apply 
thereto  a  number  of  corrections,  arising  from  those  numerous  and 
important  causes  which  influence  and  disturb  the  simple  action  of 
affinity,  and  frequently  invert  altogether  the  results,  which,  if  unim- 
peded, it  would  have  produced. 

For  the  chemical  action  of  two  bodies  does  not  arise  simply  from 
their  chemical  affinities,  but  results  from  the  combined  influences  of 
heat,  electricity,  cohesion,  and  other  physical  agencies,  which  fre- 
quently modify  the  chemical  forces  to  a  remarkable  extent.  By  a 
change  of  temperature,  an  affinity  originally  weak  may  be  made  to 
preponderate  over  one  previously  much  stronger;  by  electrical 
conditions,  the  strongest  and  most  direct  chemical  affinities  may  be 
overcome;  according  as  the  cohesion  of  the  acting  bodies  may  pre- 
vail, decompositions,  simple  or  compound,  may  be  produced  in  op- 
posite ways  j  and  thus  a  chemical  result  is  not  the  simple  conse- 
(juence  of  affinity  directly  acting,  but  is  the  resultant  of  a  number 
of  forces  acting  in  different  directions,  and  with  variable  intensities, 
of  which  affinity  is  but  one,  although  that  one  which,  for  our  ob- 
ject, is  the  most  important. 

It  is  indeed  fortunate  for  the  intellectual  progress  of  mankind  that  it  is  so  ;  for  on 
the  variability  of  the  intensity  with  which  chemical  affinity  may  be  exerted  depends 
the  existence  of  the  infinite  variety  of  organized  and  inorganic  beings  which  people 
and  beautify  this  earth.  Had  mere  affinity  been  omnipotent ;  had  those  bodies 
which  attract  each  other  most  powerfully  been  in  all  cases  able  to  combine ;  and 

X 


162         CAUSES    WHICH     INFLUENCE     AFFINITY. 

had  there  been  no  means  of  dissolving  their  connexion  when  once  formed,  immedi- 
ately on  the  origin  of  our  globe,  those  bodies  which  have  the  most  powerful  affinities 
would  have  satisfied  them  by  entering  into  eternal  union  ;  those  next  in  power  would 
subsequently  have  satisfied  their  tendency  to  combine,  and  long  since  all  nature  would 
have  been  arranged  into  some  few  chemical  combinations,  the  breaking  up  of  vi'hich 
could  not  be  accomphshed  by  any  existing  force.  The  complex  changes  of  animal 
and  vegetable  digestion  and  respiration  could  not  go  on  ;  the  working  of  the  metals, 
the  chemical  arts  of  civilized  life,  could  not  have  been  invented  ;  and  the  planet  which 
we  inhabit  would  have  revolved  in  space  a  barren  and  uninhabitable  ball. 

The  action  of  these  modifying  causes  may  be  easily  exhibited  by  one  or  two  ex- 
amples. It  has  been  already  described  how  a  solution  of  muriate  of  hme  is  decora- 
posed  by  carbonate  of  ammonia  ;  carbonate  of  lime  being  precipitated,  and  muriate 
of  ammonia  remaining  in  the  liquor  ;  but  if,  in  place  of  bringing  these  substances 
into  contact  in  solution,  they  be  brought  to  act  on  each  other  at  a  high  temperature, 
the  result  is  exactly  the  reverse.  If  muriate  of  ammonia  and  carbonate  of  lime  be 
heated  together  without  water,  carbonate  of  ammonia  is  found  to  be  sublimed,  and 
muriate  of  hme  remains  behind.  If  watery  vapour  be  brought  into  contact  with  me- 
tallic iron  heated  to  bright  redness,  it  is  decomposed,  one  of  its  constituents,  oxygen, 
combining  with  the  iron,  the  other,  hydrogen,  being  set  free  ;  here  evidently  the  af- 
finity of  iron  for  oxygen  is  greater  than  that  of  hydrogen.  But  if  oxide  of  iron  be 
heated  to  redness  also,  and  hydrogen  gas  be  passed  over  it,  the  oxygen  is  totally  re- 
moved by  the  hydrogen  in  the  state  of  water,  and  metallic  iron  is  set  free  ;  here  the 
order  of  affinity  is  exactly  the  reverse,  and  we  shall  soon  discover  the  cause  to 
which  it  must  be  attributed. 

The  philosopher  who  first  declared  that  the  order  of  decomposi- 
tion was  not  the  order  of  affinity,  and  pointed  out  the  importance 
of  attending  to  the  other  forces  that  modify  it,  was  led  by  his  ob- 
servations to  assert  that  the  power  to  which  we  have  attached  so 
much  importance,  elective  affinity,  had  no  real  existence  ;  he  said 
that  chemical  union  differed  from  mechanical  cohesion  only  in  being 
exerted  between  the  particles  of  different  substances,  and  that  in  all 
cases  where  certain  bodies  combined  in  preference  to  others,  the 
source  was  to  be  found  in  the  accidental  and  external  circumstances. 
On  his  ideas,  the  force  by  which  the  particles  of  a  fragment  of  sul- 
phate of  soda  are  united,  differs  from  the  force  by  which  the  sulphu- 
ric acid  is  united  to  the  soda  only  in  the  fact  that  the  cohesion 
unites  particles  of  the  same  kind,  while  affinity  unites  particles  of 
different  kinds.  A  salt  dissolved  in  water  is  thus  held  in  solution 
by  chemical  attraction.  Two  pieces  of  lead  which  adhere  together 
are  retained  by  mechanical  cohesion  ;  but  if  a  piece  of  lead  adhere 
to  a  piece  of  tin,  or  a  drop  of  water  to  a  surface  of  glass  or  metal, 
the  union  should  be  attributed  to  chemical  affinity.  It  will  be  seen 
hereafter  that  a  great  deal  of  this  peculiarity  of  view  arose  from  the 
principle  of  indefinite  chemical  combination,  Avhich,  although  sup- 
ported by  the  amazing  talents  of  Berthollet,  has  been  finally  and  to- 
tally given  up.  We  do  not  now  consider  such  phenomena  as  solu- 
tion to  be  produced  by  chemical  affinity,  for  we  require  that  a  chem- 
ical compound  should  have  parted  with  the  properties  of  its  constit- 
uents, and  acquired  peculiar  properties  of  its  own,  in  order  to  prove 
its  title  to  the  name. 

But  it  is  still  by  no  means  easy  to  fix  upon  the  limits  beyond 
which  the  change  of  properties  must  pass.  A  change  of  state  of  ag- 
gregation is  one  of  the  most  common  evidences  of  chemical  combi- 
nation, as  where  muriatic  acid  and  ammonia,  both  gases,  become  sol- 
id; oxygen  and  hydrogen,  both  gases,  become  liquid;  water  and 
bichloride  of  tin,  both  liquid,  become  solid,  and  innumerable  other 


AFFINITY     AND     COHESION.  163 

cases.  The  production  of  heat,  and  often  light,  is  one  of  the  most 
universal  attributes  of  chemical  action  3  and  hence  for  many  ages 
the  explanation  of  the  phenomena  of  combustion  included  all  that 
was  of  importance  in  the  philosophy  of  chemistry.  A  change  of 
volume  is  also  very  frequent,  though  not  so  universal ;  and  conse- 
quent on  this  change  of  volume,  a  change,  generally  an  increase,  of 
the  specific  gravity  of  the  body  from  the  mean  specific  gravity  of  its 
constituents  3  thus,  when  oxygen  and  nitrogen  unite  to  form  nitrous 
oxide,  the  volume  of  the  compound  is  but  |  of  that  of  the  mixed 
constituents  ;  when  nitrogen  and  hydrogen  unite  to  form  ammonia, 
the  resulting  volume  is  but  ^  of  that  of  the  gases  mixed  before  com- 
bining ;  if  100  volumes  of  alcohol  be  mixed  with  100  volumes  of 
water,  the  mixture  will  occupy  but  196  volumes  5  and  on  mixing 
similar  quantities  of  water  and  oil  of  vitriol,  the  resulting  volume  is 
but  185.  Change  of  colour  also  frequently  occurs  ;  but  in  all  these 
cases,  although  such  marked  results  indicate  an  intimacy  of  union 
that  can  scarcely  be  explained  by  mere  cohesion,  yet  other  physical 
forces  may  intervene,  and  in  addition  to  the  evidence  of  chemical 
action  already  stated,  the  most  important  and  necessary  still  remains, 
change  of  chemical  properties. 

I  have  on  several  occasions  mentioned  change  of  properties  as 
characteristic  of  chemical  combination,  but  it  may  be  proper  here 
to  enter  into  a  few  detailed  examples  of  its  nature  and  its  source 
Chemical  affinity  is  not  a  single  force,  giving  to  all  bodies  within 
its  influence  the  same  properties,  though  it  may  be  in  different  de- 
grees. On  the  contrary,  the  power  which  confers  upon  bodies  their 
chemical  properties  is  of  two  kinds,  antagonistic  to  each  other,  and 
such  that,  by  acting  with  equal  energies,  their  effects  are  mutually 
destroyed.  Gravity,  in  acting  upon  bodies,  acts  upon  all  bodies  in 
the  same  manner ;  the  molecular  forces,  which  determine  the  hard- 
ness, the  ductility,  the  solid,  or  liquid  condition  of  bodies,  may  make 
one  body  more  or  less  hard  or  ductile  than  another,  or  they  may 
render  one  body  solid  and  another  gaseous  j  but  it  is  not  in  the  na- 
ture of  cohesive  forces  to  render  the  hardness  of  one  body  opposite 
to  the  hardness  of  another,  so  that  together  they  shall  produce  soft- 
ness. Yet  such  is  the  nature  of  the  sources  of  chemical  activity  ; 
thus  sulphuric  acid  and  soda  are  actuated  by  affinities  for  each  oth- 
er ;  the  same  force  which  gives  to  them  their  tendency  to  combine, 
gives  to  one  the  properties  of  an  intense  acid,  and  to  the  other  the 
character  of  a  powerful  alkali ;  yet  these  forces  are  so  peculiarly 
related  to  each  other,  that,  when  the  bodies  have  combined,  the 
acid  and  the  alkaline  properties  disappear,  and  there  results  a  sub- 
stance, formed  by  their  union  (Glauber's  salt),  innocent,  inactive, 
with  little  tendency  to  combine,  destitute  of  chemical  affinity  for 
other  bodies,  yet  containing  in  itself  constituents  which  may  be 
again  set  free,  and  exhibited  with  all  their  active  properties. 

The  force  of  chemical  affinity  is  therefore  exerted  only  between 
bodies  possessing  opposite  qualities,  and  by  their  union  a  substance 
is  produced  possessing  qualities  which  are  not  the  mixed  qualities 
of  its  components.  The  forces  which  produce  cohesion  and  solu- 
tion are  found  most  active  where  the  resemblance  between  the 
bodies  is  most  complete.     Thus  metals  adhere  most  powerfully  to 


164  AFFINITY     AND     COHESION. 

Other  metals,  and  for  their  sohition,  mercury,  a  liquid  metal,  can 
alone  be  used  j  salts  dissolve  in  water  always  most  easily  when  they 
show  their  resemblance  to  it  by  already  containing  water  of  crystal- 
lization in  their  mass ;  inflammable  bodies,  as  sulphur  and  phospho- 
rus, do  not  dissolve  in  water,  nor  in  acids,  but  in  liquids,  themselves 
inflammable,  as  ether,  sulphuret  of  carbon,  and  the  oils ;  camphor, 
the  resins,  the  fatty  matters,  require  also,  for  their  solution,  fluid 
menstrua  of  analogous,  oily,  and  spirituous  natures.  It  is  the  con- 
trary  with  chemical  combination ,  the  more  complete  the  opposition 
of  properties  may  be,  the  more  intense  is  the  affinity  by  virtue  of 
which  combination  is  effected :  a  metal  combines  with  oxygen  or 
chlorine :  ether,  or  a  metallic  oxide,  combines  with  the  acids  to  form 
salts.  In  all  these  cases  the  opposition  of  properties  is  the  cause 
of  the  chemical  affinity,  and  the  neutralization  or  change  of  proper- 
ties is  its  effect.  Thus  the  gases,  ammonia,  and  muriatic  acid,  a 
caustic  alkali,  and  an  intense  acid,  form  the  solid  sal  ammoniac,  a 
neutral  salt,  destitute  of  the  active  properties  of  its  constituents : 
thus  carbon,  hydrogen,  and  nitrogen,  elements  of  our  daily  food, 
combine  to  generate  the  most  active  poison  that  has  been  found, 
the  prussic  acid  ;  and  this  prussic  acid,  by  farther  combination  with 
oxide  of  iron  and  with  potash,  may  generate  a  yellow  salt,  which 
is  perfectly  without  action  on  the  living  body,  and  which,  under  the 
name  of  ferro-prussiate  of  potash,  is  of  daily  extensive  employment 
in  the  arts. 

The  elements  which,  mixed  together,  constitute  our  atmospheric 
air,  combined  in  one  proportion,  form  a  gas  which,  when  breathed, 
produces  agreeable  intoxication  (nitrous  oxide) ;  in  other  propor- 
tions, a  deep  orange-coloured  gas  (nitrous  acid),  which,  by  int^se 
cold,  may  be  obtained  liquid  j  and  in  an  intermediate  form,  a  gas 
colourless  and  transparent  (nitric  oxide),  which,  when  mixed  with 
air,  produces,  by  combining  with  its  oxygen,  the  nitrous  acid.  In 
all  these  cases  new  properties  are  assumed,  the  characters  of  the 
constituent  elements  furnishing  no  means  of  predicting  the  proper 
ties  of  the  compound. 

This  clear  distinction  between  chemical  affinity  and  cohesion  was 
not  perceived  by  Berthollet ;  and  hence,  misled  by  the  supposed 
existence  of  compounds  which  connected  together  the  extremes  of 
chemical  and  mechanical  force,  he  advanced  the  principle  that  the 
differences  observed  between  them  arose  solely  from  external  cir- 
cumstances. This  principle  has  been  rejected ;  but  the  discussion 
to  which  it  was  subjected  showed  the  importance  of  attending  to 
the  influence  which  external  circumstances  really  do  exercise,  and 
which  is  frequently,  in  practice,  more  powerful  than  the  force  of  af- 
finity itself.  It  is  therefore  necessary  to  study  in  detail  the  influ- 
ence of  the  external  physical  agents  upon  chemical  affinity. 

1st.  Influence  of  Cohesion. — A  diminution  of  cohesive  power 
among  the  particles  of  one  body,  allows  those  of  another  to  come 
into  closer  approximation  to  them,  and  favours  the  chemical  action 
of  the  two  bodies.  Thus  the  ancient  chemists  expressed  the  influ- 
ence of  cohesion  by  the  Latin  proverb :  Corpora  non  agunt  7iisi  sint 
soluta ;  bodies  do  not  act  unless  they  be  dissolved.  And  of  all 
forms  of  matter,  liquidity  is  that  in  which  chemical  action  is  most 
rapid  and  most  energetic. 


INFLUENCE.    OF     COHESION.  165 

There  are  many  instances  of  bodies  acting  on  each  other,  although 
in  the  solid  form.  Thus,  when  chlorate  of  potash  and  sulphur,  or 
chlorate  of  potash  and  sulphuret  of  antimony,  are  rubbed  together, 
the  mixture  explodes  from  the  rapid  decomposition  which  ensues. 
When  fulminate  of  silver,  or  iodide  of  amidogen,  is  even  slightly 
touched,  detonation  follows.  In  these  cases,  the  original  arrange- 
ment of  particles  must  have  been  so  instable,  that  the  imperfect  ap- 
proach produced  by  mechanical  mixture,  or  the  slight  change  of  po- 
sition arising  from  a  sudden  shock,  was  sufficient  to  cause  a  new 
mode  of  combination.  But,  if  such  cases  as  these  be  considered  as 
exceptions,  we  may  look  upon  solid  bodies  in  general  as  being  with- 
out chemical  action  on  one  another. 

In  the  gaseous  form  of  matter,  chemical  affinity  appears  to  be 
controlled  and  weakened  by  the  mutual  mechanical  repulsion  of  the 
gaseous  particles.  Thus,  oxygen  and  hydrogen,  bodies  whose  af- 
finities are  so  strong,  may  remain  in  contact  as  gases  for  an  indefi- 
nite period.  Nitrogen  and  hydrogen  have  no  apparent  tendency  to 
unite  when  mixed.  Hydrogen,  in  the  form  of  a  gas,  is  without  ac- 
tion on  carbon,  or  arsenic,  or  phosphorus,  although  under  other 
circumstances  it  unites  with  them,  forming  characteristic  bodies. 
In  order  to  obtain  the  full  chemical  action  of  gaseous  bodies,  they 
must  be  brought  into  play  at  the  moment  of  their  being  set  free  or 
formed  ;  in  their  nascent  state^  as  it  is  termed.  It  may  well  be,  that, 
when  water  is  decomposed  and  hydrogen  is  liberated,  there  is  a 
moment  before  the  hydrogen  actually  assumes  the  permanently  elas- 
tic form  ;  and  being  then,  perhaps,  liquid,  and  in  a  highly  concentra- 
ted condition,  its  affinities  are  manifested  with  extraordinary  force. 
It  is  the  same  with  other  gases  j  they  act  always  with  their  full 
power  only  in  their  nascent  state. 

The  influence  of  cohesion  in  determining  chemical  action  is, 
however,  of  much  greater  importance  in  another  way,  as  serving, 
upon  the  principles  of  Berthollet,  to  explain  the  anomalous  discord- 
ance between  those  experiments  upon  which  the  tables  of  the  affin- 
ities of  bodies  for  each  other  had  been  constructed.  Thus  it  has 
been  shown,  that  in  a  table  of  affinities  of  the  bases,  oxide  of  silver 
would  appear  to  be  the  strongest  base  if  we  used  muriatic  acid : 
barytes  should  be  looked  upon  as  the  most  powerful  if  sulphuric 
acid  had  been  employed  ;  while,  if  the  relation  of  the  bases  to  nitric 
acid  were  taken  as  the  standard,  potash  would  be  found  to  excel  the 
others.  In  such  cases,  the  diversity  is  to  be  ascribed  to  the  influ- 
ence of  cohesion ;  and  in  all  cases  of  the  mutual  action  of  various 
bodies  in  solution,  the  result  is  found  to  be  the  formation  of  such 
compounds  as  are  least  soluble. 

Let  us  imagine  a  quantity  of  sulphate  of  soda  and  nitrate  of  potash 
to  be  dissolved  in  water.  Each  acid  is  attracted  at  the  same  mo- 
ment by  both  bases,  and  each  base  by  both  acids,  so  that  there  oc- 
curs a  division  of  each  acid  between  the  two  bases,  and  of  each 
base  between  the  two  acids.  There  are  thus  in  solution  sulphate 
of  soda  and  sulphate  of  potash,  nitrate  of  soda  and  nitrate  of  potash ; 
and  while  the  solution  is  dilute,  all  remain  so ;  but  if  the  liquor  be 
very  much  concentrated,  the  sulphate  of  potash,  being  a  sparingly 
soluble  salt,  is  deposited  in  crystals,  and  a  new  distribution  takes 


166  ARRANGEMENT     OF     ACIDS     AND     BASES. 

place  in  the  mother  liquid.  Supposing  all  sulphate  of  potash  re- 
moved, and  that  there  remain  sulphate  of  soda,  nitrate  of  soda,  and 
nitrate  of  potash,  the  remaining  potash  divides  itself  again  between 
the  acids,  and  a  new  portion  of  sulphate  of  potash  is  formed,  which, 
by  a  new  crystallization,  may  be  separated.  In  this  way,  according 
as  the  evaporation  is  continued,  new  quantities  of  sulphate  of  potash 
are  consecutively  formed,  until  there  remains  in  solution  neither 
potash  nor  sulphuric  acid,  but  only  soda  in  combination  with  nitric 
acid.  Here,  then,  supposing  the  chemical  affinities  of  potash  and 
soda,  of  sulphuric  and  of  nitric  acids,  to  be  exactly  equal,  the  de- 
composition which  actually  occurs,  and  the  manner  in  which  it  real- 
ly takes  place,  are  explained  perfectly  by  the  greater  cohesion  of 
the  sulphate  of  potash,  and  its  consequent  sparing  solubility. 

In  like  manner,  ordinary  hard  water  contains  soda,  muriatic  acid, 
lime,  and  sulphuric  acid.  The  soda  is  certainly  the  stronger  base, 
and  the  sulphuric  the  stronger  acid  ;  and  yet,  on  evaporating  such 
water,  the  salt  which  first  crystallizes  is  sulphate  of  lime  j  and  on 
continuing  the  evaporation,  all  sulphuric  acid  may  be  removed  in 
combination  with  the  lime.  But  the  acids  and  bases  being  divided 
among  one  another  in  solution,  there  coexist  sulphate  of  lime,  sul- 
phate of  soda,  muriate  of  lime,  and  muriate  of  soda.  But  when  the 
liquor  is  concentrated,  the  sulphate  of  lime  is  first  deposited,  and  a 
new  quantity  being  formed,  all  its  constituents  are  eliminated  in 
combination,  precisely  as  the  sulphate  of  potash  was  separated  in 
the  former  case. 

In  these  instances  the  separation  of  the  least  soluble  ingredients 
took  place  by  degrees,  and,  as  it  were,  artificially  ;  but  if  any  one 
of  the  substances  produced  be  perfectly  insoluble,  it  is  at  once  and 
in  full  quantity  expelled.  Thus,  when  we  mix  together  solutions  of 
nitrate  of  barytes  and  sulphate  of  soda,  there  is  instant  formation  of 
sulphate  of  barytes,  and  the  solution  contains  only  nitrate  of  soda. 
But  even  here,  although  the  formation  of  the  sujphate  of  barytes  ap- 
pears instantaneous  to  the  senses,  it  yet  may,  in  point  of  fact,  be 
just  as  gradual  as  in  other  cases.  Thus  there  may  have  been  a  mo- 
ment after  mixing  the  solutions  when  there  were  present,  dissolved 
together,  nitrate  of  barytes,  nitrate  of  soda,  sulphate  of  soda,  and 
sulphate  of  barytes  ;  in  the  next  moment  the  latter  precipitates,  and 
the  barytes  in  solution,  still  dividing  itself  between  the  two  acids, 
another  quantity  is  formed.  This  then  precipitates,  and  thus,  in  a 
space  of  time  that  is  too  small  to  be  detected,  the  quantity  of  ba- 
rytes in  the  solution  is  reduced  to  the  mere  trace  of  sulphate  Avhich 
the  quantity  of  water  can  dissolve,  and  which  is  too  small  to  be  de- 
tected by  our  ordinary  tests. 

The  nature  of  double  decomposition  depends  thus  on  the  relative 
solubility  of  the  compounds  formed.  In  whatever  w^ay  the  most  in- 
soluble bodies  may  be  generated,  the  decomposition  occurs.  It  is 
thus  that,  on  mixing  solutions  of  carbonate  of  ammonia  and  of  nitrate 
of  lime,  there  are  formed  carbonate  of  lime  and  nitrate  of  ammonia  j 
not  merely  that  the  divellent  affinities  were  more  powerful  than  the 
quiescent  forces,  but  that  the  insolubility  of  the  carbonate  of  lime 
produced  its  separation  from  the  liquid,  and  hence  the  union  of  the 
substances  which  compose  it 


DISTRIBUTION     NOT     INVARIABLE.  167 

The  inversion  of  affinity  which  is  produced  by  the  influence  of 
cohesion  is  not  limited  to  cases  of  double  decomposition.  There 
is  no  doubt  but  that  acetic  acid  is  a  stronger  acid  than  carbonic  acid  ; 
and  on  adding  acetic  acid  to  a  solution  of  carbonate  of  potash  in 
water,  the  carbonic  acid  is  expelled,  and  acetate  of  potash  formed. 
Yet,  if  a  stream  of  carbonic  acid  gas  be  passed  into  a  solution  of 
acetate  of  potash  in  alcohol,  the  salt  is  decomposed,  acetic  acid  be- 
ing set  free,  and  carbonate  of  potash  formed.  The  cause  of  this  is 
the  insolubility  of  the  carbonate  of  potash  in  alcohol  j  for,  on  the 
first  action  of  the  carbonic  acid,  the  potash  divides  itself  between 
the  two  acids,  and  there  is  formed  some  carbonate,  which  is  thrown 
down  ;  then  another  quantity,  which  also  separates,  until  ultimately 
all  is  precipitated,  and  thus  one  of  the  feeblest  acids  may  overcome 
the  affinities  of  another  which  is  much  stronger. 

By  this  principle  of  distribution  of  acids  and  bases,  we  are  thus 
enabled  to  account  for  a  variety  of  facts,  which  appear  totally  op- 
posed to  affinity,  if  it  were  not  subject  to  such  modifications  j  but, 
although  it  is  so  convenient  for  explanation,  it  should  not  be  ad- 
mitted as  a  principle  in  science  if  there  could  not  be  adduced  evi- 
dence of  its  actual  and  independent  truth.  That  it  does  occur  in 
many  cases  cannot  well  be  doubted ;  thus  the  solution  of  sulphate 
of  copper  in  water  is  of  a  rich  blue  colour,  and  that  of  muriate 
(chloride)  of  copper  of  an  emerald  green.  Now,  on  mixing  mu- 
riatic acid  with  a  solution  of  sulphate  of  copper,  the  blue  solution 
is  immediately  changed  to  green,  showing  that  the  weaker  acid  has 
divided  the  oxide  of  copper  with  the  stronger,  although,  so  far 
from  precipitation  occurring,  the  new  compound  is  the  more  solu- 
ble of  the  two.  Also,  on  mixing  a  solution  of  sulphate  of  iron  with 
sulpho-cyanic  acid,  the  liquor  becomes  intensely  blood-red  colour- 
ed, showing  that  a  quantity  of  sulpho-cyanide  of  iron  has  been 
formed,  although  the  sulpho-cyanic  acid  is  much  weaker  than  the 
sulphuric,  and  no  precipitation  occurs  to  favour  its  production. 

These,  and  many  other  such  examples  which  might  be  brought 
forward,  show  that  the  opinion  of  Berthollet,  that  the  acids  and 
bases,  when  mixed  together  in  solution,  arrange  themselves  so  that 
each  base  shall  be  divided  among  all  the  acids,  and  each  acid  among 
all  the  bases,  is  in  a  great  many  cases  true,  and  that  it  is  one  of  the 
most  fruitful  sources  of  the  decompositions  which  occur  in  our  ex- 
periments ;  but  it  remains  to  be  decided  whether  it  is  universally 
true,  and  whether,  if  all  acids  and  bases  act  thus  equally  on  one 
another,  we  should  abandon  the  idea  of  chemical  affinity  being 
elective. 

The  answer  to  this  question  has  been  long  since  received  in  sci- 
ence. The  principle  of  Berthollet  does  not  hold  always,  for  nn- 
merous  instances  may  be  produced  where  this  partition  of  acids  or 
of  bases  does  not  take  place.  Thus  boracic  acid  and  sulphuric 
acid  both  redden  litmus,  but  the  former  colours  it  of  a  port-wine 
colour,  while  the  latter  tinges  it  of  the  red  of  an  onion-skin.  If  a 
quantity  of  borax  (borate  of  soda)  be  dissolved  in  water  coloured 
blue  by  litmus,  and  some  sulphuric  acid 'added  thereto,  the  liquor 
becomes  coloured  wine-red  from  free  boracic  acid ;  but,  although 
the  slightest  trace  of  sulphuric  acid  in  excess  would  show  itself  by 


168      INFLUENCE    OF    ELASTICITY    ON    AFFINITY. 

changing  the  red  to  that  of  the  onion-skin,  no  sign  of  it  is  found 
until  all  the  boracic  acid  has  been  expelled.  Here,  therefore,  there 
is  no  partition  of  the  base  between  two  acids ;  all  the  sulphuric  acid 
which  is  added  unites  with  the  soda,  and  all  the  boracic  acid  is  ex 
pelled.  If  a  solution  of  carbonate  of  soda  be  coloured  blue  by 
litmus,  and  sulphuric  acid  added,  it  may  also  be  shown,  by  the  ab 
sence  of  the  peculiar  red  which  free  sulphuric  acid  gives,  that  there 
is  no  division  of  base  between  the  two.  The  carbonic  acid  is  to- 
tally expelled,  and  the  sulphuric  acid  combines  exclusively  with  the 
soda.  If  the  solution  be  dilute,  the  carbonic  acid  remains  dissolved 
in  the  liquor ;  if  it  be  concentrated,  it  is  evolved  in  the  gaseous 
form  ;  that  makes  no  difference. 

Affinities  are  not,  therefore,  as  BerthoUet  considered,  all  the  same 
in  power.  The  framers  of  the  tables  of  affinity  were  right  as  to 
the  general  principle,  that  different  bodies  have  different  degrees 
of  affinity  for  each  other ;  but  they  erred  in  supposing  that  they 
could  construct  a  table  for  the  absolute  order  of  affinities. 

To  sum  up  the  details  that  have  been  given  of  the  influence  of 
cohesion  on  the  affinities  of  bodies  acting  on  each  other  in  solution, 
it  may  be  said  that,  1st,  In  almost  all  cases  of  precipitation,  the  na- 
ture of  the  double  decomposition  is  determined  much  more  by  the 
fact  of  one  of  the  bodies  formed  being  insoluble,  than  by  the  result- 
ant of  the  united  affinities  of  the  bodies  which  are  engaged.  2d, 
That  where  there  is  no  separation  of  an  insoluble  or  of  a  sparingly 
soluble  compound,  the  acids  and  bases,  if  they  differ  very  much  in 
energy,  are  exclusively  united,  the  strongest  acid  with  the  strong- 
est base,  and  the  weakest  acid  with  the  weakest  base  ;  and  if  there 
be  not  base  sufficient  to  neutralize  all  of  the  acids,  a  corresponding 
quantity  of  the  weakest  acid  being  left  out  of  combination  alto- 
gether 5  but,  3d,  That  if  the  acids  and  bases  be  not  very  different 
in  energy  of  affinity,  they  arrange  themselves  in  such  a  manner 
that  each  base  shall  be  divided  between  all  the  acids,  and  each  acid 
divided  between  all  the  bases,  in  proportions  which  depend  upon 
the  quantities  of  each  acid  and  of  each  base  that  may  be  present, 
and  on  its  affinitary  force.  Thus,  if  there  be  two  acids  and  two 
bases  present,  there  will  be  four  salts  ;  if  three  acids  and  three 
bases,  nine  different  salts  ;  and  generally,  the  number  of  com- 
pounds in  solution  will  be  equal  to  the  whole  number  of  acids  mul- 
tiplied by  the  whole  number  of  bases  present. 

2d.  The  Influence  of  Elasticity. — The  absence  of  cohesion,  or,  still 
more,  the  substitution  for  cohesion  of  its  antagonist  power  repul- 
sion, as  shown  by  the  property  of  elasticity  in  the  form  of  gas  or 
vapour,  modifies  chemical  affinity  in  a  perfectly  analogous  manner 
to  that  which  has  been  already  described ;  for,  precisely  as  the 
formation  of  an  insoluble  substance  in  a  liquid  will  enable  lower 
degrees  of  affinity  to  preponderate  by  removing  the  body  which  is 
formed  by  its  insolubility,  so  will  repulsion  or  elasticity  determine 
the  production  of  such  substances  as  by  their  volatility  may  be 
driven  off,  even  though  the  affinities  of  their  elements  may  be  much 
feebler  than  those  of  otlfer  bodies.  In  all  such  cases  the  same 
principle  of  distribution,  so  fully  described  already,  may  be  suppo- 
sed to  hold :  thus  a  solution  of  sulphate  of  magnesia  is  perfectly 


INFLUENCE    OF    COHESION    AND    ELASTICITY.    169 

decomposed  by  ammonia,  the  magnesia  being  precipitated ;  but,  on 
mixing  sulphate  of  ammonia  with  dry  magnesia,  and  applying  heat, 
the  ammonia  is  expelled,  and  the  sulphuric  acid  remains,  united 
exclusively  with  the  magnesia.  Supposing  that  there  is  little  dif 
ference  between  the  affinities  of  these  two  bases  for  sulphuric  acid, 
the  acid  in  the  mixture  may  be  divided  between  the  two ;  in  each 
case  there  is  free  magnesia  and  free  ammonia,  for  the  acid  is  only 
able  to  saturate  a  part  of  each.  In  the  solution  the  excess  of  mag- 
nesia is  insoluble,  and  it  is  expelled  j  in  the  dry  way  the  excess  ot 
ammonia  is  gaseous,  and  it  is  driven  off;  and  thus,  with  the  same 
substances  and  the  same  affinities,  precisely  opposite  decomposi- 
tions are  produced  by  the  influence  of  cohesion  and  elasticity. 
The  decomposition  of  muriate  of  lime  by  carbonate  of  ammonia 
in  solution  has  been  already  noticed,  where  carbonate  of  lime  is 
formed  in  consequence  of  its  insolubility.  If  the  carbonate  of 
lime  and  the  muriate  of  ammonia  so  produced  be  dried  and  heated, 
the  precisely  reversed  decomposition  will  take  place  ;  there  are  at 
first  produced  muriate  and  carbonate  of  lime,  muriate  and  carbonate 
of  ammonia  ;  and  this  latter,  being  volatile  at  the  high  temperature 
which  is  used,  is  driven  off,  and  new  portions  formed  until  the  in- 
terchange of  elements  is  complete. 

The  boracic  acid  has  been  already  noticed,  as  being  one  so  fee- 
ble in  its  affinities  that  the  law  of  the  division  of  acids  and  bases 
does  not  hold  with  it,  but  that  sulphuric  acid  can  deprive  it  of  every 
particle  of  base.  This  is  quite  true  as  long  as  these  acids  are  in  the 
liquid  form,  but  at  a  high  temperature  the  reaction  is  reversed. 
If  a  mixture  of  sulphate  of  soda  and  boracic  acid  be  heated  to  redness 
in  a  crucible,  the  sulphuric  acid  will  be  driven  off  in  consequence  of 
its  volatility,  while  the  fixed  boracic  acid  will  remain  combined  with 
the  whole  quantity  of  base.  The  white,  inert,  earthy  substance,  sil- 
ica (powdered  flints),  the  acid  properties  of  which  are  so  feeble 
that  it  is  only  from  analogy  that  it  is  recognised  by  chemists  to  be 
an  acid,  may,  at  a  high  temperature,  expel  the  most  powerful  acids 
from  their  combinations ;  thus  the  commonest  sort  of  pottery  is 
glazed  by  throwing  over  it,  when  at  a  bright  red  heat,  handfuls  of 
common  salt  j  this  is  instantly  decomposed ;  the  silica  of  the  earthy 
material  of  the  vessels  combines  with  the  soda  of  the  common  salt, 
and  the  muriatic  acid  is  driven  off  in  white  clouds  of  elastic  vapour. 
Here  the  acid,  which  is  the  feeblest  when  dissolved  in  water,  may 
expel  the  strongest  when  the  temperature  is  raised  j  and  admitting 
that  in  the  commencement  a  partition  of  the  base  between  the  two 
took  place,  even  to  a  very  small  extent,  the  final  and  complete  ex- 
pulsion of  the  more  volatile  must  result. 

From  the  great  variety  of  compounds  into  which  water  enters,  it 
is  easily  expelled,  not  that  it  is  inferior  in  affinity  to  most  other 
bodies,  but  from  its  greater  volatility.  We  shall  hereafter  see  reason 
for  looking  upon  water  as  being  a  base  of  considerable  force,  and 
entering  into  combination  in  forms  which  should  possess  consider- 
able stability ;  but  when  a  compound  of  water  is  subjected  to  heat, 
the  elasticity  of  the  water  diminishes  its  affinity  so  far  that  it  may 
easily  be  expelled. 

The  elasticity  which  certain  elements  possess  when  free,  may  be 

Y 


170    INFLUENCE     OF     VARIOUS    MODIFYING    CAUSES. 

a  cause  why  the  compounds  which  they  form  are  easily  decomposed 
by  heat,  if  their  actual  affinity  to  one  another  be  not  considerable. 
Thus  the  nitrate  of  barytes,  which  contains  nitrogen  and  oxygen  in 
combination  with  barytes,  gives,  when  heated,  a  mixture  of  nitrogen 
and  oxygen  gases  :  nitrate  of  lead  gives,  when  heated,  pure  oxygen 
and  nitrous  acid  fumes.  Chlorate  of  potash,  by  a  high  temperature, 
abandons  all  its  oxygen  gas ;  and  the  remaining  elements,  having  a 
powerful  affinity  for  each  other,  resist  the  increase  of  heat,  and  re- 
main as  chloride  of  potassium. 

When  the  decomposition  of  a  body  by  heat  is  thus  determined 
by  the  elasticity  of  one  of  its  constituents,  it  is  necessary,  for  the 
success  of  the  process,  that  this  constituent  should  be  allowed  freely 
to  escape.  If  it  be  forced  to  remain  enveloping  the  residual  sub- 
stance, the  decomposition  ceases.  Thus,  by  heating  carbonate  of 
lime  to  redness,  it  is  resolved  into  lime  and  carbonic  acid ;  but  if  the 
carbonic  acid  be  not  removed,  the  decomposition  would  immediately 
cease,  and  the  carbonate  of  lime  might  be  melted  without  being  de- 
composed. The  removal  of  the  carbonic  acid  is  accomplished,  in 
burning  lime  on  the  large  scale,  by  the  limestone  beiiig  heated  in  a 
kiln,  through  which  there  is  a  continuous  draught,  by  which  the  car- 
bonic acid  is  carried  ofT  according  as  it  is  formed.  The  necessity 
for  the  removal  of  the  carbonic  acid  may  be  shown  by  placing  bits 
of  white  marble  in  a  porcelain  tube,  heated  to  redness  in  a  furnace, 
connected  with  a  pneumatic  trough,  and  fitted  to  a  retort  at  the  other 
end,  by  which  steam  may  be  passed  into  the  tube  ;  at  first  scarcely 
any  carbonic  acid  is  set  free  ;  but,  by  keeping  up  a  supply  of  steam, 
the  gas  is  rapidly  produced,  and  the  lime  becomes  very  soon  com- 
pletely caustic. 

It  is  in  this  way,  also,  that  we  may  explain  the  contrary  order  of 
decomposition  that  may  be  produced  by  oxygen,  hydrogen,  and  iron. 
If  metallic  iron  be  in  the  tube,  and  the  latter  be  kept  full  of  steam, 
every  particle  of  hydrogen  which  is  formed  is  carried  off;  and  there 
being  then  a  space  provided  into  which  the  hydrogen  can  easily 
spread  itself,  the  steam  will  be  decomposed,  and  the  iron  converted 
into  oxide.  If,  on  the  contrary,  the  tube  contain  oxide  of  iron,  and 
be  kept  full  by  a  current  of  hydrogen  gas,  there  is  presented  to 
every  molecule  of  steam  produced  room  for  its  escape  ;  and  the 
formation  of  steam  being  thus  favoured  by  its  elasticity  being  al- 
lowed full  play,  the  reduction  of  the  metal  is  completed. 

Independent  of  its  influence  on  cohesion,  a  change  of  tempera- 
ture is  capable  of  modifying  the  affinities  of  bodies  in  a  remarkable 
degree.  Thus  charcoal  is  not  capable  of  being  melted  or  vaporized, 
and  yet,  although  at  ordinary  temperatures  quite  inert,  few  bodies 
can  resist  its  deoxidizing  action  at  a  red  heat.  Bodies  which  take 
fire  when  heated  do  so  in  consequence  of  their  affinity  for  oxygen 
being  augmented  by  the  increase  of  temperature.  The  action  of  the 
electric  spark  in  producing  the  explosion  of  gaseous  mixtures,  de- 
pends on  its  heating  very  much  the  few  particles  of  gas  which  lie 
immediately  in  its  path,  and  the  combustion  being  communicated 
by  them  to  the  general  mass.  The  affinities  of  bodies  for  each  other 
appear  to  be  thus  exalted  by  the  agency  of  heat  in  many  cases,  but 
the  exaltation  does  not  appear  to  be  the  same  for  all.     Heat  appears 


BERTHOLLETS     THEORY     OF     AFFINITY. 


171 


often  to  diminish  the  affinity  of  bodies ;  thus  the  explosion  of  de 
tonating  compounds  was  so  explained ;  but  this  appears  to  arise 
from  the  heat  really  exalting  the  affinity  of  the  more  powerful  con- 
stituents, so  that  new  and  more  permanent  bodies  may  be  formed : 
thus  fulminating  silver  explodes,  not  that  its  elements  may  separate, 
but  that  bodies  of  a  more  permanent  constitution  may  be  formed 
The  iodide  and  chloride  of  azote  were  looked  upon  as  being  exam- 
ples of  mere  separation  of  elements  on  the  application  of  heat  j  but 
Marchand  and  1  have  found  that  these  bodies  contain  hydrogen,  and 
that  they  are  decomposed  in  consequence  of  the  formation  of  hy- 
drochloric or  hydriodic  acid  To  produce  many  bodies  of  instable 
nature,  it  is  necessary  to  avoid  the  use  of  heat  5  not  that  heat  dimin- 
ishes the  affinities  of  their  elements  in  general,  but  that  the  heat 
enables  those  elements  to  satisfy  their  affinities  better,  by  combining 
in  a  more  stable  form. 

It  has  been  mentioned  that  Berthollet  considered  affinity  as  be- 
ing not  elective,  but  that  the  combination  of  one  body  to  another 
was  determined  by  the  circumstances  under  which  they  were  placed; 
and  that,  in  cases  where  many  bodies  of  equal  solubilities  existed 
together,  they  were  divided  among  one  another  in  proportion  to 
thejr  masses  ;  but  he  in  this  case  introduces  a  term  which  has  caused 
great  difficulty  in  the  discussion  of  the  doctrines  which  he  advanced. 
He  says  that  the  bodies  mixed  together  combine,  not  only  in  pro- 
portion to  their  masses,  but  of  their  affinities  ;  and  hence  might  ap- 
pear to  admit  that  bodies  had  different  degrees  of  affinity,  and  that 
this  might,  therefore,  be  elective  j  but,  if  I  conceive  his  opinions 
rightly,  the  affinity  of  which  he  spoke  was  not  the  force  to  which 
we  assign  the  power  of  choice  of  one  body  over  another,  but  he  car- 
ried on  the  analogy  to  cohesion,  and  considered  that  the  affinity  of 
one  body.  A,  to  another,  B,  might  be  greater  than  to  a  third,  C,  not 
so  as  to  make  A  unite  with  B  in  preference  to  C,  but  that,  when  it 
had  been  united  with  B,  it  would  hold  it  more  firmly  than  it  could 
retain  C.  This  is  like  what  is  found  with  cohesion  ,*  if  several 
bodies  be  placed  beside  each  other,  they  show  no  power  of  elective 
cohesion  ;  but  if  they  be  brought  into  actual  close  contact,  the  degree 
of  cohesion  may  be  different  for  each.  It  is  in  this  way  that  Ber- 
thollet recognises  a  difference  of  affinity,  and  hence  the  obscurity 
that  is  often  ascribed  to  his  statement  of  his  views,  from  the  sense 
which  he  attached  to  the  word  affinity  being  mistaken. 

We  owe  to  this  philosopher  an  attempt  at  measuring  this  power  of  affinity, 
which,  though  incorrect,  yet,  as  being  one  of  the  first  steps  made  towards  numeri- 
cal laws  in  chemistry,  deserves  notice.  He  looked  upon  the  neutralizing  power  of 
a  body  as  being  the  measure  of  its  affinity  for  anoth^,  and  considered  that  the  de- 
viations from  this  rule  arose  from  the  influence  of  cohesion  or  of  elasticity :  thus 
the  same  quantity  of  potash  is  saturated  by 


Sulphuric  acid    . 

.    40  parts. 

Muriatic  acid  .    . 

.    36-5  parts 

Nitric  acid     .     . 

.     54     " 

Acetic  acic      .    . 

.     51 

Carbonic  acid     . 

.     .     22      " 

Oxalic  acid      .     . 

.    36 

Hence,  if  mere  affinity  was  allowed  to  act,  carbonic  acid  should  be  the  strongest, 
and  nitric  acid  the  weakest  in  the  list ;  in  like  manner,  the  same  quantity  of  sul- 
phuric acid  neutralizes 


Potash 48  parts. 

Soda 32     " 

Ammonia 17     " 


Lime 28  parts. 

Barytes 76      *' 

Magnesia 18     " 


172  INFLUENCE     OF     LIGHT     ON     AFFINITY. 

and  ammonia  and  magnesia  should  be  the  strongest  of  all  bases,  were  it  not  for 
the  insolubility  of  the  one  and  the  volatility  of  the  other  body. 

These  numbers,  which  are  now  known  as  expressing  the  quantities  of  substan- 
ces that  are  equivalent  to  each  other  in  combination,  are  fully  recognised  as  totally 
independent  of  the  force  of  affinity  exercised  by  each  body.  As  yet  we  have  no 
other  measure  of  affinity  than  the  order  of  decomposition,  controlled  by  the  esti- 
mate of  the  influence  which  cohesion  and  elasticity  may  exercise.  From  the 
electrical  relations  of  bodies,  attempts  have  been  made  to  estimate  the  relative 
affinities  of  chemical  substances,  the  results  of  which  will  be  described  in  their 
proper  place. 

Of  the  Influence  of  Light  on  Chemical  Affinity. — Although  attention 
has  latterly  been  very  much  directed  to  the  influence  of  light  on 
chemical  affinity,  from  the  accidental  discovery  of  some  very  re- 
markable circumstances  connected  with  it,  yet  there  have  not  been 
discovered  as  yet  any  general  principles  to  which  those  results  can  be 
reduced;  and  the  greater  number  of  the  investigations  that  have  been 
made  are  occupied  by  experiments  of  detail,  which,  from  their  want 
of  connexion  and  their  multiplicity,  cannot  be  successfully  contem- 
plated from  any  general  point  of  view  at  the  present  moment.  So 
far,  however,  as  positive  facts  have  been  discovered,  and  as  even 
plausible  explanations  of  those  facts  have  been  suggested,  I  shall  en- 
deavour to  represent,  briefly,  the  actual  condition  of  our  knowledge 
of  this  department. 

In  many  cases,  bodies  which  in  obscurity  remain  totally  without 
action  on  one  another,  are  brought  into  combination  by  exposure  to 
light,  and  the  rapidity  of  their  reaction  is  proportional  to  the  brilliancy 
of  the  light.  Thus  chlorine  and  hydrogen  mixed  remain  unaltered 
for  any  period  in  the  dark ;  if  exposed  to  the  diff'use  daylight,  they 
silently  combine,  but  explode  suddenly  if  a  direct  ray  of  sunshine 
fall  upon  the  mixture.  Chlorine  dissolved  in  water,  if  kept  in  the 
dark,  remains  a  long  time  unaltered,  but  if  exposed  to  sunshine,  is 
rapidly  converted  into  chloride  of  hydrogen,  water  being  decompo- 
sed, and  oxygen  eliminated  in  a  gaseous  form.  Chlorine  unites  with 
carbonic  oxide  only  under  the  influence  of  light,  whence  the  name 
Phosgene,  a  light-formed  gas,  was  given  to  the  compound  by  its  dis- 
coverer. Dr.  Davy.  Chlorine  and  sulphurous  acid  unite  also  only 
when  exposed  to  brilliant  sunshine ;  so  much  so,  that  in  Dublin  but 
few  days  in  summer  are  found  bright  enough  to  form  it.  The  de- 
composing action  of  chlorine,  iodine,  and  bromine  upon  organic 
bodies,  which  consists  in  the  separation  of  hydrogen,  and  the  as- 
sumption generally  of  a  corresponding  quantity  of  chlorine,  &c.,  in 
its  place,  is  regulated  also  in  a  remarkable  degree  by  the  brilliancy 
of  the  light  under  which  this  operation  is  carried  on.  Thus,  even 
in  summer,  in  Dublin,  I  never  could  deprive  acetone  of  more  than 
one  third  of  its  hydrogen,  forming  from  Cg  H3  0.,  the  body  C3H2C]. 
0. ;  but  in  Paris,  in  summer,  the  chlorine  removed  another  equiva- 
lent of  hydrogen,  and  Dumas  and  I  succeeded  in  obtaining  the  body 
C3  H.  CI2  0.  In  like  manner,  in  bright  sunshine,  the  action  of 
chlorine  on  pyroxylic  spirit  is  so  violent,  that  unless  the  vessel  be 
carefully  shaded,  the  decomposition  proceeds  by  a  series  of  explo- 
sions, while  I  have  found  it  exceedingly  difficult  in  gloomy  weather 
to  produce  any  action  whatsoever.  Instances  of  this  kind  might  be 
very  much  multiplied,  but  those  described  are  sufficient  to  point  out 
the  general  manner  in  which  light  is  found  to  act. 


PHOTOGRAPHIC     DRAWING.  173 

The  action  of  light  appears  occasionally  limited  to  the  simple 
separation  of  bodies  previously  combined.  Thus  colourless  nitric 
acid,  when  exposed  to  sunshine,  evolves  oxygen  gas,  and  becomes 
coloured  yellow  from  nitrous  acid  which  remains.  The  fading  of 
Prussian-blue  patterns  on  cotton,  which  Chevreul  found  to  depend 
on  the  escape  of  cyanogen,  and  the  conversion  of  the  blue  into  a 
white  compound,  containing  less  cyanogen,  is  also  an  example  of  this 
principle. 

Setting  aside,  for  the  present,  the  influence  of  light  on  the  pro- 
duction of  colouring  matters  in  organic  bodies,  which  will  be  de- 
scribed as  a  portion  of  the  chemical  history  of  the  individual  sub- 
stances, I  shall  now  only  advert  to  the  action  of  light  upon  the  com- 
pounds of  the  easily-reducible  metals,  particularly  silver,  by  the  study 
of  which  such  remarkable  results  have  latterly  been  obtained. 

Scanlan  first  showed  that,  when  nitrate  of  silver  blackens  under 
the  influence  of  light,  its  decomposition  is  produced  by  organic 
matter,  as  by  contact  with  paper,  or  by  the  organic  substance,  which 
even  distilled  water  contains  in  small  quantity.  Chloride  of  silver 
also  is  afl^ected  by  light  only  when  in  contact  with  organic  matter  or 
with  water,  and  in  the  latter  case,  also,  most  probably  from  acting  on 
the  organic  matter  which  the  water  held  in  solution.  When  oil  of 
vitriol  is  poured  over  chloride  of  silver,  this  is  not  altered  by  the 
light,  the  sulphuric  acid  combining  with  the  water,  and  probably  de- 
stroying the  organic  matter  therein  dissolved.  I  apprehend  that  in 
most,  if  not  all  cases  of  the  decomposition  of  a  metallic  salt  and  the 
reduction  of  the  metal  under  the  influence  of  light,  a  substance  con- 
taining hydrogen,  exclusive  of  the  water  of  solution,  must  come  into 

play- 

The  decomposition  of  the  salts  of  silver  in  contact  with  paper 
under  the  influence  of  light,  has  become  of  interest  to  the  arts  as  a 
process  of  obtaining  accurate  outlines,  and  is  called  photography^  or 
'photographic  drawing.  If  a  sheet  of  paper  be  washed  with  a  very  di- 
lute solution  of  chloride,  iodide,  or,  better,  bromide  of  potassium, 
and  then  with  a  solution  of  nitrate  of  silver,  there  is  formed  in  the 
substance  of  the  paper  chloride  iodide,  or  bromide  of  silver,  which, 
being  in  contact  with  abundance  of  organic  matter,  is  blackened  by 
a  very  short  exposure  even  to  moderate  light.  If  an  opaque  body 
be  laid  betvyeen  a  sheet  of  such  paper  and  the  light,  the  portions  to 
which  the  light  arrives  become  dark,  while  that  under  the  object  re- 
mains white,  and  thus  the  most  delicate  and  complicated  outlines  of 
foliage  or  fibres  may,  by  a  few  minutes'  exposure  to  the  solar  rays, 
be  fixed  upon  the  paper  with  a  degree  of  accuracy  inimitable  by  the 
hand.  To  render  such  a  drawing  permanent,  it  is  necessary  to  re- 
move the  silver  compound  under  the  pattern  j  for  if  it  remained,  the 
blackness  would  gradually  become  uniform  over  the  entire  surface, 
and  the  picture  would  be  efl'aced.  This  is  effected  by  washing  the 
paper,  after  the  image  has  been  completely  formed,  by  a  solution  of 
some  substance  capable  of  dissolving  out  all  of  the  undecomposed 
salt  of  silver  j  for  this  purpose,  ammonia,  hypo-sulphite  of  soda,  and 
strong  solution  of  common  salt  are  those  generally  employed. 

The  most  remarkable  features  connected  with  the  chemical  agen- 
cies of  light  result  from  the  recent  experiments  of  Herschel.     He 


174 


COLOURING  EFFECTS  O.F  THE  CHEMICAL  RAYS. 


has  shown,  as  was  slightly  noticed  when  describing  the  general  char- 
acters of  light,  that  the  chemical  effects  are  not  regulated  by,  nor 
limited  to  the  luminous  spectrum,  but  by  totally  distinct  rays,  which, 
according  to  the  substance  employed  to  show  their  decomposing  ac- 
tion, may  extend  far  beyond  the  visible  limits  on  either  side,  or  may 
stop  short  in  the  middle  of  the  coloured  space  ;  and  that  the  greatest 
effect,  which  generally  occurs  at  the  violet  extremity  of  the  spectrum, 
may  be  produced  at  other  and  widely-distant  points. 

A  singular,  and  at  present  unaccountable,  consequence  of  the  ac- 
tion of  the  prismatic  spectrum  on  paper  impregnated  with  chloride 
of  silver  is,  that  the  spaces  on  which  the  coloured  rays  fall  become 
coloured,  acquiring  a  tint  corresponding  to  that  of  the  light  incident 
upon  them,  so  that  the  spectrum  fixes  its  own  image  CHi  the  paper. 
Thus  the  colours  impressed  were  in  one  experiment : 


Spectrum  Colours. 

Colours  formed  on  the  Paper.                      | 

Extreme  red. 

None. 

Mean  red. 

None. 

Orange. 

Faint  brick  red. 

Orange  yellow. 

Brick  red,  pretty  strong. 

Yellow. 

Red,  passing  into  green. 

Yellow  green. 

Dull  bottle  green. 

Green. 

Do.,  passing  into  bluish. 

Blue  green. 

Very  sombre  blue. 

Blue. 

Black,  passing  into  metallic  yellow. 

Violet. 

Do.            Do. 

Beyond  the  violet. 

Violet,  or  purplish  black. 

It  is  in  the  lavender-coloured  space  that  the  chemical  effects  are 
generally  most  intense  ;  when  the  light  of  it  had  been  concentrated 
by  a  lens,  and  received  on  a  piece  of  prepared  paper,  the  blacken- 
ing was  instantaneous,  precisely  as  if  a  red-hot  body  had  been  ap- 
plied behind,  or  a  smoky  flame  directed  on  the  paper  over  all  the 
space  illuminated,  and  accurately  marking  its  outline. 

In  the  table  of  impressed  colours  just  given,  the  red  rays  appear 
to  have  produced  no  effect ;  but  they  are  by  no  means  destitute  of 
action.  When  a  quantity  of  diffused  light  is  allowed  to  fall  upon 
the  paper,  in  addition  to  the  more  brilliant  spectral  colours,  the 
chemical  image  is  found  to  acquire  a  pure  white  prolongation  be- 
yond the  red  space,  in  which  the  darkening  action  of  the  diffuse 
light  appears  to  have  been  suspended.  The  opposite  extremities  of 
the  spectrum  appear,  therefore,  to  have  different  powers,  the  dark- 
ening quality  of  white  light  being  due  to  the  difference  between  the 
two  in  favour  of  the  violet  end ;  and  it  is  probable  that  by  a  balance 
of  action,  a  sensitive  paper  might  be  exposed  to  the  action  of  united 
beams  of  brilliant  violet  and  red  light,  and  remain  perfectly  unalter- 
ed in  its  colour.  Herschel  did  not,  however,  succeed  so  far  :  paper 
blackened  by  violet  light  has  that  blackness  removed  by  the  action 
of  red  light  upon  it ;  but  it  was  found  impossible  to  catch  the  point 
where  the  paper  should  be  white  ;  for,  according  as  the  black  of  the 
violet  end  passed  off,  the  red  impression  was  substituted  for  it. 
When,  however,  the  different  coloured  rays  were  made  to  fall  si- 
multaneously on  the  paper,  the  neutralizing  power  of  the  opposite 
ends  of  the  spectrum  was  beautifully  shown.  The  blackening  pow- 
er of  the  more  refrangible  rays  was  suspended  over  all  the  space 


PROCESS     OF     TAKING     IMAGES.       175 

Upon  which  the  less  refrangible  rays  fell,  and  the  shades  of  green 
and  sombre  blue,  which  the  latter  would  have  impressed  upon  a 
white  paper,  were  produced  on  that  portion  which,  but  for  their 
action,  would  have  been  merely  blackened. 

The  paper  with  which  those  results  were  obtained  derived  its 
sensibility  to  light  from  chloride  of  silver ;  but  the  action  of  other 
salts  of  silver  gives  such  anomalous  and  variable  effects,  that  no 
general  principle  whatsoever  can  be  deduced  from  them  ;  thus, 
with  bromide  of  silver,  the  blackening  proceeds  uniformly  over  the 
whole  of  the  visible  spectrum,  and  the  whitening  effect  is  produced 
beyond  it  to  a  considerable  distance.  The  subject  has  been  shown 
by  Herschel  to  be  one  of  considerable  importance  and  great  extent  j 
and  from  the  popular  interest  it  excites,  some  clew  to  a  more  gen- 
eral knowledge  of  its  principles  will  probably  be  soon  obtained. 

The  process  lately  discovered  by  Daguerre,  of  fixing  the  images 
of  external  objects  upon  a  prepared  metallic  plate,  is  one  which  also 
deserves  attention,  as  being  founded  upon  the  chemical  agencies  of 
light,  although  hitherto  there  has  been  but  little  success  in  the  at- 
tempts made  to  assign  a  theory  of  it.  It  is  not  complicated  in  de- 
tail. A  plate  of  silvered  copper  is  cleaned  with  dilute  nitric  acid, 
so  that  the  surface  of  silver  may  be  absolutely  pure,  and  is  then  ex- 
posed to  the  vapour  of  iodine  until  a  gold-coloured  pellicle  of  iodine 
of  excessive  tenuity  is  deposited  upon  it.  In  this  state  it  is  very 
sensible  to  light.  The  plate  so  prepared  is  placed  in  a  camera-ob- 
scura,  and  the  image  of  the  object  required  is  allowed  to  remain  on 
it  for  a  space  of  time,. which  varies  with  the  brightness  of  the  light. 
When  it  has  been  sufficiently  exposed,  it  is  removed,  and  submit- 
ted to  the  action  of  the  vapour  of  mercury,  by  which  the  picture  is 
rendered  visible.  As  there  still  remains,  however,  a  general  sensi- 
bility to  the  farther  influence  of  light,  this  is  removed  by  dissolving 
away  all  the  iodine  and  iodide  of  silver  by  a  solution  of  hyposul- 
phite of  soda.  The  shadows  remain  then  marked  by  smooth  amal- 
gamated surfaces,  and  the  lights,  by  the  corresponding  portions  be- 
ing of  a  dull  gray  colour,  possessing  only  a  power  of  diffuse  reflec- 
tion. 

The  explanation  of  this  process,  which,  from  my  own  observations,  I  am  disposed 
to  suggest,  is,  that  the  iodine  combines  with  the  silver,  and  forms  iodide  of  silver, 
which  is  spread  in  an  amorphous  state,  forming  an  excessively  thin  layer,  like  var- 
nish, over  the  surface  of  the  plate.  Under  the  influence  of  the  light,  I  consider  that  this 
crystallizes  as  melted  sugar  does,  but  so  minutely  as  to  be  invisible  to  the  eye,  and 
the  closeness  and  completeness  of  the  crystalline  structure  being  proportional  to  the 
duration  and  intensity  of  the  light  to  which  it  had  been  exposed.  When,  then,  the 
vapour  of  mercury  attacks  the  plate,  the  iodide  of  silver  in  both  conditions  is  de- 
composed, and  the  iodine  being  replaced  by  mercury,  an  amalgam  of  silver  is  form- 
ed, uniform  in  surface,  and  perfectly  metallic  in  its  lustre,  over  the  shaded  portions  ; 
but  the  crystalline  iodide,  in  being  decomposed,  gives  a  crystalline  amalgam,  which, 
from  the  minuteness  of  its  particles,  presents  only  a  grayish  tint,  and,  being  mixed 
with  interspersed  points  of  bright,  smooth  amalgam  where  the  light  had  been  less 
powerful,  shades  off  proportionally  all  the  intermediate  effects. 

The  application  of  the  mercurial  fumes  cannot  be  pushed  far  enough  to  decom- 
pose all  the  iodide  of  silver,  for  it  would  injure  the  picture  by  depositing  itself  irreg- 
ularly and  in  excess.  It  is  therefore  necessary,  as  soon  as  enough  has  been  acted 
on  by  the  mercury  to  bring  out  the  picture  in  a  distinct  manner,  to  remove  the  re- 
mainder by  the  washing  which  has  been  described. 

The  influence  of  colour  on  the  production  of  pictures  by  Da- 
guerre's  process  is  very  marked ;  the  images  of  green  objects  are 
scarcely  at  all  defined,  so  that  the  method  is  scarcely  applicable  to 


176  PROCESS     FOR     TAKING     PORTRAITS. 

taking  landscapes.  Red  and  orange  are  also  very  feeble  in  their  ef- 
fect ',  but  blue,  even  so  intense  as  to  be  not  at  all  bright,  is  more 
powerful  than  a  brilliant  white  light.  In  order,  therefore,  to  produce 
good  effects,  objects  should  be  selected  either  white,  or  of  colours 
from  which  red  and  orange  should  be  absent.  The  fixation  of  col- 
ours in  a  manner  similar  to  that  discovered  by  Herschel,  and  already 
noticed,  has  been  remarked  in  Daguerre's  process,  although  so  ir- 
regularly that  no  advantage  has  as  yet  been  taken  of  it  for  technical 
uses ;  but  I  have  myself  seen,  on  more  than  one  occasion,  where  a 
deep  blue  sky  was  interspersed  by  patches  of  bright  white  clouds, 
a  perfect  picture  of  the  sky  in  its  natural  colours  to  be  formed  upon 
the  plate.  Time-worn  stains,  and  marks  upon  the  surface  of  stone 
buildings,  are  also  occasionally  represented  in  their  natural  colours. 
In  the  majority  of  cases,  however,  where  colours  are  produced  upon 
the  plate,  they  do  not  correspond  in  position  or  tint  to  those  of  the 
natural  objects  whose  image  had  been  obtained. 

[Since  the  preceding  paragraphs  were  written  by  Dr.  Kane,  nu- 
merous improvements  have  been  made  in  this  beautiful  chemical 
art  in  America  and  elsewhere  :  the  theory  of  the  process  is  also 
much  better  understood.  The  most  important  of  these  improve- 
ments is  the  application  of  Daguerre's  process  to  taking  portraits 
from  the  life.  This  is  due  to  Dr.  Draper,  who  succeeded  with  it 
soon  after  the  French  process  was  known  in  this  country.  At  first 
the  direct  or  reflected  rays  of  the  sun  were  required ;  but  modes  of 
preparation,  giving  the  plate  more  sensitiveness,  have  been  since  dis- 
covered, so  that  the  ordinary  diffused  light  of  day  is  now  sufficient. 

The  best  process  for  obtaining  portraits  is  as  follows :  The  plate, 
having  been  carefully  cleaned,  is  iodized  to  a  pale  lemon  colour  ;  it 
is  then  exposed  to  the  vapour  of  bromine  for  a  sufficient  length  of 
tjme  to  bring  it  to  a  golden  yellow.  It  is  a  great  advantage  to  keep 
it  in  total  darkness  for  three  or  four  hours  before  using  it.  The 
person  whose  portrait  is  to  be  taken,  having  been  seated  in  a  suita- 
ble chair,  with  a  support  to  keep  the  head  perfectly  steady,  before  a 
window,  so  that  the  light  shall  illuminate  all  those  portions  seen  in 
the  camera  with  proper  strength,  the  plate  is  to  be  exposed  to  the 
focal  image  for  a  time,  which  may  be  determined  by  previous  trials. 

Much  of  the  beauty  of  the  picture  depends  on  the  object-glass  of 
the  camera  j  very  good  proofs  may  be  had  by  an  arrangement  of 
uncompensated  convex  lenses  four  inches  in  diameter  and  eight 
inches  in  focus ;  but  the  most  finished  pictures  are  obtained  by  the 
use  of  achromatics,  which  ought  always  to  be  preferred. 

The  process  of  exposing  the  proof  to  the  mercurial  vapour  is  one 
of  great  delicacy  j  sometimes  the  object  is  suddenly  evolved,  some- 
times it  requires  the  mercury  to  be  maintained  at  175^  Fahrenheit 
for  a  long  time.  Experience  alone  can  determine  when  the  full  ef- 
fect has  been  obtained. 

After  the  picture  has  been  brought  out,  and  the  coating  of  iodide 
of  silver  removed,  it  remains  only  to  efiect  the  gilding.  This  is  ac- 
complished by  pouring  all  over  the  silver  surface  a  very  weak  solu- 
tion of  the  chloride  of  gold  in  hyposulphite  of  potash,  and  warming 
it  gently  with  the  flame  of  a  spirit-lamp.  At  a  particular  tempera- 
ture, the  shadows  increase  in  depth  and  the  lights  in  brillancy  ;  the 
plate  is  then  to  be  thoroughly  washed.     The  gilding  serves  to  render 


THEORY     OF     THE    PR^OCESS     OF     DAGUERRE.      177 

the  picture  immovable  by  ordinary  exposure  or  accident,  and  im- 
parts to  it  a  beautiful  satiny  lustre,  and  chatoyant  play  of  colour. 

The  great  difficulty  in  the  management  of  the  Daguerreotype  lies 
in  the  circumstance  that  the  iodide  of  silver  is  not  affected  corre- 
spondingly by  lights  that  are  of  different  degrees  of  brilliancy,  if 
they  should  be  of  different  colours.  And  it  is  only  under  particular 
circumstances,  not  easy  to  reproduce,  that  lights  of  the  same  colour, 
but  of  different  strengths,  produce  a  corresponding  degree  of  white- 
ness on  the  plate.  Often,  whtn  the  light  is  too  active,  the  proof 
takes  on  an  unpleasant  slate-blue  colour,  from  the  exterior  portions 
of  the  iodide  assuming  a  state  of  solarization  before  those  beneath 
have  had  time  to  undergo  change ;  a  phenomenon  resembling  what 
takes  place  when  a  sheet  of  paper  is  held  before  a  very  bright  fire, 
the  exposed  surface  becoming  scorched,  while  the  back  has  scarce- 
ly had  time  to  become  warm. 

As  respects  the  theory  of  this  process,  1  do  not  coincide  with  the 
views  expressed  by  Dr.  Kane.  In  the  shadows  no  mercury  exists ; 
the  lights  are  an  amalgam.  When  a  Daguerreotype  is  exposed  to 
the  vapour  of  mercury  to  bring  out  its  picture,  a  decomposition  of 
all  those  portions  of  the  iodide  which  have  Iseen  exposed  to  the 
light  ensues  ;  an  amalgam  is  formed,  and  the  iodine  expelled  unites 
with  the  metallic  silver  behind,  effecting,  therefore,  a  corrosion  of 
the  plate  ;  no  iodine  is  evolved,  and  for  obvious  reasons  such  an 
event  is  impossible.  The  light  therefore  imparts  to  those  portions 
of  iodide  on  which  it  has  impinged,  the  quality  of  being  decomposed 
at  a  lower  temperature  by  the  vapour  of  mercury  than  the  temper- 
ature at  which  an  unexposed  iodide  can  be  decomposed ;  an  amal- 
gam therefore  forms  on  such  positions  when  the  temperature  does 
not  rise  beyond  175°  F.,  though  the  whole  surface  might  be  decom- 
posed and  whitened  if  the  temperature  were  carried  high  enough. 

The  chemical  rays  which  affect  the  iodide  of  silver  are  chiefly 
those  of  high  refrangibility,  and  these  rays  manifest  many  habitudes 
resembling  those  of  radiant  heat.  They  are  absorbed  and  lost  in 
effecting  the  change,  so  that  a  ray  of  light  which  has  once  fallen 
on  a  Daguerreotype  plate,  and  is  reflected  by  it,  has  lost  all  its  activ- 
ity. Whatever,  therefore,  will  interfere  with  the  absorption,  will  in- 
terfere with  the  sensitiveness  of  different  compounds.  Thus  it  has 
long  been  known  that  there  is  a  proper  colour  to  which  the  plate 
may  be  brought  when  it  possesses  the  maximum  of  sensitiveness : 
this  is  the  golden  yellovN^ ;  when  it  is  red,  or  green,  or  blue,  it  is 
much  less  sensitive  j  and  when  of  a  lavender  colour,  hardly  sensitive 
at  all.  This  arises  from  the  circumstance  that  under  these  condi- 
tions the  optical  character  of  the  plate  is  such  that  it  reflects  the 
active  raj^s  in  part  or  altogether.     • 

I  have  already  remarked  that  lights  which  vary  in  intensity  do 
not  affect  these  plates  in  a  corresponding  way  ;  this  arises  from  the 
circumstance  that,  as  the  iodide  of  silver  is  undergoing  change,  a 
large  quantity  of  light  becomes  latent,  precisely  as  a  piece  of  ice  in 
the  act  of  melting  absorbs  a  large  quantity  of  heat,  not  discoverable 
by  the  thermometer  ;  this  phenomenon  accompanies  the  blueness 
which  the  compound  assumes  as  it  changes  into  the  condition  of  a 
subiodide.] 

Z 


178  NATURE     OP    COMBUSTION. 


CHAPTER  VII. 

OF    THE    LIGHT   AND    HEAT   DISENGAGED    DURING    CHEMICAL   COMBINATION. 

It  has  been  already  noticed  that  the  union  of  substances  having 
chemical  affinity  for  each  other  is  accompanied  by  increase  of  tem- 
perature ;  and  in  cases  where  the  affinity  is  powerful,  the  effect  may 
be  so  great  that  the  bodies  shall  become  luminous :  in  such  instances 
the  chemical  action  is  said  to  be  accompanied  by  combustion.  In  con- 
sidering the  relations  of  this  phenomenon  to  affinity,  it  will  be  ne- 
cessary to  notice,  first,  the  general  circumstances  of  combustion; 
secondly,  the  relation  between  the  amount  of  affinity  and  the  quan- 
tity of  heat  evolved;  and,  finally,  the  explanations  that  have  been 
ofl^ered  of  the  origin  of  the  light  and  heat. 

In  ordinary  language,  a  body  is  said  to  burn  when  its  elements 
unite  with  the  oxygen  of  the  air,  and  form  new  products.  The  ac- 
companying phenomena  are  in  general  those  on  which  popular  at- 
tention becomes  fixed,  and  for  which  the  process  is  generally  car- 
ried on  ;  and  hence,  to  the  world  at  large,  combustion  is  of  impor- 
tance only  as  a  source  of  heat  and  light.  One  of  the  bodies,  as  hy- 
drogen or  sulphur,  is  termed  the  burning  or  combustible  body,  and 
the  oxygen  is  said  to  be  the  supporter  of  combustion  ;  but  this  lan- 
guage, although  convenient  for  common  use,  is  incorrect  as  a  scien- 
tific expression  ;  for  oxygen  may  be  burned  in  a  vessel  of  hydrogen, 
as  w^ell  as  hydrogen  may  be  burned  in  a  vessel  of  oxygen  gas,  the 
one  and  the  other  being  equally  active  in  the  process,  and  being  re- 
lated to  each  other  in  every  way  alike.  In  combustion,  as,  indeed, 
in  all  cases  of  combination,  no  particle  of  matter  becomes  lost  or 
annihilated ;  it  assumes  new  forms,  in  general  gaseous  and  invisible 
to  the  eye  of  popular  observation,  but  easily  collected,  weighed, 
and  analyzed  by  the  means  that  chemistry  possesses.  The  solid 
coal  or  wood  which  burns  to  ashes,  changes  but  its  external  aspect ; 
mixing  with  the  general  mass  of  air  under  the  form  of  carbonic  acid 
gas  and  watery  vapour,  its  elements  become  the  food  of  living  plants, 
which  in  their  turn,  cut  down  or  fossilized,  form  to  succeeding  ages 
the  stores  of  light  and  warmth  such  as  we  now  enjoy. 

There  are  but  few  bodies  endowed  with  so  great  an  affinity  for 
oxygen  as  to  enter  into  combustion  at  ordinary  temperatures  by 
contact  with  it.  If  they  do  combine  at  ordinary  temperatures 
with  oxygen,  the  products  are  not  those  which  combustion  would 
tend  to  generate,  but  a  distinct  class  of  substances,  containing  a 
smaller  proportion  of  oxygen  combined.  Thus  nitric  oxide  gas 
combines  with  oxygen,  even  when  quite  cold,  forming  red  fumes 
of  nitrous  acid  gas,  which  is  an  inferior  degree  of  oxidation. 
Phosphorus,  when  burning  at  common  temperatures,  emits  but 
little  light,  and  forms  phosphorous  acid  ;  if  it  be  heated,  it  bursts 
into  brilliant  fiame,  and  forms  phosphoric   acid,  which  contains 


PRODUCTS  OF  SLOW  COMBUSTION.       179 

fths  more  oxygen.  Potassium  combines  at  common  temperature 
with  oxygen,  forming  potash ;  but  when  heated  it  burns  with  flame, 
and  combines  with  three  times  as  much  oxygen.  In  the  complete 
combustion  of  organic  matters,  the  products  are  always  water  and 
carbonic  acid.  Thus,  woody  fibre,  which  is  C.H.O.,  combines  with 
20.  to  form  C.O2  and  H.0. 5  and  alcohol,  which  is  C2H3O.,  combines 
with  60.  to  form  2(C.02)  and  3(H.O.).  But  at  common  tempera- 
tures the  slow  oxidizement  of  woody  fibre  produces  the  black  ve- 
getable mould,  a  form  of  ulmine,  the  C.H.O.  taking  O.  to  form  C.H.O2. 
At  common  temperatures  alcohol  becomes  acetic  acid,  the  C2H3O. 
combining  with  20.  to  form  C2H2O2  and  H.O.  The  pyroxylic  spirit 
at  common  temperatures  becomes,  by  slow  combustion,  formic  acid, 
C2H4O2  taking  O4  to  form  C2H2O4  and  2(H.O.). 

This  slow  combustion  produces  heat,  although  so  much  less  than 
is  evolved  by  the  more  rapid  process  that  it  may  easily  be  over- 
looked. But  if  a  number  of  sticks  of  phosphorus  be  laid  together 
and  allowed  to  oxidize,  they  will  warm  each  other  so  much  as  to. 
melt  and  burst  into  vivid  flame.  The  oils  and  tallow,  if  there  be  a 
large  surface  exposed  to  the  air,  as  when  cotton  or  linen  rags  im 
bibed  in  oil  lie  in  a  heap,  combine  so  rapidly  with  oxygen  as  to 
form  a  sort  of  resin,  that  by  the  heat  evolved  the  mass  will  be  set 
on  fire ;  and  hence  the  origin  of  those  spontaneous  fires,  so  called, 
which  consumed  the  naval  arsenal  at  St.  Petersburgh,  and,  in  many 
cases,  cotton-mills  in  England.  To  this  cause  also  may  be  ascribed 
the  light  which  issues  from  points  in  the  surface  of  a  marsh  or  bog, 
and  the  luminous  appearance  which  fish  assumes  when  decomposi- 
tion has  just  commenced.  The  energy  of  this  slow  combustion 
may  be  much  increased  by  heat  applied  below  the  point  which  pro- 
duces rapid  action :  thus  tallow,  when  heated  below  redness,  burns 
with  a  pale  lambent  flame,  invisible  in  daylight,  but  still  so  marked 
that,  if  it  be  plunged  into  a  vessel  of  oxygen,  the  whole  mass  bursts 
into  brilliant  combustion,  forming  then  the  ultimate  products,  wr  • 
ter  and  carbonic  acid. 

On  this  fact  of  the  increased  energy  in  the  process  of  slow  com- 
bustion produced  by  a  heat  below  that  at  which  the  body  is  in- 
flamed, is  founded  the  construction  of  the  lamp  without  flame,  or 
the  aphlcgistic  lamp.  If  a  wine-glass  be  taken,  and  rinsed  inside 
with  strong  alcohol  or  ether,  and  then  a  coil  of  fine  platina  wire, 
or  a  ball  of  spongy  platina  heated  to  redness,  be  suspended  in«the 
middle  of  the  glass,  it  will  remain  red  until  all  the  alcohol  or  ether 
has  been  exhausted.  The  glass  becomes  filled  with  a  mixture  of 
air  and  inflammable  vapour,  which,  by  the  influence  of  the  heated 
platina,  is  enabled  to  combine,  and  form  acetic  and  formic  acids. 
By  this  combination  heat  is  evolved,  which  prevents  the  cooling  of 
the  wire  or  ball,  and  thus,  as  long  as  any  combustible  material  re- 
mains, the  platina  is  kept  ignited.  The  platina  ball  or  wire  may 
also  be  (and  in  practice  generally  is)  fixed  over  the  wick  of  a  spirit- 
lamp,  and  the  lamp  having  been  ignited,  is  blown  out  as  soon  as  the 
platina  has  become  red,  which  then  continues  to  glow  until  the  lamp 
has  been  emptied  of  the  spirit,  the  latter  ascending  through  the 
capillary  wick,  and  forming  over  its  top  a  little  explosive  atmo- 
sphere, in  which  the  ball  of  platina  is  immersed  and  works. 


180       CONSTRUCTION    OF     THE     PLATINA    GAS    LAMP. 

This  property  of  platina  appears  to  depend  on  the  power  which 
it  possesses  of  attracting  to  its  surface  in  a  condensed  form  a  layer 
of  particles  of  whatever  gaseous  mixture  it  is  immersed  in.  Hence, 
if  its  surface  is  in  the  slightest  degree  soiled,  it  ceases  to  exert  this 
action ;  and  by  increasing  the  surface,  its  energy  may  be  augmented 
in  a  remarkable  degree.  The  form  in  which  it  is  most  powerful  is 
that  of  the  slightly  coherent  spongy  mass,  obtained  by  reducing  at 
a  full  red  heat  the  ammonia  chloride  of  platinum  j  if  a  ball  of  the 
metal  so  prepared  be  plunged  into  a  vessel  of  oxygen  and  hydrogen, 
mixed  in  suitable  proportions  to  form  water,  the  gases  instantly  ex- 
plode ;  for  the  oxygen  and  hydrogen,  being  absorbed  by  the  spongy 
platina,  are  brought  into  intimate  contact  upon  its  surface,  and  unite, 
evolving  so  much  heat  as  to  raise  the  temperature  of  the  platina 
ball  to  redness,  and  thereby  inflame  the  remaining  gas.  The  action 
of  the  spongy  platina  may  be  weakened  by  mixing  it  with  some  pipe- 
clay, or  using,  as  in  the  aphlogistic  lamp,  the  platina  in  the  form  of 
plate  or  wire.  In  this  way  all  combustible  gases  may  be  caused  to 
combine  gradually  with  oxygen,  but  they  require  different  temper- 
atures, and  the  action  is  modified  by  the  presence  of  other  gases 
in  a  manner  which  is  often  taken  advantage  of  in  gaseous  analysis. 
The  most  remarkable  application  of  this  property  is  to  procure 
instantaneous  light  by  means  of  the  hydrogen  gas 
lamp.  A  vessel,/,  contains  dilute  sulphuric  acid,  into 
which  the  tube  of  the  vessel  g  h  dips  nearly  to  the  bot- 
tom, having  attached  a  piece  of  ordinary  zinc,  e.  The 
vessels  being  ground  air-tight  where  they  fit  to  one 
another,  when  the  stopcock  b  is  closed,  and  the  acid 
S*  acts  on  the  zinc,  the  hydrogen  evolved  cannot  escape, 
and,  pressing  on  the  liquid  in  /,  forces  it  up  into  A, 
until  the  acid  falling  below  the  level  of  the  zinc,  the 
action  ceases.  To  the  stopcock  b  is  attached  a  jet, 
c,  in  front  of  which  is  fixed  a  ball  of  spongy  platina,  a, 
which,  being  in  the  air,  has  always  condensed  in  its  pores  a  quantity 
of  oxygen  gas ;  on  opening  the  stop-cock,  the  hydrogen,  issuing 
from  the  jet,  strikes  upon  the  platinum,  and  combining  with  the  ox- 
ygen, heats  the  ball  so  highly  that  it  inflames  the  jet  of  gas,  and 
thus  affords  a  flame  at  which  any  other  substance  may  be  lighted. 
This  lamp  has  assumed  a  variety  of  forms,  of  which  the  above  is 
that  which  best  shows  its  principle.  All  bodies  possess  this  prop- 
erty to  a  slight  extent,  particularly  when  hot ;  but  in  none  is  it  ac- 
tive enough  to  be  usefully  applied,  except  in  platinum. 

The  temperatures  at  which  bodies  enter  into  rapid  combustion 
are  very  various ;  thus  phosphorus  inflames  at  a  temperature  of 
120°  F.,  and  sulphur  at  300^  F.  Phosphuretted  hydrogen  gas  in- 
flames at  all  ordinary  temperatures,  while  hydrogen  requires  a  dull 
red,  and  carburetted  hydrogen  a  bright  red  heat  before  they  will 
take  fire.  The  inflammability  of  phosphorus  has  been  shown  by 
Graham  to  be  affected  by  the  presence  of  small  quantities  of  various 
substances  in  a  very  curious  manner  ;  thus  phosphorus  may  be  sub- 
limed in  air  saturated  with  vapour  of  oil  of  turpentine,  without  any 
tendency  to  combustion,  or  combination  with  oxygen,  being  evinced. 
Combustion  occurs  only  at  the  point  where  the  two  substances 


CONSTITUTION     OF     FLAME.  181 

which  enter  into  union  are  in  contact.  Thus,  in  an  ordinary  flame, 
the  true  combustion  is  limited  to  a  thin  sheet,  the  inside  of  which 
is  totally  dark,  and  occupied  by  the  combustible  material  of  the 
burning  body  in  a  state  of  gas.  This  is  easily  shown  by  holding 
over  the  flame  of  a  candle  or  a  spirit-lamp  a  piece  of  wire  gauze : 
the  burning  sheet  is  marked  by  a  ring  of  light,  but  the  interior  i? 
dark,  although  full  of  inflammable  vapour,  which  passes  through  un 
inflamed,  and  may  be  ignited  on  the  opposite  side  of  the  gauze.  L 
the  flame  of  an  ordinary  candle,  a,  four  distinct  portions  may  be  ob 
served,  having  totally  distinct  constitutions ;  at  the  base 
of  the  flame,  i  i,  a  pale,  blue-coloured  light  is  emitted,  for 
there  the  air  is  in  excess,  and  the  combustion  is  at  once 
complete ;  higher  up,  from  i  i  to  c,  the  combustible  material 
is  in  excess,  and  the  most  brilliant  light  is  produced  by  the 
active  combination  ]  this  portion  is  surrounded  by  a  sheet 
of  much  paler  and  yellower  light,  e  e,  which  is  observable 
particularly  at  the  sides  of  the  flame,  while  the  inside  of 
the  flame,  Z>,  remains  completely  black,  and  is  occupied  only 
by  vapour  incapable  of  burning  from  having  no  access  to 
the  external  air.  The  light  emitted  arises  also  from  the 
circumstances  of  the  combination  j  the  temperature  of  flame  is  in 
all  cases  exceedingly  high,  although  often  but  little  luminous,  for 
it  is  found  that  a  current  of  air  hot  enough  to  brilliantly  ignite  a 
solid  body,  is  itself  not  at  all  incandescent.  Hence,  in  all  casef 
where  bright  light  is  produced  in  combustion,  one  of  the  bodies  en- 
gaged must  be  solid,  and  the  light  is  really  derived  from  its  becom- 
ing ignited.  Thus  hydrogen  and  sulphur  give,  in  burning,  very  little 
light,  because  the  one  is  a  gas,  and  the  other,  when  burning,  is  in 
the  state  of  vapour,  and  the  products  of  combustion  are,  when  form- 
ed, in  both  cases  gaseous.  Phosphorus,  when  it,  in  burning,  forms 
a  volatile  body,  gives  but  little  light,  but  when  it  forms  a  fixed  prod- 
uct, is  one  of  the  most  brilliant  instances  of  combustion.  Iron  and 
zinc,  which  form  solid  oxides,  burn  with  great  light,  and  carbon,  al- 
though forming  a  gas,  being  itself  solid,  produces  light  also.  In  the 
case  of  a  candle,  the  source  of  light  is  to  be  found  in  the  decompo- 
sition which  the  inflammable  vapour  inside  of  the  flame  undergoes 
from  the  high  temperature  to  which  it  is  subjected ;  one  half  of  its 
carbon  is  deposited  in  the  solid  form,  forming  smoke,  and  it  is  this 
smoke  which,  becoming  ignited,  constitutes  the  great  source  of 
light.  A  body  which  could  not  form  smoke,  could  not  give  out 
much  light  in  burning.  The  separation*  of  this  carbon  (soot)  in  the 
flame  may  easily  be  shown  by  placing  over  the  flame  of  the  candle 
a  sheet  of  wire  gauze:  below  the  middle  of  the  luminous  space  the 
flame  becomes  dull,  and  the  carbon,  which  in  burning  should  have 
rendered  it  brilliant,  passes  as  smoke  through  the  gauze,  and  may 
be  inflamed  above  ;  when  the  supply  of  air  is  insufficient,  this  smoke 
is  not  completely  burned,  and  a  corresponding  quantity  of  heating 
and  lighting  material  is  lost ;  and  as  it  carries  off'  with  it  a  great 
quantity  of  the  heat  already  formed,  it  actually  cools  the  flame. 
When,  therefore,  a  high  temperature,  or  a  clear  flame  without  smoke 
is  required,  all  the  carbon  must  be  consumed.  This  is  efl^ected  by 
a  variety  of  contrivances :  in  the  burner  of  the  Argand  lamp  or  gas 


182         HEATING  EFFECTS  OF  FLAME. 

jet,  a  current  of  air  is  established  through  the  centre  of  the  flame, 
and  thus  the  combustion  of  the  inflammable  vapour  much  accelera- 
ted ;  in  the  flame  of  the  blowpipe  the  same  effect  is  produced  by 
the  current  of  air  from  the  bellows  or  the  mouth  ;  and  on  a  large 
scale  by  the  numerous  ways  of  burning  smoke,  so  necessary  in  fac- 
tories situated  in  large  cities.  In  the  employment  of  the  blowpipe, 
the  constitution  of  the  flame  is  of  great  importance ;  for  according 
as  the  body  to  be  heated  is  placed  at  6,  where  the 
^  oxygen  of  the  air  preponderates,  or  between  a  and 

\\fi^^^^^::^='b  ^j  where  it  is  immersed  in  an  atmosphere  of  inflam- 

^?j2^  mable  material,  the  most  opposite  effects  of  violent 

I  llll  oxidation,  and  of  reduction  from  the  state  of  oxide, 

ill  ^^y  ^®  produced.     Thus  a  glass   of  copper  be- 

^^^  comes  green  at  b,  and  red  from  a  to  b  ;  a  glass  of 

manganese  is  rendered  purple  at  5,  but  colourless  from  a  to  b  j  there 
being  few  bodies  whose  relations  to  the  blowpipe  can  be  completely 
known  without  a  comparison  of  the  effect  of  the  oxidizing  and  re- 
ducing flames. 

During  combustion,  the  heat  evolved  is  at  first  absorbed  by  the  body  which  is 
then  produced ;  but  it  is  afterward  distributed  through  the  mass  of  all  neighbour- 
ing bodies  in  proportion  to  their  conducting  powers.  It  is  easy  to  calculate  the 
temperature  to  which  the  product  of  the  combustion  is  in  the  first  place  raised. 
Thus  eight  parts  of  oxygen  unite  with  one  part  of  hydrogen  by  weight  to  form  nine 
of  water.  If  watery  vapour  had  the  same  capacity  for  heat  as  water,  the  tempera- 
ture of  the  vapour  produced  should  be,  since  one  part  of  oxygen  heats  twenty-nine 
parts  of  water,  180  degrees  =|  (29xl80)=:4640  above  the  freezing  point ;  but  the 
capacity  of  watery  vapour  in  equal  weight  is  only  0-847,  and  therefore  it  is  more  ea- 
sily heated  in  that  proportion  than  liquid  water ;  hence  the  temperature  really  pro- 
duced is  r=4640x0  847,  or  5478  above  the  freezing  point  of  water.  If,  however,  in 
place  of  pure  oxygen,  atmospheric  air  had  been  made  use  of,  then  23- 1  parts  of 
oxygen  are  mixed  therein  with  769  parts  of  nitrogen,  which  must  be  heated  to  the 
same  temperature  with  the  watery  vapour,  and,  of  course,  at  its  expense.  The  ca- 
pacity of  nitrogen  gas  for  heat  is  0-2865,  one  third  that  of  watery  vapour  ;  but  in 
the  air  which  is  necessary  to  form  nine  parts  of  water,  there  are  26 -8,  or  almost 
exactly  three  times  as  much  nitrogen,  so  that  precisely  one  half  of  the  quantity  of 
heat  produced  is  absorbed  by  the  nitrogen,  and  the  temperature  of  the  mixture  rises 
only  to  2739°  above  the  freezing  point. 

Such  being  the  temperatures  produced  by  hydrogen  gas  in  burning  in  oxygen  and 
in  atmospheric  air,  it  is  easy  to  understand  why  we  can  by  its  power  fuse  those 
substances  which  resist  almost  every  other  means.  The  melting  point  of  cast  iron 
is  2786°,  that  is,  almost  exactly  the  same  as  that  produced  by  hydrogen  burning  in 
ihe  open  air ;  but  the  temperature  of  5478°,  given  by  hydrogen  burning  in  oxygen, 
is  very  nearly  double  that,  and  passes,  therefore,  far  beyond  the  melting  point  of 
platinum,  and  exceeds  the  heat  of  all  our  other  artificial  fires  ;  it  is  only  in  the  dis- 
charge of  the  galvanic  battery,  or  in  the  solar  rays  concentrated  by  a  lens,  that  the 
heating  effects  of  burning  hydrogen  and  oxygen  can  be  equalled.  If  the  nitrogen 
had  been  present  in  a  quantity  ten  times  as  great,  it  would  have  absorbed  ^  of  the 
amount  of  heat  evolved,  and  hence  the  resulting  temperature  should  be  only  about 
500°.  Such  a  mixture,  therefore,  could  not  explode  at  all,  for  the  first  little  portion 
which  might  be  burned  could  not  produce  the  necessary  temperature  for  communi- 
cating the  combustion  to  the  mass.  In  this  manner,  the  combustibility  of  gaseous 
mixtures  may  be  destroyed  by  mixing  them  with  other  gases  in  such  quantities  as 
may  cool  them  below  the  temperatures  at  which  explosion  can  take  place.  One 
volume  of  a  mixture  of  oxygen  and  hydrogen  is  prevented  from  exploding  by  the 
presence  of  nine  volumes  of  hydrogen,  six  volumes  of  nitrogen,  one  of  defiant  gas, 
two  of  ammonia,  three  of  carbonic  acid ;  but  with  eight  volumes  of  hydrogen,  or 
five  volumes  of  nitrogen,  explosion  may  occur. 

The  greater  density  of  solid  bodies,  and  the  greater  rapidity  with 
which  they  are  capable  of  conducting  away  the  heat  which  they  re 


CONSTRUCTION  OF  THE  SAFETY-LAMP. 


183 


ceive,  enables  them,  in  a  still  more  remarkable  degree,  to  reduce  the 
temperature  of  flame,  and,  consequently,  to  extinguish  it.  Thus,  if 
a  piece  of  metallic  gauze  be  held  over  a  jet  of  ig- 
nited coal  gas,  the  flame  will  be  arrested  at  the  low- 
er surface  of  the  gauze ;  and  although  the  gas  and 
air  may  pass  through,  forming  an  explosive  mixture, 
yet  no  inflammation  can  be  propagated;  and  if  the 
mixture  of  air  and  gas  be  allowed  to  pass  through 
the  metallic  gauze,  and  then  ignited  at  its  upper 
surface,  it  will  burn  there ;  but,  although  the  space 
between  the  jet  and  gauze  be  occupied  by  inflam- 
mable material,  the  flame  cannot  pass  down,  the  me- 
tallic tissue  conducting  away  the  heat  so  rapidly  as  to  prevent  the 
temperature  froni  rising  to  the  necessary  degree.  Another  and  a 
very  striking  form  of  this  experiment  is  to  lay  on  the  metallic 
gauze  a  piece  of  camphor,  and  to  hold  it  over  a  lamp  ;  the  camphor 
will  melt  and  vaporize,  but  as  it  melts  it  will  in  part  filter  through 
the  gauze  ;  this  portion  takes  fire,  and  a  sheet  of  smoky  flame  cov- 
ers the  lower  surface  ;  but  above,  the  camphor  in  vapour  mixes 
with  the  air  without  inflaming. 

The  application  of  this  principle  to  the  construction  of  the  safety- 
lamp  for  mines,  constitutes  one  of  the  most  beautiful  instances  of 
the  advantages  which  may  practically  flow  from  what,  superficially 
considered,  might  appear  a  mere  abstract  principle  in  science.  The 
fire-damp,  or  light  carburetted  hydrogen,  which,  issuing  from  the 
minute  fissures  in  the  excavations  of  a  coal-mine,  is  diffused  through 
the  air  introduced  for  the  purposes  of  ventilation,  often  forms  an 
explosive  mixture,  which,  being  set  on  fire  by  accident  or  negli- 
gence, detonates  with  awful  violence,  and  destroys  all  living  beings 
which  may  at  the  time  be  in  the  mine.  This  gas  is  one  of  the  least 
easily  inflammable,  and  hence,  most  fortunately  for  humanity,  one 
to  Avhich  the  principle  of  cooling  orifices  may  be  most  successfully 
applied.  The  candle  or  lamp,  Z»,  by 
which  light  is  to  be  obtained  for  work- 
ing in  the  mine,  is  surrounded  by  a  cyl- 
inder of  wire  gauze,  of  about  1500  ori- 
fices in  the  square  inch.  Inside  of  this 
the  inflammable  mixture  may  explode, 
but  the  flame  cannot  pass  out ;  the  com- 
bustion cannot  be  communicated  to  the 
general  mass  of  external  air,  and  thus 
the  miner,  guided  by  the  never-failing 
indications  of  his  safety-lamp,  passes 
along  through  galleries  under  ground, 
where  the  emission  of  a  spark  would 
cause  destruction,  and  measures,  by  the 
appearance  of  the  lamp,  the  actual  con- 
dition of  the  air  he  breathes,  the  phe- 
nomena of  the  flame  indicating  also  its 
fitness  for  Respiration.  If  the  air  be 
pure,  the  lamp  burns  clear,  as  in  the 
upper  air  3  if  some  fire-damp  be  present, 


184   QUANTITY    OF    HEAT    EVOLVED    IN    COMBUSTION. 

the  lamp  shows  much  less  light,  the  flame  becomes  red  and  smoky, 
if  the  noxious  impregnation  be  still  increased,  the  flame  of  the  lamp 
itself  becomes  extinguished,  and  the  cylinder  of  metallic  gauze  is 
filled  by  a  sheet  of  lurid  flame  j  the  miner  being  then  enveloped  by 
an  atmosphere  fully  explosive,  and  even  fatal  to  life  if  it  be  long 
respired.  If  he  proceed  still  farther,  all  flame  is  lost ;  for,  as  the 
fire-damp  then  predominates,  there  is  produced,  from  deficiency  of 
oxygen,  only  a  slow  invisible  combustion  ;  but  even  this  is  made, 
by  the  sublime  genius  of  its  inventor,  Davy,  to  give  the  miner  the 
last  warning  to  return  to  safer  regions :  a  sheet  of  thin  platina,  being 
coiled  up  and  hung  over  the  wick  of  the  lamp,  becomes  ignited,  as 
in  the  aphlogistic  lamp,  and  continues  to  emit  a  faint,  but  most  use 
ful  beacon  glow,  until  an  atmosphere  is  obtained  where  there  is  ox- 
ygen enough  to  support  a  rapid  combustion,  or  until  a  place  is 
reached  so  destitute  of  oxygen  that  no  combustion  whatsoever  can 
take  place. 

The  determination  of  the  quantity  of  heat  produced  during  the 
combustion  of  a  given  quantity  of  combustible  substance  is  a  prob- 
lem of  great  importance  in  the  arts,  as  on  it  depends  the  economic 
value  of  all  varieties  of  fuel.  The  plan  generally  followed  has  been 
to  burn  the  substances  by  means  of  the  smallest  quantity  of  air 
which  is  suflicient,  in  a  vessel  surrounded,  as  far  as  possible,  with 
water.  If  it  be  found  that  the  burning  of  a  pound  of  wood  heats 
37  pounds  of  water  from  32°  to  212^,  no  idea  can  be  thereby  formed 
of  the  quantity  of  heat  evolved ;  but  if,  in  another  trial,  it  be  found 
that  the  burning  of  a  pound  of  charcoal  raises  the  temperature  of 
74?  pounds  of  water  through  the  same  range,  it  follows  that  the  char- 
coal had  double  the  calorific  power  of  the  wood.  True  relative 
numbers  can  thus  be  obtained,  although  they  have  independently  no 
positive  signification.  The  results  obtained  in  this  manner  have 
been  exceedingly  discordant ;  but,  by  the  late  researches  of  Des 
pretz  and  of  Bull,  which  appear  to  have  been  conducted  with  more 
attention  to  accuracy  than  former  ones,  a  very  interesting  rule  has 
been  obtained :  it  is,  that  in  all  cases  of  combustion  the  quantity  of 
heat  evolved  is  proportional  to  the  quantity  of  oxygen  which  enters 
into  combination.     Thus  Despretz  found 

.  1  lb.  of  oxygen,  uniting  with  hydrogen,  heats  from  32°  to  212°,  291  lbs.  of  water. 
"  *'  "  charcoal,  "  "  29  " 

"  "  "  alcohol,  "  "  28 

a  u  ..  gji^gj.^  u  u  281 

This  rule,  however,  must  be  liable  to  some  very  curious  changes  ;  for  one  pound 
of  oxygen,  in  combining  with  iron,  could  heat,  by  Despretz's  experiments,  53  pounds 
of  water,  or  almost  exactly  twice  as  much  as  in  the  former  list,  and  with  tin  and 
zinc  the  same  double  proportion  held.  With  phosphorus  a  singular  peculiarity 
was  observed,  which,  when  the  subject  comes  to  be  more  fully  studied,  may  throw 
some  light  upon  the  former  differences.  When  phosphorus  burns  slowly,  so  as  to 
form  phosphorous  acid,  it  heats,  in  combining  with  a  pound  of  oxygen,  S8  pounds 
of  water  ;  but  when  it  burns  brilliantly  and  forms  phosphoric  acid,  the  heat  evolved 
is  doubled,  and  becomes  the  same  as  that  produced  with  iron,  tin,  or  zinc.  As  a 
suggestion,  I  would  remark,  that  in  the  cases  where  the  smaller  proportion  of  heat 
is  evolved,  the  products  of  combustion  are  all  volatile,  and  where  the  larger  propor- 
tion is  produced,  the  products  are  fixed  and  solid  ;  even  in  the  case  of  phosphorus, 
when  it  combines,  producing  least  heat,  it  forms  a  volatile  product,  but  one  which 
resists  a  full  red  heat  in  the  case  where  the  combination  has  been  complete. 

Hess  has  lately  pointed  out  a  relation  between  the  amount  of  chemical  action 


THEORY     OF     COMBUSTION.        185 

and  the  quantity  of  heat  evolved,  which  may,  when  examined  in  a  greater  number 
of  cases,  lead  to  very  important  conclusions.  He  has  found  that  sulphuric  acid,  in 
combining  with  any  base,  generates  in  all  cases  the  same  quantity  of  heat  ;•  the  rise 
of  temperature  is,  of  course,  greatest  when  the  acid  and  base  are  both  in  an  un- 
combined  condition,  as  where  vapour  of  anhydrous  sulphuric  acid  produces,  by  con- 
tact with  dry  barytes,  brilliant  ignition ;  but,  although  the  barytes  generates,  by  con- 
tact with  dilute  sulphuric  acid,  much  less  heat,  yet,  if  the  two  quantities  evolved, 
first  by  mixing  the  strong  acid  with  water,  and  then  the  dilute  acid  with  the  base, 
be  added  together,  the  sum  appears,  from  a  great  number  of  experiments,  to  be 
constant ;  thus,  diluting  oil  of  vitriol  with  water,  and  neutralizing  it,  so  diluted, 
with  ammonia,  Hess  found  the  heat  in  each  case  to  be,  « 

with  Ammonia.       Witli  Water.  Sum. 

Oil  of  vitriol     .     .     .  5958 5958 

First  dilution  .     .     .  518-9     .     .     778    .     .     .  5967 
Second  dilution   .     .  480  5     .     .  116-7    .     .     .  597.2 

Connecting  these  results  with  those  of  Despretz,  just  given,  for  the  bodies  which 
unite  with  oxygen,  it  would  appear  likely  that  the  quantity  of  heat  evolved  in  chem- 
ical combination  may  be  connected  with  the  equivalent  number  and  the  electrical 
condition  of  the  substances  by  a  definite  law,  which  farther  investigation  may  dis- 
<*lose. 

At  all  periods  in  the  history  of  chemistry,  the  explanation  of  the  phenomena  of 
combustion  was  that  for  which  the  general  theory  of  the  science  was  constructed  ; 
and,  accordingly,  we  find  that  every  period  of  its  progress  has  been  marked  by  the 
views  adopted  to  account  for  the  heat  and  light  so  evolved.  The  coarse  and  un- 
philosophical  ideas  of  the  existence  of  inflammability  which  prevailed  before  Lavoi- 
sier's time,  do  not  require  notice ;  but  the  theory  which  he  proposed,  although  not 
now  received,  is  yet,  like  all  his  works,  of  so  much  interest  and  importance,  that 
it  would  be  improper  to  pass  it  over. 

When  Lavoisier  lived,  the  minds  of  philosophers  were  fixed  in  the  opinion 
that  heat  and  light  were  positively  existing  substances,  which  might  enter  into 
combination,  or  be  disengaged  from  combinations  in  which  they  had  previously 
been  engaged,  just  as  lead,  or  oxygen,  or  any  other  of  the  ordinary  bodies  we  oper- 
ate upon  in  our  experiments.  Gases  were  believed  to  be  compounds  of  the  true 
solid  body  with  light  and  heat ;  and  hence,  when  oxygen  gas  combined  with  iron 
or  with  phosphorus,  and  assumed  the  solid  form,  the  light  and  heat  with  which  the 
real  oxygen  had  previously  united  were  set  free.  Hydrogen  and  oxygen  gases,  in 
combining  to  form  liquid  water,  underwent  the  greatest  condensation,  and  by  their 
union,  therefore,  the  greatest  heat  was  evolved ;  and  in  all  such  cases  where  a  gas 
became  a  liquid  or  a  solid,  this  theory  was  fully  competent  to  explain  the  facts. 
However,  in  very  many  cases  it  failed  completely ;  thus,  by  the  union  of  carbon 
with  oxygen,  so  far  from  a  gas  becoming  solid  and  so  evolving  a  heat,  a  solid  be- 
comes a  gasj  and  should  produce  an  equivalent  degree  of  cold.  Lavoisier  here 
brought  in  to  his  aid  the  relative  specific  heats  of  the  gases  before  and  after  union  ; 
thus,  if  the  carbonic  acid  formed  by  burning  carbon  in  oxygen  gas  had  a  much  less 
specific  heat  than  oxygen,  there  might  be  evolved  a  quantity  of  heat  in  the  same 
way  as  it  occurs  with  water  and  sulphuric  acid ;  but  this  is  not  the  fact ;  on  thr 
contrary,  the  carbonic  acid  has  a  specific  heat  greater  than  that  of  the  oxygen  g. 
it  was  formed  from,  in  the  proportion  of  1195  to  808  ;  and  hence,  on  Lavoisier'a, 
views,  an  intense  degree  of  cold  should  be  produced  in  the  combustion  of  charcoal, 
as  well  by  the  latent  heat  which  the  solid  should  absorb  in  becoming  gaseous,  as  by 
the  increased  specific  heat  of  the  gas  so  formed.  This  example  is  sufficient  to 
show  the  way  in  which  Lavoisier's  theory  became  inapplicable  to  the  wants  of 
science. 

Dr.  Thompson  has  recently  endeavoured  to  account  for  the  heat  evolved  in  chem- 
ical combination  by  an  application  of  the  law  of  Dulong  regarding  specific  heats 
(described  page  66).  Every  molecule  of  a  simple  body  being  supposed  provided 
with  the  same  quantity  of  heat,  he  suggests  that,  when  a  number  of  them  combine 
together,  the  heat  of  one  or  more  is  expelled,  and  thus  produces  the  rise  of  tem- 
perature. Thus,  considering  oil  of  vitriol  to  contain  seven  combining  equivalents, 
two  of  hydrogen,  four  of  oxygen,  and  one  of  sulphur,  and  that  the  specific  heat  of 
all  of  these  is  the  same,  31,  as  results  from  Dulong's  law  if  it  be  supposed  rigidly 

exact,  the  specific  heat  of  oil  of  vitriol  should  be      ^^  =0442,  491  being  the 

Aa 


186 


HEAT     OF     COMBir^ATION,     WHENCE     DERIVED. 


equivalent  number  of  oil  of  vitriol ;  but  the  specific  heat  found  by  experiment  Is 
only  0  352  ;  so  that  exactly  one  fifth  of  the  total  quantity  of  heat  has  been  lost  by 
the  act  of  combination,  and  may  hence  be  supposed  to  have  caused  the  phenomena 
of  combustion. 

In  the  extension  of  this  principle  a  little  farther  than  Dr.  Thompson  appears  to 
have  contemplated  its  application,  some  coincidences,  with  results  already  known, 
are  found,  which  give  it  an  aspect  of  considerable  theoretic  interest.  Thus  we 
may  consider  certain  metallic  oxides  as  consisting  of  an  equivalent  of  each  constit- 
uent, and  hence  their  proper  specific  heat  should  be,  if  none  were  lost  by  combina- 
tion, 3-lx2=6-2  ;  but  the  specific  heat  of  the  compound  molecule  is  experimentally 
found  to  be  54,  and  thus  that  08  of  heat  had  been  lost,  producing  the  phenomena 
of  combustion  in  combination.  In  this  manner  we  can  understand  why  Despretz 
found  that  a  certain  quantity  of  oxygen  evolves  the  same  quantity  of  heat  in  com- 
bining with  very  many  bodies.  If  we  examine  the  sulphates  noticed,  p.  67,  in  re- 
lation to  the  same  principle,  we  find  that  as  there  are  in  each  six  molecules,  the 
specific  heat  should  be  18-6=3-lx6  ;  but  it  is  found  to  be  but  two  thirds  of  that, 
12-4.  Now  if  here,  as  in  the  oxides,  the  combustible  material  retains  its  heat,  and 
it  is  from  the  oxygen  that  the  portion  set  free  is  taken,  the  experimental  result 
arises  from  the  heat  of  each  oxygen  molecule  being  reduced  by  1-6,  and  hence  that 
when  oxygen  forms  a  salt  with  sulphur  and  a  metal,  the  heat  evolved  is  double  that 
produced  in  simple  oxidation.  The  fact  of  the  same  quantity  of  oxygen  giving 
double  the  amount  of  heat  when  it  converts  phosphorus  into  phosphoric  acid,  com- 
pared with  what  is  evolved  when  it  forms  only  phosphorous  acid,  may  have  its  ori- 
gin in  an  analogous  condition. 

In  the  case  of  the  carbonates,  another  form  of  the  principle  becomes  manifest ; 
but  on  this  view  it  is  necessary  to  consider  carbonic  acid  as  containing  five  mole- 
cules, one  of  carbon  and  four  of  oxygen,  and  as  uniting  with  two  molecules  of  a 
metallic  oxide.  The  carbon  and  metal  burn  each  in  half  of  the  quantity  of  oxygen 
with  which  they  ultimately  unite,  and,  like  phosphorus,  separate  from  that  oxygen 
only  the  smaller  quantity  which  it  can  lose  when  entering  into  combination  ;  the 
carbonic  acid  and  suboxide  then  unite  with  the  residue  of  oxygen,  and  from  it 
separate  the  larger  portion  of  heat  as  occurs  when  phosphoric  acid  is  produced. 
The  resulting  specific  heat  for  a  carbonate  is  therefore  9-3-j-6-9-j-5=:20-7;  or,  re- 
duced to  the  equivalent  number  used  in  p.  67,  it  is  10  35,  the  experimental  number 
being  104. 

The  results  in  these  three  cases  may  be  shown  in  the  form  of  the  following  table, 
in  which  the  first  column  contains  the  equivalent  molecule  of  the  body,  M.  denoting 
the  equivalent  of  a  metal ;  the  second  column  contains  the  specific  heats  calculated 
on  the  supposition  that  there  is  none  lost  in  combining ;  the  third,  the  calculation 
by  which  the  fourth  column  of  true  calculated  specific  heats  is  obtained  ;  and  the 
fifth,  the  specific  heats  that  have  been  found  by  experiment. 


1. 

2. 

3.                           4. 

5. 

M.  0. 

6-2 

31-1-23 

5.4 

12-2 

54 
12-4 

M.  O4S. 

18-6 

(2x31)-f(4xl-5) 

M2O6C. 

279 

(3x31)-|-(3x2-3)-f3xl-5) 

20.7J20-8| 

The  coincidences  refer  only  to  the  bodies  already  selected,  p.  67,  as  exam- 
ples of  simplicity  in  the  relation  of  their  specific  heats,  and  certainly  do  not  exist  in 
a  great  number  of  other  cases  in  which  I  have  sought  for  them  ;  they  may  there- 
fore be  accidental ;  but  there  is  yet  so  much  likelihood  of  some  physical  law  of  the 
kind  being  to  be  discovered,  that  everything  that  may  assist  in  its  detection  is  of 
importance. 

Laying  aside  altogether  the  attempt  at  deducing  the  phenomena  of  combustion 
from  any  change  in  the  amount  of  latent  or  of  specific  heat  in  the  bodies  which 
enter  into  combination,  it  remains  only  to  be  admitted  as  a  general  and  independent 
principle  that  chemical  combination  is  a  source  of  heat  and  light.  It  is,  however, 
impossible  to  arrest  inquiry  at  that  point,  and,  accordingly,  the  speculations  of  phi- 
losophers have  been  directed  in  seeking  a  cause  for  the  phenomena  of  combus- 
tion to  the  disengagement  of  electricity,  which  accompanies  all  manifestations  of 
chemical  action,  and  have  endeavoured  to  identify  the  light  and  heat  emanating 
from  a  burning  body  with  that  which  is  produced  by  the  separation  or  combination 
of  the  electric  fluids.  The  evidence  in  favour  of  this  view  will  be  best  described 
among  the  relations  of  electricity  to  affinity. 


INFLUENCE     OF     ELECTRICITY     ON     AFFINITY.    187 

CHAPTER  VIII. 

OF    THE    INFLUENCE    OF    ELECTRICITY    ON    CHEMICAL   AFFINITY. 

It  has  been  already  shown,  that  in  the  production  of  galvanic  or 
hydro-electric  currents,  there  always  occurs  between  the  liquid  and 
solid  elements  of  the  circle  a  degree  of  chemical  action,  to  which 
the  quantity  of  electricity  generated  is  exactly  proportional  in 
amount,  and  that  no  current,  such  as  was  there  described,  can  be  gen- 
erated without,  by  the  chemical  action  of  the  more  oxidizable  met- 
al, the  liquid  being  decomposed,  and  some  one  element  of  it  expell- 
ed, in  place  of  which  a  corresponding  quantity  of  zinc  may  be  sub- 
stituted. I  did  not  then  attempt  to  discuss  the  question  of  whether 
the  chemical  action  in  the  battery  be  the  cause  or  the  effect  of  the 
current  of  electricity  which  arises,  as  that  can  be  best  done  when 
the  action  of  the  current,  no  matter  from  what  source  it  may  have 
been  derived,  upon  chemical  substances,  similar  to  those  that  are 
used  as  exciting  liquids  in  the  galvanic  battery,  has  been  described. 

If  the  wires  belonging  to  the  plates  Z  C,  of  the  simple  circuit  in 
the  figure,  be  brought  into  communication  by  means 
of  a  cup  of  water,  the  current  passes,  and  it  is  found 
that  at  the  terminations  of  the  wires  bubbles  of  gas 
form  in  considerable  number,  which,  when  collected, 
are  found  to  be,  from  the  wire  in  connexion  with  the 
.copper  plate,  oxygen  gas,  and  hydrogen  gas  from 
the  wire  which  is  attached  to  the  plate  of  zinc.  If 
the  conducting  liquid  had  been  muriatic  acid,  hydro- 
gen would  have  been  evolved  as  gas  at  the  zinc  extremity,  and  chlo- 
rine liberated  upon  the  wire  of  the  copper  plate,  though  from  its 
solubility  in  the  liquid  it  would  not  be  disengaged  as  gas. 

If  a  solution  of  iodide  of  potassium  had  been  employed,  iodine 
would  appear  upon  the  copper  side,  and  potassium  should  be  set 
free  upon  the  zinc  wire ',  but  by  the  action  of  the  water,  the  metal 
is  instantly  converted  into  potash,  and  hydrogen  set  free. 

It  is  not  necessary  that  such  bodies  should  be  in  solution,  for  this 
only  serves  to  give  to  their  particles  the  freedom  of  motion,  which 
may  allow  their  elements  to  separate.  If  chloride  of  lead  melted  in 
a  cup  be  used  to  complete  the  voltaic  circuit,  chlorine  is  evolved 
upon  the  +,  and  lead  upon  the  —  wire ;  with  oxide  of  lead  (litharge), 
the  evolution  of  lead  at  the  — ,  and  of  oxygen  upon  the  +  extrem- 
ity of  the  wires,  occurs  similarly  ;  protochioride  of  tin,  iodide  of 
lead,  chloride  of  silver,  all  act  in  the  same  way. 

In  place  of  bodies  consisting  of  two  elements,  such  as  those  above 
described,  we  may  employ  in  solution,  or  in  a  fused  state,  secondary 
compounds,  consisting  of  an  acid  and  a  base.  If  the  current  of  elec- 
tricity pass  through  a  solution  of  sulphate  of  soda,  the  sulphuric 
acid  appears  upon  the  +,  and  the  alkali  upon  the  —  wire.  With 
sulphate  of  magnesia,  the  earth  passes  to  the  negative,  and  the  acid 
to  the  positive  extremity  of  the  liquid  circuit  j  in  these  cases  water 


188  CHEMICAL    AFFINITY    ELECTRICAL  ATrRACTION. 

is  also  decomposed,  of  which  the  hydrogen  accompanies  the  hase, 
and  the  oxygen  the  acid ;  but,  on  using  a  salt  of  lead,  of  silver,  or 
of  copper,  the  metallic  oxide  is  reduced  by  the  action  of  the  nascent 
hydrogen,  or,  at  least,  it  may  be  so  expressed,  and  the  metal  is  de- 
posited in  crystals  upon  the  —  wire,  while  the  acid  and  the  oxygen 
are  evolved  together  upon  the  extremity  of  the  positive  conductor. 

The  affinity  which  held  together  these  bodies  in  combination  is 
superseded  during  the  passage  of  the  electric  current.  The  elements 
previously  united  appear  to  repel  each  other,  and  to  be  at  the  same 
time  attracted  by  the  excited  terminations  of  the  metallic  wires,  by 
which  the  battery  is  placed  in  connexion  with  the  substance  to  be 
decomposed. 

The  simplest  mode  of  accounting  for  these  phenomena  is  to  say 
that  water  is  decomposed,  because  the  oxygen  is  attracted  more 
powerfully  by  the  positive  pole  of  the  galvanic  battery  than  by  the 
hydrogen  with  which  it  had  previously  been  associated,  while  this 
last  is  more  powerfully  attracted  by  the  negative  pole  than  by  the  ox- 
ygen. The  elementary  bodies  separate,  therefore,  from  each  other ; 
but,  not  being  capable  of  entering  into  combination  with  the  substance 
of  the  poles,  they  are  evolved  as  gas.  This  explanation  may  be  ap- 
plied to  all  such  cases.  Oxygen,  chlorine,  iodine,  sulphur,  as  well 
as  the  various  acids,  are  attracted  by  the  positively  electric  pole, 
while  hydrogen,  potassium,  sodium,  copper,  silver,  lead,  and  the 
various  bases,  are  attracted  to  the  negative  pole  of  the  battery.  But 
one  force  cannot  completely  supersede  another,  as  electricity  here 
supersedes  affinity,  unless  it  be  of  the  same  kind,  or,  at  least,  closely 
resembling  it  in  nature.  What,  then,  is  the  relation  between  the 
chemical  force  which  had  kept  the  elements  united,  and  the  elec- 
trical force  which  makes  them  separate  1  The  cause  was  easily 
found  :  they  are  identical.  The  oxygen  and  hydrogen  united  ori- 
ginally from  being  in  opposite  electrical  states,  and  they  are  forced 
to  separate  from  being  subjected  to  the  action  of  still  more  power- 
ful attractions ;  the  decomposition  of  water  by  the  voltaic  current 
becoming  thus  a  case  of  double  decomposition,  in  which  the  original 
electricities  of  the  two  simple  bodies  were  the  quiescent,  and  the 
excitation  of  the  opposite  poles  of  the  battery  were  the  divellent 
forces. 

Chemical  substances  were  thus  considered  to  have  affinities  for 
each  other,  from  being  in  opposite  electric  states,  and  the  peculiar 
play  of  affinity  of  each  body  depended  on  which  electricity  it  was 
naturally  excited  by  when  in  combination  5  those  bodies  which  are 
attracted  by  the  positive  pole  of  the  battery  being  necessarily  in  the 
negative  condition,  and  vice  versa.  Thus,  all  substances  may  be  di- 
vided into  two  classes  ,  those  being  termed  electro-negative  which 
are  evolved  at  the  copper  pole  of  a  simple,  or  at  the  zinc  pole  of  a 
compound  circle,  and  those  which  appear  at  the  opposite  pole  being 
termed  electro-positive.  The  simple  bodies  thus  classified  are  ran- 
ged as  in  the  following  list : 


ELECTRO-CHEMICAL     CLASSIFICATION. 


189 


Electro-negative. 

Mercury. 

Palladium. 

Electro-positive,      j 

Oxygen. 

Potassium. 

1  Fluorine. 

Chrome. 

A  Silver. 

Sodium. 

t  Chlorine. 

Vanadium. 

i  Copper 

1  Lithium. 

1  Bromine. 

i  Iridium. 

iLead. 

T  Barium. 

Iodine. 

T  Rhodium. 

Tin. 

y  Strontium. 

Sulphur. 

Y  Uranium. 

Bismuth. 

Calcium. 

Selenium. 

Osmium. 

Cobalt. 

Magnesium. 

A  Tellurium. 

Platinum. 

Nickel. 

Glucinum. 

T  Nitrogen. 

Titanium. 

.Iron. 

Yttrium. 

1  Phosphorus. 

iGold. 

t  Manganese. 

1  Thorium. 

Arsenic. 

T  Molybdenum. 

4  Cadmium. 

T  Aluminum. 

Antimony. 

'  Tungsten. 

'"Zinc. 

t  Zirconium. 

Silicon. 

Columbium. 

Hydrogen. 

Lanthanum. 

Boron. 

J 

Carbon. 

Cerium. 

Tht  most  powerfully  negative  bodies  are  placed  in  the  first,  and 
those  most  powerfully  positive  in  the  fourth  column,  these  being 
connected  by  the  intermediate  columns  in  the  order  marked  by  the 
brackets  and  arrows.  Any  substance  in  the  list  is  positive  with  re- 
gard to  any  other  towards  which  the  arrow  points,  and  negative  in 
relation  to  any  from  which  the  arrow  is  directed.  Thus  hydrogen 
is  negative  to  all  in  the  fourth,  but  positive  to  all  in  the  three  pre- 
ceding columns,  and  so  on.  These  positions  should  also  indicate 
the  relative  affinities  of  the  simple  bodies  towards  each  other  \  but, 
in  interpreting  such  arrangements,  it  must  be  recollected  that  the 
order  of  affinities  may  be  totally  changed  by  heat  or  by  cohesion, 
and  that  the  electrical  order  may  be  completely  different,  according 
to  the  nature  of  the  exciting  liquid,  as  in  the  table,  p.  129. 

Two  bodies  in  combination  are  therefore  like  two  pith  balls  which 
mutually  adhere,  but  of  which  the  attraction  is  permanent  from  their 
electricities  not  being  discharged.  How  do  these  bodies  acquire 
those  oppositely  excited  states  1  and  why,  if  their  condition  resem- 
bles that  of  ordinary  electricity,  do  they  remain  combined,  when 
their  opposite  fluids  might  unite,  and  neutralization  being  produced, 
all  combination  cease  1 

These  two  questions  have  not  yet  been  answered.  Several  times  their  explana- 
tion has  been  attempted ;  and  thus  the  electro-chemical  theories  of  Davy,  Ampdre, 
and  Berzelius  have  been  proposed.  I  shall  briefly  notice  the  leading  features  of 
these  before  "proceeding  to  discuss  the  remarkable  advance  recently  made  in  our 
ideas  of  the  electro-chemical  relations  of  bodies  by  Faraday  and  Graham. 

The  theory  of  Davy  was  based  upon  the  principle  that  bodies  in  their  ordinary 
uncombined  condition  do  not  contain  free  electricity,  but  that  by  contact  they  be- 
come excited.  Thus  a  disk  of  sulphur  touched  to  a  disk  of  copper  becomes  nega- 
tive, and  the  copper  positive ;  its  charge  increases  in  intensity  on  applying  heat, 
until,  at  a  certain  temperature,  the  tension  of  the  electricities  becomes  so  great  that 
they  suddenly  lecombme,  carrying  with  them  the  molecules  of  the  sulphur  and  cop- 
per which  thus  enter  into  union,  and  producing  the  evolution  of  light  and  heat  by 
which  the  chemical  action  is  accompanied.  The  sulphuret  of  copper,  when  forffied, 
is  no  longer  electric ;  it  remains  permanent  in  virtue  of  a  force  which  Davy  does 
not  strictly  define,  but  which  he  appears  to  have  considered  an  intimate  cohesion 
between  the  particles  which  had  been  closely  approximated  by  their  electrical  at- 
tractions ;  and  when,  by  an  electric  current,  the  molecules  of  copper  and  sulphur  are 
brought  into  the  reverse  state  to  that  which  favoured  their  combination,  they  sep- 
arate. This  view  supposes,  therefore,  the  electrical  excitation  to  be  only  moment- 
ary, dunng  the  act  of  combination  and  during  the  moment  of  disunion  ;  before  and 
after,  all  is  neutral.  To  all  phenomena  of  decomposition  this  theory  suffices,  but 
it  is  vitally  deficient  in  the  principle  upon  which  it  is  based.    It  has  been  since 


190    THEORIKS    OF    DAVY,    AMPERE,    AND    BERZELIUS. 

completely  proved  that  it  is  not  the  contact  which  evolves  electricity,  but  the 
chemical  action ;  and  also,  on  Davy's  views,  the  electrical  disturbance  only  suffi- 
ces to  account  for  the  secondary  phenomena  of  union,  the  light  and  heat,  leaving 
the  act  of  combination  to  be  ascribed  to  a  different  and  independent  force  of  affin- 
ity or  cohesion. 

A  more  complete  theory  was  proposed  by  Ampere,  whose  philosophical  views  in 
magnetism  and  other  sciences  have  been  found  so  singularly  in  accordance  with 
experiment.  He  proposed  to  consider  that  each  substance  in  nature  is  endowed 
with  a  definite  amount  of  one  or  of  the  other  electricity,  and  is  thus  naturally  and 
invariably  electro-positive  or  electro-negative,  and  stands  higher  or  lower  in  the 
list  of  bodies,  according  to  the  intensity  of  the  charge.  Such  an  excited  body  he 
considered  to  attract  round  its  mass  an  atmosphere  of  electricity  of  the  opposite 
kind,  and  corresponding  in  intensity.  Now,  on  bringing  into  contact  an  electro- 
positive and  an  electro-negative  body,  their  atmospheres  unite,  and  produce  the  heat 
and  light  resulting  from  their  chemical  action  on  each  other ;  but  the  bodies  them- 
selves must  remain  permanently  combined,  as  each  retains  its  own  excitement, 
and  they  hence  attract  without  cessation.  When  one  body  is  exactly  as  negative 
as  the  other  is  positive,  the  resulting  compound  cannot  manifest  any  signs  of  elec- 
tro-chemical activity ;  but  if  the  charge  of  the  negative  body  be  more  powerful  than 
that  of  the  positive  element,  the  resulting  compound  will  be  negatively  excited  to 
the  amount  of  the  difference  between  the  two  ;  if  the  proportions  be  reversed,  the 
new  body  formed  will  be  positive  in  the  same  degree  ;  and  such  compound  electro- 
negative and  electro-positive  bodies,  being  acids  and  bases,  attract  each  other,  and 
unite  to  form  neutral  salts. 

All  that  was  difficult  to  comprehend  upon  the  theory  of  Davy  is  here  beautifully 
explained.  The  light  and  heat  of  combination  are  produced  by  the  atmospheres 
of  electricity ;  the  permanence  of  combination  by  the  invariable  excitation  of  the 
molecules.  The  gradually  diminishing  intensity  of  charge,  according  as  the  bodies 
formed  become  more  complex,  necessarily  follows ;  but  the  assumption  that  any 
one  body  is  naturally  and  invariably,  positive  or  negative,  is  contradicted  by  the 
history  of  almost  all  the  simple  substances. 

Thus,  if  sulphur  or  arsenic  be  heated  in  oxygen  gas,  they  burn,  and  the  combina- 
tion is  effected  with  all  the  phenomena  of  intense  action,  the  resulting  compounds 
being  acid  and  electro-negative.  The  sulphur  and  arsenic  are  thus  shown  to  have 
been  feebly  positive  bodies.  But  if  sulphur  or  arsenic  be  heated  with  potassium, 
there  is  similarly  combustion,  showing  that  chemical  combination  has  taken  place  ; 
and  as  potassium  is  the  most  positive  body  in  the  series,  the  sulphur  and  arsenic 
must  be  the  negative  elements  of  the  compounds.  Sulphur  and  arsenic  are  there- 
fore at  one  time  positive,  and  at  another  negative.  There  is,  indeed,  no  substance 
known  which  can  be  said  to  be  invariably  negative  or  positive.  Nor  can  the 
amount  of  negative  or  positive  excitement  be  in  any  case  looked  upon  as  constant, 
for  oxygen  is  often  found  to  be  less  negative  than  chlorine,  and  potassium  to  be 
less  positive  than  iron  or  than  carbon ;  and  hence,  if  electrical  forces  be  considered 
as  representing  affinitary  power,  they  must  be  capable  of  the  same  fluctuations  in 
intensity. 

It  was  for  the  purpose  of  bringing  Ampere's  theory  into  harmony  with  the 
changes  of  chemical  decomposition,  that  Berzelius  proposed  the  modification  of  it 
which  now  remains  to  be  described.  He  suggested  that  each  body  should  be 
looked  upon  as  containing  the  two  electricities,  but  that  the  one  might  be  more 
powerfully  developed  than  the  other,  as  in  a  magnet  one  pole  may  be  stronger  than 
the  other  ;  also,  from  the  analogy  of  certain  bodies,  which  were  supposed  to  admit 
the  passage  of  one  electricity  rather  than  the  other,  he  imagined  that  a  body  thus 
excited  with  the  two  fluids  might  discharge  the  one  and  yet  retain  the  other.  Thus 
oxygen  possesses  high  negative  and  feeble  positive  excitation  ;  hydrogen  an  intense 
positive,  but  a  feeble  negative  charge.  When  these  bodies  combine,  the  phenomena 
of  combustion  follow  from  the  union  of  the  positive  fluid  of  the  oxygen  with  the 
negative  of  the  hydrogen,  and  the  more  intense  and  more  permanent  charges  retain 
the  bodies  in  combination.  To  account  in  this  way  for  certain  bodies  being  at  one 
time  electro-negative  and  at  another  electro-positive,  Berzelius  considers  that,  when 
potassium  is  brought  into  contact  with  sulphur,  the  naturally  feeble  negativity  of 
the  latter  is  heightened  by  induction,  while,  if  the  sulphur  be  acted  on  by  oxygen,  it 
is  its  positive  charge  that  is  increased  ;  and  thus  any  substance  near  the  midd'e  of 
the  electro-chemical  series  may  become  positive  or  negative,  according  as  it  com- 
bines with  a  body  situated  nearer  to  the  negative  or  positive  extremity. 


DISENGAGEMENT  OCCURS    AT   LIMITING    SURFACES.   191 


This  ^iew  might  explain  most  chemical  phenomena ;  but  it  is,  like  Davy's  theory, 
founded  on  physical  principles  which  cannot  be  considered  sound.  Thus,  although 
the  effect  of  one  pole  of  a  magnet  may  be  weaker  than  another,  that  only  happens 
where  the  action  is  complicated  by  the  existence  of  more  poles  than  two  ;  and  in  all 
cases  the  amount  of  north  and  south  magnetism  present  is  exactly  equal.  Also,  the 
fact  of  the  existence  of  bodies  which  conduct  the  one  better  than  the  other  electricity, 
is  now  abandoned  by  all  sound  reasoners,  and  cannot  be  looked  upon  as  even  in  any 
degree  probable  in  theory.  Indeed,  all  views  like  those  of  Berzelius  and  Ampere, 
which  are  founded  on  the  existence  of  different  degrees  of  electrical  excitement, 
which  represent  the  different  powers  of  affinity  by  which  chemical  substances  com- 
bine, must  be  now  abandoned ;  for  it  has  been  proved  by  Faraday  that  a  molecule  of 
oxygen,  in  uniting  with  hydrogen  to  form  water,  or  with  zinc  to  form  its  oxide,  a 
molecule  of  iodine  or  chlorine  uniting  with  lead,  with  tin,  with  silver,  or  with  potas- 
sium, bodies  so  far  separated  in  the  electro-chemical  scale  founded  on  their  reactions, 
evolve  in  uniting  the  same  quantity  of  electricity,  and  require  for  their  separation, 
when  combined,  the  same  amount  of  current  derived  from  another  source. 

Before  more  definite  and  correct  ideas  of  the  electrical  relations 
of  chemical  substances  can  be  obtained,  it  is  necessary  to  study 
somewhat  more  in  detail  the  chemical  phenomena  which  occur  in 
the  galvanic  battery,  which,  for  simplicity,  shall  be  considered  as  a 
simple  circle,  and  in  the  liquid  through  which  the  circuit  is  com- 
pleted ;  the  former  is  generally  termed  the  generating,  and  the  latter 
the  decomposing  cell. 

The  decompositions  hitherto  described  have  been  considered  as 
resulting  from  the  attractive  and  repulsive  forces  of  the  extremities 
of  the  wires,  on  which  the  charge  of  the  battery  was  supposed  to  be 
collected.  But,  when  the  circuit  is  completed,  no  such  accumula- 
tion can  exist ;  once  the  current  passes,  it  is  everywhere  present 
in  equal  quantity  and  of  uniform  tension  ;  and  such  forces  of  attrac- 
tion and  repulsion,  acting  upon  molecules  already  electrically  exci- 
ted, were  only  imagined  for  the  foundation  of  the  imperfect  theories 
already  noticed,  and,  when  impartially  examined,  are  found  to  have 
no  real  existence.  It  is  also  fatal  to  the  idea  of  attractive  forces  ex- 
ercised by  the  poles,  that  the  substances  evolved  upon  their  surface 
do  not  necessarily  combine  with  them  ;  thus,  if  one  platina  pole  have 
such  attraction  for  oxygen  as  to  separate  from  the  hydrogen  it  had 
been  united  with,  it  is  unreasonable  that  it  should  lose,  suddenly  and 
completely,  this  power,  and  allow  the  oxygen  totally  to  escape  j  the 
other  platina  pole  behaving  similarly  to  the  hydrogen. 

Faraday  has  definitely  shown  that  the  disengagement  of  the  sub- 
stances, which  are  separated  from  each  other  by  the  current,  takes 
place  in  all  cases  at  the  bounding  surfaces  of  the  body  decomposed,- 
and  that  where  they  are  evolved  on  the  metallic 
conducting  wires,  it  is  only  because  those  are  the 
limits  of  the  decomposing  fluid.  The  proofs  of 
this  principle  are  numerous  and  simple  :  thus,  in 
a  glass  basin,  a  partition  of  mica,  a,  is  cemented  so 
as  to  be  completely  water  tight,  and  extending  half 
way  to  the  bottom  5  a  strong  solution  of  sulphate 
of  magnesia  is  poured  in  until  it  rises  a  little  above 
the  edge  of  the  partition,  and  then  distilled  water 
poured  in  on  the  side  c,  d,  with  such  precaution 
that  it  shall  not  mix  with  the  saline  .solution,  but 
shall  float  on  it,  the  surface  separating  the  two 
liquids  remaining  perfect  at  c.     The  solution  of  sulphate  of  magne 


192  ELEMENTS     NOT     EVOLVED     ON      POLES. 

sia  is  now  to  be  connected  with  the  negative  pole  of  a  battery  by 
means  of  the  platina  plate  b,  and  the  water  with  the  other  pole  of 
the  battery  by  the  plate  e,  which  dips  slightly  inclined  below  the 
surface.  When  the  circuit  is  completed,  the  sulphate  of  magnesia 
and  the  water  are  simultaneously  decomposed,  the  oxygen  appears 
upon  the  plate  b,  the  hydrogen  gas  upon  the  plate  e  ;  but,  although 
the  sulphuric  acid  is  liberated  freely  upon  the  plate  b,  no  magnesia 
travels  farther  than  the  limiting  surface  of  the  saline  liquor  c.  Here 
the  metal  e  serves  as  a  pole  to  the  hydrogen,  but  not  to  the  magne- 
sia ;  and  the  water  on  which  the  magnesia  has  evolved  has  no  power 
to  prevent  the  farther  passage  of  the  hydrogen. 

If  A,  C,  B  be  filled  with  solution  of  sulphate  of  soda,  and  by  means 
-^  >^^  of  the  plates  P  and  N,  a  current  from  a  battery 

A^  ^  T  .  .  ^g  passed  through  it,  the  acid  will  collect  upon 
the  one  and  the  alkali  upon  the  other  plate : 
but  if,  by  means  of  pieces  of  bladder,  a  and  b, 
the  vessel  be  divided  into  three  compartments 
A,  C,  and  B,  and  the  central  one  being  filled 
with  a  solution  of  sulphate  of  soda,  dilute  nitric  acid  is  poured 
into  those  at  the  side  in  order  to  aflfbrd  a  conducting  medium, 
the  acid  and  alkali  do  not  appear  at  the  metallic  poles  when  the  cur- 
rent passes,  but  are  evolved  upon  the  inner  surfaces  of  the  partitions 
a  and  b :  it  is  only  when,  by  mechanical  filtration,  some  of  the  liquor 
of  C  passes  into  A  and  B,  that  the  slightest  trace  of  sulphuric  acid 
or  of  soda  can  be  found  upon  the  metallic  plates. 

By  the  electricity  of  the  machine  the  same  principle  can  be  de- 
monstrated :  if  a  slip  of  paper  moistened  with  solution  of  iodide  of 
potassium  be  held  near  the  insulated  prime  conductor  of  the  elec- 
trical machine  while  in  action,  and  the  rubber  be  connected  with  the 
ground  so  as  to  ensure  a  continuous  discharge  of  positive  electricity 
into  the  air,  iodine  will  be  evolved  in  quantity  upon  the  point  of  the 
paper  nearest  the  prime  conductor,  while  hydrogen  and  potash  may 
be  traced  as  liar  a»  any  liquid  conductor  admitting  of  their  passage 
goes.  Here  there  is  nothing  that  can  be  termed  a  pole  ;  the  iodine 
is  discharged  upou  the  limiting  surface,  which  is  here  that  of  the 
atmospheric  air. 

Hence  the  idea  of  poles  which  produce  attractions  and  repulsions 
in  a  closed  circuit  must  be  abandoned,  and  some  other  way  of  ex- 
plaining the  decomposition  of  the  liquid  elements  of  the  circuit  must 
be  obtained.  The  word  poles  must  first  be  laid  aside,  and  the  ex- 
pressions proposed  by  Faraday  in  their  place  deserve  universal  adop- 
tion. The  surfaces,  whether  of  metal,  of  water,  of  acid,  or  of  air, 
by  which  the  current  passes  from  one  kind  of  conductor  to  another, 
he  terms  electrodes  {jiXen-pov^  o(5of),  they  being  the  routes  through 
which  the  electricity  makes  its  way.  I  shall  therefore,  in  future, 
speak  of  the  positive  and  negative  electrodes  in  relation  to  the  sur- 
faces, generally  of  metal,  by  which  the  battery  is  brought  to  act  upon 
the  substance  which  is  to  be  decomposed. 

Since  there  are  thus  no  attractive  forces  by  which  the  chemical 
affinities  of  the  substances  in  the  decomposing  cell  can  be  overcome, 
to  what  mechanism  can  we  attribute  the  separation  of  elements 
which  occurs  1     Concerning  this,  as  yet,  there  is  only  speculation  to 


ELECTRO-CHEMICAL     DECOMPOSITION.  193 

be  presented.  The  decomposition  is  certainly  propagated  from 
particle  to  particle,  that  is  to  say,  at  the  moment  that  the  molecule 
of  water  loses  oxygen  at  the  positive  electrode,  a  diiferent  mole- 
cule gives  off  its  hydrogen  upon  the  negative  electrode ;  neither 
the  hydrogen  of  the  former  nor  the  oxygen  of  the  latter  become 
free,  but  the  decomposition  is  transferred  from  one  particle  to  an- 
other along  the  line,  all  particles  of  oxygen  advancing  a  step  against 
the  current,  and  the  molecules  of  hydrogen  moving  in  a  correspond- 
ing manner  in  the  direction  of  it.  Thus,  if  a  line  of  particles  of 
water  in  a  decomposing  cell  be  represented  ^  ^ 

before  the  current  passes,  the  electrodes  be-  -}-0.H.  O.H.  O.H. — 
ing  represented  by  the  plus  and  minus  signs, 
on  the  current  passing,  a  molecule  of  oxygen  ^    ^ 

will  be  evolved  upon  the  positive,  and  one  of  — H.  *  xj*  '  tt'  *  0.-\- 
hydrogen  upon  the   negative  side,  as  in  the 
second  line  5  and  as  this  motion  is  participated  2«» — v 

in  by  every  molecule  of  oxygen  and  hydrogen       4"0.H.  O.H. — 
in  the  circuit,  they  will  come  into  the  final  po-  .^    ^ 

sition  of  the  third  line.     The  current  still  pass-  O.     ^    , 

ing,  another  molecule  of  each  will  be  evolv-  "•  *  H.  * 

ed,  as  in  the  fourth;  and,  ultimately,  all  the 
intervening  water  may  be  decomposed ;  the  ,  ^tt* 

separation  of  the  elements  being  thus  accom-  "^    '    * 

panied  by  a  continual  rotation  on  each  other  of  the  intermediate 
molecules,  each  molecule  of  oxygen  being  successively  united  with 
every  molecule  of  hydrogen  in  the  series,  and  each  molecule  of  hy- 
drogen combining  in  turn  with  every  particle  of  oxygen  as  it  passes 
along.  In  Faraday's  words,  the  current  is  an  axis  of  power,  equal, 
and  exerted  in  opposite  directions,  by  which,  in  every  case  of  a 
true  binary  compound,  the  molecules  of  one  element  are  carried  in 
one  direction,  while  those  of  the  other  constituent  move  in  the  re- 
verse course. 

From  this  idea,  the  evolution  of  the  iodine,  the  soda,  the  magne- 
sia on  surfaces  of  air,  of  bladder,  or  of  water,  is  easily  understood. 
The  sulphates  of  magnesia  and  soda  are  decomposed,  because  there 
exists  in  the  solution  a  chain  of  particles  of  sulphuric  acid  capable 
of  conveying  their  bases  along,  and  these  are  evolved  where  that 
chain  of  acid  particles  is  broken,  although  there  may  be  other  con- 
ductors to  complete  the  circuit.  The  iodine  is  evolved  where  the 
air  touches  the  surface  of  the  paper,  because  the  air  has  no  potas- 
sium by  which  it  could  be  carried  farther.  The  decomposition  ap- 
pears thus  to  be  effected,  not  by  annulling  chemical  affinity,  but 
with  its  assistance,  for  it  is  exactly  with  those  conducting  bodies 
whose  elements  have  the  strongest  affinities  for  each  other  that  de- 
composition is  most  easily  effected.  Thus  iodide  of  potassium  is 
decomposed  much  more  easily  than  iodide  of  lead,  yet  the  affinity 
of  potassium  for  iodine  is  certainly  greater  than  that  of  lead  for  the 
same  element. 

It  is  in  this  manner  that  arise  the  remarkable  phenomena  of  transfer  observed  first 
by  Humphrey  Davy. 

If  a  solution  of  sulphate  of  soda  be  placed  in  the  glass  a,  dilute  sulphuric  acid  in 
the  glass  b,  and  water  in  the  glass  c,  and  they  be  connected  together  vj^ith  slips  of 
amianthus,  moistened  to  allov^r  the  passage  of  the  current,  and  the  positive  electrode 

Bb 


194     ELECTROLYSIS  AND  ELECTROLYTES. 

imMHrifc.  '      itif^^       ^    ^^  ^  battery  be  immersed  in  a,  and  the  nega- 

^^iSr~~^^^^^~MS^^^~^^  ^i"*'®  ^^  ^»  ^^^  sulphate  of  soda  will  be  decom- 

,   ^HM^      liteipi      rallSH       posed,  and  its  alkali  will  appear  in  c,  although 

V^Sr       'BSli'       ^IB^^      the  acid  in  b,  through  which  it  must  have 

'^miffr       ^^^ypgr         /!Sg  passed,  retains  all  its  power.    Here,  then,  was 

^Vi^i    S^S^^    ^J^^^  ^^^  affinity  of  the  acid  in  b  for  soda  complete- 

0 — jS^^      — JL-       v._„seE=-    j^  annulled  by  the  superior  attraction  of  the 

negatively  electric  pole  in  c,  and  this  was  considered  to  be  farther  proved  by  the 

acid  preventing  the  passage  of  barytes,  for  which  its  affinity  was  so  much  stronger ; 

when  a  contained  nitrate  of  barytes,  the  earth,  on  entering  into  b,  combined  with 

the  sulphi»ric  acid,  and  went  no  farther.     But  in  these  experiments,  considered  at 

the  time  so  decidedly  in  favour  of  Davy's  theory,  that  which  was  believed  to  be  the 

obstacle  »o  the  passage  of  the  soda  is  in  reality  the  cause  of  it.     Had  there  been  no 

acid  in  b,  no  alkali  could  have  passed  across  it,  and  the  barytes  remained  combined 

only  because,  becoming  insoluble,  it  no  longer  formed  any  portion  of  the  hquid-con- 

ducting  medium. 

It  has  been,  indeed,  found,  that  although  a  feeble  current  may- 
be transmitted  through  liquid  conductors  without  any  sign  of  de 
composition,  yet,  in  general,  the  passage  of  a  more  powerful  cur- 
rent can  only  be  accomplished  by  means  of  bodies  which  are  at  the 
same  time  decomposed  by  its  influence.  Faraday  proposes  to  term 
the  decomposition  by  the  current  electrolysis  [TjXetcrpoVj  Avw],  and 
such  bodies  as  undergo  electrolysis  electrolytes.  It  is,  therefore, 
only  electrolytes  that  are  capable  of  conducting,  and  they  do  so  by 
the  opposite  directions  in  which  the  chains  of  liberated  particles 
move.  That  electrolysis  may  occur,  it  is  necessary  that  the  sub- 
stance be  in  the  liquid  state,  and  hence  all  conducting  power  is  lost 
when  the  body  becomes  solid;  ice  is  a  non-conductor,  and  it  is  only 
by  being  melted  that  the  chlorides  and  iodides  of  lead  and  silver, 
and  such  bodies,  become  capable  of  conduction,  and  of  being  hence 
decomposed.  But  there  are  many  bodies  which  insulate  when  cold, 
and  yet,  when  heated,  allow  the  current  to  pass  even  before  they 
fuse,  its  passage  being  unattended  by  any  electrolysis,  even  though 
the  current  be  very  powerful.  Sulphuret  of  silver,  iodide  and  chlo- 
ride of  mercury,  and  fluoride  of  lead,  are  remarkable  examples  of 
this  anomaly. 

Faraday,  considering  that  the  words  electro-positive  and  electro- 
negative involve  too  much  those  ideas  of  attractive  and  repulsive 
forces  emanating  from  the  poles,  which  have  been  proved  to  be  in- 
correct, proposed  some  changes  of  nomenclature,  which,  if  not 
adopted,  deserve  to  be  at  least  described.  If  we  consider  a  voltaic 
battery  lying  on  the  ground,  with  the  positive  end  to  the  east,  and 
the  wire  connecting  the  ends  bent  into  an  arch,  similar  to  that 
which  the  sun  describes  in  his  daily  rotation,  the  current  will  flow 
up  from  the  point  of  the  sun's  rising,  and  pass  down  into  the  battery 
opposite  the  point  at  which  he  sets.  If  the  wire  be  now  interrupt- 
ed by  a  decomposing  cell,  the  surface  at  which  the  current  enters 
the  liquid  may  be  termed  the  anode  (dvd,  upward),  and  the  other  the 
cathode  (fcard,  downward)  ;  oxygen,  chlorine,  and  such  bodies  are 
evolved  upon  the  surface  of  the  anode,  while  from  the  cathode  hy- 
drogen and  the  metals  are  liberated.  The  elements  which,  by  their 
combination,  form  electrolytes,  Faraday  proposes  to  term  ions,  ir}\ii, 
and  to  distinguish  them  into  anions  which  pass  to  the  anode,  and 
cations  which  pass  to  the  cathode.  Electro-negative  bodies  are 
therefore  anions^  and  electro-positive  substances  are  cations  in  Far- 


THE     CHEMICAL    VOLTAMETER.  195 

aday's  nomenclature.     These  names  are  shorter,  and  involve  less 
theory  than  the  older  terms,  and  hence  deserve  adoption. 

The  most  important  principle  that  has  been  as  yet  discovered, 
connecting  the  agencies  of  electricity  and  affinity,  is  the  law  of  def- 
inite electro-chemical  decomposition.  If  the  same  current  of  elec- 
tricity pass  through  a  series  of  electrolytes,  it  will  decompose  a 
quantity  of  each  which  is  proportional  to  its  chemical  equivalent. 
Thus,  at  the  same  time  and  by  the  same  force,  there  are  obtained 

8    grains  of  Oxygen  and      1     of  Hydrogen  from     9    parts  of  water. 
35-4       "        Chlorine  and     1     *'  Hydrogen    "      364      "      muriatic  acid. 
35-4       "        Chlorine  and  108     "Silver  "     1434      "      chloride  of  silvei. 

126-3       "        Iodine  and     103-6  "  Lead  "    229-9      "      iodide  of  lead. 

The  principle  of  definite  electro-chemical  action  may  be  applied 
to  measure  the  quantity  of  electricity  which  is  circulating  in  the 
current,  for  by  collecting  the  substances  evolved  in  the  decomposing 
cell,  we  may  obtain  a  standard  to  which  all  other  effects  may  be  re- 
duced. In  such  case  the  decomposing  cell  becomes  a  voltameter^  or 
measurer  of  voltaic  electricity.  One  ^ 
of  its  most  convenient  forms  consists 
in  a  conical  vessel.  A,  terminated  by  a 
tube,  B,  in  the  neck  of  which  are  sol- 
dered the  platina  electrodes  in  connex- 
ion with  the  battery ;  the  vessel  and 
tube  being  filled  with  water,  which  is  A^ 
rendered  easily  decomposible  by  the 
addition  of  sulphuric  acid,  the  circuit 
is  completed ;  a  quantity  of  oxygen  and  hydrogen,  proportional  to 
the  amount  of  electricity  which  passes,  is  evolved,  and,  issuing  from 
the  aperture  at  C,  may  be  collected  in  an  inverted  glass  and  meas- 
ured. A  variety  of  other  forms,  not  differing  in  principle,  have  been 
proposed  and  are  in  use. 

If  the  absolute  identity  of  electrical  and  chemical  agency  be  in- 
sisted on,  then,  in  all  electrolytes,  the  elements  must  be  held  togeth- 
er by  the  same  force,  since  they  require  the  same  amount  of  elec- 
tricity to  produce  decomposition ;  and  we  should  return  nearly  to 
the  principles  of  Berthollet,  that  chemical  affinity  was  equally  pow- 
erful for  all  bodies,  and  merely  appeared  to  vary  from  external  in- 
fluences ;  but  this  would  be  a  rash  and  unphilosophical  conclusion ; 
the  electrolytes  are  but  one  class  of  chemical  bodies,  those  which 
are  primary  compounds,  of  an  equivalent  of  each  element  j  the  cur- 
rent does  not  act  upon  deutoxides  or  bichlorides,  and  on  double 
salts  its  agency  is  exceedingly  complicated.  All  that  can  be  infer- 
red from  this  very  beautiful  result  is,  that  the  elements  of  bodies 
combine,  in  separating  from  each  other  under  the  influence  of  a  cur- 
rent, all  with  the  same  quantity  of  electricity,  and  that,  as  the  spe- 
cific heats  of  the  ultimate  particles  of  bodies  have  been  already 
found  to  bear  a  simple  relation  to  each  other,  the  specific  electrici- 
ties may  follow  an  equally,  or  still  more  simple  law. 

Having  thus  examined  the  important  phenomena  produced  in  the 
decomposing  cell,  the  current  being  considered  as  originating  in 
any  sufficient  source,  we  shall  pass  to  the  discussion  of  what  oc- 
curs in  the  generating  cell,  where  the  current  which  passes  through 


196  ACTION     IN     THE     GENERATING     CELL. 

the  Other  is  evolved  by  the  mutual  action  of  the  liquid  and  solid 
elements  of  the  voltaic  battery. 

For  the  generation  of  the  current,  it  has  been  already  shown  to 
be  necessary  that  the  liquid  excitant  should  be  an  electrolyte,  and 
that  the  solid  elements  should  occupy  positions  in  the  electro- 
chemical scale  as  remote  as  possible  froni  each  other  in  relation  to 
the  liquid  which  is  employed.  That  the  solid  elements  also  should 
be  conductors,  by  which  the  selection  is  limited  to  the  metals  and 
to  some  forms  of  carbon.  Now,  when  a  slip  of  zinc  is  immersed  in 
an  electrolyte,  which  we  shall,  for  simplicity,  consider  for  the  future 
to  be  muriatic  acid,  the  particles  of  the  acid  are  brought 
into  a  state  of  excitation,  the  molecules  of  hydrogen  be- 
coming positively  excited,  and  those  of  chlorine  becom- 
ing negative.  This  condition  has  been  already  described 
(page  132)  as  being  that  of  the  acid  particles ;  but  it  is 
now  necessary  to  indicate  more  nearly  the  immediate 
manner  in  which  it  is  produced.  The  mass  of  zinc  itself,  which 
we  before  considered  as  having,  like  a  magnet,  its  positive  excita- 
tion referrible  to  one,  and  its  negative  to  the  other  extremity,  must 
also,  like  the  magnet,  be  looked  upon  as  consisting  of  a  great  num- 
ber of  excited  elements,  each  of  which  has  its  positive  and  nega- 
tive extremities  ;  or,  for  greater  definiteness,  they  may  be  consid- 
ered as  grouped  in  pairs,  of  which  one  molecule  is  positively  and 
the  other  negatively  excited.  The  condition  of  the  slip  of  zinc  of 
the  last  figure  may  therefore  be  represented  as  in  the  figure  at  the 
A  side,  the  particles  of  zinc  being  con- 

W  V.  Y  ▼j.^/0\(^/^~^(^i^  t^ii^^d  ^^  the  shaded  bar,  and  those 
^^J^i^^^J^j^V-J V^v^^vly  of  the  liquid,  consisting  of  chlorine 
Zn.  Zn.  Zn.  Zn.  CI.  H.  CI.  H.  and  hydrogen,  represented  outside 
of  it.  The  terminal  particle  of  zinc  becoming  positive,  and  the 
nearest  particle  of  chlorine  becoming  negative,  there  would  result 
immediate  union  if  no  other  action  interfered ;  but  the  chlorine  is 
held  back  by  the  positive  molecule  of  hydrogen  with  which  it  is 
united,  and  so  the  action  continues  balanced,  no  matter  how  far  the 
series  may  extend  on  either  side.  If,  now,  the  plate  of  copper  be 
introduced  so  ««•  o  <:omplete  the  circuit,  and  to  allow  the  passage  of 
the  galvar'  ^arrent,  it  is  easy  to  see  how  the  decomposition  of  the 
exciting  nuid  follows  5  for  although,  in  the  arrangement  above  de- 
scribed, the  inductive  excitement  is  most  active  at  A,  and  diminish 
es  from  thence  as  it  extends  along  the  zinc  upon  the  one  hand,  and 
through  the  fluid  upon  the  other,  yet  when,  as  in 
the  figure,  the  circuit  is  completed,  the  action  be- 
comes equally  powerful  all  through  ;  the  particles 
of  copper  assume  a  condition  similar  to  those  of 
the  zinc,  but  in  the  reverse  order,  the  molecule 
next  the  acid  being  negative,  and  that  becoming 
positive  which  is  in  contact  with  the  zinc,  and  hence 
a  complete  chain  of  inductively  polarized  particles 
being  established,  precisely  such  as  are  represented 
by  cuttings  of  silk  thread  which  convey  a  current 
from  an  electric  machine  through  oil  of  turpentine  ;  the  molecular 
arrangement  being  represented  in  the  following  figure.     Such  be- 


ORIGIN     OF     THE     GALVANIC     CURRENT.  197 

ing  the  position  of  the  mutually-excited 
molecules,  the  electricities  of  the  particles 
of  zinc  and  chlorine  nearest  to  each  other 
comhine,  and  their  neutralization  is  follow-  zn. 
ed  by  that  of  the  entire  chain ;  the  adjacent 
particles  of  zinc  and 
chlorine  then  unite,  ^|#C)(+YCY+^ 
ZmQ.JkTI     T  \  \Cop.  and  the  hydrogen,  dis-  ^^kJ\J^^ 

engaged,     is     thrown  ^^^^• 

upon  the  second  particle  of  chlorine,  its  hy- 
drogen upon  the  third  chlorine  molecule,  by 
which  the  hydrogen  it  had  previously  been 
united  with,  being  thrown  off,  is  emitted  under 
the  form  of  gas. 

The  three  distinct  stages  in  this  reaction  are,  therefore,  1st,  The 
mutual  excitation,  by  inductive  polarization  of  the  zinc  and  muriatic 
acid.  This  is  the  fundamental  fact  due  to  the  chemical  relations  of 
these  bodies.  2d,  The  completion  of  the  chain  of  inductively  polar- 
ized particles,  by  the  intervention  of  the  copper  plate  and  connect- 
ing wire.  3d,  The  passage  of  the  current,  and  the  consequent  de- 
composition of  the  liquid  electrolyte  in  the  cell,  the  chlorine  being 
evolved  upon  the  zinc,  with  which  it  enters  into  combination,  and 
the  hydrogen  being  eliminated  upon  the  surface  of  the  copper  plate. 
The  source  of  the  current  is  therefore  not  to  be  found  in  the  de- 
composition of  the  acid,  for  it  precedes  it ;  but  the  quantity  of  chem- 
ical action  in  the  generating  cell  is  proportional  to  the  quantity  of 
electricity  which  passes,  for  it  is  produced  entirely  by  its  agency. 
There  is,  therefore,  no  difference  in  reality  between  the  generating 
and  the  decomposing  cell  ;  the  action  in  each  is  equally  produced 
by  the  passage  of  the  electric  current  ;  but  in  the  generating  cell, 
one  element  at  least,  the  chlorine,  is  absorbed  by  the  electrode  (the 
zinc)  on  which  it  is  evolved,  and  the  amount  of  obstacle  presented 
to  the  passage  of  the  current  is  proportionally  less. 

Such  is  the  theory  of  galvanism  which  I  believe  to  be  most  con- 
sistent with  all  the  results  hitherto  obtained.  The  current  cannot 
have  its  origin  in  the  contact  of  solid  bodies,  for  it  remains  the  same, 
no  matter  how  much  the  circumstances  of  contact  maybe  changed; 
and  by  every  alteration  of  the  conditions  of  chemical  action,  it  va- 
ries in  direction  and  in  power,  although  the  relations  of  the  solid 
bodies  which  are  in  contact  are  not  affected.  Neither  does  the  cur- 
rent arise  from  the  transfer  of  elements  which  occurs  in  the  gener- 
ating cell,  for,  on  the  contrary,  the  transfer  of  elements  results  from 
the  passage  of  the  current,  indicating  its  direction  and  measuring 
its  amount ;  but  the  current  arises  from  the  continuous  restoration 
through  the  copper,  or  positive  element,  of  the  excitation  produced 
by  the  tendency  of  the  zinc  to  combine  with  the  chlorine  of  the  mu- 
riatic acid.  In  fact,  although  I  have  hitherto  considered  the  zinc  as 
only  influencing  the  acid  by  means  of  a  disposition  to  unite  with  one 
of  its  constituents,  yet  such  expressions,  being  rather  abstract  and 
indefinite,  may  in  the  present  case  be  laid  aside.  The  zinc  does, 
on  immersion,  decompose  a  certain  quantity  of  acid,  of  which  the 
hydrogen  is  evolved  in  the  form  of  gas,  constituting  upon  the  sur- 


198  COMPOUND  BODIES  FORMED  BY  THE  CURRENT. 

face  of  the  zinc  an  exceedingly  thin  layer.  The  chlorine  is  then  in 
a  .state  of  combination,  which  is  not  without  analogy  in  other  cases ; 
that  is,  in  presence  of  two  substances  for  which  its  affinity  is  equal- 
ly intense,  it  is  disposed  to  unite  with  either,  according  as  external 
forces  intervene,  and  is  determined  to  the  zinc  by  the  establishment 
of  the  current. 

The  proofs  that  hydrogen  must  be  thus  nascently  liberated  upon 
the  surface  of  the  zinc  are  to  be  found  in  a  phenomenon  already 
noticed  under  the  head  of  affinity — the  precipitation  of  one  metal 
from  its  salts  by  means  of  another  having  a  greater  affinity  for  ox- 
ygen than  it.  If  we  immerse  in  a  solution  of  sulphate  of  copper  a 
slip  of  pure  zinc,  there  is  instantly  a  deposition  of  copper,  which 
we  must  ascribe  to  the  superior  affinity  of  zinc  for  oxygen  and  sul- 
phuric acid  ;  but  when  the  zinc  has  become  thus  sheathed  in  metal- 
lic copper,  the  decomposition  would  cease,  by  the  access  of  the  acid 
being  prevented,  were  it  not  that  the  copper  deposited  acts  as  the 
copper  element  of  a  galvanic  circuit,  and  the  subsequent  decompo- 
sition proceeds,  each  new  portion  of  copper  being  deposited  on  the 
outside,  farthest  from  the  zinc,  the  action  of  which  becomes  thus 
at  every  moment  more  intense.  If  hydrogen  had  a  physical  consti- 
tution, such  as  would  enable  it  to  act  as  the  positive  element  of  a 
simple  galvanic  circle,  then,  no  doubt,  the  purest  zinc  would  decom- 
pose the  muriatic  acid,  the  circuit  being  completed  by  the  hydrogen 
evolved ;  but  such  is  not  the  case,  owing  to  its  gaseous  form  \  but  it 
being  that  alone  which  is  the  obstacle,  the  previous  step,  which  de- 
pends simply  on  the  chemical  affinity  of  hydrogen  and  chlorine,  may 
reasonably  be  considered  to  have  occurred. 

The  action  of  electricity  in  separating  the  elements  of  bodies  is  scarcely  of  greater 
interest  or  importance  from  the  ideas  it  suggests  of  the  nature  of  chemical  affinity, 
than  it  becomes  as  a  means  of  presenting  to  each  other,  under  the  most  favourable 
circumstances  for  union,  the  different  elements  of  the  voltaic  circuit,  and  thus 
causing  the  formation  of  bodies  for  whose  construction  the  ordinary  processes  of 
the  laboratory  are  much  too  violent  and  abrupt.  In  this  way  some  of  the  most  re- 
markable substances  of  the  mineral  kingdom  may  be  artificially  produced,  the  se- 
cretion of  the  raetalhferous  ores  into  the  veins  and  cavities  of  rocks  accurately  rep- 
resented, and  bodies,  whose  affinities  for  each  other  rank  as  the  most  intense,  com- 
pletely, though  silently  and  gradually,  separated  from  each  other.  It  is  to  Becque- 
rel  that  we  owe  almost  all  our  knowledge  of  this  important  function  of  electricity ; 
from  him  we  have  also  received  the  important  lesson,  that  it  is  not  in  the  brilliant 
effects  of  the  great  batteries  of  Davy  or  of  Daniell  that  we  must  seek  a  clew  to  the 
history  of  the  electrical  processes  of  chemical  affinity,  but  in  the  slow  but  uninter- 
mitting  action  of  currents  of  such  low  intensity  that  a  drop  of  pure  water  would  be 
an  insuperable  obstacle  in  their  path.  The  electricity  to  be  employed  in  the  artifi- 
cial formation  of  compound  bodies  must  be  such  as  is  generated  by  a  single  pair, 
and  these  generally  of  metals  whose  similarity  prevents  that  current  from  being  of 
great  amount. 

These  phenomena,  into  the  examination  of  which  I  cannot  enter  with  much  de- 
tJiil,  are  best  observed  by  means  of  a  tube  bent  into  a  U  shape,  and  at  the  bottom 
of  which  is  interposed  a  porous  partition  of  clay  or  plaster  of 
Paris ;  the  liquids,  whose  mutual  reaction  is  to  generate  the  new 
substance,  are  placed  in  the  legs  of  the  tube,  one  at  each  side  of 
the  partition,  through  the  pores  of  which  they  gradually  mix  with 
each  other.  The  voltaic  current  is  then  supplied  either  by  con- 
necting the  hquids  with  the  p^es  of  a  feeble  battery,  or  by  im- 
mersing in  one  leg  a  zinc,  and  in  the  other  a  copper  or  platina 
plate,  connected  by  a  wire  with  each  other.  If  a  solution  of  car- 
bonate of  soda  and  of  sulphate  of  copper  be  thus  brought  to  act 
on  one  another,  a  double  carbonate  of  copper  and  soda  crys- 
tallizes on  the  plate  immersed  in  the  copper  liquor ;  and  if  then 


SYNTHETIC     ACTION     OF     ELECTRICITY. 


199 


the  solution  of  soda  be  replaced  by  ordinary  water,  a  new  current  is  generated 
which  decomposes  the  first  product,  and  forms  a  liew  crystallization  of  carbonate  of 
copper.  If  the  zinc  leg  be  filled  with  a  solution  of  oxide  of  zinc  in  potash  water, 
and  a  solution  of  nitrate  of  copper  be  placed  on  the  copper  side,  a  crystallization  of 
oxide  of  zinc  is  produced  upon  the  zinc  plate,  and  a  deposition  of  crystallized  cop- 
per upon  the  metallic  surface  in  the  other  tube. 

By  using  two  liquids  which  have  unequal  chemical  actions  on  a 
strip  of  metal,  this  may  be  made  to  precipitate  itself,  being  reduced  at 
one  extremity  according  as  it  is  dissolved  at  the  other.  Thus,  if  the 
glass  A  be  filled  with  solution  of  nitrate  of  copper  to  a,  and  then  water, 
rendered  slightly  acid  by  nitric  acid,  be  gently  added,  up  to  the  level 
of  B,  a  slip  of  copper,  introduced  so  as  to  present  equal  surfaces  to 
the  two  Uquids,  generates  a  current  which  passes  up  through  its  mass, 
and  down  from  the  lighter  to  the  denser  fluid :  the  copper  dissolves,  (c\ 
therefore,  above,  and  the  salt  formed  being  electrolyzed  by  the  current, 
its  metal  is  deposited  on  the  lowest  surface  under  the  form  of  crystals, 
and  this  is  continued  until  the  free  acid,  and  hence  the  electromotive 
force  in  the  liquid,  becomes  equal,  when,  of  course,  no  current  passes. '        

Dr.  Bird,  who  has  extended  considerably  the  results  obtained  by  Becquerel,  has 
constructed  an  apparatus  for  such  reactions,  with  which  he  has  obtained,  in  an  iso- 
lated form,  those  simple  bodies,  as  boron,  silicon,  potassium,  &c.,  whose  compounds 
resist  ordinary  means  most  obstinately.  It  consists  of  a  generating  and  of  a  decom- 
posing cell.  This  last  is  a  glass  cylin- 
der, a,  within  another  glass  cylinder, 
b.  The  inner  one,  a,  is  four  inches 
long,  and  an  inch  and  a  half  in  diame- 
ter, and  is  closed  at  the  lower  end  by 
a  plug  of  plaster  of  Paris,  07  inch  in 
tliickness.  This  cylinder  is  supported 
within  the  other,  b,  which  is  an  ordi- 
nary jar,  about  eight  inches  deep  and 
two  inches  diameter,  by  means  of 
wedges  of  cork.  A  piece  of  sheet  cop- 
per, c,  four  inches  long  and  three  inch- 
es wide,  having  a  copper  conducting 
wire  soldered  to  it,  is  loosely  coiled  up 
and  placed  in  the  inner  cylinder,  while 
a  piece  of  sheet  zinc,  of  equal  size,  is  also  coiled  up  and  laid  on  the  bottom  of  the 
outer  cylinder,  it  being  also  furnished  with  a  conducting  wire.  The  outer  cylinder 
is  then  to  be  nearly  filled  with  a  weak  brine,  and  the  smaller  with  a  saturated  so- 
lution of  sulphate  of  copper ;  the  two  fluids  being  prevented  from  mixing  by  the 
plaster  of  Paris  diaphragm.  After  it  has  been  in  action  for  some  weeks,  chloride  of 
zinc  is  found  in  the  external  cylinder,  and  beautiful  crystals  of  metallic  copper,  fre- 
quently mixed  with  the  ruby  protoxide  (closely  resembling  the  native  ruby  copper 
ore),  and  large  crystals  of  sulphate  of  soda,  are  found  adhering  to  the  copper  plate 
in  the  smaller  cyhnder,  especially  on  that  part  where  it  touches  the  plaster  diaphragm. 
The  apparatus  is  completed  by  the  decomposing  cell,  which  is,  in  fact,  a  counterpart 
of  the  battery  itself,  consisting,  like  it,  of  two  glass  cylinders,  one  within  the  other, 
the  smaller  one  having  a  bottom  or  floor  of  plaster  of  Paris  fixed  into  it ;  this 
smaller  tube  may  be  about  half  an  inch  wide  and  three  inches  in  length,  and  is  in- 
tended to  hold  the  metallic  solution  submitted  to  experiment,  the  external  tube,  b, 
into  which  it  is  immersed  being  filled  with  a  weak  solution  of  common  salt.  Into 
the  latter  solution,  a  slip  of  amalgamated  zinc  (for  the  positive  electrode),  soldered 
to  the  wire  coming  from  the  copper  plate  of  the  battery,  is  immersed,  while  for  the 
negative  electrode,  a  slip  of  platina  foil,  fixed  to  the  wire  from  the  zinc  plate  of  the 
battery,  passes  through  a  cork,  c,  fixed  in  the  mouth  of  the  smaller  tube,  and  dips 
into  the  metallic  solution  it  contains. 

The  influence  which  electricity  thus  exercises  upon  affinity,  and  the  modifications 
in  its  results  producible  by  its  means,  although  proving  a  most  intimate  connexion 
do  not  go,  as  I  beUeve,  so  far  as  to  demonstrate  a  complete  identity  of  cause.  It 
is  possible  that,  hereafter,  some  sublime  generalization  may  embrace  the  phenom- 
ena of  heat,  of  light,  and  of  electricity,  of  cohesion  and  gravity,  as  well  as  of  chem- 
ical affinity,  within  one  law,  and  indicate  how,  by  varied  manifestations  of  a  single 
agent,  their  separate  peculiarities  may  arise ;  but,  though  we  may  look  forward  to 


200       ELECTRO-CHEMICAL     THEORY     PROPOSED. 

such  a  state  of  science,  we  dare  not  rashly  seek  to  anticipate  its  approach ;  and  I 
look  upon  electricity  as  producing  and  being  produced  by  chemical  phenomena, 
precisely  as  we  find  heat  to  influence  as  well  as  to  be  evolved  by  chemical  combi- 
nation. 

Where  electricity  is  brought  into  play  so  powerfully  by  the  action  of  a  simple 
body  upon  a  compound  fluid,  it  is,  I  consider,  unreasonable  to  imagine  that,  in  the 
combination  of  simple  bodies,  or  of  compound  bodies  with  each  other,  no  electricity 
should  be  set  free,  particularly  when  it  is  proved  that  in  such  cases  some  electri- 
city does  appear,  although  in  quantity  bearing  no  proportion  to  that  of  the  feeblest 
galvanic  battery.  If  I  were  to  suggest  an  electro-chemical  theory,  such  as  might 
agree  with  the  facts  that  have  hitherto  been  discovered,  I  should  consider  that  bod- 
ies in  their  free  state  are  perfectly  destitute  of  excitation ;  but  that  chemical 
union,  or  the  degree  of  intimate  approximation  which  precedes  union,  may  be  a 
source  of  electrical  disturbance,  and  is  that  which,  in  all  ordinary  cases,  gives  ori- 
gin to  the  electricity  employed  in  our  experiments.  When  united,  bodies  are  like- 
wise destitute  of  electrical  properties ;  in  iodide  of  potassium,  the  bond  is  the  afiin- 
ity  of  iodine  and  potassium  for  each  other,  and  not  that  the  iodine  is  in  a  perma- 
nent state  of  negative  excitation  while  the  potassium  remains  positive. 

If  hydrogen  gas  be  burned  in  oxygen,  there  is  evolution  of  electricity,  of  which 
only  a  trace  escapes  immediate  recombination  under  the  form  of  light  and  heat,  but 
the  existence  of  which,  in  a  highly  intense  form,  has  been  demonstrated  by  Pouil- 
let.  The  oxygen  and  the  vapour  of  water  produced  assume  the  positive  condition  ; 
the  residual  hydrogen  becomes  negative.  If  carbon  be  burned  in  oxygen,  there  is 
likewise  combustion  and  evolution  of  electricity,  of  which  the  positive  passes  off 
with  the  carbonic  acid,  and  the  negative  rests  upon  the  carbon.  The  evolution  of 
heat  may  be  in  these  cases  an  independent  effect  of  combination,  but  I  would  look 
upon  it  as  being  more  probably  the  result  of  the  union  of  the  electricities  evolved. 
If  the  bodies  which  act  upon  each  other  are  dissolved  in  water,  there  is  no  combus- 
tion, but  heat  is  still  evolved,  and  the  electricities  unite  with  one  another  without 
the  necessity  for  any  intermediate  circuit.  It  is  only  where  the  replacement  of 
one  body  by  another  occurs,  that  the  establishment  of  the  chain  of  inductively  po- 
larized molecules  becomes  necessary ;  for  the  particles  of  zinc  and  hydrogen,  which 
become  oppositely  united,  have  no  power  to  combine,  and  hence  cannot  be  restored 
to  neutrality  unless  by  the  medium  of  a  third  body,  to  which  both  may  impart  their 
excitations.  That  the  zinc  and  hydrogen  upon  the.  one  hand,  and  the  copper  and 
hydrogen  upon  the  other,  do  not  unite,  is,  I  conceive,  fatal  to  those  views  which 
assume  the  identity  of  chemical  and  electrical,  or,  as  they  call  it,  current  or  induc- 
tive affinity  ;  for  if  a  molecule  of  copper  in  the  acid  stood  in  the  place  of,  and  acted 
as  a  molecule  of  chlorine,  it  should  unite  with  the  hydrogen  in  place  of  allowing  it 
to  pass  off  free. 

The  act  of  chemical  union  being  such  as  to  produce  electrical  excitation  and  dis- 
charge before  it  is  completed,  and  the  permanent  combination  of  the  elements 
being  the  result  of  the  return  to  the  neutral  state,  it  is  easy  to  understand  that, 
when  these  conditions  are  reversed,  the  chemical  affinity  should  be  superseded,  and 
the  bodies  brought  into  the  state  in  which  they  had  been  at  the  moment  of  excita- 
tion, and  while  their  elements,  oppositely  excited,  were  yet  separate  from  each 
other.  A  compound  body  is  therefore,  as  I  apprehend,  decomposed  by  the  bat- 
tery, from  having  this  electrical  state  given  to  it  by  the  current ;  and  the  transfer 
of  its  elements  across  the  liquid  is  accomphshed  by  a  series  of  neutralizations  and 
excitations,  accompanying  the  unions  and  decompositions  by  which  they  pass  to  the 
electrodes,  on  which  they  yield  up  their  ultimate  excitation,  and  appear  isolated 
and  completely  neutral.  The  quantity  of  electricity  necessary  to  decompose  a 
body  is  therefore  the  same  as  it  had  evolved  when  its  elements  entered  into 
union,  and  it  should  hence  follow  that  the  current  of  electricity  evolved  in  the 
union  of  chemical  equivalents  of  the  simple  bodies  with  each  other  should  be  the 
same.  That  this  actually  occurs  appears  probable  from  the  analogy  of  heat ;  an 
equivalent  of  oxygen,  in  combining  with  various  metals,  evolves  the  same  quantity 
of  heat,  and  if  the  heat  be  a  consequence  of  the  neutralization  of  electricity,  the  quan- 
tity of  this  evolved  should  be  the  same  also.  It  appears,  likewise,  that  an  equiva- 
lent of  sulphuric  acid,  in  combining  with  different  bases,  evolves  the  same  quantity 
of  heat,  and  to  decompose  the  various  salts  thus  formed,  the  same  quantity  of 
electricity  should  be  required  ;  and  hence,  that  the  two  actions,  so  completely  equiv- 
alent to  each  other,  may  satisfactorily  be  referred  to  the  same  source. 

Such  is  the  interpretation  I  put  upon  the  phenomena  of  electro-chemical  decOTO 


becquerel's   electro-chemical   theory.  201 

position,  and  the  relations  of  electrical  forces  to  affinity.  In  the  molecular  condition 
of  polar  excitation  which  accompanies  the  passage  of  a  current,  I  adopt  fully  the 
{peculiarly  explicit  mode  of  representing  he  actions  of  the  bodies  on  each  other 
proposed  by  Graham,  but  I  consider  it  too  hypothetical  to  assume  that  such  mole- 
cular state  naturally  exists  in  bodies  ;  it  may  or  it  may  not ;  but  in  the  absence  of 
evidence  that  it  does,  I  am  not  inclined  to  presuppose  it  unnecessarily.  I  look  upon 
the  current  as  being  produced  by  the  union  of  opposite  polarities,  which  are  them- 
selves not  the  cause,  but  the  consequence,  of  the  chemical  affinities  of  bodies. 
Graham  is  not  disposed  to  admit  that  the  union  of  simple  bodies  may  be  accom- 
panied by  an  electrical  phenomena,  and  to  exclude  also  from  the  application  of  an 
electro-chemical  theory  the  combination  of  acids  and  of  bases  with  each  other,  as 
not  capable  of  generating  currents  ;  but  the  reason  of  this  is,  as  I  imagine,  that  the 
currents  so  generated  are  necessarily  closed. 

In  concluding  the  admirable  treatise  on  electricity  with  which  he  has  enriched 
scientific  literature,  M.  Becquerel  details  the  views  which  he  has  adopted  regarding 
the  electro-chemical  relations  of  bodies ;  and  although  they  are  not  expressed  with 
the  definiteness  which  might  be  wished  from  so  admirable  a  philosopher,  I  shall 
endeavour,  in  concluding  this  section,  to  give  a  short  description  of  them.  In  the 
main,  they  do  not  differ  much  from  the  principles  of  electro-chemical  combination 
which  I  have  long  since  adopted,  and  which  have  been  already  noticed. 

M.  Becquerel  considers  that  in  all  bodies  there  is  distributed  a  quantity  of  elec- 
tricity indefinitely  great,  which  is  so  intimately  connected  with  their  molecular 
constitution,  that  it  is  disturbed,  and  excitation  produced  in  all  cases  where  molci- 
cular  disarrangement  is  produced  ;  hence  pressure,  friction,  an  unequal  distribution 
of  heat,  &c.,  are  sources  of  electricity. 

Chemical  affinity  is  also  a  source  of  electrical  disturbance.  When  an  acid  com- 
bines with  an  alkali,  the  first  sets  free  positive  electricity,  and  the  second  an  equal 
quantity  of  negative  electricity  ;  these  two  combine  immediately  in  the  liquor,  form- 
ing neutral  fluid,  and  produce  as  many  currents  as  there  had  been  particles  in  ac- 
tion ;  now  this  multitude  of  little  currents  ought  to  determine  the  production  of  a 
quantity  of  heat,  depending  on  the  energy  with  which  the  affinity  was  manifested, 
and  the  conducting  power  of  the  liquid.  In  decompositions,  the  electrical  effects 
are  inverse,  that  is,  the  acid  takes  the  negative,  and  the  alkali  the  positive  electri- 
city ;  hence  it  may  be  concluded,  as  M.  Becquerel  had  already  stated  with  regard 
to  aggregation,  that  if  electricity  does  not  constitute  affinity,  it  is  at  least  indispen- 
sable to  its  manifestation,  since  it  is  always  subjected  to  the  same  laws  every  time 
that  simple  or  compound  atoms  unite  or  separate.  From  all  considerations,  it  ap- 
pears that  the  electricity  produced  by  chemical  action  is  only  an  effect  resulting 
from  the  action  of  the  affinities  brought  into  play  ;  and  this  effect  being  brought  into 
inverse  action  in  decomposition,  announces  at  the  same  time  a  molecular  electric 
state,  indispensable  to  the  permanent  union  of  the  elements  of  compound  bodies. 

To  explain  decomposition  by  a  current  of  electricity,  M.  Becquerel  adopts  Am- 
pere's idea  of  electrical  atmospheres,  although  he  denies  that  any  bodies  are  natu- 
rally or  permanently  in  a  positive  or  negative  condition ;  but  he  supposes  that  the 
neutral  condition  of  a  body  consists  in  the  molecule  being  either  positive  or  nega- 
tive, and  being  surrounded  by  an  atmosphere  in  an  opposite  state.  When  bodies 
unite,  the  union  of  their  atmospheres  produces  light  and  heat,  and  the  molecules  re- 
main excited  while  in  union,  although  the  union  is  the  cause  of  the  electrical  dis- 
turbance, and  not  its  effect.  Now,  when  zinc  is  put  in  contact  with  water,  this  last 
is  decomposed,  and  there  is  hence  a  disturbance  of  electricity ;  the  particle  of  zinc 
abandons  its  negative  atmosphere,  and  unites  in  a  positive  condition  with  the  neg- 
ative and  nascent  oxygen  ;  the  hydrogen  is  liberated  nascent  also,  and  highly  pos- 
itive ;  in  this  state  the  oxygen  would  be  balanced  between  the  two  equally  positive 
particles  of  zinc  and  hydrogen,  and  the  decomposition  could  ^ot  proceed;  but,  if  a 
slip  of  copper  be  introduced,  this  supplies  a  negative  atmosphere  to  the  hydrogen, 
which,  becoming  neutral,  is  evolved  as  gas,  and,  transferring  its  positive  electricity 
to  the  point  of  contact  with  the  zinc,  neutralizes  its  excess  of  negative  excitement, 
and  generates  the  current.  M.  Becquerel  refers  the  chemical  action  of  the  current 
in  the  decomposing  cell  to  each  electricity  setting  the  same  electricity  of  the  com- 
pound in  motion  in  the  same  direction  with  which  the  particles  are  transferred  by 
a  series  of  combinations  and  decompositions,  as  has  been  already  described,  until 
the  limits  of  the  substance  are  attained,  and  then  the  elements  are  evolved  in  the 
neutral  state. 

M.  Becquerel  has  endeavoured  to  apply  the  agency  of  electricity  to  determine  the 

Cc 


202 


LAWS     OF     COMBINATION. 


relative  affinities  which  bodies  have  for  each  other.  His  principle  is  as  follows :  ii 
nitrate  of  copper  and  nitrate  of  silver  be  dissolved  together  in  equal  quantities,  and 
decomposed  by  a  galvanic  current,  the  nitrate  of  silver  alone  is  at  first  affected,  be- 
cause the  affinity  of  the  silver  for  the  oxygen  and  acid  is  so  much  less  than  that 
of  the  copper  for  the  same.  But,  when  the  quantity  of  nitrate  of  copper  is  gradually 
increased,  a  term  is  arrived  at  when  the  electric  current  is  exactly  equally  divided 
between  the  two  metals,  the  greater  quantity  of  copper  making  up  for  the  greater 
resistance  it  offers  to  the  decomposing  power.  His  results  are,  that  when  the  solu- 
tion contains  twenty  parts  of  copper  to  one  of  silver,  the  current  acts  equally  on 
both ;  when  the  copper  is  25  to  1,  the  current  acts  as  if  it  divided  itself  §  to  the 
copper  and  J  to  the  silver ;  and  when  the  quantity  of  copper  is  thirty  times  that 
of  the  silver,  there  are  three  equivalents  of  the  copper  salt  decomposed  for  one  of 
the  salt  of  silver.  M.  E.  Becquerel  has  essayed  the  same  important  problem  in  a 
different  way,  by  testing  the  power  of  solutions  of  chlorine,  iodine,  and  bromine^  to 
absorb  nascent  hydrogen  and  nascent  oxygen,  evolved  in  their  mass  by  means  of  a 
galvanic  current.  His  results  appear  to  show  that  the  affinities  are  expressed  by 
the  nmnbers ;  for  - 


Hydrogen. 

For  Chlorine 922 

Bromine 712 

Iodine 212 


Oxygen. 

For  Chlorine 169 

Bromine 380 

Iodine  .......  469 


These  two  series  are,  however,  independent  of  each  other,  and  afford  no  mutual 
term  of  comparison  whatsoever. 

It  is  to  be  trusted  that  such  investigations,  conducted  with  the  ingenuity  and  ac- 
curacy which  the  Becquerels  can  so  well  apply,  may  lead  to  results  of  the  highest 
interest  to  science.  The  reduction  to  numerical  laws  of  the  influence  of  quantity 
on  affinity,  and  the  determination  in  numbers  of  the  tendencies  of  the  simple  bodies 
to  unite,  would  certainly  advance  the  condition  of  chemistry,  as  an  exact  science, 
in  a  remarkable  degree. 


CHAPTER  IX. 


ON    THE    LAWS    OF    COMBINATION. 


The  gensral  nature  of  affinity,  and  the  modifications  which  it  un- 
dergoes from  the  influence  of  the  physical  agents,  having  been  now 
stated,  I  shall  proceed  to  discuss  the  numerical  laws  to  which  its  re- 
sults are  subjected,  the  discovery  of  which  was  the  first  step  in  con- 
ferring upon  chemistry  the  character  of  an  exact  science. 

It  is  characteristic  of  chemical  affinity,  that  the  proportions  in 
which  bodies  are  brought  to  unite  by  its  agency  are  limited  upon 
both  sides,  whereas,  in  those  cases  where  molecular  forces  alone 
prevail,  the  proportions,  although  perhaps  limited  in  one  direction, 
are  indefinite  in  the  other.  Thus  a  saturated  solution  of  chloride 
of  sodium  cannot  take  up  any  more  salt,  but  it  may  be  mixed  with  any 
quantity  of  water,  whereas  the  chloride  and  the  sodium,  which  con- 
stitute the  salt,  form  it  only  in  certain  proportions  which  are  inva- 
riable, 100  parts  containing  always  39-66  of  sodium  and  60-34i  of 
chlorine.  If  it  were  not  for  this  constancy  of  proportion,  the  science 
of  chemistry  could  never  have  advanced  beyond  its  merest  elements ; 
for,  had  chlorine  and  sodium  been  capable  of  combining  in  all  inde- 
terminate proportions,  or  had  the  properties  which  we  recognise  in 
chloride  of  sodium  been  ascribable  to  compounds  of  those  elements 


CHEMICAL    EQUIVALENTS.  203 

in  every  possible  proportion,  no  accurate  ideas  regarding  the  con- 
stitution or  properties  of  bodies  could  have  been  acquired,  and  none 
of  the  benefits  derivable  from  experience  or  experiment  could  have 
been  attained.  The  first  law  of  constitution  is,  therefore,  that  the 
composition  and  properties  of  any  given  substance  are  always  the 
same. 

When,  by  the  intervention  of  superior  affinities  or  by  double  de- 
composition, a  compound  body  is  decomposed  and  a  new  compound 
formed,  the  proportions  by  weight  of  the  various  substances  brought 
mto  action  have  a  constant  relation  to  one  another,  and,  as  they  rep- 
resent the  quantities  of  the  bodies  which  exercise  equal,  or,  at  least, 
equivalent  combining  powers,  they  are  termed,  when  reduced  to 
numbers,  the  combining  proportions  or  equivalents  of  these  bodies. 
Thus,  if  100  parts  of  oxide  of  copper  be  heated  in  a  current  of  hy- 
drogen gas,  it  is  reduced,  and  the  hydrogen,  uniting  with  the  oxygen 
which  it  contained,  forms  water.  In  the  100  of  oxide  there  were  79*83 
of  metallic  copper  and  20-17  of  oxygen,  which  last,  taking  2*52  of 
hydrogen,  forms  22-69  of  water.  Now,  in  this  case,  the  2-52  of  hjr 
drogen  produce  the  same  result  of  satisfying  the  combining  power  of 
the  20-17  of  oxygen  as  the  79-83  of  copper ;  and  hence  these  quanti- 
ties of  hydrogen  and  copper  are  equivalent  to  each  other.  This  ex- 
ample may  be,  however,  brought  much  farther.  If,  in  place  of  treat- 
ing the  oxide  of  copper  by  hydrogen  gas,  it  had  been  acted  on  by 
cliloride  of  hydrogen,  the  oxygen  should  have  been  carried  off  by  the 
hydrogen,  which  would  abandon  its  chlorine  for  that  purpose  j  but 
the  chlorine  should  not  be  set  free ;  it,  on  the  contrary,  would  unite 
with  the  copper  from  which  the  oxygen  had  been  taken,  and  the  re- 
action would  be  so  proportioned  that  the  quantity  of  copper  reduced 
by  the  hydrogen  of  the  chloride  of  hydrogen  would  be  exactly  suf- 
ficient to  unite  with  all  the  chlorine  which  was  therein  contained,  and 
form  with  it  chloride  of  copper.  In  this  case  the  100  parts  of  oxide 
of  copper  would  require  for  its  decomposition  91-73  of  chloride  of 
hydrogen,  and  there  would  be  formed  169-04  of  chloride  of  copper 
and  22-69  of  water.  Here,  as  before,  the  20-17  of  oxygen  uniting 
with  79-83  of  copper  and  2-52  of  hydrogen,  show  their  equivalency  ; 
but  we  learn  in  addition,  that  79-83  of  copper  and  2-52  of  hydrogen 
unite  equally  with  89-21  of  chlorine,  and  hence  that  that  quantity  of 
chlorine  corresponds,  and  is  equivalent  in  combination,  to  20-17  of 
oxygen. 

Starting  from  this  point,  we  may  proceed  to  a  still  more  extend- 
ed range  of  instances.  If  we  treat  sulphuretted  hydrogen  gas  with 
iodine,  we  find  that  it  is  totally  decomposed,  sulphur  being  pre- 
cipitated, and  iodide  of  hydrogen  being  formed.  Now,  taking  the 
quantity  of  the  sulphuret  of  hydrogen,  containing  the  weight  obtain- 
ed in  the  former  example,  2-52  of  hydrogen,  we  find  it  to  be  43-09, 
and  hence  to  contain  40-57  of  sulphur,  which  separates  by  the  action 
of  the  iodine,  of  which  318-28  parts,  uniting  with  the  2-52  of  hydro- 
gen, form  320-79  of  iodide  of  hydrogen.  If  this  iodide  of  hydrogen 
be  next  treated  with  chlorine,  it  abandons  its  iodine,  and  forms  91-73 
of  chloride  of  hydrogen. 

Setting  out,  therefore,  from  100  parts  of  oxide  of  copper,,  and 
tracing  its  elements  throus:h  a  variety  of  decompositions,  in  all  of 


204  SCALES     OF     CHEMICAL     EQUIVALENTS. 

which  the  quantities  engaged  effect  the  same  purpose  of  satisfying  the 
tendency  to  combine,  we  found  for  the  numbers  which  express  the 
equivalent  quantities  of  the  simple  bodies  employed  the  following : 

Copper 79-83 

Hydrogen 2-52 

Oxygen 20- 17 

and  as  the  compound  bodies  formed  are  also  equivalent,  from  their 
being  produced  by  the  same,  or  equivalent  combining  actions,  we 
may  express  also  in  numbers  their  combining  proportions  thus : 


Chlorine 89-21 

Sulphur 40-57 

Iodine 318-28 


Oxide  of  copper  .  .  .  100-00 
Oxide  of  hydrogen  .  .  22-69 
Chloride  of  hydrogen    .     9 1  •  73 


Sulphuret  of  hydrogen  .  4309 
Iodide  of  hydrogen  .  .  320-79 
Chloride  of  copper    .     .  16904 


It  is  evident  that  if,  in  place  of  oxide  of  copper,  any  other  metal- 
lic oxide  reducible  by  hydrogen  had  been  employed,  its  equiv- 
alent should  have  been  obtained,  and  in  this  way  the  equivalents  of 
the  majority  of  metals  have  been  determined. 

These  numbers  are  quite  arbitrary ;  and  any  other  body  in  the 
list  might  as  well  have  been  taken  for  the  origin  as  oxide  of  copper. 
In  practice  such  numbers  are  reduced  to  a  standard,  which  is  taken 
as  1  or  100,  and  for  this  purpose,  oxygen  or  hydrogen,  the  most 
important  bodies,  are  selected. 

Any  number  experimentally  obtained,  as  the  above,  may  be  re- 
duced to  the  standard  scale  by  the  rule  of  simple  proportions  :  thus, 
the  equivalent  of  copper  being  79'83,  oxygen  being  20*17,  and  hy- 
drogen 2*52,  it  is 

20-17  :  79-83  :  :  100-=395-7     Oxygen  =100 
and  2-52  :  79-83  :  :       1  =  31-71     Hydrogen  =1 

It  is  difficult  to  decide  which  of  the  two  scales  thus  formed  de- 
serves preference  :  the  hydrogen  scale  has  been,  by  the  authority 
of  Davy,  so  long  prevalent  in  these  countries,  that  it  is  difficult  to 
supersede  it ;  and  it  possesses  the  advantage  that  hydrogen  has  the 
smallest  equivalent  of  all  bodies.  The  standard  of  oxygen  is,  how- 
ever, for  use,  the  more  convenient,  as,  in  consequence  of  the  greal 
preponderance  of  bodies  in  which  oxygen  exists,  the  calculations 
are  much  simplified  by  its  number  being  100 ;  and  there  are  but 
two  or  three  bodies  which,  on  that  scale,  require  to  be  expressed 
in  a  fractional  form. 

When  the  study  of  these  equivalent  proportions  first  occupied  the 
minds  of  chemists.  Doctors  Prout  and  Thompson  were  led,  from 
speculations  regarding  the  physical  constitution  of  gaseous  bodies, 
to  suggest  that  the  equivalent  numbers  of  all  substances  were  sim- 
ple multiples  of  that  of  hydrogen ;  and  as,  representing  hydrogen 
by  1,  the  other  numbers  therefore  became  all  whole  numbers,  the 
spale  acquired  thereby  considerable  simplicity.  The  researches  of 
Berzelius  appeared,  however,  to  controvert  that  hypothesis  ;  and  in 
his  numbers,  which  are,  for  the  most  part,  those  given  in  the  follow- 
ing list,  no  trace  of  such  a  law  can  be  detected:  later  researches 
have  also,  in  the  hands  of  Turner  and  of  Penny,  afforded  additional 
support  to  this  opinion ;  but  Phillips  has  lately  reopened  the  dis- 
cussion, and  Dumas  is  inclined  to  consider  the  original  views  of 
Prout  as  being  probably  correct.     In  any  case,  the  numbers  given 


SCALES     OF     CHEMICAL     EQUIVALENTS. 


205 


in  the  list  must  be  looked  upon  as  being,  in  a  slight  degree,  still 
open  to  revision. 

In  the  following  table,  the  equivalents  of  all  the  simple  bodies  are 
expressed  on  each  of  these  scales ;  and  throughout  this  work  the 
two  equivalent  numbers  will  be  given  for  each  compound  body,  ex 
cept  where  it  is  otherwise  remarked. 


1VTn«nAA     nf    TPIa 

Equivalents.         l 

IVr^moe     nf    CiiKc 

Equivalents.          | 

riames  of  Lileiueuis. 

O.=  100 

H.=  l     1 

JNames  oi  oubsiiuuca. 

O.=100 

H.=  l 

Aluminum  .     .     . 

171-2 

13-7 

Mercury .... 

12658 

101-43 

Antimony 

1612-9 

129-2 

Molybdenum 

598-5 

47-96 

Arsenic  . 

940  1 

7534 

Nickel     .     . 

369-7 

29-62 

Barium  . 

856-9 

68  66 

Nitrogen 

1750 

1400 

Bismuth 

886-9 

7110 

Osmium 

1244-5 

99-72 

Boron     . 

136-2 

10-91 

Oxygen  . 

1000 

801 

Bromine 

978-3 

7839 

Palladium 

665-9 

53  36 

Cadmium 

696-8 

55  83 

Phosphorus 

392-3 

31-44 

Calcium  . 

2560 

20-52 

Platinum 

1233-5 

98-84 

Carbon   . 

76  0 

608 

Potassium 

489-9 

39-26 

Cerium   . 

5747 

46  05 

Rhodium 

651-4 

52-2 

Chlorine 

442-6 

35-47 

Selenium 

494-6 

39-63 

Chromium 

351-8 

2819 

Silicon    . 

277-3 

22-22 

Cobalt     . 

369-0 

29-57 

Silver     . 

1351-6 

108-3 

Columbium 

2307-4 

184-90 

Sodium  . 

290-9 

23-31 

Copper    . 

395-7 

31-71 

Strontium 

5473 

43-85 

Fluorine . 

233-8 

18-74 

Sulphur  . 

20117 

1612 

Glucinum 

331-3 

26-54 

Tellurium 

801-76 

64-25 

Gold  .     . 

24860 

199-21 

Thorium 

744-9 

59-83 

Hydrogen 

12-5 

1-00 

Tin     .     . 

735  29 

58  92 

Iodine     . 

1579-5 

126-6 

Titanium 

30366 

24  33 

Iridium  . 

12335 

98-84 

Tungsten 

11830 

94-80 

Iron    ,     . 

339-2 

27-18 

Vanadium 

856-9 

68  66 

Lanthanum 

Uranium 

2711-4 

217-26 

Lead  .     . 

1294-5 

103-73 

Yttrium  . 

4025 

32  25 

Lithium  . 

803 

6-44 

Zinc  .     . 

403-2 

3231 

Magnesium      .     . 

1583 

1269 

Zirconium 

4202 

3367 

Manganese  .     ,     . 

3459 

27-72 

The  determination  of  the  equivalents  of  compound  bodies  is  an 
equally  remarkable  application  of  the  principles  that  have  been  laid 
down.  The  equivalent  number  of  a  compound  is  the  sum  of  the 
equivalent  numbers  of  its  constituents,  as  has  been  already  seen  in 
the  numbers  obtained  for  the  oxides  and  chlorides  of  copper  and  of 
hydrogen.  In  this  way  may  be  constructed  lists  of  the  equivalents 
of  compound  bodies ;  thus,  reducing  the  substances  already  noti- 
ced to  the  scales,  there  are : 


Substances. 

Equivalents.     | 

Substances. 

Equivalents.        | 

O.  =  I00 

H.=  I 

O.=100 

H.=l 

Oxide  of  copper     .     . 
Oxide  of  hydrogen      . 
Chloride  of  hydrogen . 

495-7 
112-5 
4451 

39-72 

9-01 

36-47 

Chloride  of  copper      . 
Iodide  of  hydrogen 
Sulphuret  of  hydrogen 

838-3 

15920 

213-7 

6718 

127-57 
1712 

It  IS  m  relation,  however,  to  the  mutual  decomposition  of  saline 
bodies  that  the  principle  of  equivalent  proportion  becomes  of  most 
interest,  and  by  which  it  is  best  illustrated.  If  to  a  solution  of  ni- 
trate of  barytes  we  add  a  solution  of  sulphate  of  soda,  there  is  im- 
mediate decomposition,  by  the  mutual  interchange  of  acids  and  ba 
ses,  and  the  neutrality  of  the  solution  remains  completely  undisturb 
ed  J  the  salts  which  exist  after  mixture  are  equally  neutral  with 


206 


EQUIVALENTS     OF     COMPOUND     BODIES. 


those  which  had  existed  previously,  and  the  quantities  of  acids  and 
bases  which  are  involved  in  the  decomposition  are  hence  equiva- 
lent to  each  other.  Thus,  if  we  take  130'7  parts  of  nitrate  of  ba- 
rytes, we  find  that  they  require  for  their  decomposition  exactly  71-3 
parts  of  dry  sulphate  of  soda,  and  that  there  are  formed  116-7  parts 
of  sulphate  of  barytes  and  85*3  parts  of  nitrate  of  soda.  The  com- 
position of  these  four  salts  is : 


Sulphate  of  Barytes. 
Sulphuric  acid    .    .      40 
Barytes     ....      767 
116-7 

Nitrate  of  Barytes. 
Nitric  acid    ...      54 
Barytes    ....      767 
130-7 


Nitrate  of  Soda. 
Nitric  acid    ...      54 

Soda 31-3 

85  3 

Sulphate  of  Soda. 
Sulphuric  acid      .     .    40 

Soda 31-3 

71-3 


All  four  are  neutral ;  the  acids  and  bases  are  in  all  equally  neutral- 
ized, and  hence  the  40  of  sulphuric  acid  and  54<  of  nitric  acid,  being 
capable  of  saturating  the  same  quantity  of  base,  whether  it  be  soda 
or  barytes,  are  equivalent  quantities,  and  represent  the  combining 
proportions  of  these  acids  j  and  the  76*7  of  barytes  and  the  31-3  of 
soda  being  likewise  shown  to  possess  equal  powers  of  neutralizing 
the  acid,  whether  nitric  or  sulphuric,  are  the  numerical  equivalents  of 
those  bases.  If  there  had  been  a  larger  quantity  of  either  salt  pres- 
ent, it  would  have  remained  unaffected,  the  interchange  of  elements 
taking  place  only  in  equivalent  proportions.  Had  nitrate  of  lead  been 
employed  in  place  of  nitrate  of  barytes,  the  proportion  necessary 
would  have  been  different,  and  a  different  quantity  of  sulphate  of  lead 
would  have  been  produced  from  the  same  sulphate  of  soda.  Thus, 
to  the  71*3  of  sulphate  of  soda,  there  should  be. 

Nitric  acid  .  .  540,  producing  Sulphuric  acid  .  .  40- 1 
Oxide  of  lead  .  111-7,  «  Oxide  oflead  .  .  .  lU-7 
Nitrate  of  lead        165-7  Sulphate  of  lead  151.8 

If,  in  place  of  sulphate  of  soda,  we  take  oxalate  of  soda,  we  shall 
jRnd  that  67-3  of  it  will  exactly  fulfil  the  functions  of  71-3  of  sulphate 
of  soda,  and  these,  consisting  of  31*3  of  soda  and  36-0  of  oxalic  acid, 
will,  by  decomposing  130-7  of  nitrate  of  barytes  or  165-7  of  nitrate 
of  lead,  produce  147-7  of  oxalate  of  lead  or  112*7  of  oxalate  of  ba- 
rytes. 36  of  oxalic  acid  are  therefore  equivalent  to  40- 1  of  sulphuric 
acid  and  54-0  of  nitric  acid. 

A  table  of  equivalents  of  acids  and  bases  might  thus  be  drawn  up : 
there  should  be, 


Substasoefl. 

Equivalents. 

■■ 

Substances. 

Equivalents.       | 

O.=  100. 

H.=  I. 

540 
40- 1 
360 

0  =  100. 

H.  =  l. 

Nitric  acid    .     . 
Sulphuric  acid  . 
Oxalic  acid 

6770 
501-1 
4529 

Soda    .... 
Barytes    .     .     . 
Oxide  of  lead    . 

3901 

956-9 

1394-5 

31-3 

76-7 
111-7 

It  was  in  this  form  that  the  equivalency  of  different  quantities  of 
chemical  substances  was  first  recognised,  and  numbers  assigned  with 
extraordinary  skill,  by  Wenzel,  whose  labours,  although  overlooked 
at  the  time,  must  be  considered  as  the  first  and  greatest  step  towards 
assigning  the  numerical  conditions  of  chemical  action. 


LAW     OF     MULTIPLE     PROPORTIONS.  207 

The  mode  of  determining  the  equivalent  number  of  a  new  sub- 
stance can  now  be  easily  understood.  If  it  be  an  acid,  it  is  to  be 
combined  with  some  base  of  which  the  equivalent  is  known  j  if  it  be 
a  base,  it  must  be  united  with  an  acid.  If  it  be  a  metal,  it  may  be 
united  with  chlorine  or  oxygen.  If  it  be  a  simple  non-metallic  body, 
it  may  be  united  with  a  metal.  In  any  case,  a  well-defined  com- 
pound of  the  new  body  with  one  whose  equivalent  number  is  already 
known  must  be  obtained  and  accurately  analyzed.  The  equivalent 
numbers  of  the  two  bodies  are  proportional  to  the  quantities  in 
which  they  were  combined,  provided  we  have  reason  to  consider 
that  the  compound  examined  contained  an  equivalent  of  each. 
Thus,  if  the  new  body  form  with  sulphuric  acid  a  perfectly  neu- 
tral and  soluble  salt,  and,  on  analysis,  this  yields  37*3  of  sulphuric 
acid  and  62*7  of  the  new  base  in  100,  the  equivalent  is  found  by  the 
proportion,  as,  37*3  :  62*7  :  :  40*1  :  x=67-4,  which  is  the  equiva- 
lent of  the  body,  40*1  being  that  of  sulphuric  acid,  and  hydrogen 
being  =1. 

A  calculation  of  this  kind  requires,  however,  to  be  checked  by  a 
knowledge  of  the  next  law  of  combination,  that  of  multiple  propor- 
tions ;  for,  as  has  been  stated,  we  presume,  in  the  example,  the  salt 
analyzed  to  be  composed  of  an  equivalent  of  each  constituent.  It 
may  be,  however,  that  it  contained  two  equivalents  of  acid  to  one 
of  base,  in  which  case  the  number  for  the  latter  would  become 
134<*8  5  or  two  equivalents  of  base  to  one  of  acid,  which  would  make 
the  number  33*7.  The  proportions  might  be  even  still  more  com- 
plex ;  and  hence,  before  attempting  to  decide  on  the  equivalent  num- 
ber of  a  body,  its  general  history  must  be  studied. 

The  third  law  of  combination  is,  that  where  one  body  unites  with 
another  in  more  proportions  than  one,  there  exists  a  simple  relation 
between  the  quantities  of  the  second,  which,  in  the  different  com- 
pounds, unite  with  the  same  quantity  of  the  first.  Thus,  taking  man- 
ganese and  nitrogen,  which  are  remarkable  for  the  number  of  com- 
pounds which  they  form  with  oxygen,  there  are, 

345-9  of  manganese  unite  with  100  of  oxygen,  forming  protoxide. 
345-9  "  150  "  sesquioxide. 

345-9  "  200  "  peroxide. 

346-9  "  250  "  manganous  acid. 

345-9  "  300  "  manganic  acid. 

345-9  "  350  "  permanganic  acid. 

And  with  nitrogen, 

175  of  nitrogen  unite  witli  100  of  oxygen,  forming  nitrous  oxide. 
175  "  200  "  nitric  oxide. 

175  "  300  "  hyponitrous  acid. 

175  "  400  «  nitrous  acid. 

175  "  500  "  nitric  acid. 

Here  the  successive  quantities  of  oxygen  taken  by  the  manganese 
are  as  the  numbers  2,  3,  4,  5,  6,  7,  and  those  which  combine  with  the 
nitrogen  are  as  1,  2,  3,  4,  5.  In  the  last  case  they  are  all  simple 
multiples  of  the  first  proportion,  but  in  the  case  of  manganese  they 
are  multiples  of  one  half  of  the  quantity  contained  in  the  protoxide. 
The  analogy  of  some  other  similar  bodies,  however,  renders  it  ex- 
tremely probable  that,  though  it  has  not  been  yet  discovered,  there 


52-2  chromic 

acid- 

104-4 

- 

156-6 

H 

208  LAW     OF     MULTIPLE     PROPORTIONS. 

exists  a  compound  of  348*9  of  manganese  with  50  of  oxygen^  and 
this  should  then  be  the  first  term  of  the  series. 

This  law  of  multiple  proportions  holds  not  only  with  regard  to  the 
simple  bodies  already  stated,  but  also  with  compound  bodies  of  every 
class.  Thus  chromic  acid  combines  with  potash  in  three  different 
^proportions,  forming  by 

•47.3  potash,  neutral  chromate  of  potash. 
-47-3       "      bichromate  of  potash. 
■47-3       "      terchromate  of  potash. 

Sulphuric  acid  combines  with  potash  in  two  proportions, 

40- 1  sulphuric  acid  -|-47-3  potash,  neutral  sulphate. 
80-2  "  4-47-3       "      bisulphate. 

It  was,  indeed,  by  the  verification  of  it  in  the  carbonates  and  ox- 
alates of  potash  by  Wollaston,  that  this  law  obtained  in  the  first 
instance  general  acceptation. 

22  of  carbonic  acid  -|-47-3  potash,  form  carbonate  of  potash. 
44  "  -  -47-3  "  bicarbonate  of  potash. 

36  of  oxalic  acid  -  -47-3  potash,  form  oxalate  of  potash. 
72  "  4-47-3  "  binoxalate  of  potash.    ' 

144  "  -|-47-3  "  quadroxalate  of  potash. 

In  salts  with  excess  of  base,  the  same  principle  holds.  Thus,  in 
the  sulphates  of  copper,  I  have  shown  that 

39-7  oxide  of  copper  -{-401  sulphuric  acid,  form  neutral  sulphate. 

79-4  "  440-1  "  bibasic  sulphate. 

158-8  "  4-40  1  "  quadribasic  sulphate. 

317-6  "  4-401  "  octobasic  sulphate. 

In  other  cases  the  series,  though  not  so  complete,  evidently  follows 
the  same  law. 

The  great  use  of  the  symbolical  nomenclature,  noticed  already  in 
page  156,  consists  in  its  supplying  an  exact  expression  of  this  law 
of  multiple  proportions.  The  ordinary  symbol  of  a  simple  body  in- 
dicating an  equivalent  of  it,  the  number  by  which  that  symbol  is 
multiplied,  in  the  formula  of  each  compound  body,  represents  the 
number  of  equivalents  therein  contained.  Thus,  for  manganese  and 
nitrogen,  already  used  as  instances,  the  symbolical  expression  of  the 
law  is  given  in 


N.O.  Nitrous  oxide. 
N.O2  Nitric  oxide. 
N.O3  Hyponitrous  acid. 
N.O4  Nitrous  acid. 
N.O5  Nitric  acid. 


Mn.O.  Protoxide  of  manganese. 
MuaOa  Sesquioxide. 
Mn.O,  Peroxide. 
Mn.Oa  Manganic  acid. 
MugOy  Permanganic  acid. 

The  numerical  coefficient  is  sometimes  placed,  as  here,  below 
and  to  the  right  of  the  letter  symbol;  by  other  chemists  it  is  placeld 
to  the  left  and  on  the  same  line,  asPb.  +  20.  Cr.+30.,  and  sometimes 
to  the  right  and  above  the  letter,  as  Pb.O^  Cr.O^.  This  makes  no 
difference  m  chemistry ;  but  the  student  must  be  careful  not  to 
confound  chemical  with  mathematical  symbols,  in  which  the  posi- 
tion of  the  number  might  alter  its  power  and  meaning  altogether. 
It  must  be  noticed,  however,  that  numbers  written  as  the  above  af- 
fect only  the  immediate  symbol  to  which  they  are  attached  j  but 


RESEARCHES      OF     PROUST.  209 

sometimes  a  number  affects  a  group  of  symbols:  thus,  3Mn.O.  is 
three  equivalents  of  protoxide  of  manganese  =Mn303:  thus,  also, 
S.O3  K.O.+AI2O3.  3S.O3,  the  formula  of  dry  alum,  contains  four  fig- 
ures of  3,  of  which  the  first,  second,  and  fourth  only  affect  the  O., 
to  which  they  are  subjoined,  but  the  third  affects  the  S.O3,  to  which 
it  is  prefixed.  A  little  practice  will  enable  the  student  to  become 
quite  familiar  with  the  arrangement  of  the  symbols,  or  formulae,  as 
they  are  termed,  of  bodies,  even  of  the  most  complicated  nature. 

This  is  the  principle  of  multiple  proportions:  that  the  successive 
quantities  in  which  one  body  may  unite  with  another  are  multiples 
of  the  first  by  a  whole  number  j  and  the  cause  of  this  is  at  once 
seen,  and  a  simple  and  positive  meaning  given  to  this  law,  by  say- 
ing that  the  first  body  contains  an  equivalent  of  each  element ;  the 
second,  one  equivalent  of  one  and  two  equivalents  of  the  other,  and 
so  on ;  the  successive  steps  being  formed  by  the  number  of  com- 
bining proportions  of  the  second  body  which  unite  with  one  com- 
bining proportion  of  the  first. 

This  principle,  which  establishes  a  remarkable  distinction  between  the  action  of 
chemical  affinity  and  of  cohesion,  was,  at  the  moment  of  its  first  being  traced,  at- 
tacked by  BerthoUet,  to  whose  exclusive  doctrines  it  was  quite  fatal.  BerthoUet, 
in  fact,  considered  that  the  affinity  of  bodies  should  make  them  unite  in  all  possible 
proportions,  and  that  it  was  only  by  the  influence  of  cohesion  and  elasticity  that  the 
formation  of  the  bodies  actually  produced  resulted.  Thus  he  asserted  that  sulphu- 
ric acid  and  barytes  actually  unite  in  all  proportions  ;  but  those  of  40- 1  of  acid  tc 
76-7  of  base  forming  the  body  of  the  least  solubility,  the  whole  quantity  of  acid  is 
determined  to  unite  with  the  barytes  in  those  proportions,  and  in  none  others 
Thus  he  imagined,  also,  that  mercury  and  oxygen  should  unite  in  all  proportions 
and  that  it  was  only  by  the  intervention  of  external  causes  that  their  union  was  de- 
termined in  preference  to  occur  in  the  proportions  of  101-4  of  mercury  to  4  of  oxy- 
gen, and  101 -4  of  metal  to  eight  of  oxygen.  We  owe  to  Proust  the  complete  refu- 
tation of  BerthoUet's  views  in  this  respect ;  he  cleared  away  a  heap  of  incorrect 
ideas  which  had  prevailed  regarding  compound  bodies,  showing  that  numerous  de- 
grees of  oxidation,  which  had  been  looked  upon  as  intermediate,  and  connecting 
the  extreme  limits,  as  BerthoUet  thought  they  ought  to  be  connected,  were  impure 
and  badly  prepared  mixtures  of  the  true  compounds,  and  that,  when  pure,  the  tran- 
sition from  one  state  to  the  other  is  sudden  and  definite,  as  has  been  shown  to  be 
the  consequence  of  the  law  of  multiple  proportion.  It  is  interesting  to  notice,  how- 
ever, as  an  example  of  how  easily  a  great  discovery  in  science  may  be  lost,  that,  al- 
though Proust  had  in  his  hand  all  materials  necessary  for  establishing  the  laws  ot 
combination,  such  as  they  have  been  described,  they  escaped  his  notice,  from  his 
having  contemplated  his  results  only  in  one  point  of  view ;  thus  he  found  that  in 
100  parts. 


1st  Oxide  of  copper  contained 

Oxygen 11-22 

Copper 88-78 

1  St  Oxide  of  mercury 

Oxygen 3-80 

Mercury 96  20 

I  St  Sulphuret  of  iron 

Sulphur 37-23 

Iron 62-77 


2d  Oxide  of  copper  cpntained 

Oxygen 20- 17 

Copper 79-83 

2d  Oxide  of  mercury 

Oxygen 7-32 

Mercury 92-68 

2d  Sulphuret  of  iron 

Sulphur ,54-26 

Iron 45-74 


He  proved  that  no  indefinite  intermediate  degree  of  combination  could  be  traced, 
and  that  the  influence  of  cohesion  could  not  be  supposed  to  be  the  only  cause  of  the 
definiteness  of  constitution  ;  but,  had  he  made  a  trifling  change  in  his  way  of  calcu- 
lation ;  had  he  taken  a  certain  weight  of  one  element  as  the  standard,  and  not  100 
parts  of  the  compound  body,  his  numbers  would  have  become, 
1st  Oxide  of  copper 

Oxygen 100-0 

Copper 791-4 


Dd 


2d  Oxide  of  copper 

Oxygen 2000 

Copper 791-4 


210 


METHODS     OF    DETERMINING    THE 


1st  Oxide  of  mercury 

Oxygen 1000 

Mercury 2531-6 

1st  Sulphuret  of  iron 

Sulphur 201-2 

Iron 339-3 


2d  Oxide  of  mercury 

Oxygen 2000 

Mercury 2531-6 

2d  Sulphuret  of  iron 

Sulphur 402-4 

Iron 339-2 


And  thus  the  fact  of  the  quantity  of  oxygen  or  sulphur  in  the  second  range  of 
compounds,  being  exactly  double  that  in  each  of  the  first,  would  have  been  evident, 
and  the  law  of  multiple  proportions  been  discovered  twenty  years  before  its  exist- 
ence was  suspected. 

We  are  now  in  a  condition  to  examine  more  in  detail  the  method 
of  determining  the  equivalent  number  of  a  body,  which,  as  was  be- 
fore noticed,  is  rendered  difficult,  sometimes,  when  the  substances 
in  question  unite  in  more  proportions  than  one.  Thus  it  is  evident 
that  the  manganese  series  might  be  represented  as 

100  of  oxygen  -|-345-9  of  manganese,  forming  protoxide. 

100  "  230-5  "  "  sesquioxide. 

100  "  172-9  "  "  peroxide. 

100  "  138-3  "  "  manganous  acid. 

100  "  115-3  "  "  manganic  acid. 

100  "  98-8  "  "  permanganic  acid. 

And  the  metallic  oxides  and  sulphurets  above  described  might  be 
written,  and  express  still  the  law  of  multiple  proportion  ;  as. 


1st  Oxide  of  copper 

Oxygen 1000 

Copper 791-4 

1st  Oxide  of  mercury 

Oxygen 1000 

Mercury 2531-6 

1st  Sulphuret  of  iron 

Sulphur 201-2 

Iron 339-2 


2d  Oxide  of  copper 

Oxygen 100-0 

Copper 395-7 

2(L  Oxide  of  mercury 

Oxygen 1000 

Mercury       .     .     .     .1265  8 

2d  Sulphuret  of  iron 

Sulphur 201-2 

Iron 1696 


There  might  thus  be  deduced  from  each  kind  of  compound  a  dif- 
ferent equivalent  for  each  simple  body,  and  it  is  therefore  neces- 
sary to  lay  down  some  general  principles  by  which  one  must  be 
guided  in  their  choice. 

First.  Whenever  there  exists  but  one  proportion  in  which  two 
bodies  are  capable  of  combining,  it  may  be  concluded,  unless  there 
are  good  reasons  to  the  contrary,  derived  from  other  sources,  that 
the  proportion  is  one  equivalent  of  each  element.  Thus  lime  and 
magnesia  are  the  only  compounds  formed  by  the  metals  calcium 
and  magnesium  uniting  with  oxygen,  and  are  hence  looked  upon 
as  protoxides. 

Second.  Whenever  one  body  combines  with  another  in  two  pro 
portions,  as  a  metal  with  oxygen,  and  the  quantities  of  oxygen  are 
as  2  :  1,  it  may  be  concluded,  unless  there  are  other  reasons  for  an 
opposite  decision,  that  the  bodies  consist  either  of  one  equivalent 
of  metal  united  respectively  with  one  and  two  of  oxygen,  or  of  one 
equivalent  of  oxygen  united  respectively  with  one  and  two  of  metal. 
To  decide  between  these  views,  it  must  be  considered,  that  as  the 
tendency  of  the  metal  and  of  oxygen  to  unite  is  pretty  well  satiated 
by  the  combination  of  an  equivalent  of  each,  if  the  protoxide  so 
formed  unite  with  another  equivalent  of  either  metal  or  of  oxygen, 
this  will  be  retained  with  inferior  power,  and  when  the  substance 
80  produced  is  exposed  to  decomposing  agencies,  it  may  be  resolved 


EQUIVALENT     CONSTITUTION     OF     BODIES.     211 

into  protoxide  and  metal  in  the  one  case,  and  protoxide  and  free 
oxygen  in  the  other.  Thus  copper,  lead,  and  mercury  unite  each 
with  oxygen  in  two  proportions ;  and  if  black  oxide  of  mercury 
be  heated,  it  resolves  itself  easily  into  metallic  mercury  and  red 
oxide,  while  the  red  oxide  undergoes  no  change  except  total  de- 
composition into  mercury  and  free  oxygen.  Red  oxide  of  copper 
decomposes  itself  easily  into  metallic  copper  and  black  oxide  of 
copper ;  but  this  last  does  not  admit  of  any  decomposition  which 
is  not  total.  If  we  take  yellow  oxide  of  lead,  we  cannot  change  it 
by  the  application  of  heat ;  but  if  we  heat  brown  oxide  of  lead,  it 
gives  off  one  half  of  its  oxygen,  and  yellow  oxide  remains;  similarly, 
when  peroxide  of  manganese  is  heated  by  deoxidizing  agents,  it 
abandons  one  half  of  its  oxygen,  but  the  oxide  so  formed  cannot  be 
farther  reduced.     In  this  way,  therefore,  we  conclude  that 

Red  oxide  of  copper  is  suboxide.     CuzO. 
Black  oxide  of  jcopper  is  protoxide.     Cu.O. 
Black  oxide  of  mercury  is  suboxide.     HggO. 
Red  oxide  of  mercury  is  protoxide.     Hg.O. 
Yellow  oxide  of  lead  is  protoxide.     Pb.O. 
Brown  oxide  of  lead  is  deutoxide.     Pb.Oa. 
Olive  oxide  of  manganese  is  protoxide.     Mn.O. 
Black  oxide  of  manganese  is  deutoxide.     Mn.Og. 

Thus,  also,  hydrogen  and  oxygen  unite  in  two  proportions,  to  form,  m 
one,  water,  a  body  remarkably  neutral  in  properties  and  permanent  in 
constitution,  and  in  the  other  oxygenated  water,  of  which  half  of 
the  oxygen  is  so  loosely  combined  that  its  decomposition  is  provo- 
ked by  the  slightest  causes,  and  is  explosively  violent.  It  is  hence 
concluded  that 

Water  is  protoxide  of  hydrogen.     H.O. 
Oxygenated  water  is  deutoxide.     H.Og. 

If  there  be  still  more  degrees  of  combination  of  the  two  bodies, 
these  principles  apply  still  more  determinately  to  their  characteristic 
properties. 

Third.  The  constitution  of  an  acid  may  be  frequently  determin- 
ed by  the  consideration  that  an  equivalent  of  it  is  the  quantity 
which  neutralizes  an  equivalent  of  a  well-characterized  base.  Thus 
the  equivalent  number  of  potash  on  the  hydrogen  scale  is  47*3,  and 
this  combining  with  40*1  of  sulphuric  acid  to  form  neutral  sulphate 
of  potash,  this  number  is  determined  to  be  the  equivalent  of  the 
acid;  and  as  it  is  made  up  of  16*1  of  sulphur  and  24  of  oxygen,  the 
acid  is  considered  to  be  composed  of  one  equivalent  of  sulphur 
16-1,  and  three  equivalents  of  oxygen  8x3  =  24.  Its  formula  is 
therefore  S.O3.  In  the  same  way,  on  analyzing  hyposulphate  of 
potash,  it  is  found  to  consist  of  47-3  of  potash,  united  to  72-2  of  the 
acid,  which  is,  therefore,  its  equivalent  number.  But  this  number 
is  made  up  of  32-2,  or  two  equivalents  of  sulphur,  and  40,  or  five 
equivalents  of  oxygen,  and  the  formula  expressing  its  constitution 
is  S2O5. 

Where  an  acid  forms  several  classes  of  salts,  it  is  difficult  to  de- 
termine which  is  that  containing  an  equivalent  of  each  element,  and 


212  METHODS     OF     DETERMINING     THE 

hence  this  mode  of  ascertaining  the  constitution  of  the  acid  may  be 
occasionally  at  fault.  This  happens  particularly  with  the  acids  of 
phosphorus  and  arsenic  j  and  in  these  cases  it  is  necessary  to  recur 
to  considerations  regarding  the  constitution  of  their  salts,  which 
will  be  described  when  we  come  to  speak  of  salts  in  general. 

Fourth.  In  cases  where  the  ratio  between  the  quantities  in  which 
the  bodi-es  combine  does  not  follow  the  simple  proportion  of  1 :  2  :  3, 
&c.,  but  assumes  the  more  complex  form  of  2  :  3,  or  3  :  4,  or 
3  ;  5  :  7,  it  is  necessary  to  seek  for  analogies  between  the  members 
of  the  series  and  certain  other  bodies  with  regard  to  which  there  is 
not  the  same  uncertainty.  Thus  there  are  two  oxides  of  iron 
which  may  be  looked  upon  as  consisting,  either 

the  1st  of  27*9  of  iron  +  8  oxygen, 
the  2d         27-9       "       +12       " 
or  the  2d         18-6       "       +8       " 
the  1st       27-9       "       +  8       « 

In  the  first  mode  of  view  the  oxygen  varies  as  2  :  3,  but  in  the  sec- 
ond it  is  the  metal  which  changes  in  proportion.  Here  we  obtain  a 
guide  in  the  study  of  the  salts  formed  by  these  bodies.  It  is  found 
that  the  oxide  which  contains  27*9  of  iron  to  8  of  oxygen  agrees  in 
its  laws  and  properties  with  magnesia,  with  black  oxide  of  copper, 
and  with  olive  oxide  of  manganese,  which  are  all  protoxides,  and 
that  it  differs  totally  in  its  relations  from  such  bodies  as  are  very 
fully  known  to  be  suboxides.  This  oxide  of  iron  contains,  therefore, 
an  equivalent  of  each  element,  and  its  formula  is  Fe.O.  The  per- 
oxide of  iron  then  becomes  Fe.O  1^  ;  but  as  the  equivalent  of  oxygen 
cannot  be  considered  to  be  divided,  we  look  upon  it  as  being  rather 
FciOg,  and  having  its  equivalent  number  twice  as  large.  This  view 
is  confirmed  by  finding  that  when  sulphate  of  peroxide  of  iron  unites 
with  sulphate  of  potash  to  form  iron  alum,  it  does  so  in  the  propor- 
tion of  Fe203,  dry  iron  alum  being  S.O3,  K.O.+Fe203,  3S.O3 ;  and  as 
this  is  the  only  proportion  in  which  these  two  salts  unite,  it  is  rea- 
sonable to  suppose  that  it  contains  an  atom  of  each  element. 

This  mode  of  controlling  the  equivalent  numbers  is  beautifully 
shown  in  the  instance  of  the  compounds  of  chrome  with  oxygen. 
There  are  two  j  the 

Green  oxide  of  chrome  consists  of  18-79  chrome  +  8  oxygen. 
Chromic  acid  «  18-79       "        +16 

Here  the  quantity  of  oxygen  is  doubled  in  the  second  compound ; 
and  as  this  yields  half  of  its  oxygen  readily,  either  by  heat,  or  to  any 
substance  having  an  affinity  for  it,  it  would  appear  highly  probable 
that  the  18-79  is  the  equivalent  of  chrome,  and  that  the  oxide  of 
chrome  should  be  looked  upon  as  a  protoxide ;  but  such  is  not  the* 
case.  Sulphate  of  chrome  combines  with  sulphate  of  potash  to  form 
a  chrome  alum,  resembling  in  all  characters  and  constitution  the  iron 
alum  already  noticed,  and  hence  oxide  of  chrome  corresponds  to 
peroxide  of  iron,  and  its  formula  is  CraOg.  This  is  farther  proved 
by  the  relations  of  chromic  acid  to  bases.  The  chromates  resemble 
perfectly  the  sulphates  with  which  they  are  isomorphous,  and  to 
saturate  47-3  of  potash  52-2  of  chromic  acid  are  required,  consisting 


EQUIVALENT     CONSTITUTION     OF     BODIES.        213 

of  28-2  of  chrome  and  24  of  oxygen  ;  and  hence  the  formula  of 
chromic  acid  is  Cr.Oa,  resembling  that  of  sulphuric  acid  S.O3. 

Fifth.  In  cases  where  there  is  only  one  compound  of  a  body  with 
oxygen,  we  may  be  induced  to  consider  it  not  to  be  composed  of  an 
equivalent  of  each  element  from  analogical  grounds,  such  as  those 
now  described.  Thus  aluminum  and  oxygen  form  only  one  com- 
pound, alumina  j  but  this  resembles,  in  all  its  laws  of  combination 
and  crystalline  form,  oxide  of  chrome  and  peroxide  of  iron,  and 
hence  it  is  considered  to  be  a  compound  of  two  equivalents  of  metal 
and  three  of  oxygen,  and  its  formula  to  be  AI2O3. 

Sixth.  When  bodies  are  found  combined  in  proportions  expressed 
by  high  numbers,  they  are  generally  looked  upon  as  secondary  com- 
pounds, formed  by  the  reunion  of  others,  the  ratio  of  whose  elements 
are  simple.  Thus  lead  forms  with  oxygen  compounds  intermediate 
to  the  two  true  oxides  already  described,  the  one  containing  three 
equivalents  of  lead  and  four  of  oxygen,  the  other  four  of  lead  and 
five  of  oxygen  ;  these  consist  really  of  the  protoxide  and  peroxide 
united  in  the  proportions  shown  by  the  equations : 

Pb^Os^SPb.O.+Pb.Oa,  and  Pb304-2Pb.O.+Pb.02. 

In  like  manner,  between  the  two  proper  oxides  of  iron  there  inter- 
vene the  two  magnetic  oxides,  the  formulae  of  which  are  Fe^O^  and 
Fe304,  being  compounds  of  protoxide  and  peroxide,  as, 

FeA=2Fe.O.+Fe203,  and  Fe304=Fe.O.+Fe203. 

By  this  means  the  constitution  of  an  extensive  class  of  complex  bod- 
ies is  reduced  to  very  simple  forms. 

If  we  take  oxygen,  hydrogen,  chlorine,  and  nitrogen  in  the  pro 
portions  by  weight  which  correspond  to  their  equivalent  numbers, 
and  measure  the  volumes  which,  as  gases,  they  occupy,  an  exceed- 
ingly striking  relation  will  be  found  between  them,  the  volume  of 
oxygen  being  exactly  one  half  that  of  each  of  the  other  gases.  If, 
also,  we  heat  iodine  and  bromine  in  quantities  proportional  to  their 
equivalents  by  weight,  we  shall  find  that,  when  converted  into  va- 
pour, they  occupy  precisely  the  same  voliime  as  the  equivalent  of 
hydrogen  gas  at  the  same  temperature  and  pressure.  On  convert- 
ing into  gas  equivalent  weights  of  arsenic  and  phosphorus,  they  oc- 
cupy precisely  the  same  volume,  which  is  equal  to  that  of  the  equiv- 
alent of  oxygen  gas  5  and  by  similarly  treating  an  equivalent  of  sul- 
phur, its  volume  becomes  one  third  that  of  the  oxygen.  Finally, 
when  a  quatitity  of  mercury,  representing  its  equivalent  number,  is 
converted  into  vapour,  its  volume,  reduced  to  the  same  standard  of 
temperature  and  pressure,  is  four  times  that  of  oxygen,  and  double 
that  of  hydrogen  or  chlorine  gases.  It  hence  results,  that  although 
the  equivalent  weights  of  the  simple  bodies  may  be  totally  uncon- 
nected, and  may  range  within  very  extensive  limits,  yet  the  volumes 
which  these  equivalent  quantities  occupy  when  in  the  state  of  gas 
or  vapour,  have  a  very  simple  relation  to  one  another ;  thus,  taking 
the  equivalent  weight  of  oxygen  as  100,  and  its  equivalent  volume 
as  1,  the  proportion  of  the  other  bodies  mentioned  are ; 


214    EQUIVALENT    VOLUMES    OF   COMPOUND   BODIES. 


Name  of  Substance, 

Equivalent  Weight. 

Equivalent 
Volume. 

Sp.Gr.ofV^po,r. 

Oxygen      .     • 

1000 

1 

1102-6 

Hydrogen  .    • 
Chlorine     .    . 

12-5 
442-6 

2 
2 

68-8 
24700 

Iodine    .    .    . 

1579-5 

2 

8701-0 

Bromine     .     • 

978-3 

2 

53930 

Nitrogen    .     • 
Sulphur      .     . 
Phosphorus    . 
Arsenic      .     . 

175-0 
201-2 
3923 
940  1 

2 

1 
1 

9760 

•  6048-0 

4327-0 

10362-0 

Mercury     .    . 

1265-8 

4 

69690 

Not  merely  does  this  simple  proportion  of  equivalrat  volumes 
hold  among  the  simple  bodies,  but  it  determines  in  the  compounds 
which  they  form  an  equally  regular  constitution. 

The  volumes  of  the  gases  which  unite  are  necessarily  in  simple 
equivalent  proportion  to  each  other,  and  when  the  same  gases  unite 
in  more  than  one  proportion,  the  second  is  a  multiple  of  the  first.  In 
all  cases,  also,  where,  after  union,  a  condensation  of  volume  occurs, 
the  resulting  volume  is  simply  related  to  the  volumes  which  the 
constituents  had  occupied  before  combination.  Thus,  in  the  forma- 
tion of  water,  one  volume  of  oxygen  unites  with  exactly  two  of  hy- 
drogen, and  the  volume  of  watery  vapour  which  is  formed  is  equal 
to  that  of  the  hydrogen  employed.  To  form  ammonia,  one  volume 
of  nitrogen  unites  with  three  of  hydrogen,  and  the  four  volumes  are 
condensed  into  two  by  the  combination.  There  may,  therefore,  be 
arranged  for  the  various  bodies  which  assume  the  gaseous  form,  a 
series  of  equivalents  in  volume,  which  will  not  be  totally  unconnect- 
ed numbers,  like  those  of  the  equivalents  by  weight,  but  are  found 
to  be,  as  the  weights  should  become  if  the  suggestion  of  Proust  were 
verified,  simple  multiples  of  the  equivalent  of  some  standard  body 
which  may  be  selected,  as  oxygen  in  the  table. 


Name  of  the  Compound  Vapour. 


Water 

Nitrous  oxide   .     .     . 
Nitric  oxide      .     .     . 
Sulphurous  acid    .     . 
Sulphuric  acid  .     .     . 
Sulphuretted  hydrogen 
Muriatic  acid    .     .    . 
Hydriodic  acid  .     ,     . 
Hydrobromic  acid 
Ammonia     .... 
Arseniuretted  hydrogen 
Terchloride  of  arsenic 

Calomel 

Corrosive  sublimate  . 
Arsenious  acid  .  . 
Sulphuret  of  mercury 
Chloride  of  sulphur  . 
Protochloride  of  phosphorus 
Perchloride  of  phosphorus  . 


Formula. 


H.O. 
N.O. 
N.O2 
S.O2 
S.O3 
S.H. 
Cl.H. 


I.H. 

Br.H. 

N.H3 

AS.H3 

AS.CI3 

Hg2Cl, 

Hg.Cl. 

AS.O3 

Hg.S. 

S2CI. 

P.CP 

P.CI5 


1125 

275-0 

375-0 

401-2 

501-2 

213-7 

455  1 

1592-0 

990-8 

214-5 

9526 

2268-0 

2974-3 

1708-5 

1240- 1 

1467-0 

845-0 

1720-1 

2505-3 


Equivalent 
Volume  of 
Constituents. 


3 
3 

4 
7 

10 
7 
4 
4 
4 
4 
7 
7 
6 
8 
4 
7 
4 
7 

11 


Up.  Gr.  ol 
the  Vapour. 
Air=10000. 

620-2 
1527-3 
1039-3 
22106 
2761-9 
1177-0 
1269-5 
4385-0 
2731-0 

591-5 
2694-0 
6295-0 
82040 
9439  0 
136700 
5384-0 
4686  0 
4741  1 
4788-1 


The  simplicity  thus  shown  to  exist  between  the  volumes  of  the 
constituent  and  compound  vapour  enables  us  very  often  to  calculate 
beforehand  what  the  specific  gravity  of  a  vapo^ur  should  be,  and  thus 


SPECIFIC    GRAVITIES    OF    COMPOUND    VAPOURS.    215 

to  ascertain  how  closely  the  numbers  found  experimentally  by  the 
methods  described  in  the  first  chapter  may  approach  to  absolute 
correctness.  Thus,  to  calculate  the  specific  gravity  of  ammonia : 
it  is  formed  by  the  union  of  three  volumes  of  hydrogen  and  one  of 
nitrogen,  aiid  the  weights  of  these  volumes  being  as  their  specific 
gravities,  the  weight  of  the  ammonia  formed  should  be  976+(3x 
69)=  1183  if  the  four  volumes  of  constituents  were  condensed  into 
one ;  but  as  the  condensation  is  into  two,  the  specific  gravity  of 
the  ammonia  is  1183-^2=591-5,  as  given  in  the  table.  Sulphur 
and  hydrogen  unite  in  the  proportion  of  one  volume  of  sulphur  to 
six  of  hydrogen,  and  hence,  if  there  were  but  one  volume  of  result- 
ing gas,  the  specific  gravity  should  be  6648+ (6  X  69)=7062  j  but  as 
there  are  six  volumes  of  gas  formed,  the  true  specific  gravity  of  sul- 
phuretted hydrogen  is  7062H-6  =  1177.  The  general  rule  being  to 
multiply  the  specific  gravities  of  the  simple  gases  or  vapours  re- 
spectively by  the  volumes  in  which  they  combine,  to  add  those 
products  together,  and  then  to  divide  the  sum  by  the  number  of  vo]- 
umes  of  the  compound  gas  produced. 

By  the  application  of  this  principle,  we  may  often  decide  with 
great  probability  on  the  specific  gravity  which  certain  bodies  should 
have  in  the  state  of  vapour,  although  it  has  not  been  as  yet  pos- 
sible to  weigh  their  vapours  experimentally.  Thus  the  temperature 
at  which  antimony  is  volatile  is  so  high  that  the  specific  gravity  of 
its  vapour  may  possibly  never  be  determined  by  experiment ;  but 
the  chloride  of  antimony  resembles,  in  all  its  chemical  relations, 
chloride  of  arsenic,  and  there  is  the  greatest  probability  that  the 
constitution  of  the  two  are  alike  in  the  state  of  vapour.  Now  we 
know  that  chloride  of  arsenic  consists  of  six  volumes  of  chlorine 
and  one  volume  of  arsenic  vapour  condensed  into  four  volumes  ; 
and  hence,  if  we  multiply  the  specific  gravity  of  the  vapour  of  chlo- 
ride of  antimony,  which  is  8106-5,  by  four,  we  obtain  324260,  and 
subtracting  from  it  the  weight  of  six  volumes  of  chlorine  =14820, 
there  remains  17606,  which,  if  the  analogy  between  the  arsenic  and 
antimony  be  correct,  must  be  the  specific  gravity  of  the  vapour  of 
antimony  reduced  to  the  standard  of  air  =1000. 

Similar  principles  have  been  applied  to  the  determination  of  the 
specific  gravity  which  carbon  should  possess  if  it  were  converted 
into  vapour.  This  number  would  be  of  great  importance  in  all  cal- 
culations of  the  specific  gravities  of  the  vapours  of  organic  bodies, 
most  of  which  contain  carbon  as  an  element;  but,  unfortunately, 
there  is  no  volatile  body  so  similar'  to  carbon  as  that  its  analogies 
can  be  taken  as  a  guide,  and  hence  the  bases  of  the  calculated 
density  of  gaseous  carbon  are  purely  hypothetical.  Indeed,  chem- 
ists are  not  agreed  upon  the  precise  number,  some  making  it  the 
double  of  what  it  is  estimated  at  by  others.  If  we  look  upon  car- 
bonic acid  as  consisting  of  equal  volumes  of  vapour  of  carbon  and 
oxygen,  the  two  condensed  into  one,  the  specific  gravity  of  carbon 
is  1524-1 — 1102-6=421-5;  but  if  the  carbonic  acid  consist  of  two 
volumes  of  oxygen  and  one  of  carbon,  the  three  volumes  condensed 
into  two,  the  calculated  specific  gravity  of  the  latter  vapour  is 
3048-2— 2205-2=843-0.  On  the  first  idea,  the  carbonic  oxide  con- 
sists of  two  volumes  of  carbon  vapour  and  one  of  oxygen,  the  three 


216       CHEMICAL     AND     MOLECULAR     CONSTITUTION. 

condensed  to  two  (2x421-5  +  1102-6)-^2=972-8  ;  and  on  the  latter, 
of  equal  volumes  united  without  condensation  (843'0  +  1102'6)-7-2= 
972'8.  It  is  this  latter  view  which  I  adopt,  and  in  any  calculations 
that  may  occur  hereafter,  I  shall  consider  the  specific  gravity  of 
gaseous  carbon  as  843.  It  does  not  at  all  necessarily  follow  that 
the  true  specific  gravity  is  either  of  these  numbers,  as  it  may  be 
that  the  relations  by  volume  of  carbonic  acid  and  carbonic  oxide 
are  much  more  complex.  Before  the  specific  gravity  of  the  vapour 
of  sulphur  had  been  experimentally  determined,  it  was  considered, 
from  similar  theoretic  grounds,  to  be  2216,  but  it  is  actually  three 
times  as  great,  6648,  and  we  must  hence  not  reckon  too  implicitly 
on  the  relations  by  volume  at  present  given  for  the  gaseous  com- 
pounds of  carbon. 

In  the  combination  by  volume,  the  same  laws  of  multiple  propor- 
tion hold  as  in  combination  by  equivalents;  thus  the  compounds  of 
chlorine  and  oxygen,  which  are  by  weight  CI.  O.,  CI.O4,  CI.  O5,  and 
CI.  O7,  are  by  volume  two  of  chlorine  to  one,  to  four,  to  five,  and  to 
seven  volumes  of  o.  ygen  respectively,  and  so  in  all  other  instan- 
ces ;  and,  consequently,  all  remarks  that  have  been  made  regard- 
ing the  law  of  multiple  proportions  in  equivalents  by  weight,  apply 
to  combinations  of  equivalents  by  volume  also. 


CHAPTER  X. 

OF  THE  RELATIONS  OF  CHEMICAL  CONSTITUTION  TO  THE  MOLECULAR 
STEUCTURE  OF  BODIES. 

It  has  been  abundantly  shown,  throughout  the  preceding  portions 
of  this  work,  that  even  the  most  purely  physical  properties  of  a 
body  are  closely  connected  with  its  chemical  constitution  ;  and  that 
thus  the  density,  the  crystalline  structure,  or  the  electrical  relations 
of  a  substance,  or  the  manner  in  which  it  is  acted  on  by  heat,  may, 
by  affording  distinctive  characters,  or  by  influencing  its  affinities, 
become  necessary  to  its  chemical  history.  The  numerical  laws  of 
constitution  last  described  yield  additional  evidence  of  the  intimate 
relation  of  chemical  to  molecular  constitution ;  and  in  the  present 
chapter  I  purpose  to  conclude  the  description  of  the  general  histo- 
ry of  chemical  action,  by  an  account  of  such  principles  as  have 
been  advanced,  and  such  facts  as  have  been  discovered  illustrative 
of  this  connexion.     They  are  as  follow : 

1st.  The  connexion  between  the  molecular  constitution  and  the 
equivalent  numbers  of  bodies.     The  atomic  theory. 

2d.  The  connexion  between  the  crystalline  form  and  the  chemical 
equivalency  of  bodies.     Isomorphism. 

3d.  The  relation  of  constitution  to  composition.  Of  Dimorphism 
and  Isomerism.     The  theory  of  types. 

4th.  Of  chemical  action  independent  of  affinity.     Catalysis. 


THEATOMICTHEORY.  217 

SECTION  I. 
OF    THE   ATOMIC    THEORY. 

It  was  natural  that,  as  soon  as  the  remarkable  laws  of  combination 
discussed  in  the  last  chapter  had  been  discovered,  philosophers 
should  be  anxious  to  ascend  to  the  causes  in  which  they  had  their 
rise,  and  to  trace,  in  the  operation  of  some  one  general  principle, 
the  three  determinate  numerical  conditions  to  which  experiment 
proved  chemical  action  to  be  subjected  5  accordingly,  such  theoreti- 
cal views  were  promulgated  even  before  the  laws  of  combination 
were  fully  understood  ;  and  it  has  been  since  one  of  the  most  difficult 
tasks  of  the  philosophic  chemist  to  disentangle  the  real  and  practi 
cal  from  the  merely  speculative  portions  of  atomic  chemistry. 

For  Dalton,  in  promulgating  the  law  of  multiple  combination,  the 
most  beautiful,  as  well  as  the  most  extensive  principle  that  had  been 
conferred  on  chemistry  since  the  epoch  of  Lavoisier,  announced  it 
as  the  result  of  speculations  which,  though  in  their  general  nature 
true,  and  constituting  still  the  essential  basis  of  all  theories  of  chem- 
ical action,  were  yet  overlaid  by  a  tissue  of  hypotheses  so  irregular 
and  so  unnecessary,  that  for  a  long  time  the  real  dignity  and  excel- 
lence of  the  experimental  laws  were  underrated  and  misunderstood. 
These  accessory  speculations  have  now,  however,  passed  away,  and 
the  theory  of  combination  laid  down  by  Dalton  may,  in  all  its  essen- 
tial conditions,  be  very  briefly  expressed  as  follows : 

All  substances  are  supposed  to  be  constituted  of  particles  per- 
fectly indivisible,  and  hence  truly  atoms.  In  different  kinds  of  mat- 
ter, these  atoms  are  of  different  weights,  and  probably  of  different 
magnitudes ;  but  this  latter  quality  is  of  no  material  interest.  When 
bodies  combine  chemically,  their  combination  must  be  so  effected 
that  one  atom  of  one  unites  with  one  atom  of  another  j  or  one  of  the 
first  with  two,  or  three,  or  four  of  the  second ;  or  two  of  the  first 
with  three,  or  five,  or  seven  of  the  second ;  but  no  intermediate  de- 
grees can  possibly  occur,  for  the  atom  being  absolutely  indivisible, 
no  intermediate  degree  of  union  can  take  place.  The  relative 
weights  of  these  atoms  are  the  equivalent  numbers  of  the  bodies 
combined  5  eight  parts  of  oxygen  unite  with  one  part  of  hydrogen, 
by  weight,  to  form  water,  because  the  simplest  proportions  in  which 
they  can  unite  are  one  atom  of  each,  and  the  atom  of  oxygen  is 
eight  times  as  heavy  as  the  atom  of  hydrogen ;  eight  parts  of  oxygen 
are  equivalent  to  35-4i  parts  of  chlorine,  because,  when  an  atom  of 
hydrogen  leaves  the  atom  of  oxygen,  it  combines  with  an  atom  of 
chlorine  in  its  place,  which  is  heavier  than  that  of  oxygen  in  the 
proportion  of  35-4  to  8,  and  the  quantity  must  be  consequently  so 
determined.  When  a  second  atom  of  oxygen  combines  with  hy- 
drogen, it  being  equally  heavy  with  the  first,  doubles  the  quantity 
of  oxygen  which  the  equivalent  of  hydrogen  has  taken  up,  and,  as 
might  be  illustrated  by  any  series  of  examples,  introduces  as  a  ne- 
cessary consequence  the  law  of  multiple  combination. 

Such  is  the  atomic  theory  of  Dalton.  It  expresses  faithfully  the 
laws  of  combination  ;  1st,  the  law  of  definite  constitution  ;  2d,  the 
principle  of  equivalent  proportion  ;  and,  3d,  the  law  of  multiple  com- 

Ee 


218  PHYSICAL    AND     CHEMICAL     ATOMS. 

bination.  It  is  therefore,  even  in  this  form,  the  most  embracing  and 
perfect  generalization  that  has  ever  been  proposed  in  chemistry;  but, 
before  committing  ourselves  implicitly  to  its  adoption,  it  is  neces- 
sary to  examine  into  its  bases  with  some  detail. 

Dalton  assumes  that  matter  is  constituted  of  indefinitely  small 
particles,  atoms,  but  he  advances  no  proof  that  it  is  so  j  he  adopts, 
unreservedly,  that  side  of  the  discussion  which,  from  the  earliest 
ages,  has  divided  the  opinions  of  philosophers,  and  shows  that  on 
that  hypothesis  all  the  most  remarkable  phenomena  of  chemistry  can 
be  explained.  But  I  have  already,  in  the  first  chapter  of  this  work, 
pointed  out,  that  the  question  of  the  ultimate  constitution  of  matter 
is  now  no  nearer  its  solution  than  it  was  twenty  centuries  ago  ;  and 
I  will  now  proceed  to  show,  that  for  the  explanation  of  the  laws  of 
combination,  the  atomic  theory  of  Dalton  is  unnecessary,  or,  at  least, 
that  it  becomes  only  one  out  of  a  variety  of  molecular  conditions 
which  matter  may  assume.  In  the  first  place,  it  is  necessary  to  as- 
certain in  what  manner  the  relative  weights  of  the  atoms  of  bodies, 
if  they  really  exist,  are  to  be  determined. 

I  pointed  out  in  the  last  chapter  the  number  of  circumstances 
which  should  be  taken  into  account  for  the  determination  of  the 
equivalent  number  of  a  body ;  it  is  by  such  considerations  that  in 
similar  cases  the  atomic  weight  of  a  body  is  determined  ;  and  where 
the  idea  of  the  existence  of  such  ultimate  combining  molecules  is 
adopted,  the  atom  is  the  equivalent,  and  the  number  is  its  weight. 
If,  therefore,  the  theory  of  molecular  constitution  involved  chemical 
results  alone,  no  difficulty  would  occur  ;  but  when  we  consider  these 
atoms  as  building  up  the  mass,  and  conferring  upon  it  its  physical 
properties  at  the  same  time  that  they  produce  its  chemical  consti- 
tution, inconsistencies  are  found  which  must  prevent  our  coming 
too  hastily  to  a  conclusion. 

When  Gay  Lussac  first  determined  the  existence  of  those  simple 
relations  which  have  been  described  as  existing  between  the  volumes 
of  gases  which  combine  together,  it  was  considered  certain  that 
all  gases  contained  in  the  same  volume  the  same  number  of  atoms. 
The  gases  are  remarkable  for  all  possessing  the  same  physical  con- 
stitution. Their  relations  to  pressure  and  to  heat  are  governed  by 
the  same  law  in  all  cases,  which  can  be  best  explained  by  supposing 
that  in  the  same  space  they  contain  the  same  number  of  ponderable 
atoms,  set  at  equal  distances  from  each  other,  and  whose  material 
repulsion  is  expressed  by  the  same  law.  Hence,  when  one  volume 
of  chlorine  unites  with  one  of  hydrogen,  an  equal  number  of  atoms 
of  each  element  come  into  play,  and  an  atom  of  the  compound  con- 
sists of  an  atom  of  each  constituent.  But  here  a  difficulty  occurs ; 
the  chloride  of  hydrogen  which  results  occupies  two  volumes,  and 
yet  it  is  in  physical  properties  identical  with  the  hydrogen  or  chlo- 
rine ;  all  physical  evidence  would  lead  us  to  believe  that  muriatic 
acid  gas  contained  in  the  same  volume  the  same  number  of  atoms 
as  its  constituents,  but  the  most  positive  chemical  evidence  shows 
that  it  contains  but  half  so  many.  In  like  manner,  on  physical 
grounds,  there  should  be  the  same  number  of  atoms  in  the  same 
volume  of  oxygen  and  hydrogen ;  and  as  water  is  formed  by  the 
union  of  one  volume  of  oxygen  with  two  of  hydrogen,  it  should 


\ 
PHYSICAL     AND     CHEMICAL     ATOMS.  219 

consist  of  one  atom  of  oxygen  and  two  atoms  of  hydrogen  3  but  the 
most  perfect  chemical  evidence  we  possess  proves  that  water  is 
composed  of  an  equivalent  of  each  element.  The  number  of  chem- 
ical molecules  in  gases  is  different,  therefore,  for  each  gas ;  it  is  the 
combining  or  equivalent  volume  which  contains  equal  numbers  of 
chemically  equivalent  molecules  or  atoms,  and,  as  has  been  shown 
in  the  tables  in  the  last  chapter,  those  volumes  differ  remarkably  from 
one  gas  to  another. 

Another  physical  condition,  which  is  intimately  connected  with 
the  molecular  constitution  and  the  chemical  relations  of  bodies,  is 
their  spe'cific  heats,  on  the  remarkable  law  of  which,  regarding  the 
simple  bodies,  as  discovered  by  Dulong  and  Petit,  and  extended  to 
many  compound  bodies  by  Nauman  and  Avogadro,  I  have  already 
fixed  attention  (page  67).  If  we  look  upon  the  specific  heats  of  all 
the  ultimate  particles  of  simple  bodies  as  being  the  same,  we  should 
at  once  have  a  mode  of  determining  their  atomic  weights,  and  these 
should  coincide  with  the  equivalents  deduced  from  chemical  consid- 
erations. 

In  the  great  majority  of  cases,  the  atomic  weights  of  the  solid  sim- 
ple bodies,  deduced  from  their  specific  heats,  coincide  with  those 
adopted  from  chemical  considerations ;  and  in  some  of  the  excep- 
tional instances,  as  bismuth  and  silver,  there  is  doubt  as  to  the 
true  number,  which  may  be  fairly  interpreted  as  so  far  remaining 
neutral.  But  in  other  cases  we  find  that  it  completely  fails  ;  thus, 
the  atomic  weight  of  iodine,  deduced  from  its  specific  heat,  is  63*  1, 
while  there  is  no  doubt  but  that  its  chemical  equivalent  is  126'3, 
twice  as  much.  Also,  the  history  of  arsenic  and  phosphorus  is  so 
complete,  that  there  is  no  doubt  that  their  equivalents  are  75'4  and 
31*4«;  but  when  we  calculate  the  atomic  weights  from  their  specific 
heats,  we  find  as  the  result  for  arsenic  37*7,  and  for  phosphorus 
15*7,  that  is,  in  each  case  but  the  half  of  the  real  number.  In  the 
gases,  also,  there  is  complete  discordance  between  the  specific  heats 
and  the  chemical  equivalents,  no  matter  whether  we  consider  their 
purely  molecular  constitution,  by  which  they  should  have  an  equal 
number  of  atoms  and  equal  specific  heats  in  equal  volumes,  or 
whether  we  compare  their  combining  volumes  with  their  specific 
heats.  The  specific  heats  of  equal  volumes  (p.  69)  of  oxygen  and 
of  hydrogen  have  been  proved  by  Apjohn  to  be  as  808  to  1459, 
while  on  chemical  grounds  that  of  oxygen  should  be  double,  and 
on  molecular  considerations  the  same  as  that  of  the  hydrogen. 

It  follows,  from  what  has  been  said,  that  it  is  totally  impossible 
to  adopt  completely  the  opinion  of  Dalton,  that  bodies  are  composed 
of  ultimate  and  indivisible  particles,  which,  aggregating  together, 
give  origin  to  sensible  masses  of  the  same  nature  when  similar  par- 
ticles unite,  and  to  the  phenomena  of  chemical  combination  when 
the  union  is  between  particles  of  different  kinds;  I  adopt  fully  the 
idea  of  Dumas,  that  it  is  possible,  and,  indeed,  more  consonant  to 
experiment,  to  explain  all  the  laws  of  chemical  combination  quite 
independent  of  all  considerations  as  to  whether  the  masses  which 
combine  are  indivisible  or  the  reverse.  The  word  atom,  if  interpret 
ed  in  its  strict  and  proper  sense,  is  unnecessary,  and  may  be  inju 
rious  if  employed  with  any  vague  or  undefined  meaning. 


220   VARIOUS  ORDERS  OF  MOLECULAR  GROUPS. 

I  consider,  as  I  have  already  stated  (page  17),  that  sensible  masses 
of  matter  are  constituted  of  a  number  of  lesser  masses,  which  again 
may  be  made  up  of  similar  constituent  groups,  proceeding  down- 
ward to  any  extent,  but  still  without  involving  the  question  of  a  limit 
to  the  degree  of  possible  division.  One  class  of  these  groups  of 
particles  I  consider  to  be  represented  by  the  equivalent  numbers ; 
and  it  is  possible  that  these  numbers  may  indicate  the  manner  in 
which  the  chemically  combining  groups  may  be  supposed  to  subdi- 
vide themselves,  in  order  to  generate  a  set  of  groups  of  an  inferior 
class.  The  specific  heats  of  bodies  may  be  considered  to  have  ref- 
erence to  an  order  of  groups  of  particles  often,  but  not  ne*cessarily, 
coincident  with  those  which  combine  to  produce  chemical  com- 
pounds ;  and  the  third,  probably  the  most  remote,  engaged  in  the  or- 
dinary properties  of  matter,  may  be  such  as,  being  uniformly  distrib- 
uted in  the  gaseous  form,  confers  upon  those  bodies  the  properties 
which  characterize  mechanically  that  condition,  and  are  independent 
alike  of  the  chemical  properties  and  specific  heats  which  appertain 
to,  and  are  exhibited  by,  groups  of  a  more  complex  structure  and 
superior  order. 

From  this  point  of  view  I  contemplate  the  atomic  theory  j  for 
these  groups,  engaged  in  chemical  combination,  and  indivisible  by 
chemical  means,  are,  in  all  chemical  relations,  atoms.  Their  relative 
weights  are  our  equivalent  numbers.  From  their  union  the  laws  of 
definite  and  multiple  combination  directly  follow.  But,  when  we 
remove  them  from  their  proper  sphere,  when  we  subject  them  to 
physical  forces,  we  may  dissect  them,  and  separate  them  into  other 
groups ;  or  we  may  unite  many  of  them  together  to  form  a  larger 
group,  characterized  by  the  relations  to  heat  and  to  pressure  that 
have  been  already  stated,  but  no  longer  the  group  or  atom  engaged 
in  chemical  operations.  Thus  the  group  which  is  acted  on  by  the 
heat  when  a  gas  expands,  occupies  only  half  the  space  in  muriatic 
acid  that  the  chemical  group  takes  up ;  but  in  gaseous  sulphur  it 
occupies  three  times  the  space  of  the  chemical  atom.  In  gaseous 
oxygen,  arsenic,  and  phosphorus,  the  mechanical  atom  is  of  the 
same  volume,  but  the  chemical  atom  only  of  half  the  volume  that 
fhey  respectively  occupy  in  hydrogen,  chlorine,  and  iodine.  In 
most  of  the  simple  bodies  the  same  groups  produce  chemical  com- 
bination, and  determine  the  specific  heat  j  but  in  iodine,  in  arsenic, 
and  in  phosphorus,  the  group  which  enters  into  chemical  combina 
tion  contains  two  of  the  groups  which  are  pointed  out  from  the 
specific  heats  of  these  bodies. 

I  shall  frequently  employ  the  word  atom  in  the  course  of  the  fol- 
lowing page^,  but  I  do  so  only  as  an  abbreviation  for  the  terms 
equivalent  quantity  or  combining  masses.  Of  the  ultimate  particles  of 
matter,  or  true  atoms,  we  know  nothing  j  and  all  of  the  discussions 
that  have  taken  place,  from  the  earliest  and  vaguest  speculations  of 
Democritus  or  Leucippus,  to  the  modern  experiments  of  WoUaston 
and  Faraday,  must  be  considered  as  absolutely  without  influence  on 
the  positive  decision  of  the  question. 


RELATION     OF     CONSTITUTION     TO     FORM.       221 


SECTION  II. 
OF    ISOMORPHISM. 

The  general  principles  of  the  isomorphism  of  crystallized  sub- 
stances have  been  already  noticed,  with  relation  to  the  fact  of  their 
substitution  for  each  other  (page  31),  and  of  the  advantage  with 
Avhich  this  property  may  be  applied  to  determine  equivalent  num- 
bers (page  212)  j  it  now  remains  to  study  this  character,  as  indica- 
tive of  the  molecular  constitution  of  the  body. 

It  must,  in  the  first  place,  be  carefully  observed,  that  identity  of 
crystalline  form  does  not  imply  similar  chemical  constitution,  un- 
less under  limiting  circumstances,  which  require  to  be  studied  with 
great  care.  The  principle  upon  which  all  subsequent  reasoning 
must  rest  is,  that  in  proportion  as  the  structure  of  the  crystal  be- 
■comes  more  complex,  and  the  conditions  necessary  for  its  forma- 
tion, consequently,  more  varied,  the  greater  probability  is  there 
that  two  bodies  shall  not  assume  exactly  the  same  form,  unless  their 
chemical  constitution  and  the  molecular  arrangement  belonging  to 
it  be  the  same,  or,  at  least,  similar  in  both.  Hence,  in  the  regular  sys- 
tem, there  can  be  no  inference  whatsoever  drawn  with  regard  to 
constitution  from  the  crystalline  form  alone.  Bodies  the  most  con- 
trasted possible  in  their  properties  and  composition  have  identical 
external  figures,  as  fluor  spar,  bismuth,  alum,  sulphuret  of  lead,  com- 
mon salt.  The  conditions  of  molecular  arrangement  for  the  forms 
belonging  to  this  system  being  the  easiest  possible  to  fulfil,  the 
greatest  variety  in  the  number  and  grouping  of  the  chemical  con- 
stituents is  allowable. 

In  the  other  systems  of  crystallization,  where  the  double  refrac- 
tion and  the  rings  produced  by  polarized  light,  transmitted  along 
their  principal  axis,  indicate  a  much  greater  complexity  of  struc 
ture,  it  becomes  highly  improbable  that  the  molecules  of  two  bod- 
ies shall  be  so  similar  to  each  other  as  to  produce  identity  of  crystal- 
line form,  unless  there  is,  if  the  body  be  compound,  a  similarity  of 
composition,  or,  if  the  body  be  simple,  such  similarity  of  properties 
as  brings  the  two  into  the  same  group  in  a  natural  classification. 
This  probability  increases  with  the  complexity  of  molecular  struc- 
ture of  the  crystals. 

The  isomorphism  of  compound  bodies  has  been  explained  upon 
the  supposition  that,  in  such  cases,  the  replacing  elements  were 
themselves  isomorphous,  and  hence  might  change  places  without 
disturbing  the  mechanical  arrangement  of  the  other  components  of 
the  crystal.  Thus,  in  the  sulphuric,  chromic,  selenic,  telluric,  and 
manganic  acids,  which  contain  each  three  equivalents  of  oxygen, 
the  molecules  of  sulphur,  chrome,  tellurium,  selenium,  and  manga- 
nese have  all  the  same  form.  The  perfect  determination  of  wheth- 
er those  elements  are  really  thus  isomorphous,  is  very  difficult,  from 
the  fact  of  comparatively  very  few  being  crystallizable.  Thus  tel- 
lurium and  sulphur  are  those  of  which,  alone,  we  know  the  crystal- 
line form,  for  the  only  crystals  of  selenium  that  have  been  observ- 
ed are  microscopic  and  imperfect,  and  neither  chrome  nor  manga- 
nese can  be  had  crystallized  at  all.     We  must,  therefore,  be  guided 


222  ISOMORPHISM     OF     COMPOUND     BODIES. 

by  analogy  in  such  cases ;  and  if  we  examine  another  group  of  com- 
pounds into  which  chrome  and  manganese  enter,  we  find  that  Crg 
O3  and  Mn203  are  isomorphous  with  FejOa,  and  Mn.O.  and  Fe.O.  are 
isomorphous  with  Cu.O.  Now  we  here  arrive,  by  a  chain  of  iso- 
morphous conditions,  at  a  metal  which  may  be  obtained  crystallized, 
but  the  crystalline  form  of  copper  is  always  one  of  the  regular  sys- 
tem, as  the  cube,  octohedron,  rhombohedron,  dodecahedron,  «Scc.  ; 
while  sulphur,  with  which  it  should  be  isomorphous,  if  this  princi- 
ple were  absolutely  true,  crystallizes  in  two  forms,  of  which  one  be- 
longs to  the  oblique  prismatic,  and  the  other  to  the  right  prismatic 
system  j  while  tellurium  belongs  to  the  rhombohedral  system,  af- 
fecting a  totally  different  form  altogether.  Numerous  other  instan- 
ces might  be  taken ;  thus  the  periodic,  perchloric,  and  permanga- 
nic acids  are  isomorphous  (I.O7,  CI.O7,  and  MngO;),  while  the  ele- 
ments themselves  are  certainly  not  necessarily  isomorphous,  as 
iodine  belongs  to  the  right  prismatic  system.  Also  the  isomorphx 
ism  of  the  phosphoric  and  arsenic  acids  (P.O5  and  As.O.)  is  one 
of  the  best  examples  that  has  been  found  ;  but  phosphorus  and  arse- 
nic are  so  far  from  being  isomorphous,  that  phosphorus  crystallizes 
in  the  regular,  and  arsenic  in  the  rhombohedral  system.  The  prin- 
ciple that  compound  bodies  are  isomorphous,  because  their  repla- 
cing elements  have  necessarily  the  same  figure,  is  therefore  one 
which  cannot  be  received  in  science. 

Another  idea  suggested  for  the  explanation  of  the  phenomena  of 
isomorphism  is,  that  the  crystalline  form  of  a  body  is  completely 
independent  of  its  chemical  composition,  and  is  produced  only  by 
the  number  of  ultimate  particles  or  atoms  by  which  it  is  made  up. 
Thus  alum  has  the  same  form,  whether  it  contains  aluminum  or  iron, 
or  manganese  or  chrome,  not  because  their  particles  have  the  same 
figure,  but  because,  in  all  these  cases,  the  molecule  of  alum  is  made 
up  of  the  same  number  (71)  of  simple  atoms.  This  idea  is,  however, 
even  less  tenable  than  the  former ;  for  it  supposes  that  we  have  ar- 
rived at  the  ultimately  simple  bodies,  the  true  elements,  which  is  a 
very  unphilosophical  assumption ;  and  according  to  it,  bodies  could 
replace  each  other  only  when  they  were  all  simple  or  all  of  the  same 
degree  of  composition,  which  is  not  the  case ;  and  also  among  the 
simple  bodies,  that  the  replacement  should  be  always  by  an  equal 
number  of  ultimate  molecules,  which  is  also  negatived  by  experi- 
ment. Thus  we  find  that  an  equivalent  of  a  simple  body,  K.,  is  re- 
placed by  a  group  of  five  equivalents,  N.H4,  and  that  the  simple  atom, 
CI.,  is  replaced  by  the  two  atoms  Mua.  This  suggestion  cannot,  there- 
fore, be  considered  as  satisfactory,  and  we  must  examine  farther 
into  the  conditions  of  isomorphous  replacement  before  we  attempt 
the  farther  discussion  of  the  source  from  whence  it  has  its  rise. 

It  is  necessary  first  to  study  the  crystalline  relations  of  the  unde 
composed  bodies,  both  so  far  as  they  have  been  really  observed,  and 
as  they  generate  similar  compounds  which  are  isomorphous.  The 
simple  bodies  which  are  known  to  crystallize  are  : 


ISOMORPHOUS     GROUPS. 


223 


Regular  System. 
Carbon. 
Phosphorus. 
Selenium. 
Copper. 
Silver. 
Gold. 
Platinum. 
Mercury. 
Bismuth. 
Titanium. 
Lead. 


Rhomhohedral, 
Carbon. 
Tellurium. 
Arsenic. 
Antimony. 

Right  Prismatic. 
Sulphur. 
Iodine. 

Oblique  Prismatic. 
Sulphur. 


It  is  thus  seen  that,  of  the  simple  bodies  which  may  be  obtained 
crystallized,  two  thirds  crystallize  in  the  regular  system,  which,  as 
already  noticed,  prevents  our  resting  upon  their  forms  any  chemical 
reasoning ;  and  the  bodies  whose  isomorphous  equivalency  is  best 
established,  are  not  found  to  belong  even  to  the  same  system.  Car- 
bon and  sulphur  are  known  also  to  have  each  two  forms  of  diiBTerent 
systems,  and  to  be  thus  dimorphous.  It  must  be  observed,  however, 
that  the  assumption  of  the  forms  of  the  regular  system  by  so  many 
of  the  simple  bodies,  particularly  among  the  metals,  may  arise  from 
circumstances  such  as  confer  the  external  cubical  figure  on  analcime 
or  boracite,  and  that  their  internal  structure  may  be,  in  reality,  more 
complex,  and  their  arrangement  different ;  for  the  metals  do  not  reflect 
light  as  other  bodies  of  the  regular  system  do ;  they  change  it  into 
the  state  of  elliptical  polarization  j  and  in  the  only  case  where  light 
can  be  examined,  after  having  been  refracted  through  a  metal,  that 
of  gold  leaf,  it  is  found  to  be  elliptically  polarized  also.  The  dia- 
mond resembles  the  metals  in  this  property,  and  is  found  sometimes 
to  possess  double  refraction,  which  should  belong  also  to  the  metals, 
probably,  if  their  nature  allowed  it  to  be  tried.  The  cubic  crystals 
of  gold,  copper,  and  bismuth,  the  octohedrons  of  lead,  silver,  and 
zinc,  may  therefore  belong  to  the  square  or  right  prismatic  systems, 
the  three  axes  being  equal  among  each  other,  and  hence  the  iso- 
morphism of  the  simple  bodies  be  rendered  still  less  probable. 

The  examples  of  isomorphism  in  compound  bodies,  which  are  most  deserving  ot 
attention,  are  the  following : 


Sulphuric  acid 
Telluric  acid  . 
Selenic  acid  . 
Chromic  acid  . 
Manganic  acid 


Magnesia 

Protoxide  of  iron  .  . 
Protoxide  of  manganese 
Oxide  of  copper  .  .  . 
Protoxide  of  cobalt  .  . 
Protoxide  of  nickel  .  . 
Oxide  of  zinc  .... 
»      Oxide  of  cadmium    .    . 


These  acids,  the  composition  of  which 
is  similar  in  all,  form  salts,  which,  when 
they  contain  the  same  base,  and  the 
Cr  0^  Tsame  proportion  of  base  and  of  water  of 
Mn  n^  crystallization,  have  the  same  crystalline 
^"•^^'yform. 


S.O3 
Te.Og 
Se.O, 


GROUP 

Mg.O 
Fe.O 
Mn.O 
Cu.O 


These  protoxides  combine  with  acids 
and  form  salts,  which,  when  in  the  same 
degree  of  saturation  with  base  and  water 


QqQ   /*of  crystallization,  have  the  same  form. 


Ni.O. 
Zn.O. 
CdO 


The  sulphates  of  these  oxides  combine 
with  sulphate  of  potash  to  fonn  isomorph- 
ous double  salts. 


224  ISOMORPHOUS     GROUPS. 

GROUP    III. 

Sesquioxide  of  iion  ....  Fe203^  These  sesquioxides,  combined  with 
,  Sesquioxide  of  manganese    .     .  Mn203  I  sulphuric  acid,  with  sulphate  of  potash, 

Oxide  of  chrome Cr203  [and  with  water,  form  the  different  spe- 

Alumina AI2O3  7  cies  of  alum,  which  have  all  the  octohe- 

dral  form.    They  are  themselves  also  isomorphous. 

GROUP   IV, 

Potash K.O.  -N      These  fixed  alkalies  may  be  substitu- 

Soda Na.O.  I  ted  for  each  other  in  the  different  spe- 

Hydrated  ammonia  ....  N.H3H.O.  r  cies  of  alum.  The  hydrated  ammonia. 
Hydrate  of  lime Ca.O.H.O.;  H.O.N.H3  (often  called  oxide  of  ammoni- 
um, N.H4O.),  is  truly  isomorphous  with  potash  in  all  its  compounds  ;  but  it  is  only 
rarely  that  the  compounds  containing  soda  appear  to  have  the  same  form.  In  min 
erals,  and  in  some  forms  of  alums,  potash  is  replaced  by  an  atom  of  any  oxide  in 
Group  II.,  united  with  an  atom  of  water,  as  hydrate  of  hme,  or  by  two  atoms  of 
such  compound  without  water. 

GROUP    V, 

Phosphoric  acid P.O5  ^     These  acids  combine  with  bases  in 

Arsenic  acid AS.O5  5  different  proportions  to  form  each  three 

classes  of  salts,  between  which  respectively  the  isomorphism  is  complete.  It  was 
by  the  study  of  the  forms  of  the  corresponding  arseniates  and  phosphates  that  Mit- 
scherlich  first  established  the  principle  of  isomorphism,  although  the  true  laws  of 
their  constitution  escaped  his  notice,  and  were  only  brought  into  view  by  the  later 
excellent  researches  of  Graham.  Even  now  there  is  no  example  of  isomorphism 
between  two  complete  series  of  compounds  so  well  established  as  that  of  the  ar- 
seniates and  phosphates. 

GROUP    VI. 

Perchloric  acid C1.07^      The  corresponding  salts  of  these  acids 

Permanganic  acid Mn207  >are  truly  isomorphous,  and  this  gi-oup  af- 

Periodic  acid LO7  j  fords  an  example  of  a  form  to  which  I 

shall  recur,  that  of  one  equivalent  of  one  body  being  replaced  by  two  of  another,  as 
CI.  by  Mng. 

GROUP    VII. 

Sulphuret  of  antimony    .     .    .     .  Sb.Sa^      These  bodies,  which  are  found  crystal- 

Sulphuret  of  arsenic As.Ss  >lized  in  nature,  have  the  same  form. 

vSulphuret  of  bismuth  ....  Bi2S3  /  The  oxide  of  antimony  and  the  arsenious 
acid,  Sb.Os  and  AS.O3,  though  they  are  not  found  crystallized  in  the  same  form,  ap- 
pear to  replace  each  other  in  some  salts  without  changing  its  figure,  and  may, 
therefore,  be  sometimes  isomorphous. 

GROUP    VIII. 

Stannic  acid Sn.02 )     These  are  found  native  crystallized  in 

Titanic  acid Ti.02  5  the  same  form. 

There  are  many  other  cases  in  which  similarity  of  crystalline  form  has  been  ob- 
served between  bodies  of  more  or  less  analogous  constitution  ;  but  as  here  I  wish 
to  bring  forward  only  a  sufficient  number  of  the  most  remarkable  examples  of  the 
principle,  I  shall  postpone  for  the  present  the  consideration  of  the  remainder. 

The  principle  of  isomorphism,  as  thus  described,  has  been  sup- 
posed to  require  that  the  angles  of  the  crystals  of  the  isomorphous 
bodies  should  be  truly  equal,  which  they  are  not  found  really  to  be, 
for  even  in  the  best  examples  taken  slight  differences  appear.  Thus, 
in  the  carbonates  of  lime  and  magnesia,  the  angles  of  the  rhombs 
differ  by  2°  36' ;  in  the  sulphates  of  zinc  and  magnesia  they  differ 
by  38' ;  in  the  sulphates  of  barytes  and  strontia  the  difference  is  2^ 
48'.  To  express  this,  the  word  plesiomorphism^  indicating  that  such 
crystals  are  not  exactly,  but  nearly,  of  the  same  form,  has  been 
proposed  ;  but  it  is  totally  useless,  as  absolutely  isomorphous  forms 
would  then  be  extremely  rare.     It  is  easy  to  understand  that  slight 


ISOMORPHISM  IMPORTANT  TO  THE  CHEMIST.  225 

changes  in  external  circumstances  might  prevent  the  absolute  iso- 
morphism of  two  bodies,  particularly  as  it  is  found  that  the  value 
of  the  angles  in  different  specimens  of  even  the  same  substance  is 
liable  to  fluctuation  even  to  nearly  a  degree.  I  apprehend  thai  we 
must  seek  the  cause  of  these  plesiomorphic  differences  in  the  pecu- 
liar circumstances  under  which  the  body  forms,  particularly  with 
regard  to  temperature  j  for  when  a  crystallized  body,  not  of  the  reg- 
ular system,  is  heated  or  cooled,  it  expands  in  different  degrees,  ac- 
cording to  the  direction  of  its  axis,  and  may  even  contract  in  one 
direction  while  it  is  expanding  in  another  j  thus,  when  carbonate  of 
lime  is  heated  from  32^  to  212^,  the  linear  expansion  in  the  direction 
of  the  principal  axis  is  0*001961,  while  in  the  direction  of  each  hor- 
izontal axis  a  contraction  of  0*00056  occurs  ;  in  consequence  of  this, 
the  obtuse  angle  of  the  rhomb,  which  at  50^  Fah.  is  equal  to  105° 
4',  becomes  more  acute  by  8^',  and  the  acute  angles,  which  are  74° 
54'  15",  become  more  obtuse  in  a  corresponding  degree.  Hence,  if 
we  heated  or  cooled,  through  a  certain  range  of  temperature,  the 
various  crystallized  bodies  of  that  group,  they  might  be  brought  to 
coincide  absolutely  in  form,  and  possibly,  when  at  first  generated, 
they  were  thus  coincident ;  but  by  change  of  figure,  when  brought 
to  ordinary  temperatures,  the  small  plesiomorphic  differences  may 
have  occurred. 

Isomorphism,  considered  as  thus  sketched,  affords  to  the  chemist 
the  most  valuable  criterion  at  present  at  his  disposal  for  determin- 
ing those  substances  which  replace  each  other  most  truly  in  com- 
bination ;  and  where  a  number  of  bodies  are  so  connected  by  exter- 
nal form,  very  important  conclusions  may  be  obtained  as  to  the  in- 
ternal arrangement  of  their  constituents.  In  this  manner  it  has 
been  satisfactorily  established,  that  bodies  may  replace  each  other 
in  proportions  quite  different  from  their  ordinary  equivalents,  and 
thus  pass,  as  it  were,  by  a  doubling  or  trebling  of  their  atomic 
weights,  into  a  different  natural  group  j  and  that  even  two  bodies, 
combined  in  an  equivalent  of  each,  may  form  a  complex  group,  ca- 
pable of  being  substituted  for  one  of  simpler  structure.  Thus  an 
equivalent  of  chlorine  is  replaced  by  two  equivalents  of  manganese ; 
mi  equivalent  of  silver  is  replaced  by  two  equivalents  of  copper  j  an 
equivalent  of  soda  or  of  potash  is  replaced  by  two  equivalents  of 
lime,  or  of  one  of  lime  and  one  of  water,  or  by  one  of  Ihne  and  one 
of  oxide  of  manganese  or  of  iron,  or  by  ammonia  and  water  united 
to  each  other,  or  to  an  equivalent  of  a  protoxide  of  the  magnesian 
group.  By  such  observations  we  obtain  the  foundations  of  a  philo- 
sophical classification  of  bodies,  with  which  the  analogies  drawn 
from  purely  chemical  characters  are  found  remarkably  to  corre- 
spond. 

But  it  is  important  to  ascertain  whether  the  isomorphism  of  various  bodies  rs- 
tabhshes  necessarily,  or  even  probably,  in  the  absence  of  other  reasons,  grounds  for 
assimilating  the  formulae  of  the  bodies,  or  imagining  that  their  chemical  constitu- 
ents are  equivalent  and  are  arranged  in  the  same  way.  This  is  a  point  which  has 
been,  as  I  consider,  much  misunderstood,  and  has  led  to  some  error  and  confusion. 
Thus  anhydrous  sulphate  of  soda  crystallizes  in  the  same  form  as  perchlorate  of 
barytes  and  permanganate  of  barytes  ;  and  if  it  be  necessary,  as  a  consequence  of 
isomorphism,  that  these  bodies  should  have  similar  constitutions,  we  must  change 
the  formula,  S.O3  .  Na.O.  into  S2O7 .  Na20.,  in  order  to  make  it  resemble  Mn207 . 
Ba.O.    This  requires  us  to  compare  the  sulphates  whose  elements  are  most  oow. 

Ff 


226   PRINCIPLES   OF    ISOMORPHOUS   REPLACEMENT. 

erfully  united,  with  some  of  the  most  easily  decomposed  salts  that  we  know ;  it  re- 
quires us  to  consider  the  alkalies  as  being  suboxides,  which  is  opposed  by  every 
circumstance  in  their  history ;  and  it  requires  us  to  consider  two  equivalents  of  so- 
dium as  being  equivalent  to  one  of  barium,  for  which  no  other  evidence  can  be  had 
from  other  examples.  But,  again,  the  anhydrous  sulphate  of  soda  is  isomorphous 
with  sulphate  of  silver,  and  hence  the  formula  of  this  last  should  be  S2O7 .  Ag-aO., 
which  is  so  totally  unsupported  by  other  evidence  that  it  has  been  proposed  to  sub- 
divide the  atomic  weight  of  silver  and  sodium,  for  the  purpose  of  explaining  the  iso- 
morphism of  Cu2  and  Ag.  These  examples  are  sufficient  to  show  how  unphilosoph- 
ical  is  the  attempt  at  rashly  inverting  the  principle  of  isomorphism,  and  seeking  to 
deduce,  as  a  necessary  consequence  of  the  mere  similarity  of  form,  similarity  of 
chemical  constitution.  Bodies  of  similar  chemical  constitution  affect  the  same 
crystalline  form ;  but  bodies  of  the  most  diverse  natures  may  have  the  same  crys- 
talline form  also.  Even  without  speaking  of  the  regular  system,  where  fluor  spar 
and  alum,  Ca.F.  and  K.O.  .  S.O3-I-AI2O3  .  3S.03-f  24H.O.,  have  the  same  form,  we 
find  numerous  examples  of  this  fact ;  nitrate  of  soda  and. carbonate  of  lime  are  iso- 
morphous in  the  rhorabohedral  system,  and  nitrate  of  potash  and  carbonate  of  lead 
in  the  right  prismatic  system ;  the  chemical  constitution  of  the  formulae  N.O5 .  Na.O., 
and  C.O2  .  Ca.O.,  and  that  of  the  formulae  N.O5  .  K.O.,  and  C.O2  .  Pb.O.,  are 
widely  different,  but  the  forces  by  which  the  assumption  of  crystalline  form  is  gov- 
erned are  alike.  Even  in  these  instances  the  attempts  at  generalizing  the  chemical 
formulae  have  been  tried,  and  the  nitrates  of  soda  and  potash  have  been  written 
N.Oe  K.  and  N.Oe .  Na.,  with  which  the  formulae  of  the  carbonates,  when  doubled, 
C206Ca2  and  C206Ba2,  have  been  compared.  In  this  way  one  equivalent  of  soda  is 
made  isomorphous  with  two  of  barytes,  while  by  a  former  and  similar  reasoning, 
one  of  barytes  was  made  isomorphous  with  two  of  soda.  Bisulphate  of  potash, 
K.O.  .  S.O3-I-H.O.  .  S.O3,  crystaUizes  in  two  forms,  one  of  which  is  that  of  sul- 
phur, a  simple  body,  and  the  other  of  which  is  that  of  feldspar,  K.O.  .  Ss-j-AkOs  . 
3S03.    Here,  in  neither  case  is  there  the  shghtest  similarity  of  constitution. 

The  circumstances  of  isomorphous  replacement  may  be  reduced 
to  the  following  simple  propositions,  with  which  I  shall  terminate 
the  subject : 

1st.  Similarity  of  crystalline  form  requires  that  the  molecular 
structure  of  the  bodies  shall  be  alike,  but  has  no  necessary  reference 
to  the  chemical  nature  or  composition  of  these  molecules.  Exam- 
ples.— Nitrate  of  soda  and  carbonate  of  lime,  sulphate  of  soda  and 
perchlorate  of  barytes,  bisulphate  of  potash  and  sulphur. 

2d.  When  the  physical  molecules  consist  of  chemical  elements 
which  follow  the  same  laws  of  combination,  and  which  belong  to 
the  same  chemical  family,  the  similarity  of  molecular  structure  is 
most  completely  and  most  easily  produced,  and  such  crystals  are 
isomorphous.  Examples. — Sulphate  of  zinc  and  sulphate  of  magnesia, 
carbonate  of  lime  and  carbonate  of  zinc,  sulphate  of  barytes  and  sul- 
phate of  strontia. 

3d.  But  identity  of  molecular  structure  may  result  from  the  ag- 
gregation of  substances  the  most  different  in  their  chemical  relations, 
and  hence  isomorphous  bodies  are  not  necessarily  of  similar  chem- 
ical constitutions. 

4th.  As  the  influence  of  the  chemical  constitution  does  not  extend 
to  the  absolute  determination  of  the  molecular  structure,  a  body, 
chemically  the  same,  may  assume  incompatible  crystalline  forms, 
and  so  become  dimorphous  ;  but  as  the  chemical  structure  influences 
the  molecular  arrangement  in  some  degree,  dimorphous  bodies, 
which  are  isomorphous  in  one  form,  are  generally  so  in  the  other, 
they  are  isodimorphous.  Examples. — Sulphur,  bisulphate  of  potash, 
nitrate  of  potash  and  carbonate  of  lime,  garnet  and  idocrase,  arse- 
nious  acid  and  oxide  of  antimony. 

5th.  We  cannot  assert  that  the  similarity  of  form  of  truly  isomorph- 


OF     DIMORPHISM     AND     ISOMERISM.  227 

ous  bodies  results  from  the  isomorphism  of  their  elements  ;  for, 
BO  far  as  our  observation  goes,  their  simple  constituents  are  not 
necessarily,  or  even  usually  isomorphous.  Examples. — Arseniates 
and  phosphates,  sulphates  and  seleniates. 

6th.  We  cannot  assert  that  isomorphism  results  from  the  aggre- 
gation of  the  same  number  of  simple  molecules  j  for  we  do  not 
know  what  bodies  are  truly  simple,  nor  do  we  know,  without  doubt, 
that  we  can  value  the  relative  number  of  atoms  present ;  but,  even 
in  the  existing  state  of  our  knowledge,  we  have  numerous  exam- 
ples of  bodies  truly  isomorphous  which  contain  an  unlike  number 
of  atoms  according  to  our  present  ideas.  Examples. — Potash  and 
ammonia,  natrolite  and  mesotype,  sulphur,  feldspar,  and  bisulphate 
of  potash. 

Finally.  Isomorphism  does  result  from  the  aggregation,  according 
to  the  same  laws,  of  similar  molecular  groups,  which  are  most  gen- 
erally formed  by  the  reunion  of  similar  chemical  substances  in  the 
same  state  of  combination. 

SECTION  III. 

OF   DIMOEPHISM   AND    ISOMERISM,    AND    OF    THE    THEORY   OF    TYPES. 

The  fact  of  the  same  body  being  capable  of  crystallizing  in  forms 
belonging  to  two  different  systems  has  been  already  frequently  re- 
ferred to,  but,  for  convenience  of  reference,  a  more  detailed  list  of 
such  cases  is  here  inserted,  taken  from  Professor  Johnston's  excel- 
lent report  on  the  subject  made  to  the  British  Association. 


228 


LIST     OF     DIMORPHOUS    BODIES. 


I.  Elementary  bodies 
Sulphur  .    , 


Carbon 


Symbol  or  Form. 


II.  Bi-elementary  Compounds : 
Dioxide  of  Copper    .  A  l 


B 


Disulphur.  of  Copper  A 


:i 


Sulphuret  of  Silver  .  A 

1 .  B 

Sulph.  of  Manganese  A 


Bisulphuret  of  Iron 


i\ 


A 
B 

Biniodide  of  Mercury  A 

B 

Bichlor.  of  Mercury  .  A 

.  B 

Arsenious  acid 


.  A> 
.  Bf 


Oxide  of  Antimony  .  A  \ 

.  B  S 

III.  Compounds  of  2  Elements : 
Carbonate  of  Lime   .  A  \ 

.  B^ 

Carbon,  of  Magnesia  A  ) 

B  S 

A^ 


Carbonate  of  Iron 

Carbonate  of  Lead 

Nitrate  of  Potash 

Chromate  of  Lead 

IV.  Compounds  of  A  or  mare 
Eh 


laments : 
Sulphate  of  Nickel  .  A 

.  B 

Seleniate  of  Zinc     .  A 

.  B 

Bisulphate  of  Potash  A 

_   B 

Biphosphate  of  Soda  A 


a  A) 

-  bS 


Garnet A 

Idocrase 6 

Baryto-Calcite  .  A 


Sulphato-  Tricarbon-       i 
ate  of  Lead       .    .       S 


S. 
C. 

CujO. 

Cu.S.orCuaS. 

Ag.S.  or  AgaS. 
Mn.S. 
Fe.Sz. 
Hg.Ia. 
Hg.Cla. 
AS2O3. 
SbjOj. 

Ca.O.+C.Og. 
Mg.O.+C.Os. 
Fe.0.+C.02. 
Pb.O.+C.Og. 
K.O.+N.Os. 
Pb.O.+Cr.Os. 

Ni.O.+S.03+7H.O. 
Zn.O.+Se.03+7H.O. 


K.O.+S.Oa+H.O.+S.Oj 

Na.O.+P2  05+4H.O. 
or  Na.H2P.+2H. 


Ca,si.+— 


Si. 


Fe. 


Pb.S.+3Pb.C. 


Crystalline  Form. 


j  Rt.  Rh.  Pr.,  M.  on  M.  101-59,  Haid. 
\  Oblique  Rh.  Pr.  of  90°  32',  M. 
I  Reg.  Octohedron. 
I  Rhombohedral. 

iCube. 
Rh.  of  99°  15',  6  sid.  Pr.  Rhomb. 
cleav.,  Sk. 
I  Do.,  Primary  a  Rhomb.,  P.  on  P'. 
^     =71°  30'. 
(  Reg.  Octohedrons. 
(  Cube  in  Silver  glance. 
\  Rhomboid. 
(  Cubes. 
(  Rhomboid. 
i  Cubes. 

\  Rt.  Rh.  R.,  M.  on  M'.  106°  2'. 
5  Octohed.  with  square  base. 
^Rt.  Rh.  Pr.,  M.M.=zll4o. 
i  Rt.  Rh.  Pr.,  M.M.=71-55. 
\  Octohed.  with  rect.  base. 
j  Reg.  Octohedrons. 
\  Rt.  Rh.  Pr. 
\  Do.,  M.  on  M'.  136°  58'. 
(  Reg.  Octohedrons. 

5  Rhomb,  of  105°  4',  M. 

^Rt.  Rh.  Pr.  ofI16°  16',  Xm. 

<  Rhomb,  of  106°  15'. 

\  Rt.  Rh.  Pr. 

j  Rhomb,  of  107-0. 

I  Rt.  Rh.  Pr.,  108°  26',  118°  0'? 

j  Rhomboid,  104°  53^'? 

\  Rt.Rh.Pr.  of  117°  14',  Xu. 

\  Rt.  Rh.  Pr.,  M.on  M'.=118°  52',  Lv. 

I  Rhomboid  of  106-36,  Fm. 

\  Ob.  Rh.  Pr. 

\  Square  Prism. 


(  Rt.  Rh.  Pr.,  M.  on  M'.  91°  lO',  Bk. 

\  Square  Prism. 

\  Rt.  Rh.  Pr. 

(  Square  Prism. 

I  Rhombic  Octohed.  (form  of  sulphur) 

<     M. 

i  Ob.  Rh.  Pr.  (form  of  feldspar),  M. 

C  Rt.  Rh.  Pr.  of  M.  on  M'.93°  54'. 

/  Do.  of  78°  SC. 

Reg.  Dodecahedron. 


Square  prism, 

i  Oblique  Rh.  Prism. 
Right  Rh.  Prism  (form  of  arrago- 
nite). 
5  Acute  rhomboid  of  72°  30'. 
I  Rt.  Rhomb.  Prism,*  M.  on.M=120. 


*  Haidinger  sajrs  an  oblique  rhombic  prism,  which,  according  to  the  subsequent  moasorement  of  Brooke,  i«  in 
norrect.    Bi.,  Brooke    id*.,  Kupfer ;  Ziv.,  Levy ;  JJf .,  Mitscherlich ;  Si.,  Suckow. 


VARIOUS    STRUCTURE    OF    DIMORPHOUS    B  O  D  I  E  S.   229 

The  molecular  arrangements  which  produce  this  diversity  of  form 
are  not  in  general  of  equal  stability  j  on  the  contrary,  one  figure  ap- 
pears to  be  in  general  forced  upon  the  body,  and  is  abandoned  by 
it  upon  very  slight  disturbance.  Thus,  when  a  prism  of  arragonite 
is  heated  in  the  flame  of  a  spirit-lamp,  it  breaks  up  into  a  congeries 
of  little  rhombs  of  common  calc  spar  at  a  temperature  far  below 
that  at  which  the  carbonate  of  lime  commences  to  be  decomposed  j 
but  no  alteration  of  temperature  can  convert  calc  spar  back  again 
into  arragonite.  Indeed,  arragonite  appears  to  be  formed  only  be 
tween  very  narrow  limits  of  temperature.  When  chalk  is  melted, 
it  forms,  on  cooling,  marble,  whose  fracture  shows  it  to  have  the 
rhombohedral  structure  ;  and  when  carbonate  of  lime  is  precipitated 
at  ordinary  temperatures,  the  microscopic  crystals  produced  are 
rhombohedrons ;  but  when  it  is  precipitated  from  a  boiling  solution, 
it  deposites  minute  crystals  of  arragonite,  which  a  hi  her  or  a  lower 
temperature  would  have  prevented. 

When  sulphur  has  been  crystallized  by  fusion  in  oblique  rhombic 
prisms,  these  lose  their  transparency  after  a  day  or  two,  and  change 
into  a  mass  of  very  minute  right  rhombic  octohedrons.  When  the 
arsenious  acid  is  crystallized  in  rhombic  prisms,  it  alters  slowly, 
and  eventually  becomes  a  dull  white  mass,  which  is  a  congeries  of 
regular  octohedrons  ;  but  if  the  rhombic  form  of  the  acid  be  dissolved 
in  muriatic  acid,  and  the  solution  set  to  crystallize,  it  is  deposited 
in  the  octohedral  form,  and  the  formation  of  each  crystal  is  accom- 
panied by  a  brilliant  flash  of  light,  indicating  probably  the  moment 
of  the  change  of  molecular  condition.  One  form  is  therefore  the 
stable  condition  of  arrangement,  the  other  being  produced  by  the 
sudden  fixation  of  the  molecules  in  a  form  which  is  naturally  only 
transitive,  and  from  which  they  free  themselves  as  soon  as  the  ex- 
ternal circumstances  admit  of  their  suitable  motion  among  each 
other. 

Independent  of  the  change  in  external  figure,  dimorphous  bodies 
present  remarkable  differences  in  physical  properties  j  thus  the  den- 
sity is  generally  different ;  in  one  form  the  substance  is  more  solu- 
ble than  in  the  other  5  they  differ  also  in  hardness,  and,  generally 
speaking,  in  all  characters  derived  from  the  physical  arrangement 
of  molecules. 

A  body  in  its  dimorphous  conditions  presents  frequently  a  differ- 
ence of  chemical  properties  deserving  of  particular  notice.  The 
bisulphuret  of  iron,  in  its  cubical  form,  is  remarkably  permanent, 
not  being  acted  on  either  by  air  or  water  j  but  in  its  right  rhombic 
form,  when  exposed  to  moist  air,  it  absorbs  oxygen  with  avidity, 
and  is  converted  into  a  crystalline  mass  of  copperas.  On  this  prin- 
ciple depends,  most  probably,  the  change  of  molecular  condition 
which  takes  place  in  oxide  of  chrome,  peroxide  of  tin,  zirconia,  and 
alumina,  when  exposed  to  a  temperature  just  below  redness.  These 
substances,  which  had  been  easily  soluble  in  acids,  become  almost 
totally  insoluble,  except  in  boiling  oil  of  vitriol,  and  this  change  is 
generally  accompanied  by  the  spontaneous  ignition  of  the  body, 
which  the  temperature  applied  would  be  quite  insuflicient  to  pro- 
duce. 

Independent  of  crystalline  form,  we  must  refer  to  circumstances 


230  CHANGILS     APPROACHING     DIMORPHISM, 

similar  to  those  which  produce  dimorphism,  a  variety  of  differences 
in  phj^sical  constitution  observable  in  certain  bodies ;  thus  melted 
sulphur  is,  at  230"^  F.,  perfectly  liquid  j  on  being  heated  to  430°  it 
becomes  thick,  and  so  tenacious  that  the  vessel  containing  it  may 
be  inverted  without  it  running  out  j  when  heated  farther  to  480°,  it 
becomes  again  liquid,  and  continues  so  till  it  begins  to  boil.  When 
the  red  oxide  of  mercury  is  heated  nearly  to  redness,  it  becomes 
almost  quite  black.  If  the  red  iodide  of  mercury,  formed  by  pre- 
cipitation, be  sublimed,  it  becomes  yellow  j  but  if  the  sublimed  mass 
be  scratched  with  a  pin,  the  edges  of  the  scratch  turn  red,  and  the 
redness  spreads  from  thence  until  the  whole  mass  is  converted  into 
its  original  condition.  Even  in  liquids  and  gases,  this  difference  in 
molecular  condition,  whether  produced  by  temperature  or  by  other 
causes,  appears  frequently  to  occur.  Thus  the  liquid  hyponitrous 
acid  (N.O3)  is  deep  green  at  60°,  but  at  4°  it  is  quite  colourless ; 
and  the  deep  red  gas  of  nitrous  acid  (N.OJ  becomes,  when  heated 
to  212°,  absolutely  black  and  opaque.  The  compound  of  starch  and 
iodine,  so  beautifully  blue-coloured  at  ordinary  temperatures,  be- 
comes colourless  when  heated  to  200°,  but  acquires  its  original  tint 
in  proportion  as  it  again  cools.  In  all  such  cases,  there  is  scarcely 
room  to  doubt  but  that,  if  we  had  as  perfect  methods  of  determining 
the  molecular  structure  as  is  afforded  by  the  measure  of  the  angles 
and  the  optical  properties  of  the  bodies  when  crystallized,  we  should 
find  these  phenomena  to  depend  upon  causes  of  the  same  kind. 

In  solid  bodies,  a  difference  of  molecular  structure,  fully  equiva- 
lent to  that  to  which  dimorphism  may  be  referred,  is  capable  of  being 
produced  by  very  simple  means.  Thus,  when  a  plate  of  glass  is  com- 
pressed by  means  of  a  screw,  it  assumes  a  doubly  refracting  structure, 
and  gives  with  polarized  light  a  cross  and  rings,  variously  disposed 
according  to  the  direction  of  the  pressure.  In  this  case,  the  change 
of  structure  arises  necessarily  from  an  increase  of  density  in  the 
compressed  portions ;  but  the  same  effect  may  be  produced  by  the 
converse  process  ;  a  plate  of  glass  which  has  been  suddenly  cooled 
from  having  been  red-hot,  assumes  a  similar  doubly  refracting  and 
polarizing  structure,  although  here  the  density  is  diminished  in  place 
of  being  increased.  I  have  found  the  sp.  gr.  of  glass  suddenly 
chilled  to  be  about  yi^  less  than  that  of  glass  of  the  same  kind 
which  had  cooled  slowly,  indicating  that  the  volume  was  the  same 
that  it  had  occupied  at  a  dull  red  heat,  and  that  hence  the  internal 
molecules  were  arranged  so  as  to  occupy  a  greater  space  than  in  the 
usual  condition. 

The  differences  of  chemical  properties  may,  however,  proceed 
much  farther,  so  that  in  place  of  considering  that  there  is  one  chem- 
ical substance  which  may  exist  in  two  molecular  conditions,  we  are 
obliged  to  consider  that  the  individuality  of  the  body  is  lost,  and 
that  in  its  two  forms  it  constitutes  two  distinct  and  independent 
chemical  substances.  Thus,  by  the  action  of  sulphuric  acid  on  al- 
cohol, we  obtain  a  gas  consisting  of  carbon  and  hydrogen,  in  the 
proportion  of  an  equivalent  of  each.  In  the  destructive  distillation  ol 
wood,  a  solid  substance  is  obtained,  fusible  like  wax,  and  volatile  only 
at  a  high  temperature  ;  this  consists  also  of  carbon  and  hydrogen, 
and  in  the  same  proportions.     These  elements,  so  combined,  preseni, 


PRINCIPLE     OF     ISOMERISM.  231 

therefore,  a  difference  in  molecular  arrangement  still  greater  than 
those  which  have  heen  observed  among  merely  dimorphous  bodies, 
and  when  we  examine  their  chemical  relations,  the  diversity  becomes 
still  more  marked.  The  gas  (olefiant  gas)  is  remarkable  for  the  num- 
ber of  compounds  to  which  it  gives  rise,  and  has  been,  from  the  va- 
riety of  its  reactions,  of  great  influence  on  the  existing  theories  of 
organic  chemistry.  The  solid  is  inattackable  even  by  the  strongest 
agents,  and,  from  its  total  indifference  to  combination,  has  been  called 
paraffine  (parum  affinis.)  In  this  case,  the  difference  of  properties 
indicates  a  difference  of  structure  much  more  profound  than  that  by 
which  change  of  density,  colour,  or  even  crystalline  arrangement 
could  have  its  source ;  it  is  not  merely  that  the  molecules  are  dif- 
ferently placed,  but  that  the  molecules  are  different ;  the  carbon  and 
hydrogen  which  unite  to  constitute  the  chemical  equivalent  of  the 
body  are  themselves  differently  arranged,  and  thus  give  rise  to  dif- 
ference of  properties ;  and  the  physical  molecules  formed  by  their 
reunion  being  again  grouped  according  to  dissimilar  laws,  produce 
the  diversity  of  physical  properties  and  states  of  aggregation;  the 
bodies  being  thus  in  every  property  unlike,  are  to  be  looked  upon 
as  independent  substances ;  they  are  said  to  be  isomeric  (from  laog 
[ispog)  because  they  have  the  same  ultimate  composition,  but  in  all 
their  chemical  relations  they  may  differ  as  widely  as  bodies  which 
have  no  element  in  common. 

When,  therefore,  the  groups  of  chemical  molecules  are  differently 
arranged,  the  various  differences  in  colour,  density,  solubility,  and 
figure  which  belong  to  dimorphous  bodies  are  produced  ;  but  when 
the  difference  of  arrangement  extends  to  the  chemical  constituents 
of  these  molecular  groups,  independent,  but  isomeric  bodies  are 
produced. 

It  is  generally  found  that  this  difference  in  the  constitution  of  the 
chemical  molecule  has  the  effect  of  changing,  in  a  simple  manner, 
the  equivalent  number  of  the  body.  Thus  oil  of  turpentine  and  oil 
of  citron  are  isomeric,  each  having  the  composition  C5H4  j  but  when 
we  combine  these  oils  with  muriatic  acid,  we  find  that  the  equiv- 
alent group  of  oil  of  turpentine  contains  C2oH,6,  while  that  of  oil  of 
citron  is  only  CioHg ;  it  is  remarkable  that,  though  the  chemical 
group  of  oil  of  citron  is  only  one  half  the  weight  of  that  of  oil  of 
turpentine,  it  exercises  the  same  power  of  circular  polarization,  but 
in  the  opposite  direction.  Another  example  of  this  simplicity  of 
proportion  in  weight  between  the  equivalents  of  isomeric  bodies,  is 
met  with  in  common  alcohol  and  methylic  ether,  that  of  the  former 
being  C4H6O2,  that  of  the  latter  being  C2H3O. 

The  difference  of  the  chemical  constitution  in  isomeric  bodies  is 
not  limited  to  magnitude,  as  determined  by  the  weight  of  their 
equivalent,  but  extends  to  internal  structure.  Thus  alcohol  is  com- 
posed of  ether  and  water,  C4H30.-[-H.O.,  while  methylic  ether  cannot 
be  resolved  into  those  substances.  Formiate  of  methylene  and  glacial 
acetic  acid  are  each  C4H4O4,  not  differing  even  in  the  w^eight  of  their 
equivalent  ,•  but  all  the  properties  of  these  bodies  show  that  glacial 
acetic  acid  is  C4H3O3+H.O.,  while  formiate  of  methylene  is  C^H.Oa-f 
C2H3O.  Instances  of  this  kind  might  be  multiplied  to  any  extent, 
^ut  these  will  be  sufficient  to  illustrate  the  principle. 


232   CONNEXION    OF    DIMORPHISM    AND   ISOMERISM. 

It  is  necessary,  however,  in  studying  such  cases  of  isomerism,  to 
bear  in  mind  what  has  been  so  beautifully  shown  by  Graham,  that 
the  presence  of  foreign  bodies,  in  quantities  so  small  as  to  be  total- 
ly unappreciable,  except  in  the  most  rigidly  accurate  analysis,  may 
change  so  completely  the  properties  of  bodies  that  they  will  sim- 
ulate isomerism.  Thus  phosphuretted  hydrogen  may  exist  in  two 
conditions,  in  one  of  which  it  is  spontaneously  inflammable,  and  in 
the  other  not.  They  both  give,  on  analysis,  the  same  formula, 
P.H3 ',  but  the  first  may  be  changed  into  the  second  by  mere  admix- 
ture with  a  very  small  quantity  of  the  vapour  of  ether,  and  the  sec- 
ond may  be  converted  into  the  first  by  the  most  minute  bubble  of 
nitrous  acid  gas.  Such  bodies,  therefore,  which  owe  their  diversity 
of  properties  to  accidental  circumstances,  are  not  isomeric,  and 
must  be  carefully  distinguished  from  those  before  described. 

As  we  have  thus  traced  a  gradual  transition  from  the  feeblest  in- 
dications of  dimorphism,  to  the  complete  difference  of  structure  and 
properties  constituting  isomerism,  it  becomes  an  interesting  ques- 
tion whether  we  may  not  have  occasion  to  retrace  our  steps,  and 
to  seek  in  those  bodies  which  we  have  hitherto  considered  as  only 
differing  in  physical  properties,  for  evidence  of  difference  in  chem- 
ical arrangement.  May  not  a  simple  substance,  as  sulphur  or  anti- 
mony, enter  into  combination  with  equivalents  of  different  weights, 
and  so  resemble  oil  of  turpentine  and  oil  of  citron ;  and  may  not 
this  difference  in  equivalents  be  the  source  of  diversity  in  formi 
When  sulphur  crystallizes  in  the  form  of  bisulphate  of  potash,  may 
we  not  reasonably  suppose  that  its  molecules  are  grouped  into  a 
complex  figure,  like  that  of  the  compound  salt,  and  that  its  equiv- 
alent is,  in  proportion,  greater  than  when  it  crystallizes  as  a  simple 
body  %  We  say  that  two  ordinary  equivalents  of  manganese  replace 
one  of  chlorine,  but  is  it  not  really  that  when  manganese  replaces 
chlorine,  its  equivalent*  is  double  what  it  is  when  it  replaces  hydro- 
gen or  copper  1  Manganese  replacing  chlorine,  is  to  manganese  re- 
placing copper,  what  oil  of  turpentine  is  to  oil  of  citron  ;  and  hence 
it  may  be  isomeric  with  itself,  for  the  functions  it  performs  in  its 
two  modes  of  combination  are  the  most  widely  different  possible. 
The  bisulphuret  of  iron,  in  its  cubical  form,  is  Fe.S2,  and,  like  Mn.02, 
is  decomposed  only  by  a  red  heat,  when  it  parts  with  one  third  of 
its  volatile  constituent ;  but  in  its  rhombic  form,  may  not  its  equiv- 
alent be  Fe2S4,  resembling  CI.O4,  and,  like  it,  be  decomposed  by  the 
slightest  causes  1 

The  circumstance  that  isomeric  bodies  are  almost  universally  con- 
nected by  simple  relations  between  their  atomic  weights,  coupled 
with  the  idea  that  even  among  the  simple  bodies  a  kind  of  isomer- 
ism may  be  the  cause  of  their  dimorphous  conditions,  acquires  re- 
markable interest  from  the  fact  that  the  equivalent  numbers  of  many 
of  the  simple  bodies  are  closely  related  to  one  another,  as  is  shown 
in  the  following  table : 


NATURE  OF  COMPOUND  RADICALS. 


233 


1    equivalent  of  zinc  =  32-31 

1  "  yttrium  .  .  .  3225 
\  "  antimony  .  .  .  32  40 
1           "           tellurium   .     .     .  32 13 

2  "  sulphur      .     .     .  32-24 

1    equivalent  of  cobalt   .    ,    .    .  29  57 

1  "  nickel    ....  29-62 

^  "  tin    ....     .  29-46 


1^  equivalent  of  bismuth            =  106-65 

2             "           palladium.     .     .  106-72 

2    equivalent  of  osmium     .     .     .  199-72 

1             "           gold      ....  199-21 

1    equivalent  of  platina  .    .    .'    .  98-84 

I             "           iridium      .     .     .  9884 

L    equivalent  of  molybdenum  .     .  4796 

i           "          tungsten    .    .    .  47-40 

May  it  not  be  possible  that  science  shall  hereafter  find  the  metals 
so  connected  to  be  truly  isomeric  1  In  no  case  are  their  properties 
more  different  j  and  we  find  in  the  racemic  and  tartaric  acids  an 
example  of  the  general  similarity  of  properties  in  the  compounds 
of  isomeric  bodies,  which  is  so  remarkable  in  the  combinations  of 
sulphur  and  tellurium,  or  of  cobalt  and  nickel,  among  the  simple 
substances. 

Considerable  probability  is  given  to  the  idea  of  the  compound  na- 
ture of  bodies  at  present  considered  simple,  by  the  existence  of 
certain  compound  bodies  which  simulate  the  properties  of,  and 
enter  into  combination  subject  to  the  same  laws  as  the  undecom- 
pounded  substances.  Thus  carbon  and  hydrogen  unite  to  form  a 
gas,  cyanogen,  which  combines  with  the  metals,  with  oxygen,  with 
hydrogen,  &c.,  precisely  as  chlorine  does ;  it  is  the  origin  or  root 
of  a  series  of  cyanides,  as  chlorine  is  of  a  series  of  chlorides,  and 
it  is  hence  called  a  compound  radical.  The  discovery  of  this  prin- 
ciple by  Gay  Lussac  was  the  foundation  of  all  that  is  exact  and 
philosophical  in  our  views  of  organic  chemistry.  Bodies  which 
contain  the  same  ultimate  elements  may  be  different,  because  they 
contain  different  radicals,  precisely  as  the  salts  of  nickel  and  the 
salts  of  cobalt  will  remain  quite  distinct,  even  should  nickel  and  co- 
balt be  hereafter  shown  to  be  isomeric  bodies.  This  principle  of 
compound  radicals  is  so  beautiful  and  so  easily  applied,  that  its  use 
has  been,  as  I  conceive,  somewhat  too  extensively  adopted ;  and 
hence,  wherever  simplicity  of  expression  was  sought  for,  or  a  dif- 
ference of  properties  was  to  be  explained,  the  formulae  of  organic 
bodies  were  perhaps  too  hastily  grouped,  by  the  assumption  of  a 
hypothetic  radical,  of  which  the  different  bodies  of  the  series  were 
supposed  to  be  combinations.  It  is  certain  that,  in  many  cases,  this 
plan  has  been  of  great  use  to  science,  as  in  the  benzyle  theory  of 
Liebig,  and  in  the  ether  and  ammonia  theories  proposed  by  Ber- 
zelius  and  myself;  but  I  consider  the  degree  to  which  it  has  latterly 
been  extended,  by  which  the  existence  of  a  great  variety  of  bodies 
has  been  assumed,  for  which  there  is  scarcely  any  reason,  except 
some  additional  simplicity  of  formulae,  which  often  served  to  con- 
ceal the  truth,  to  have  been  productive  of  much  disadvantage  to 
true  science  and  a  misdirection  of  thought,  which  we  should  seek 
as  much  as  possible  to  avoid. 

In  all  that  has  been  described  of  the  arrangement  of  the  elements 
of  compound  bodies,  their  union  has  been  considered  as  resulting 
from  their  antagonistic  and  mutually  neutralizing  properties,  and 
the  successive  stages  of  composition  being  effected  in  binary 
groups :  thus  crystallized  alum  is  a  compound  of  water  and  dry 
alum ;  this  last,  a  compound  of  sulphate  of  potash  and  sulphate  of 

Gg 


234 


CONSTITUTION     OF     ORGANIC     BODIES. 


alumina;  these  respectively,  compounds  of  sulphuric  acid  and  a  base 
which  consists  of  oxygen  united  to  a  metal ;  the  sulphuric  acid  it 
self  being  formed  by  the  union  of  oxygen  and  sulphur.  This  view 
results  necessarily  from  what  has  been  said  of  the  nature  of  chem- 
ical affinity,  and  expresses  faithfully  the  principle  upon  which  the 
electro-chemical  theory  has  been  formed ;  there  is  no  doubt  but  that 
the  constitution  of  inorganic  bodies  is  regulated  in  this  way,  but  we 
meet  with  considerable  difficulty  in  applying  its  principles  to  or- 
ganic chemistry.  Thus  I  myself  suggested  a  few  years  ago,  that 
the  formic  and  acetic  acids  should  be  looked  upon  as  oxides  of  com- 
pound radicals,  formyle  and  acetyle,  C2H.03=Fo.03  and  C4H303= 
AC.O3,  by  which  means  a  variety  of  bodies  of  analogous  constitution 
were  simply  connected  together,  as  the  formyle  or  acetyle,  which 
combine  with  oxygen  to  form  those  vegetable  acids,  combine  with 
iodine,  chlorine,  sulphur,  and  cyanogen  to  form  binary  compounds, 
precisely  as  manganese  (a  simple  radical)  combines  with  oxygen  to 
form  manganic  acid,  and  with  chlorine,  &c.,  to  form  an  analogous 
series  of  bodies.  I  am  far  from  abandoning  this  view :  the  question 
of  its  full  applicability  will  be  discussed  among  the  general  laws  of 
organic  chemistry,  but  at  present  we  will  attend  to  only  one  circum- 
stance connected  with  it.  Hydrated  acetic  acid  is  formed  from  al- 
cohol, by  the  latter  losing  two  equivalents  of  hydrogen,  and  gaining 
two  of  oxygen  in  their  place ;  and  in  like  manner,  hydrated  formic 
acid  is  produced  from  pyroxylic  spirit,  by  losing  H2  and  gaining  O2, 
thus: 


Alcohol C4H6O2 

gives  by      .    .     — H2-}-Q2 
Hydrated  acetic  acid  ,    C4H4O4. 


Pyroxylic  spirit      .     .    C2H4O2 

gives  by      .     .     — H2-{-Q2 

Hydrated  acetic  acid  .    C2H2O4. 


Now,  if  acetic  acid  contains  acetyle,  does  it  exist  in  alcohol ;  or 
must  we  consider  that,  by  the  gradual  process  of  oxidation,  the 
molecular  structure  of  the  alcohol  is  totally  broken  up,  and  that  the 
acetic  acid  formed  has  no  natural  or  necessary  connexion  with  itl 

We  owe  to  Dumas  the  introduction  of  a  principle  into  organic 
chemistry,  which,  applied  to  changes  such  as  those  described  above, 
promises  to  shed  considerable  light  upon  the  reactions  and  consti 
tution  of  organic  bodies ;  but  it  yet  involves  conditions  so  opposed 
to  our  present  ideas  of  chemical  affinity,  that  we  can  only  look  on 
it  as  a  proposition  which  merits  profound  attention.  He  considers 
that  the  elements  of  organic  bodies  are  not  united  by  affinity  arising 
from  opposition  of  properties,  but  that  they  represent  a  group  of 
molecules  connected  by  a  single  force,  precisely  as  the  planetary 
masses  are  by  gravitation,  and  just  as  any  of  the  planets  might  be 
replaced  in  the  solar  system  by  a  ball  of  matter  of  totally  different 
chemical  properties,  provided  its  gravitating  mass  remained  the 
same,  without  disturbing  in  the  least  the  conditions  of  mechanical 
equilibrium ;  so,  in  an  organic  substance,  elements  of  the  most  di- 
verse characters  may  be  substituted  for  each  other,  and  yet  the 
molecular  group  remain  unaltered  in  structure  and  physical  consti- 
tution. Thus  the  molecular  group  of  alcohol  (C4H6O2)  contains 
twelve  chemical  atoms.  When  it  is  changed  into  acetic  acid  ('C4H4O4), 
the  numbei  of  chemical  atoms  is  the  same ;  the  mechanical  type  of 


OF     ACTIONS     BY    CONTACT.  23o 

the  body  is  unaltered,  although  its  chemical  properties  are  complete- 
ly changed  and  a  new  substance  formed.  Bodies,  therefore,  are 
classified  by  Dumas  according  to  certain  types  or  models.  When 
the  number  of  molecules  in  the  equivalents  of  the  bodies  remains 
the  same  while  the  nature  of  the  elements  changes,  the  bodies  have 
the  same  mechanical  type  ;  but  if  the  substitution  of  elements  is  ac- 
companied by  a  change  of  properties,  the  chemical  type  of  the  ori- 
ginal body  is  destroyed.  Thus  alcohol  and  acetic  acid  have  not  the 
same  chemical  type. 

When  acetic  acid  is  treated  with  chlorine,  it  loses  three  equiva- 
lents of  hydrogen  and  gains  three  of  chlorine  (C4H4O4 — H3+Cl3= 
C4CI3H.O4),  forming  chloroacetic  acid.  The  sum  of  the  molecules 
is  here  twelve,  and  this  substance  has  the  same  mechanical  type  as 
alcohol  and  common  acetic  acid ;  but  in  changing  to  this  body,  com- 
mon acetic  acid  scarcely  changes  its  properties,  and  hence  is  said 
to  retain  its  chemical  type.  When  ether  (C4H5O.)  is  treated  with 
chlorine,  its  hydrogen  is  totally  replaced  by  chlorine,  and  the  body 
(C4CI5O.),  chlorine  ether,  is  produced  5  the  number  of  molecules  being 
the  same,  the  mechanical  type  is  preserved  ;  but  more,  the  chlorine 
ether  combines  with  acids  forming  salts  like  those  of  common  ether, 
which  it  resembles  in  all  essential  chemical  characters,  and  hence, 
in  this  case,  the  chemical  type  is  undisturbed,  notwithstanding  the 
total  substitution  of  chlorine  for  hydrogen,  a  body  differing  from  it 
so  much  in  general  characters. 

The  question  how  far  this  theory  of  types  should  be  adopted,  and 
how  far  the  law  of  substitution  on  which  it  rests  is  verified  by  ex- 
periment, will  be  hereafter  examined.  The  theory  is  here  only  no- 
ticed as  involving  important  relations  between  the  mechanical  struc- 
ture and  the  chemical  constitution  of  organic  bodies. 

SECTION  IV. 

OF     CATALYSIS. 

The  decomposition  of  compound  bodies  is  frequently  eflfected  by 
the  intervention  of  causes  which  cannot  be  referred  to  ordinary  af- 
finity ;  and  in  many  cases,  bodies  which  have  but  little  tendency  to 
unite,  enter  into  combination  when  brought  into  contact  with  a  sub- 
stance for  which  neither  has  affinity,  and  which  remains,  after  the 
action  is  completed,  perfectly  unaltered.  Thus,  when  hydrogen  and 
oxygen,  mixed  together  in  a  gaseous  form,  are  brought  into  contact 
with  a  clean  slip  of  platinum,  they  gradually  unite,  and  so  much 
heat  may  be  evolved  by  their  rapid  combination  as  to  ignite  the 
platinum,  and  explode  the  remainder  of  the  gas.  In  this  case  we 
seek  to  explain  the  phenomenon  by  supposing  that  the  platinum 
condenses  powerfully  on  its  surface  a  layer  of  mixed  gaseous  par- 
ticles, and  thus  brings  them  within  the  sphere  of  their  mutual  attrac- 
tion. But  this  explanation  does  not  apply  to  other  cases.  If  we 
boil  starch  (Ci2H,oO,o)  with  diluted  sulphuric  acid,  it  is  converted  suc- 
cessively into  dextrine,  gum,  starch-sugar,  and,  finally,  crystallizable 
grape-sugar  (Ci^HiaO,^),  hiiving  associated  to  itself  the  constituents 
of  two  equivalents  of  water.  At  the  termination  of  the  process,  the 
sulphuric  acid  is  found  unaltered  in  properties  and  in  quantity,  so 


236  ANALYSTS     AND     CATALYSIS. 

that  the  smallest  portion  of  sulphuric  acid  is  sufficient  to  convert 
into  sugar  an  indefinitely  great  quantity  of  starch.  If  oxamide 
(C2O2N.H2)  be  diffused  through  water,  in  contact  with  the  smallest 
possible  quantity  of  oxalic  acid,  it  gradually  disappears,  and,  appro- 
priating to  itself  the  elements  of  an  equivalent  of  water,  is  converted 
into  neutral  oxalate  of  ammonia,  (C2O3+N.H3),  the  small  quantity  of 
oxalic  acid  originally  added  remaining  unaltered  and  in  excess. 

Among  instances  of  decomposition  by  forces  of  this  kind,  the  ox- 
ygenated water  (H.O2)  may  be  taken  as  an  example.  This  substance, 
when  pure,  separates  spontaneously,  after  some  time,  into  water  and 
oxygen  gas,  but  its  decomposition  may  be  rendered  violent  and  in- 
stantaneous by  putting  it  into  contact  with  finely-divided  metallic 
platinum,  or  metallic  silver,  or  black  oxide  of  manganese,  or  fibrine, 
or  a  variety  of  other  bodies.  In  all  these  cases,  the  body  added  re- 
mains quite  unaltered ;  no  affinity  can  be  traced  between  it  and  the 
oxygenated  water,  the  mere  presence  of  the  foreign  body  appearing 
to  cause  the  decomposition. 

Berzelius,  who  first  directed  general  attention  to  these  phenomena, 
proposed  to  attribute  them  to  a  peculiar  force,  differing  from  ordi- 
nary affinity.  When  one  body  is  decomposed  by  another,  in  virtue 
of  a  superior  affinitary  power,  the  decomposing  body  combines  with 
one  element  of  the  body  which  is  decomposed,  and  the  other  is  then 
expelled.  It  is  in  this  way  that  we  obtain  the  constituents  of  bodies 
by  or  dinar  Y  analysis  ;  and  for  distinction,  he  proposes  to  term  such 
decompositions  as  those  just  described,  operations  of  catalysis,  and 
to  name  the  power  which  these  bodies  have  of  acting  by  mere  con- 
tact, a  catalytic  force. 

It  is  evident,  certainly,  that  by  giving  a  name  to  this  class  of  phe- 
nomena, we  are  enabled  usefully  to  contemplate  them  as  a  group, 
and  to  examine  more  easily  their  relations  to  each  other  and  to 
ordinary  action ;  yet  the  word  catalysis  really  teaches  us  nothing  of 
the  phenomena,  and  it  is,  indeed,  improbable  that  such  varied  cases 
of  union  and  separation  should  be  derivable  from  one  single  force.  It 
is  hence  necessary,  before  concluding  on  the  nature  of  this  action, 
to  trace  it  through  a  greater  variety  of  cases,  and  to  revert  briefly 
to  the  conditions  of  affinity  by  which  the  elements  of  compound 
bodies  are  held  together. 

The  elements  of  a  compound  substance  are  retained  together  in 
a  certain  molecular  arrangement,  because  the  affinities  are  then  sat- 
isfied ;  but  it  is  natural  to  suppose  that,  while  the  elements  remain 
the  same,  their  affinities  for  each  other  might  be  just  as  completely 
satisfied  by  a  different  molecular  arrangement.  The  original  body 
might  therefore  be  changed  into  another,  by  a  change  in  the  action 
of  its  own  particles,  independent  of  any  substance  acting  chemically 
on  it  from  without ;  and  hence  the  principle  of  catalytic  decompo- 
sition resolves  itself  into  a  means  of  disturbing  the  molecular  equi- 
librium of  a  compound  body,  so  that  it  can  be  only  restored  when 
the  particles  are  differently  arranged.  Catalysis  may,  therefore,  be 
produced  not  merely  by  the  presence  of  various  bodies,  but  stil^ 
more  remarkably  by  the  action  of  physical  agents,  among  which 
heat  is  the  most  powerful ;  thus,  when  acetate  of  lime  (C4H304Ca.) 
is  strongly  heated,  the  equilibrium  of  its  molecular  group  is  over 


COMMUNICATION     OF     MOTION.  237 

turned,  and  when  the  affinities  again  satisfy  themselves,  two  new 
bodies  result,  acetone  and  carbonate  of  lime  (C3H3O.  and  COgCa.). 
Destructive  distillation  is  therefore  a  catalytic  process,  and  the  or- 
igin of  all  pyrogenic  products  is  to  be  traced  to  the  new  conditions 
under  which  the  affinities  are  satisfied,  which  had  originally  united 
the  elements  of  the  body  exposed  to  heat.  The  sudden  decomposi- 
tion of  explosive  bodies  by  an  elevation  of  temperature  or  by  a 
slight  blow,  is  traceable  to  the  same  disturbance  of  the  old  equilib- 
rium, and  establishment  of  the  new.  A  most  important  means  of 
thus  setting  into  motion  the  particles  of  bodies,  and  enabling  them 
to  rearrange  themselves  under  new  forms,  consists  in  bringing  them 
into  contact  with  a  substance  already  in  a  state  of  decomposition ; 
thus,  if  oxygenated  water  be  brought  into  contact  with  oxide  of  sil- 
ver, the  decomposition  is  propagated  to  the  latter,  which  is  com- 
pletely resolved  into  oxygen  and  metallic  silver ;  if  peroxide  of  lead 
be  used,  it  is  converted  into  protoxide  by  the  escape  of  half  its  ox- 
ygen, and  even  the  black  oxide  of  manganese  may  be  reduced  to, 
the  state  of  protoxide  if  the  solution  contain  an  acid ;  in  all  these 
cases,  the  decomposition,  which  commenced  with  the  oxygenated 
water,  extends  to  the  metallic  oxide,  in  virtue  of  the  motion  com- 
municated to  their  particles,  enabling  the  new  arrangement  to  be 
effected.  In  some  instances,  in  organic  chemistry,  this  principle  is 
still  more  beautifully  shown.  If  a  solution  of  sugar  (CiaHnO,,)  be 
brought  into  contact  with  a  little  decomposing  gluten  or  yeast,  it 
unites  with  the  elements  of  an  equivalent  of  water,  and  divides  it- 
self into  two  equivalents  of  alcohol,  2  (C^eOg),  and  four  of  carbonic 
acid,  4  (C.O2).  If  a  solution  of  urea  (C.O.N.H2)  be  put  in  contact 
with  yeast,  it  unites  also  with  an  atom  of  water,  and  is  then  decom- 
posed into  an  equivalent  of  ammonia  (N.H3)  and  one  of  carbonic 
acid.  The  conversion  of  starch  into  sugar  in  the  processes  of  ger- 
mination and  of  malting,  is  effected  by  a  substance  which  accompa- 
nies the  starch  in  the  grain.  This  substance  is  called  diastase,  and 
is  analogous  in  most  of  its  properties  to  vegetable  gluten.  The 
slow  decomposition  of  the  diastase  communicates  to  the  molecules 
of  many  thousand  times  its  weight  of  starch  the  degree  of  motion 
necessary  for  their  rearrangement,  and  the  appropriation  of  the 
elements  of  water  requisite  for  the  formation  of  starch-sugar. 

If  platinum,  which  is,  by  itself,  totally  unacted  on  by  nitric  acid, 
be  alloyed  with  silver,  the  alloy  dissolves  in  dilute  nitric  acid  with- 
out leaving  any  residue.  Pure  copper  is  not  acted  upon  by  dilute 
sulphuric  acid  j  but  when  it  is  alloyed  with  nickel  and  zinc,  as  in 
the  argentine,  or  German  silver  of  commerce,  it  dissolves  complete- 
ly. In  these  cases,  the  molecular  action  which  produces  the  com- 
bination with  the  acid  was  not  possessed  by  the  platina  or  copper 
when  alone,  but  is  acquired  by  them,  being  transmitted  from  the 
other  metals  with  which  ihey  are  alloyed. 

It  may  not  be  easy  to  reduce  to  the  action  of  this  principle  all 
phenomena  of  catalysis;  for,  in  the  imperfect  light  by  which  we 
contemplate  them,  it  is  possible  that  we  may  rank  together  circum- 
stances whose  real  nature  is  very  different ;  but,  at  all  events,  we 
must  recognise  in  this  principle,  the  definite  introduction  of  which 
into  science  is  due  to  Liebig,  a  cause  of  chemical  decomposition 


238  CLASSIFICATION     OF     BODIES. 

peculiarly  important  in  explaining  the  complex  reactions  of  organic 
bodies.  It  is  remarkable,  also,  that  this  law,  of  which  the  simplest 
expression  is,  that  where  two  chemical  substances  are  in  contact, 
any  motion  occurring  among  the  particles  of  the  one  may  be  com- 
municated to  the  particles  of  the  other,  is  of  a  more  purely  mechan- 
ical nature  than  any  other  principle  as  yet  received  in  chemistry  ; 
and  when  more  definitely  established  by  succeeding  research,  it 
may  be  the  basis  of  a  dynamical  theory  in  chemistry,  as  the  law  of 
equivalents  and  of  multiple  combination  expresses  the  statical  con- 
dition of  bodies  which  unite  by  chemical  force. 

We  must,  at  least,  look  upon  these  actions  of  catalysis^,  the  con- 
ditions of  molecular  arrangement  which  give  rise  to  isomerism  and 
dimorphism,  and  the  introduction  of  the  principle  of  types  in  oppo- 
sition to  that  of  mere  binary  combination,  as  tending  towards  a 
change  in  our  ideas  of  the  nature  of  chemical  affinity,  which  may^ 
before  long,  remodel  the  whole  constitution  of  the  science. 


CHAPTER  XI. 

ON    THE    CLASSIFICATION    OF    THE    ELEMENTARY   BODIES. 

The  principal  classifications  of  the  simple  bodies  that  have  been 
proposed  are  those  of  Berzelius,  founded  on  their  electro-chemical 
relations,  and  of  Thompson,  who  divided  them  into  supporters  and 
I  on-supporters  of  combustion.  It  has,  however,  been  fully  shown, 
that  in  combustion  each  body  is  mutually  a  supporter  and  a  com- 
bustible :  oxygen  burns  in  hydrogen  or  in  the  vapour  of  sulphur,  just 
as  much  as  hydrogen  or  sulphur  burn  in  oxygen  ;  Thompson's  prin- 
ciple is  therefore  radically  defective ;  and  the  electro-chemical  the- 
ory, although  far  superior  as  a  principle,  is  liable  to  weighty  objec- 
tions of  a  somewhat  similar  kind.  These  have  been  already,  how- 
ever, so  far  noticed,  and  the  arrangement  of  the  simple  bodies  in  that 
series  so  fully  given,  p.  188,  that  it  is  unnecessary  to  recur  farther 
to  the  subject. 

The  kind  of  classification  that  is  suited  to  the  present  wants  of 
chemistry  must  be  founded  upon  the  general  analogy  of  properties 
between  substances  belonging  to  the  same  class,  and  on  their  iso- 
morphous  replacement  of  one  another.  This  last  character  is  not 
absolute  j  for,  from  the  dimorphism  of  many  of  the  simple  bodies, 
it  is  often  difficult  to  assign  their  true  crystalline  relations  to  each 
other,  and  in  many  cases  we  do  not  possess  any  positive  information 
of  their  forms. 

Graham  has  recently  proposed  a  classification  which  expresses, 
more  completely  than  any  other,  the  natural  relations  of  the  simple 
bodies.  The  first  class  consists  of  oxygen,  sulphur,  selenium,  and 
tellurium.  The  parallelism  in  properties  of  the  last  three  is  com- 
plete, and  their  compounds  are  strictly  isomorphous  j  their  similar- 
ity to  oxygen  is  not  so  perfect,  but  they  resemble  it  in  their  method 
of  combination  and  in  the  characters  of  the  substances  which  they 
form  in  uniting  with  hydrogen  and  the  metals. 


CLASSIFICATION     OP     ELEMENTS.  239 

The  second  class  comprises  magnesium,  calcium,  manganese,  iron, 
cobalt,  nickel,  zinc,  cadmium,  copper,  hydrogen,  bismuth,  chromi- 
um, aluminum,  glucinum,  vanadium,  zirconium,  yttrium,  thorium. 
The  similar  salts  of  the  protoxides  of  this  class  are  isomorphous  ; 
and,  as  has  been  already  shown  under  the  head  of  Isomorphism,  two 
equivalents  of  a  protoxide  of  this  class  replace  one  equivalent  of  an 
aliali.  Chromium,  aluminum,  glucinum,  vanadium,  and  zirconium 
do  not  form  protoxides,  but  sesquioxides,  the  salts  of  which  are  iso- 
morphous with  those  of  the  sesquioxides  of  iron  and  manganese.  A 
remarkable  connexion  is  established  between  this  class  and  the  prece- 
ding by  the  ismorphism  of  the  manganic  acid  (Mn.Oa)  and  chromic 
acid  (Cr.Oa)  with  sulphuric  acid  (S.O3),  indicating  that  under  cer 
tain  circumstances  these  metals  may  change  from  one  natural  fam- 
ily to  another. 

The  third  class  contains  barium,  strontium,  and  lead.  Their  salts 
are  strictly  isomorphous,  and  they  are  connected  together  by  great 
similarity  of  chemical  properties.  Thus  the  sulphates  of  the  metals 
of  the  second  class  are  soluble  in  water,  while  the  sulphates  of  this 
class  are  almost  insoluble.  Calcium  approximates  to  this  condition 
by  the  sparing  solubility  of  sulphate  of  lime  ;  and  the  connexion  be- 
tween the  two  families  is  still  more  fully  shown  by  the  dimorphism 
of  carbonate  of  lime,  it  having  in  one  form  the  figure  of  the  carbon- 
ates of  magnesia  and  of  iron,  and  in  the  other  that  of  the  carbonates 
of  barytes  and  of  lead. 

The  fourth  class  consists  of  potassium,  sodium,  and  silver.  The 
similarity  of  chemical  properties  of  potassium  and  sodium  is  suffi- 
ciently evident ;  and  although  their  compounds  are  not  frequently 
isomorphous,  yet  there  is  good  reason  for  attributing  that  to  the  di- 
morphism of  each.  Silver  differs  remarkably  in  its  chemical  rela- 
tions from  potassium  and  sodium,  and  the  only  grounds  for  inserting 
it  in  this  class  is  the  isomorphism  of  sulphate  of  silver  with  anhy- 
drous sulphate  of  soda. 

The  salts  of  potash  are  perfectly  isomorphous  with  the  salts  of 
ammonia  which  contain  an  atom  of  water ;  and. hence,  if  the  base 
of  the  ammoniacal  salts  (N.H3+H.O.)  be  written  N.H^ .  0.,  it  may 
be  considered  as  an  oxide  of  a  compound  radical  which  is  isomorph- 
ous with  potassium,  and  would  rank,  did  we  not  know  its  compo- 
sition, in  the  present  group.  This  view  of  the  composition  of  the 
ammoniacal  salts  was  suggested  by  Berzelius,  who  gave  to  that  com- 
pound radical  the  name  ammonium  ;  but  I  have  since  shown  that 
the  replacement  is  really  by  two  equivalents  of  a  hydrogen  com- 
pound, as  already  noticed  in  speaking  of  the  second  class. 

Fifth  class,  chlorine,  iodine,  bromine,  and  fluorine.  This  group 
is  best  characterized  by  similarity  of  chemical  properties ;  and,  so 
far  as  observation  extends,  their  isomorphism  appears  to  be  com- 
plete. It  is  connected  with  the  first  and  second  classes  by  means 
of  manganese,  of  Which  two  equivalents  replace,  in  truly  isomorph- 
ous compounds,  one  of  chlorine. 

Sixth  class,  nitrogen,  phosphorus,  arsenic,  and  antimony.  In  their 
chemical  history  these  compounds  exhibit  considerable,  though  not 
complete  similarity.  The  corresponding  compounds  of  arsenic,  an- 
timony, and  phosphorus  are  generally  isomorphous,  but  in  no  case 


240  CLASSIFICATION     OF     ELEMENTS. 

has  isomorphism  been  observed  between  their  compounds  and  those 
of  nitrogen.  A  certain  analogy  appears  to  exist  between  nitrogen 
and  the  substances  of  the  fifth  class,  as  the  nitric  acid  corresponds 
remarkably  in  properties  to  the  chloric  and  iodic  acids,  with  which, 
however,  it  is  not  isomorphous.  Nitrogen  appears  also  to  replace 
oxygen  in  marly  cases  in  the  proportion  of  one  third  of  its  equiva- 
lent weight. 

Seventh  class,  tin  and  titanium,  connected  by  the  isomorphism  of 
titanic  acid  and  peroxide  of  tin. 

Eighth  class,  silver  and  gold,  from  their  isomorphism  in  the  me- 
tallic state. 

Ninth  class,  platinum,  palladium,  iridium,  and  osmium,  from  the 
isomorphism  of  their  double  chlorides,  by  which  also  Graham  con- 
siders this  class  to  be  connected  with  the  seventh. 

Tenth  class,  tungsten  and  molybdenum  ;  the  tungstates  and  mo- 
lybdates  being  isomorphous.  These  metals  Avill  probably  be  found 
to  be  of  the  same  family  with  chrome,  as  chromate  of  lead  has  been 
found  crystallized  in  the  same  form  as  the  molybdate. 

Eleventh  class,  carbon,  boron,  and  silicon:  of  these  substances 
no  isomorphous  relations  are  known ;  they  are  brought  together  by 
a  general,  though  imperfect  analogy  of  properties. 

Graham  makes  no  attempt  at  classifying  mercury,  cerium,  colum- 
bium,  lithium,  rhodium,  or  uranium. 

I  agree  completely  with  the  general  principles  of  this  classifica- 
tion, but,  in  a  few  cases,  researches  made  since  it  was  drawn  up  by 
Graham  render  some  alterations  necessary  5  thus  the  similarity  of 
constitution  between  the  compounds  of  bismuth  and  copper,  which 
had  induced  him  to  insert  bismuth  in  the  second  class,  has  no  real 
existence,  and  I  would  transfer  it  to  the  same  class  with  antimony; 
their  sulphurets  being-  isomorphous,  and  their  chemical  properties 
being,  generally  speaking,  very  similar.  Indeed,  it  is  almost  certain 
that  the  oxide  of  bismuth  is  not  a  protoxide,  but  a  sesquioxide,  and 
hence  corresponds  to  the  oxide  of  antimony. 

I  do  not  consider  the  isomorphism  of  sulphate  of  soda  and  sul- 
phate of  silver  as  being  a  sufficient  ground  for  ranking  the  latter 
metal  in  the  fourth  class.  We  have  already  seen  numerous  examples 
of  isomorphism  among  substances  of  totally  different  chemical  con- 
stitution, and  the  properties  of  the  compounds  of  silver  resemble  so 
completely  those  of  lead,  as  to  demonstrate  positively  that  it  be- 
longs to  the  same  natural  group.  "When  copper  enters  into  combi- 
nation in  a  double  equivalent  Cuj,  it  becomes  likewise  a  member  of 
the  lead  and  barytes  group,  as  is  shown  by  the  sparing  solubility  of 
its  sulphate  and  chloride  ;  and  its  being  isomorphous  with  silver  fur- 
nishes additional  evidence  of  its  true  position. 

Silver  and  gold  being  isomorphous  only  in  the  regular  system, 
and  their  compounds  being  totally  dissimilar  in  constitution,  I  do 
not  retain  the  eighth  class  of  Graham. 

I  have  satisfied  myself  of  the  perfect  analogy  of  palladium  with 
copper ;  it  therefore  must  be  separated  from  platinum,  and  removed 
to  the  second  class.  When  mercury  enters  into  combination  with 
the  equivalent  10 1,4  (Hg.),  it  coincides  in  the  nature  of  its  com- 
pounds with  palladium  and  copper,  and  attaches  itself  to  the  second 


NON-METALLIC     BODIE  S.— O  X  Y  G  E  N  . 


241 


class  ;  but  when  its  equivalent  is  202,8  (Hgj),  its  compounds  resem- 
ble those  of  lead  and  silver,  and,  like  copper,  it  then  becomes  a  mem- 
ber of  the  third  class. 

A  classification  such  as  this,  although  necessary  for  the  philosoph- 
ical study  of  the  relations  of  the  simple  bodies,  could  not,  without 
considerable  inconvenience,  be  strictly  adhered  to  in  an  elementary 
work  like  this  j  I  shall,  therefore,  having  thus  laid  down  these  gen- 
eral principles,  place  it  for  a  time  aside,  and  commence  the  study 
of  the  non-metallic  bodies,  and  their  compounds  with  each  other, 
without  reference  to  any  arrangement,  except  that  of  treating  first 
those  subjects  that  may  be  useful  towards  understanding  or  illustra- 
ting: those  that  follow. 

■J 


CHAPTER  XII, 


OF  THE  SIMPLE  NON-METALLIC  BODIES,  AND  THEIR  COMPOUNDS  WITH  EACH 

OTHER. 

Of  Oxygen. 

From  the  great  quantity  in  which  it  exists  in  nature,  the  numer- 
ous processes  into  which  it  enters  as  an  agent,  and  the  influence 
which  its  discovery  exercised  upon  the  progress  of  chemical  theory, 
oxygen  may  be  looked  upon  as  the  most  important  of  the  simple 
bodies.  It  constitutes  more  than  a  fifth  of  the  atmosphere  by  which 
our  planet  is  invested,  eight  ninths  of  the  whole  quantity  of  water 
which  exists  upon  its  surface,  and,  besides  existing  in  great  quanti- 
ty in  most  animal  and  vegetable  bodies,  it  forms  at  least  a  third  of 
the  total  weight  of  the  mineral  crust  of  the  globe.  On  it  the  pro- 
cesses of  combustion  and  of  respiration  are  dependant,  and  the 
functions  of  organized  existence,  in  both  its  forms,  are  essentially 
connected  and  sustained  through  its  agency. 

Oxygen  exists  only  under  the  form  of  gas  5  it  is  colourless  and 
transparent;  its  specific  gravity  is  1102-6;  100  cubic  inches  of  it 
weigh  34-2  grains;  its  refractive  index  is  0-8616,  that  of  air  beintr 
1-0000.  It  is  very  spa- 
ringly dissolved  by  wa- 
ter, 100  cubic  inches  of 
water  taking  up  only  be- 
tween three  and  four  of 
the  gas.  It  is,  conse- 
quently, in  most  cases, 
collected  over  water,  by 
forms  of  apparatus  that 
shall  be  now  described. 

For  the  collection  and  pres- 
ervation of  gases,  such  as  ox- 
ygen, the  instruments  gener- 
ally employed  are  the  pneu- 
matic trough  and  the  gasom- 
eter    The  former  is  any  ves- 

Hh 


^42  GASOMETERS.  — 'PREPARATION  OF  OXYGEN. 


sel,  g,  containing  water,  for  such  gases  as  are  not  absorbed  by  it,  in  which  is 
inverted  a  glass  vessel  full  of  water,  which  is  sustained  in  it  by  the  pressure  of  the 
external  air,  as  is  the  mercury  in  the  tube  of  the  barometer.  The  orifice  of  the 
tube  c,  from  which  the  gas  issues,  being  brought  under  the  edge  of  the  jar,  which 
is  generally  sustained  upon  a  shelf,  the  water  descends  according  as  the  bubbles 
of  gas  ascend ;  and  when  the  jar  in  the  water  has  been  all  replaced  by  the  gas,  the 
jar  may  be  removed  on  a  tray,  containing  as  much  water  as  serves  to  prevent  all 
communication  from  the  interior  with  the  external  air. 

The  gasometer,  or  gas-holder,  consists  of  a  cylindrical 
copper  vessel,  on  which  another  is  secured  by  five  props  of 
copper,  of  which  two  are  hollow  tubes,  in  connexion  with 
the  cylinder  below.  The  tube  m  passes  down  nearly  to  the 
bottom  of  the  cyhnder,  but  the  other,  n,  only  extends  to 
the  upper  surface ;  both  are  provided  with  stopcocks,  so 
that  the  communication  between  the  cylinder  and  the 
upper  vessel  may  be  opened  or  cut  off  at  pleasure.  At  / 
there  is  also  a  small  tube  with  a  stopcock,  and  below  there 
is  a  large  orifice  at  i,  which  can  be  tightly  closed  by  means 
of  a  screw-plug. 

To  fill  the  cylinder  with  water,  the  orifice  i  is  to  be 
3losed,  and  all  the  stopcocks,  m,  n,  I,  left  open.  Water 
being  then  poured  into  the  upper  vessel,  it  flows  in  through 
the  tubes  m  and  n,  while  the  air  issues  at  /.  When  water 
begins  to  flow  out  at  I,  that  stopcock  is  to  be  closed,  and 
then  the  air  which  still  remains  escapes  by  the  tube  n,  bub- 
bling through  the  water  in  the  upper  vessel.  When  this 
also  ceases,  the  stopcocks  m  and  n  are  to  be  closed,  and 
the  orifice  i  being  then  opened,  the  cylinder  remains  full  of  water  by  the  external 
pressure.  The  tube  from  which  the  gas  issues  is  inserted  at  i,  and  a  quantity  of 
water  escapes  by  that  aperture  equal  in  volume  to  the  gas  which  passes  in. 

A  great  variety  of  processes  may  be  put  in  practice  for  the  pur- 
pose of  obtaining  oxygen  gas  ;  one,  which  is  very  simple  in  theory, 
and  of  great  interest  in  history,  from  being  that  by  which  the  impor- 
tant agencies  of  oxygen  in  chemistry  were  first  recognised,  al- 
though it  is  not  at  present  practicably  useful,  is  the  following : 

Some  red  oxide  of  mercury  (Hg.O.)  is  to  be  introduced  into  a 
retort,  a,  of  hard  glass,  to  which  is  then  attached  a  receiver,  b^  with 


a  tube,  c,  passing  to  the  pneumatic  trough.  On  applying  the  heat  of 
the  argand  spirit-lamp  to  the  oxide  of  mercury,  it  is  decomposed  ; 
the  oxygen  is  given  off  in  the  state  of  gas,  and  may  be  collected  in 
the  bell  glass  e,  and  the  mercury  distils  over,  and,  condensing  in 
the  neck  of  the  retort,  collects  in  drops  which  flow  into  the  receiv- 
er. The  substance  used  is  thus  resolved  into  mercury  and  oxygen; 
from  1094  grains,  there  would  have  been  obtained  101'4^  grains  of 
metallic  mercury,  and  8  grains  of  oxygen  gas,  occupying  at  the 
standard  temperature  and  pressure  23*4  cubic  inches.     It  was  by  an 


PREPARATION     OF     OXYGEN. 


243 


experiment  of  this  kind  that  Lavoisier  demonstrated  the  true  con- 
stitution of  the  metallic  oxides. 

Although  there  are  few  metallic  oxides  which,  as  that  of  mercury, 
admit  of  being  resolved  by  heat  completely  into  free  metal  and  ox- 
ygen, yet  many,  when  heated,  give  off  a  portion  of  their  oxygen, 
the  metal  remaining  in  a  lower  degree  of  oxidation.  Of  this  kind 
are  the  peroxides  of  lead  and  of  manganese ;  and  it  is  generally  from 
the  latter  that  oxygen  is  obtained  for  experimental  purposes,  when 
it  is  not  required  to  be  absolutely  pure.  The  peroxide  of  manga- 
nese (Mn.Oa)  abandons,  when  at  a  red  heat,  one  third  of  its  oxygen, 
and  a  complex  oxide,  Mn304,  remains,  analogous  to  the  black  mag- 
netic oxide  of  iron,  and  formed  by  the  union  of  equivalents  of  pro 


<Z 


toxide  and  of  sesquioxide  (Mn.O.  +  MnaOa).  For  this  purpose  tne 
manganese  is  introduced  in  an  iron  bottle,  a,  to  the  neck  of  which 
is  attached  a  piece  of  gun-barrel,  6,  and  this  connected  by  a  cork,  c, 
with  a  smaller  tube,  d.  For  sake  of  freedom  of  motion,  the  tube/, 
which  passes  to  the  pneumatic  trough  or  the  gasometer,  is  attached 
to  c?  by  a  caoutchouc  connector,  e.  The  bottle  having  been  filled 
about  two  thirds  with  oxide  of  manganese,  may  be  placed  either  in 
a  common  fire  or  in  a  furnace,  its  parts  being  all  arranged  as  in  the 
figure.     When  first  heated  some  water  passes  off,  and  frequently. 


from  the  occurrence  of  carbonate  of  lime  and  of  ammonia  in  the 
substance,  the  first  portions  of  gas  are  mixed  ivith  carbonic  acid  or 
with  nitrogen ;  these  should  be  allowed  to  pass  away,  and  the  oxy- 
gen collected  only  when  a  small  tube  full  of  it  is  capable  of  relight- 
ing a  taper  four  or  five  times.  The  pure  dry  oxide  of  manganese 
consists  of  27-7  of  manganese,  united  to  sixteen  of  oxygen,  of  which 
5*3  are  given  off,  and  hence  1  lb.  troy  of  it  is  capable  of  furnishing 
about  700  grains,  or  nearly  2000  cubic  inches,  equal  to  seven  impe- 


244 


PREPARATION     OF      OXYGEN. 


rial  gallons  of  gas.  The  oxide  of  manganese  found  in  commerce  is, 
however,  not  pure  ,*  in  general  it  does  not  contain  more  than  65  per 
cent,  of  pure  oxide,  and  hence  the  quantity  of  oxygen  furnished  by 
a  pound  of  it  is  about  two  thirds  only  of  that  just  stated. 

Peroxide  of  manganese  yields  more  of  its  oxygen  when  treated 
with  oil  of  vitriol  than  when  simply  ignited,  one  half  becoming 
free,  while  the  manganese,  with  the  remainder,  forms  protoxide, 
which  combines  with  the  sulphuric  acid  thus :  H.O.  .  S.03-hMn.02= 
H.O.  .  S.O3  .  Mn.O.+O. 

This  operation  is  conducted  by  placing  the  manganese  in  a  flask, 

a,  supported  in  a  little 
cup  of  sand,  6,  over  a 
lamp,  and  mixing  it  with 
twice  its  weight  of  oil  of 
vitriol;  a  tube,  c,  bent,  as 
in  the  figure,  passes  to 
the  pneumatic  trough, 
and  dips  under  the  edge 
of  the  jar  in  Avhich  the 
gas  is  to  be  collected. 
When  the  flask  is  heat- 
ed, oxygen  gas  is  rapid- 
ly disengaged,  but  care 
must  be  taken  that,  to- 
^  wards  the  close,  the  wa- 
ter of  the  trough  may  not  pass  back  into  the  flask,  where,  mixing 
with  the  hot  oil  of  vitriol,  it  might  produce  an  unpleasant  explosion. 
The  decomposition  which  here  occurs  has  been  supposed  to  con- 
sist simply  in  the  expulsion  of  the  second  atom  of  oxygen  by  the 
sulphuric  acid  which  takes  its  place.  This,  however,  is  not  the  case. 
By  a  very  gentle  heat,  the  sulphuric  acid  decomposes  the  peroxide, 
Mn.Oj,  into  protoxide,  Mn.O.,  and  permanganic  acid,  Mn207  (SMn.Oj 
=  3Mn.O.+Mn207).  This  last  is  decomposed,  when  the  temperature 
rises,  into  2(Mn.03), manganic  acid,  giving  out  one  equivalent  of  ox- 
ygen ;  but  the  temperature  must  be  raised  very  much  to  complete 
the  separation  of  the  Mn.Og  into  O2  and  Mn.O.  Hence,  in  this  pro- 
cess, as  ordinarily  conducted,  the  residue  in  the  flask  is  found  to  be 
green,  from  manganic  acid  ;  and,  although  in  theory  a  more  abun- 
dant source  of  oxygen  than  that  by  simple  ignition,  in  the  propor- 
tion of  3  to  2,  it  is  not  so  useful  in  practice. 

When  oxygen  is  required  completely  pure,  it  is  generally  prepared 
by  heating  in  a  glass  tube  or  flask,  to  which  a 
bent  tube  is  attached,  as  in  the  figure,  a  small 
quantity  of  chlorate  of  potash.  This  salt  con- 
sists of  chloric  acid  united  to  potash  Cl.Os-j-K.O., 
and  when  heated  somewhat  above  its  melting 
point,  it  is  decomposed,  all  the  oxygen  it  con- 
tains being  evolved  in  the  state  of  gas,  and  the 
other  elements  remaining  combined  as  chloride 
of  potassium.  The  constituents  of  this  salt  are 
by  weight  35-4  chlorine,  39*7  potassium,  and  48 
of  oxygen.  Hence  100  parts  of  it  give  39  of 
oxygen  by  weight,  or  an  ounce  troy,  187  grains, 


PROPERTIES     OF     OXYGEN. 


245 


or  543  cubic  inches.     An  ounce  of  it  is  therefore  equivalent  in  ef- 
fect to  six  ounces  of  ordinary  peroxide  of  manganese. 

The  most  remarkable  property  of  oxygen  is  the  energy  with  which 
it  supports  combustion.  If  a  lighted  taper  be  blown  out,  so  that  a 
point  of  the  wick  shall  continue  red,  it  will  be  brilliantly  relighted 
on  being  plunged  into  a  vessel  of  oxygen  gas,  and  this  may  be  re- 
peated several  times  in  succession.  A  bit  of  charcoal,  heated'  to 
redness  at  a  single  point,  burns,  when  immersed  in  oxygen,  with 
rapid  scintillations  of  exceeding  brilliancy ;  and  when  phosphorus 
is  inflamed  in  oxygen,  the  splendour  of  the  combustion  is  insupport- 
able to  the  eye.  Even  bodies  which  are  not  combustible  under  or- 
dinary circumstances,  may  be  made  to  burn  in  oxygen.  Thus,  if  an 
iron  wire  be  tipped  at  its  extremity  Avith  sulphur,  or  have  attached 
to  it  a  small  bit  of  waxed  cotton  wick,  on  lighting  this,  and  plunging 
the  whole  into  the  gas,  the  combustion  extends  from  the  sulphur  or 
wick  to  the  iron,  which  is  converted  into  oxide,  with  the  disengage- 
ment of  m.ost  brilliant  light.  The  heat  evolved  by  the  combination 
of  the  oxygen  and  iron  is  so  great,  that  the  oxide  formed  is  melted, 
and  flows  down  in  drops  from  the  extremity  of  the  burning  wire, 
which,  even  after  having  passed  through  a  layer  of  water,  fuse  them- 
selves into  the  substance  of  the  earthenware  plate,  upon  which  the 
gas  jar  generally  stands.  If,  at  the  moment  when  a  drop  of  oxide 
is  about  to  fall,  it  be  projected  by  a  little  jerk  against  the  side  of  the 
glass,  it  will  melt  its  way  into  its  substance,  or  even,  if  it  be  not 
thick,  pass  completely  through. 

The  heat  evolved  when  the  body  burns  in  pure  oxygen  may  be  readily  shown  bv 
simple  methods.  If  a  jet,  u,  be  attached  to  the  lat- 
eral stopcock,  I,  of  the  gasometer,  and  the  flame  of  a 
spirit-lamp,  h,  be  urged  by  the  issuing  stream  of  gas, 
as  by  a  blov^pipe,  the  most  refractory  substances 
may  be  fused  by  it.     If  the  tube  be  curved  Aoyvn- 

ward,  the  jet  may  be  brought  to  bear  on  a  little  cup      ^^^^^^^    u     _A 
of  red-hot  charcoal,  in  which  the  body  to  be  fused  ~ 

may  be  laid,  and  thus,  upon  a  small  scale,  the  con- 
struction and  effect  of  the  most  powerful  wind  fur- 
naces may  be  imitated. 

Oxygen  gas  is. necessary  to  the  support 
of  animal  life.  It  is  the  oxygen  which  ex- 
ists in  the  atmospheric  air  that  fits  it  for 
its  uses  in  the  economy  of  nature.  The 
blood  which  returns  dark  and  venous  into  the  lungs  is  there  changed 
into  the  bright  arterial  state,  by  absorbing  oxygen  and  evolving  car- 
bonic acid,  in  a  manner  of  which  the  exact  details  will  be  hereafter 
studied.  This  change  occurs  even  with  blood  which  has  been  re- 
moved from  the  body.  If  a  quantity  of  dark  blood,  drawn  from  a 
vein,  be  agitated  in  a  vessel  of  oxygen  gas,  it  is  immediately  changed 
into  the  vermilion-coloured  arterial  blood.  An  animal  can  live  long- 
er in  a  vessel  of  pure  oxygen  than  in  the  same  volume  of  atmosphe- 
ric air ;  but  still,  pure  oxygen  is  not  fitted  for  the  support  of  life.  It 
is  too  stimulating  ;  the  animal  lives  too  fast,  and  ultimately  dies  with 
[i  symptoms  of  general  inflammatory  fever,  even  though  there  may  re- 
main still  a  quantity  of  oxygen  gas  capable  of  supporting  the  life  of 
^another  animal  for  a  considerable  time. 

The  name  of  oxygen  was  given  to  this  body  from  the  idea  of  its 


246  PREPARATION   OF  HYDROGEN. 

peculiar  power  of  conferring  acid  properties  on  its  compounds  j  and, 
in  reality,  most  of  the  bodies  recognised  by  chemists  among  the 
class  of  acids  contain  oxygen.  But  this  is  not  invariable  ;  other 
simple  bodies  possess  the  same  power,  as  has  been  already  noticed 
on  more  than  one  occasion,  and  I  shall  have  opportunities  of  recur- 
ring to  it  when  describing  the  properties  of  those  bodies. 

Of  Hydrogen, 

Hydrogen  exists  abundantly  in  nature  as  a  constituent  of  animal 
and  vegetable  substances,  and  is  particularly  of  interest  by  forming 
a  constituent  of  water.  From  this  fact  it  derives  its  name,  vduip 
yevvao)  (I  form  water),  and  it  is  by  the  decomposition  of  water  that 
hydrogen  is  almost  always  obtained  for  experimental  purposes. 

If  1  small  quantity  of  the  metal  potassium  be  placed  in  contact 
with  water,  it  immediately  abstracts  the  oxygen,  forming  potash, 
which  is  an  oxide  of  potassium.  The  hydrogen  is  set  free,  and  ap- 
pears as  a  gas.  If  the  experiment  be  performed  under  a  bell  glass, 
inverted  in  a  basin  of  mercury  or  water,  the  gas  may  be  collected ; 
but  if  the  decomposition  takes  place  in  contact  with  the  atmospheric 
air,  so  much  heat  is  evolved  by  the  rapidity  and  intensity  of  the 
action,  that  the  hydrogen  takes  fire,  and  burns  according  as  it  is 
produced.  This  is  the  simplest  form  under  which  the  decomposi- 
tion of  water  can  be  exhibited,  the  reaction  being  K.+H.O.=K.O. 

If  the  circuit  of  the  electrical  current  from  a  voltaic  battery  be 
completed  through  water,  which  has  been  rendered  a  good  con- 
ductor by  the  addition  of  sulphuric  acid,  or  common  or  Glauber  salt, 
the  two  constituents  of  the  water  are  evolved  at  the  opposite  elec- 
trodes, or  terminating  surfaces  of  the  liquid,  and  the  two  gases  may 
be  collected  either  separately  or  mixed  together,  and  will  be  then 
found  to  have  been  evolved  in  such  proportions  that  the  hydrogen 
will  be  double  the  volume  of  the  oxygen.  The  theory  of  this  mode 
of  obtaining  hydrogen  has  been  described,  so  far  as  we  are  compe- 
tent to  explain  it,  in  a  former  chapter. 

These  methods,  although  the  simplest,  are  yet-not  applicable  to 
ordinary  purposes,  from  their  expense ;  those  usually  employed  are 
the  following.  There  are  many  metals  which,  although  having  a 
powerful  affinity  for  oxygen,  are  yet  not  able  to  abstract  it  from  hy- 
drogen, and  so  to  decompose  water  at  ordinary  temperatures;  but 
at  a  red  heat  the  decomposition  rapidly  takes  place.  For  this  pur- 
pose iron  is  generally  employed.  A  gun-barrel,  or  an  iron  tube,  c  c, 
is  taken,  and  the  interior  having  been  loosely  filled  with  iron  turn- 
ings or  coils  of  iron  wire,  it  is  placed  horizontally  in  a  furnace,  by 
means  of  which  it  can  be  brought  to  a  full  red  heat.  To  one  extrem 
ity  of  the  tube  is  connected  a  small  glass  retort,  a,  containing  water  ; 
to  the  other,  a  flexible  metal  tube,/,  which  passes  under  the  shelf  of 
the  pneumatic  trough.  The  iron  tube  being  red  hot,  the  water  in 
the  retort  is  made  to  boil ;  the  vapour  passes  into  the  tube,  and 
comes  into  contact  with  the  red-hot  iron  ;  decomposition  immedi- 
ately occurs,  and  the  iron  is  oxidized,  while  the  hydrogen  gas  is 
disengaged  in  large  quantity.  The  state  of  combination  into  which 
the  iron  is  found  to  have  passed  is  that  of  the  black  oxide,  such  as  the 


PREPARATION     OF     HYDROGEN. 


247 


scales  that  are  formed  at  the  smith's  forge  by  the  action  of  the  at- 
mospheric air  on  iron,  and  which  is  also  formed  when  iron  is  burn- 
ed in  oxygen  gas.  The  action  may,  however,  be  simply  represent- 
ed as  follows : 

Fe.-f  H.0.=  H.-fFe.O.  Protoxide  of  iron. 
2Fe.H-3H.O.=:3H.+FeA  Peroxide  of  iron. 
3Fe.+4H.O.=4H.+Fe304  Black  oxide  of  iron. 

The  action  of  the  iron  in  thus  decomposing  water  might  appear 
paradoxical,  as  it  will  be  seen  hereafter  that  by  means  of  a  current  ot 
hydrogen  gas,  acting  at  a  red  heat,  oxide  of  iron  may  be  decomposed, 
the  iron  separating  in  the  metallic  state,  and  water  being  produced  j 
and  thus,  at  the  same  temperature,  two  decompositions,  precisely  the 
reverse  of  each  other,  may  go  on.  It  would  appear  that  this  is  one 
of  those  cases  in  which  affinities,  nearly  equal  otherwise,  are  direct- 
ed to  one  or  the  other  object,  according  as  one  or  the  other  sub- 
stance is  in  excess.  When  the  iron  is  kept  in  a  stream  of  watery 
vapour,  this  latter  is  decomposed,  and  the  hydrogen  being  carried 
away,  according  as  it  is  formed,  by  the  current,  it  cannot  interfere 
by  its  presence  in  any  opposing  manner.  On  the  other  hand,  when 
oxide  of  iron  is  heated  in  a  stream  of  hydrogen  gas,  it  is  decompo- 
sed, and  the  water  being  removed  as  rapidly  as  it  is  produced,  the 
tendency  to  reaction  is  prevented. 

By  the  agency  of  a  dilute  acid  we  may  also  increase  the  tenden- 
cy of  a  metal  to  combine 
with  water,  so  that  the  de- 
composition of  water  can 
be  effected  rapidly  even  at 
common  temperatures.  If 
a  few  slips  of  zinc  or  iron 
be  placed  in  a  flask,  to 
which  a  bent  tube,  /,  is 
adapted,  as  in  the  appara- 
tus represented  in  the  fig- 
ure, and  then  oil  of  vitri- 


248  PREPARATION  AND  PROPERTIES  OF  HYDROGEN. 

ol,  diluted  with  eight  times  its  weight  of  water,  be  poured  upon  it 
through  the  funnel,  an  abundant  effervescence  occurs,  arising  from 
the  escape  of  hydrogen  gas,  and  the  zinc  or  iron  rapidly  dissolves. 
The  action  continues  until  the  acid  has  been  all  neutralized  by  the 
zinc,  or  the  zinc  all  dissolved  by  the  acid ;  or,  finally,  until  so  much 
of  the  compound  formed  during  the  reaction  has  been  produced, 
that  the  water  present  cannot  dissolve  any  more.  This  compound 
consists  of  oxide  of  zinc  or  of  iron  united  to  the  sulphuric  acid,  the 
oxygen  of  the  decomposed  water  uniting  with  the  metal,  while  the 
hydrogen  is  set  free.  The  process  may  be  thus  represented,  zinc 
being  used,  Zn.+S.Oa+H.O.^H.-f  (S.Oa+Zn.O.) 

To  account  for  the  circumstances  of  this  reaction,  a  peculiar 
power  was  at  one  time  supposed  to  exist,  termed  disposing  affinity  ; 
and  it  was  said  that  the  presence  of  the  sulphuric  acid  disposed  the 
zinc  to  decompose  the  water,  because  the  oxide  of  zinc,  when  formed 
by  the  decomposition,  might  unite  with  the  acid.  This  theory  is 
quite  futile.  There  can  be  no  oxide  of  zinc  to  influence  the  acid 
until  the  water  has  been  decomposed,  and  the  effect,  the  source  of 
which  was  to  be  sought  for,  had  consequently  passed  away.  It  ap 
pears  to  me  that  the  explanation  is  of  a  much  simpler  form.  Zinc 
and  iron  decompose  water  at  ordinary  temperatures,  even  without 
the  presence  of  any  acid,  but  with  excessive  slowness,  so  that  the 
effect  is  almost  imperceptible.  In  fact,  the  first  minute  trace  of  ox- 
ide which  is  formed,  being  insoluble  in  water,  coats  over  the  metallic 
surface  with  a  varnish  impermeable  to  the  fluid,  and  thus  prevents 
its  farther  action.  This  coating  of  metallic  oxide  is  soluble  in  acids  ', 
and  thus,  by  the  presence  of  an  acid,  a  fresh  surface  of  bright  metal 
is  kept  constantly  exposed,  and  the  decomposing  action  is  allowed 
to  proceed  without  hinderance.  It  is  possible,  however,  that  this 
simple  view  may  require  some  alteration,  and  that  this  mode  of  ob- 
taining hydrogen  gas  may  be  found  to  involve  voltaic  conditions 
which  at  present  are  not  well  understood.  Pure  zinc  is  but  very 
feebly  acted  on  even  by  a  diluted  acid ;  and  the  rapid  action  which 
occurs  with  commercial  zinc  or  iron  may  be  referred  to  decompo- 
sition by  the  electric  currents  which  circulate  from  one  portion  of 
the  impure  metal  to  the  other,  through  the  liquid.     See  page  135. 

Hydrogen  gas,  when  it  has  been  prepared  by  any  of  these  process- 
es, is  seldom  pure.  The  iron  and  zinc  of  commerce  contain  gen- 
erally traces  of  carbon,  of  sulphur,  and  sometimes  of  arsenic,  which, 
combining  with  some  hydrogen,  form  gaseous  or  volatile  products, 
which  give  to  the  hydrogen  a  peculiar  disagreeable  odour,  and  col- 
our its  flame.  Occasionally,  also,  traces  of  potassium  and  zinc,  in 
very  minute  division,  are  carried  up  with  the  hydrogen  by  the  me- 
chanical force  of  the  effervescence,  but  by  repose  these  latter  impu- 
rities are  found  completely  to  separate.  To  get  rid  of  the  former 
class  of  impurities,  the  gas  may  be  made  to  bubble  very  slowly 
through  solutions  of  potash  and  of  corrosive  sublimate,  by  which 
the  arsenic  and  sulphur  would  be  absorbed,  and  through  alcohol, 
which  would  for  the  most  part  dissolve  the  carburetted  hydrogen. 
It  is,  however,  better,  when  pure  hydrogen  is  required,  to  prepare 
it  by  acting  upon  water  with  metallic  sodium  mixed  with  quicksilver, 
so  as  to  moderate  the  rapidity  of  the  decomposition.     Zinc,  which 


PROPERTIES     OF     HYDROGEN.  24^ 

has  been  refined  by  distillation,  gives  also,  with  sulphuric  acid  and 
water,  a  gas  almost  completely  pure. 

When  free  from  foreign  matters,  hydrogen  gas  burns  with  a  very 
pale  white  flame,  almost  invisible  in  bright  day.  In  burning,  it  com- 
bines with  the  oxygen  of  the  air,  and  forms  water.  If  a  jar  of  hy- 
drogen gas  be  suddenly  turned  with  the  orifice  upward,  and  infla- 
med, the  whole  mass  of  gas  rushes  out,  and  gives  a  sheet  of  pale 
white  or  yellowish  flame.  If  it  be  mixed  with  air  previous  to  being 
set  on  fire,  the  combustion  of  the  mixture  is  instantaneous,  and  ac- 
companied with  an  explosive  report.  The  proper  proportions  are  two 
volumes  of  hydrogen  gas  to  five  of  air.  If  a  lighted  taper  be  plunge^l 
into  a  jar  of  hydrogen,  it  is  immediately  extinguished,  the  gas  not 
being  able  to  support  combustion. 

Hydrogen  gas  is  colourless  and  transparent ;  it  is  absorbed  by  wa 
ter  in  very  small  quantity,  and  hence,  for  ordinary  purposes,  is  al- 
ways collected  over  that  liquid.  It  refracts  light  strongly,  its  re- 
fractive index  being  6*61,  air  being  1*00.  In  its  capacity  for  heat 
it  exceeds  all  other  gases,  being  21*9  by  Apjohn's  experiments,  air 
being  1-00  for  equal  weights,  or  1'46  for  equal  volumes.  It  is  the 
lightest  substance  known,  being  only  one  fifteenth  of  the  specific 
gravity  of  air  j  or,  more  accurately,  its  specific  gravity  is  68*8,  air 
being  1000-0. 

It  is  hence  used  for  filling  balloons ;  as'  the  balloon  full  of  hydrogen  weighs  less 
than  the  same  volume  of  air,  it  ascends  with  a  force  equal  to  the  difference  of 
weight.  For  the  purpose  of  illustrating  this  property  of  hydrogen,  a  small  balloon 
made  of  gold-beater's  skin,  or  of  the  serous  membrane  of  the  turkey's  craw,  may 
be  made  use  of  On  this  minute  scale,  however,  the  gas  should  be  used  dry,  as, 
when  prepared  and  collected  over  water,  its  specific  gravity  may  be  so  much  in- 
creased by  the  watery  vapour  it  may  contain,  that,  although  good  enough  for  a 
larger  balloon,  it  could  not  carry  up  a  small  one,  the  small  balloon  being  really 
much  heavier  in  proportion  to  the  quantity  of  gas  it  can  contain ;  consequently,  the 
hydrogen  should  be  dried,  which  may  be  effected  by  causing  it  to  stream  from  the 
gasometer  through  a  tube  filled  with  fragments  of  fused  chloride  of  calcium,  which 
absorbs  water  with  great  avidity,  and  from  thence  to  enter  the  balloon.  At  present, 
hydrogen  gas  is  but  seldom  employed,  it  being  found  cheaper  to  make  the  balloon 
very  large,  and  to  use  coal  gas,  which,  although  much  heavier  than  hydrogen,  is 
considerably  lighter  than  atmospheric  air  under  the  same  volume. 

By  the  same  experiment,  the  three  most  remarkable  properties  of  hydrogen  may 
be  exhibited  in  an  interesting  form.  If  a  jar  of  hydrogen  be  held  vertically,  with 
the  orifice  downward  and  open,  it  will  remain  filled  by  the  hydrogen  for  a  certain 
time,  as  the  air,  being  so  much  heavier,  mixes  itself  with  the  lighter  gas  but  very 
slowly.  If  a  lighted  taper  be  now  appUed,  the  gas  will  inflame  at  the  surface 
where  it  is  in  contact  with  the  atmosphere,  but,  on  plunging  the  taper  upward  into 
the  pure  gas,  it  will  be  extinguished ;  being  then  lowered,  it  can  be  relighted  at  the 
sheet  of  flame  which  marks  the  surface  of  contact  of  the  gas  and  the  atmosphere, 
and  when  again  raised  into  the  pure  gas,  it  will  again  be  extinguished ;  this  can  be 
repeated  very  often :  the  horizontal  sheet  of  flame  having  been  gradually  rising  into 
the  jar  according  as  the  hydrogen  consumed,  if  then  the  jar  be  suddenly  turned 
with  the  orifice  directed  upward,  the  residual  gas  will  at  once  rush  out,  and,  mixmg 
with  the  air,  will  burn  explosively  with  a  single  flash. 

The  same  experiments  on  the  combustion  of  hydrogen  may  be  made  with  pure 
oxygen  gas  in  place  of  atmospheric  air,  but  then  the  results  are  at  least  five  times 
more  brilliant.  The  proportions  for  burning  hydrogen  with  oxygen  gas  are  two 
volumes  of  hydrogen  and  one  of  oxygen ;  then,  if  the  gases  were  pure,  nothing  but 
pure  water  should  remain. 

If  a  bladder  be  filled  with  the  two  gases  mixed  in  these  proportions,  and  being 
punctured,  the  flame  of  a  taper  be  applied  to  the  orifice,  the  whole  explodes  with  a 
flash  of  briUiant  light  and  deafening  explosion,  the  strongest  bladder  being  torn  to 
shreds  by  the  expansive  force  of  the  ignited  gases.     In  this  experiment  the  bladder 

I  I 


250 


PROPERTIES    OF     HYDROGEN. 


must,  of  course,  be  secured,  which  is  easily  done  by  tying  the  stopcock  by  which 
the  gas  has  been  passed  into  the  bladder  between  two  nails,  with  some  stout  cord 
or  copper  wire. 

A  mixture  of  hydrogen  and  oxygen  may  also  be  exploded  by  means  of  the  elec- 
tric spark ;  for  this  purpose  a  strong  tube,  closed  at  the  top,  and  graduated  into 
parts  of  a  cubic  inch,  is  taken,  and  two  brass  or  platina  wires  are  inserted  through 
the  opposite  sides  near  the  top,  their  extremities  being  kept  about  one  eighth  of  an 

inch  asunder.  This  tube  is  termed  a  eudiometer, 
as  it  is  frequently  used  to  measure  the  quantity  of 
oxygen  in  the  atmosphere,  and  generally  for  the 
analysis  of  gaseous  mixtures.  The  oxygen  and 
hydrogen  gases  being  confined  in  this  tube  over 
water  or  mercury,  an  electric  spark  is  passed 
through  the  mixture  by  means  of  the  wires ;  the 
gases  explode,  and,  if  the  proportions  had  been 
accurately  observed,  no  residue  is  found ;  if  one 
or  the  other  gas  had  been  in  excess,  the  excess 
remains  behind,  one  third  of  the  volume  which 
disappears  being  oxygen,  and  the  other  two  thirds 
being  hydrogen.  In  order  to  explode  a  bladder 
full  of  the  mixed  gases  by  means  of  electricity,  a 
very  simple  plan  is  to  fasten  the  bladder  upon  a 
large  cork,  having  in  the  centre  an  opening,  into 
which  a  stopcock  is  screwed  for  the  passage  of 
the  gas,  and  through  which,  near  the  edges,  pass 
two  stout  brass  wires,  terminating  inside  the 
bladder  in  small  knobs  ;  these  ends  being  brought 
near  each  other,  and  tlje  external  ends,  being  connected  by  long  wires  with  the 
coatings  of  a  charged  Leyden  jar,  the  spark  passes  between  the  terminal  knobs  in 
the  bladder,  and  the  explosion  immediately  occurs. 

Hydrogen  and  oxygen  are  capable  of  entering  into  combination, 
and  forming  water  without  any  explosion  or  visible  combustion. 
If  the  mixed  gases  be  transmitted  through  a  tube  heated  to  scarcely 
visible  redness,  they  quietly  combine,  and  this  effect  occurs  at  a 
still  lower  temperature,  if  the  tube  contains  coarsely-powdered 
glass  or  sand.  Slips  of  gold  and  silver  are  still  more  favourable; 
but  the  most  rapid  union  is  effected,  even  at  ordinary  temperatures, 
by  platinum.  This  effect  appears  to  be  due  to  the  metallic  surface 
retaining  a  thin  layer  of  gas  by  so  strong  a  force  as  by  condensation 
to  bring  the  molecules  within  the  sphere  of  their  mutual  chemical 
attraction  ;  they,  combining,  form  water,  and  a  new  quantity  of  the 
gaseous  mixture  comes  into  contact  with  the  platinum,  and  follows 
the  same  course.  If  the  platinum  be  in  the  form  of  a  sponge,  in 
which  the  acting  surfaces  are  very  great,  the  union  takes  place  so 
rapidly,  that  the  heat  evolved  raises  the  temperature  of  the  platinum 
ball  to  bright  redness,  and  then  the  remaining  gas  explodes.  Pla- 
tinum in  form  of  sponge  always  contains  a  quantity  of  air  in  this  con- 
densed condition,  and  hence,  when  a  jet  of  hydrogen  gas  is  caused 
to  play  upon  a  morsel  of  spongy  platina,  it  is  absorbed,  and  water  be- 
ing formed,  the  ball  of  platinum  becomes  red  hot,  and  inflames  the 
jet  of  gas.  This  constitutes  a  sort  of  lamp  for  instantaneous  light, 
equally  pretty  and  ingenious,  the  jet  of  hydrogen  in  its  turn  being 
contrived  to  fall  upon  and  light  a  little  lamp.  See  p.  179  and  235. 
Spongy  platinum  introduced  into  a  mixture  of  oxygen  and  hydro- 
gen explodes  them  instantly,  but  it  can  be  usefully  diluted,  as  it 
were,  by  being  made  into  balls  with  a  little  pipe-clay,  and  then  it 
can  only  produce  their  union  in  the  slow  and  silent  way.  This  mode 
is  accordingly  often  used  in  the  analysis  of  mixtures  of  gases,  and 


HYDRO-OXYGEN     BLOWPIPE.  251 

tne  energy  of  the  platinum  balls  can  be  graduated  by  the  proportions 
of  metal  and  of  pipe-clay  which  are  employed.  Hydrogen  and  oxy- 
gen, however,  are  not  the  only  gases  which  can  be  made  to  unite  by 
the  agency  of  platinum -surfaces,  as  will  be  elsewhere  shown. 

The  heat  produced  by  the  combustion  of  oxygen  and  hydrogen 
gases  is  the  most  intense  that  can  be  obtained  by  any  artificial 
means.  It  is  hence,  at  present,  much  used  in  an  instrument  termed 
the  hydro-oxygen  blowpipe.  The  apparatus  employed  must  be  of 
such  a  nature  as  to  prevent  any  risk  of  injury  from  explosion,  which, 
with  any  large  quantity  of  the  gases,  might  produce  most  serious 
accidents.  The  safest  form  for  experiment  on  a  large  scale  con- 
sists in  having  the  gases  separate,  in  two  gasometers  connected  by 
tubes,  and  of  such  a  size  and  pressure  as  that  in  the  same  time 
there  will  be  delivered  two  volumes  of  hydrogen  to  one  of  oxygen 
gas.  The  hydrogen  gas  tube  terminates  in  a  hollow  cylindrical  jet, 
inside  of  which  passes  the  jet  of  oxygen  gas ;  the  flame  thus  pro- 
duced resembling  that  of  a  candle,  into  the  interior  of  which  is  in- 
jected a  stream  of  air  by  the  blowpipe  in  common  use.  Another  form 
consists  of  a  metallic  box,  made  so  exceedingly  strong  that,  even 
were  the  gases  to  explode  within  it,  there  could  be  no  danger  of  its 
being  burst.  The  gases,  previously  mixed  in  a  bladder,  are  forced, 
by  means  of  a  condensing  syringe,  into  the  box,  and  a  sufficient 
quantity  having  been  introduced,  the  condensing  syringe  is  removed, 
and  a  stopcock  connected  with  a  jet  opened.  The  pressure  of  the 
condensed  gas  inside  forces  out  a  stream,  which  is  ignited,  and,  if 
the  flame  be  not  allowed  to  burn  too  long,  the  rapidity  of  the  cur- 
rent is  sufficient  to  prevent  the  passage  backward  of  the  flame. 
This  form  is  now,  however,  almost  totally  superseded  by  the  very 
ingenious  safety  cylinder  and  jet  of  Mr.  Hemming.  It  consists  of 
a  brass  cylinder  of  about  five  or  six  inches  long,  by  three  fourths 
of  an  inch  in  diameter,  which  is  filled  as  closely  as  possible  by  a 
bundle  of  fine  brass  wires,  into  the  centre  of  which  a  wedge-shaped 
brass  rod  is  introduced  and  driven  very  hard,  so  as  to  pack  the 
wires  closely.  The  interstices  between  the  wires  form  thus  a  col- 
lection of  exceedingly  minute  tubes,  through  which  the  gas  must 
pass.  To  one  end  of  this  cylinder  is  connected  a  bladder  contain- 
ing the  mixed  gases  j  the  other  end  terminates  in  a  jet  from  which 
the  gas  issues ;  the  flame,  in  passing  backward  from  the  jet,  must, 
in  its  way  to  the  bladder,  stream  through  the  metallic  cylinder,  and 
then  comes  into  contact  with  so  great  a  surface,  and  so  large  a  mass 
of  material  which  conducts  heat  rapidly,  that  the  gases  are  cooled 
far  below  the  temperature  at  which  their  union  can  occur,  and  their 
farther  combustion  is,  of  course,  prevented. 

For  experiments  upon  a  small  scale,  this  little  apparatus  combines 
the  highest  qualifications  of  convenience,  security,  and  simplicity. 

In  the  flame  of  the  hydro-oxygen  blowpipe,  the  most  infusible  sub- 
stances  are  melted ;  flint,  pipe-clay,  the  most  refractory  metals,  as 
platinum,  not  merely  fuse,  but  even  appear  to  evaporate  :  a  rod  of 
iron  takes  fire,  and  burns  with  a  brilliancy  surpassing  that  of  its 
combustion  in  oxygen  gas.  Some  of  the  earths  alone,  are  capable 
of  resisting  its  highest  power.  These,  as  lime  and  magnesia,  par- 
ticularly the  former,  become,  in  the  flame  of  the  mixed  gases,  so 


252  CHEMICAL     RELATIONS     OF     HYDROGEN. 

brightly  luminous  as  to  rival  in  intensity  the  noonday  sun,  and 
hence  furnish  one  of  the  most  important  uses  of  the  blowpipe,  by 
serving  for  optical  purposes  as  a  substitute  for  the  solar  ray,  which, 
in  our  climate,  is  so  uncertain  in  its  supply.  The  solar  microscope 
fitted  up  with  a  ball  of  lime,  ignited  by  a  jet  of  the  mixed  gases  in 
place  of  the  solar  rays,  constitutes  the  hydro-oxygen  microscope, 
now  a  common  exhibition  in  our  large  towns  ;  and  the  same  light  has 
been  proposed  for  use  in  lighthouses,  and  has  been  actually  employ- 
ed for  signals  in  connecting  the  trigonometrical  surveys  of  the  Brit- 
ish islands.  In  one  case  the  light  emitted  by  the  ball  of  lime  was 
distinctly  visible  at  a  distance  of  seventy  miles. 

A  singular  phenomenon,  which  is  best  produced  by  the  flame  of  hydrogen,  al- 
though not  peculiar  to  it,  is  the  production  of  musical  sounds,  if  an  open  tube  be 
held  over  the  flame.  The  flame,  in  fact,  although  uniform  to  the  eye,  consists  of  a 
succession  of  little  explosions  of  mixed  air  and  gas,  which  recur  too  rapidly  to  be 
individually  distinguishable.  If  the  tube  be  now  held  over  the  flame,  it  will  be  seen 
to  flicker,  and  after  a  few  irregular,  interrupted,  explosive  sounds,  a  distinct  musi- 
cal note  is  heard.  The  explosions  set  the  air  in  the  tube  to  vibrate,  at  first  irregu- 
larly, but  at  last  with  such  a  velocity  of  vibration  as  corresponds  to  the  length  of 
the  tube,  and  to  the  rapidity  with  which  the  explosive  mixtures  of  air  and  gas  can 
be  formed  ;  and  thus,  by  any  of  the  known  methods  of  determining  the  number  of 
vibrations  corresponding  to  a  given  note,  the  frequency  of  the  little  explosions  may 
be  found.  Occasionally,  also,  a  distinct  beat,  or  alternations  of  sound  and  silence, 
may  be  heard,  as  in  two  organs,  .which  being  nearly,  but  not  completely  in  unison, 
sound  together ;  this  arises  from  a  current  of  hot  air  ascending  in  the  centre  of  the 
tube,  while  a  current  of  cold  air  is  formed  next  the  side.  These  do  not,  for  a  time, 
vibrate  completely  as  one  mass  ;  and  hence,  at  certain  periods,  alternately  redouble 
and  destroy  the  sounds  which  they  produce. 

In  its  relation  to  other  bodies,  hydrogen  plays  a  very  remarkable 
and  peculiar  part.  It  was  at  one  time  supposed  that  it  shared  with 
oxygen  the  power  of  generating  acids;  and  as  sulphur,  chlorine,  cy- 
anogen, iodine,  &c.,  form  one  class  of  acids  by  combining  with  ox- 
ygen, so  they  jformed  a  second  class,  called  hydracids,  by  entering 
into  union  with  hydrogen  ;  and  hydrogen  was  believed  to  be  related 
to  hydrochloric  acid,  as  oxygen  was  to  the  sulphuric  or  the  phospho- 
ric acids.  In  the  year  1832, 1  proved  that  this  view  was  totally  incor- 
rect, and  that  all  the  properties  of  the  compounds  of  hydrogen  com- 
bined to  show  that  it  was  an  eminently  electro-positive  body  ;  that  it 
took  a  place  along  with  iron,  manganese,  and  zinc  ;  and  that  the  com- 
pounds of  hydrogen  with  chlorine,  oxygen,  iodine,  and  sulphur  were 
almost  universally  electro-positive  in  combination,  and  possessed  ba- 
sic characters  derived  from  the  pre-eminent  positive  energies  of  the 
hydrogen  itself.  These  views  have,  since  that  period,  been  still  far- 
ther corroborated  by  the  researches  of  Graham,  and  by  additional 
investigations  of  my  own  ;  and  although  the  old  familiar  nomencla- 
ture will  still  retain  its  place  to  a  great  extent,  yet  there  rests  now 
no  doubt  upon  the  minds  of  philosophical  chemists,  that  hydrogen 
is  most  closely  allied  to  the  metals,  particularly  to  zinc  and  copper; 
that  the  chlorides,  iodides,  and  fluorides  of  hydrogen,  although  they 
simulate  some  of  the  characters  which  we  assign  to  acids,  resemble, 
in  all  important  points,  the  chlorides,  iodides,  &c.,  of  the  metals 
above  mentioned ;  that,  in  fact,  hydrogen  is  a  metal  enormously 
volatile,  standing  probably  in  the  same  relation  to  mercury  that 
mercury  does  to  platinum  in  that  respect,  but  still  possessed  of  all 
truly  chemical  peculiarities  of  the  metallic  state,  and  no  more  de- 


CONSTITUTION     OF     WATER.  253 

prived  of  the  commonplace  qualities  of  lustre,  hardness,  or  brillian- 
cy, than  is  the  mercurial  atmosphere  which  fills  the  apparently  empty 
top  of  the  tube  of  a  barometer,  or  the  salivating  atmosphere  of  a 
quicksilver  mine  or  of  a  gilder's  workshop. 

Of  Water — Oxide  of  Hydrogen. 
H.O. 
It  has  been  already  shown  that  water  consists  of  hydrogen  ana 
oxygen  combined,  in  the  proportions  of  two  volumes  of  the  former 
gas  to  one  volume  of  the  latter,  and  by  weight  of  one  part  of  hy- 
drogen united  to  eight  of  oxygen,  or  of  ll-l  hydrogen  and  88*9  of 
oxygen  in  100  parts. 

The  exact  determination  of  the  composition  of  water  is  one  of  the 
most  important  investigations  in  the  domain  of  chemistry,  as  from 
the  great  range  of  affinities  which  oxygen  and  hydrogen  exercise, 
and  the  variety  of  compounds  into  which  they  respectively  enter, 
the  numbers  adopted  for  the  combining  proportions  of  almost  all 
other  bodies  hinge  upon  those  which  are  employed  for  the  constit- 
uents of  water.  It  has,  consequently,  attracted  the  attention  of  many 
distinguished  chemists.  But,  although  the  determination  of  the  re- 
spective volumes  in  which  the  oxygen  and  hydrogen  unite,  as  de- 
termined by  Gay  Lussac,  gave  a  very  accurate  result,  yet  the  most 
positive  determination  was  obtained  by  Berzelius,  with  the  method 
now  to  be  described. 

A  known  weight  of  black  oxide  of  copper  is  introduced  into  a 
glass  tube,  on  which  a  bulb  is  blo^vn,  and  to  the  extremity  of  which 
a  flask,  containing  the  materials  for  generating'  pure  hydrogen  gas, 
is  connected.     As,  however,  the  hydrogen  gas  passes  off  in  a  damp 
condition,  and  thus  introducing  water  might  falsify  the  result,  there 
is  interposed  a  tube  containing  fragments  of  fused  chloride  of  cal- 
cium, by  which  the  hydrogen   gas  is  completely  dried  before  it 
comes  into  contact  with  the  oxide  of  copper.     When  the  apparatus 
has  been  filled  with  pure  dry  hydrogen,  heat  is  applied  to  the  bulb 
containing  the  black  oxide  of  copper,  and,  as  soon  as  its  temperature 
has  been  raised  to  dull  redness,  decomposition  commences.     The 
oxide  of  copper  becomes  glowing  red,  and  then,  even  if  the  heat  of 
the  lamp  be  much  reduced,  the  reaction  still  goes  on ;  the  glowing 
gradually  pervades  the  whole  mass,  water  is  formed  and  condensed 
on  the  colder  parts  of  the  tube  in  considerable  quantity,  and  when 
the  reaction  is  completed,  there  remains  in  the  bulb  a  porous  mass 
of  pure  metallic  copper.     It  is  necessary,  however,  to  determine 
exactly  the  quantity  of  water  formed :  for  this  purpose,  a  small  tube 
filled  with  fragments  of  fused  chloride  of  calcium  is  attached  to  the 
bulb  tube  by  means  of  a  caoutchouc  connector,  and  the  stream  of 
hydrogen  gas  is  allowed  to  continue  through  the  apparatus  until 
the  residual  copper  has  become  quite  cold,  and  all  traces  of  water 
have  been  carried  into  the  chloride  of  calcium  tube,  where  it  is  com- 
pletely absorbed  and  retained.     The  oxide  of  copper  tube  having 
been  weighed  before  and  after  the  experiment,  the  loss  found  is  the 
oxygen  which  has  been  carried  off:  the  chloride  of  calcium  tube 
having  been  also  weighed  before  and  after,  the  gain  gives  the  weight 
of  water  formed,  and  hence  the  composition  of  water  may  easily 
be  calculated,  thus : 


254  CONSTITUTION     OF     WATER. 

100  parts  of  black  oxide  of  copper  give 
79*85  of  metallic  copper,  and  lose 
20- 15  of  oxygen,  which  form 
22-67  of  water  j 

consequently,  22*67  of  water  consist  of 

20.15  of  oxygen, 
2*52  of  hydrogen ; 

or  in  100  parts, 

88-9  of  oxygen, 
11*1  of  hydrogen. 

To  determine  the  combining  equivalents  of  these  substances,  or, 
in  theoretical  language,  their  atomic  weights,  it  is  first  necessary  to 
ascertain  what  grounds  there  are  for  deciding  on  the  atomic  consti- 
tution of  water. 

It  has  been  already  mentioned  that  at  one  time  equal  volumes  of 
all  gases  were  considered  to  contain  the  same  number  of  atoms  ; 
and  hence,  as  water  is  formed  by  the  union  of  one  volume  of  oxy- 
gen and  two  of  hydrogen,  it  was  considered  by  some  chemists  to 
consist  of  one  atom  of  oxygen  united  to  two  of  hydrogen ;  there- 
fore, if  we  take  oxygen  as  the  standard  of  atomic  weights,  and  call  its 
equivalent  number  100,  the  result  would  be  that  88*9  :  11*1  :  :  100  : 
12*48=  weight  of  two  atoms  of  hydrogen ;  and  hence  the  atomic 
weight  of  hydrogen  should  be  6*24.  To  the  adoption  of  this  number 
there  are  very  many  objections  :  1st,  The  ground  upon  which  it  was 
first  adopted  has  been  proved  to  be  false,  as  the  same  volumes  of  all 
gases  certainly  do  not  contain  the  same  number  of  chemical  atoms  ; 
and,  although  hydrogen  enters  so  much  into  combination,  it  is  but 
very  rarely  that  it  does  so  in  the  proportion  of  6*24.  Likewise  wa- 
ter, in  all  the  modes  in  which  it  is  capable  of  combining,  does  so  in 
a  quantity  containing  12*48  and  not  6*24 ;  and,  finally,  water  in  com- 
bination allies  itself  to  a  variety  of  metallic  oxides,  all  of  which 
there  is  the  strongest  reason  for  supposing  to  be  composed  of  one 
equivalent  or  atom  of  the  metal  united  with  one  of  oxygen. 

Water  is  therefore  assumed  to  be  composed  of  an  equivalent  of 
each  of  its  constituents ;  and  according  as  the  standard  of  oxygen  or 
of  hydrogen  is  taken,  its  atomic  weight  is 

One  atom  of  oxygen        100*00  8 

One  atom  of  hydrogen  ...       12*24  1 

112*24  "9 

Water  is  colourless,  transparent,  destitute  of  taste  and  smell.  If 
agitated,  it  solidifies  at  a  temperature  of  32°  F.  (0  Centigrade),  but 
if  preserved  quiescent,  it  may  be  cooled  much  lower  without  freez- 
ing ;  if  it  be  then  touched  or  shaken,  a  portion  is  immediately  con- 
verted into  ice,  and  the  temperature  of  the  whole  is  raised  to  32°. 
In  freezing,  water  expands  very  much,  and  exerts  therein  so  great 
a  force  as  to  burst  the  strongest  vessels  in  which  it  is  contained. 
It  is  thus  that  the  surfaces  of  the  hardest  rocks  are  gradually  crum- 
bled into  soil  fit  for  the  support  of  vegetable  life  ;  the  water  perco- 


SOLUTION     OF      GASES     IN     WATER.  255 

latmg  into  minute  crevices  and  fissures  during  the  warmer  months, 
and,  when  frozen  in  winter,  breaking  down,  by  repeated  and  in- 
creasing expansive  efforts  during  successive  years,  the  substance 
of  masses  which  would  appear,  from  compactness  and  hardness,  fit- 
ted to  withstand  the  severest  effects  of  time  and  climate. 

The  specific  gravity  of  steam,  such  as  it  would  be  at  the  standard 
temperature  and  pressure,  is  found  to  be  620-1,  atmospheric  air  be- 
ing lOOO'O.  Two  volumes  of  steam  contain  two  of  hydrogen  and 
one  of  oxygen ;  hence  there  is  a  condensation  of  three  volumes  to 
two  produced  by  the  union  of  the  gases.  The  calculated  result  is 
thus  found : 

Two  volumes  of  hydrogen    .     68-8  X  2=   137-6 

One  volume  of  oxygen —1102-6 

give  two  volumes  of  vapour  of  water    — 1240-2 
hence  one  volume  of  vapour  of  water  =  620-1 

In  forming  steam  at  212°,  and  a  pressure  of  30  inches  mercury, 
water  expands  to  1696  times  its  volume  according  to  the  determina- 
tion of  Gay  Lussac,  which  gives  almost  exactly  the  proportion  of  a 
cubic  inch  of  water  forming  a  cubic  foot  of  steam,  which  contains 
1728  cubic  inches. 

The  solution  of  gases  in  water  appears  to  be  governed  by  prin 
ciples  similar  to  those  which  regulate  the  solvent  action  of  water 
upon  solid  bodies.  In  some  instances  there  certainly  takes  place 
chemical  union,  as  in  the  case  of  muriatic  acid  gas  and  ammonia;  and 
in  these  cases  the  condensation  of  the  gases  by  the  water  is  accom- 
panied by  the  evolution  of  considerable  heat.  But  in  other  cases, 
particularly  where  the  quantity  of  gas  is  small,  the  result  appears 
to  be  merely  a  mechanical  distribution  of  the  molecules  of  the  gas 
throughout  the  mass  of  the  liquid.  The  following  is  a  table  of  the 
quantity  of  these  gases  absorbed  by  water  without  combination 
100  volumes  of  water  at  60°  Fahr.  and  30  inches  bar.  absorb  of 

Sulphuretted  hydrogen 253  volumes 

Sulphurous  acid 438        " 

Chlorine 206        « 

Carbonic  acid 100        " 

Nitrous  oxide 76        " 

defiant  gas 12-5     » 

Oxygen 37     " 

Nitrogen    )  16     « 

Hydrogen  5 

The  mixture  of  nitrogen  and  oxygen,  which  constitutes  the  air 
we  breathe,  is  absorbed  by  water,  and  it  is  to  the  air  thus  dissolved 
that  water,  in  great  part,  owes  its  refreshing  taste.  If  water  be 
boiled  this  air  is  expelled,  and  this  should  be  done  if  it  be  wished 
to  saturate  the  water  with  any  other  gas,  as  the  power  of  water  to 
absorb  any  other  gas  is  remarkably  diminished  by  the  presence  of 
even  a  small  quantity  of  air.  If  water  already  saturated  with  one 
gas  be  exposed  to  the  action  of  a  second,  it  lets  a  portion  of  the 
first  escape,  and  absorbs  a  corresponding  quantity  of  the  second. 
In  this  way,  a  very  small  quantity  of  a  sparingly  soluble  gas  may 
expel  a  large  quantity  of  one  much  more  soluble.  A  familiar  exam- 
ple of  this  fact  consists  in  taking  a  glass  half  full  of  Champagne,  and 


/ 


256  CHEMICAL     RELATIONS     OF     WATER. 

having  formed  the  palm  of  the  hand  into  a  hollow  cup,  to  strike  the 
top  of  the  glass,  closing  the  glass  and  flattening  the  hand  at  the  same 
time  ;  the  air  above  the  wine  is  thus  forcibly  compressed,  and  a  por- 
tion is  then  absorbed,  under  pressure,  by  the  fluid,  from  which  a 
quantity  of  carbonic  acid  is  expelled,  greater  than  that  of  air  absorb- 
ed in  the  proportion  of  1060  to  16,  and  thus  the  effervescent  char- 
acter of  the  wine  restored. 

Notwithstanding  this  character  of  neutrality,  which  renders  wa- 
ter so  useful  as  a  vehicle  or  solvent  for  more  energetic  bodies,  wa- 
ter is  actively  engaged  in  a  great  variety  of  chemical  reactions,  in 
which  its  elements,  separating  from  one  another,  appear  in  an  iso- 
lated state,  or,  by  combining  with  other  substances  which  may  be 
present,  generate  new  compounds.  Even,  however,  independent  of 
decomposition,  water  plays  a  most  important  part  in  chemical  theory, 
from  the  numerous  classes  of  compounds  of  which  it  forms  a  con- 
stituent. The  generality  of  saline  bodies,  in  crystallizing,  retain  a 
quantity  of  water,  often  more  than  one  half  their  weight ;  this  is 
termed  water  of  crystallization.  On  the  application  of  a  moderate 
heat  this  water  separates,  and  frequently  the  salt  dissolves  in  its 
own  water  of  crystallization  on  being  heated,  undergoing  what  is 
termed  watery  fusion. 

Salts  containing  water  of  crystallization  often  attract  still  more 
if  surrounded  by  damp  air,  and  fall  into  a  liquid  state :  such  are 
termed  deliquescent  salts ;  others,  on  the  contrary,  give  off  their 
water  of  crystallization  even  at  ordinary  temperatures,  if  the  air  be 
moderately  dry ;  some,  such  as  the  carbonate  and  sulphate  of  soda, 
losing  all  j  others,  as  the  phosphate  of  soda,  only  a  portion  of  that 
constituent :  these  are  termed  efflorescent  salts ;  when  the  efilores- 
cence  is  complete,  they  lose  their  crystalline  arrangement  and  fall 
to  powder. 

Graham  has  shown,  that  in  many  classes  of  salts,  particularly  in 
the  sulphates,  one  portion  of  the  water  is  much  more  intimately 
united  than  the  remainder;  that,  in  fact,  in  addition  to  the  mere 
water  of  crystallization,  which  may  be  removed  without  injury,  there 
is  water  essential  to  the  constitution  of  the  salt,  and  replaced  by 
other  bodies  when  the  salt  enters  into  combination.  Thus,  in  the 
common  crystallized  sulphate  of  copper  there  are  five  atoms  of  wa- 
ter, of  which  four  are  removable  by  a  temperature  of  150^,  but  the 
fifth  withstands  a  temperature  of  300^.  The  formula  of  this  salt  is, 
therefore,  not  Cu.O. .  S03  +  5H.O.,  but  Cu.O. .  S.O3  H.0.H-4H.0.,  the 
four  atoms  being  water  of  crystallization  j  now  if  this  salt  be  com- 
bined with  sulphate  of  potash,  this  fifth  atom  of  water  disappears, 
and  the  double  salt  is  (Cu.O.  .  S.O3)  (K.O. .  S.O3)  +4H.0. ;  the  K.O. 
S.O3  having  entered  into  the  place  of  the  water  which  had  been  ex- 
pelled ;  water  thus  circumstanced  is  termed  constitutional  water, 
as  being  necessary  to  the  complete  constitution  of  the  substance. 

Water,  in  combination  with  the  stronger  acids,  is  capable  of  act- 
mg  as  a  base,  and,  indeed,  Ave  know  of  the  existence  of  many  acids 
only  in  the  form  of  their  compounds  with  water.  Thus  the  nitric, 
the  chloric,  the  oxalic,  the  acetic  acids,  have  never  been*  obtained 
in  a  separate  form ;  what  we  generally  term  those  acids  being,  in 
reality,  compounds  of  these  acids  with  water — salts  of  water.     Oil 


WATER     IN     CHEMICAL     COMBINATION.  25? 

of  vitriol  is  a  compound  of  sulphuric  acid  and  water,  sulphate  of 
water,  and  it  combines  with  more  water,  producing  great  heat,  to 
form  a  sulphate  of  water  with  excess  of  base,  precisely  as  the  sul- 
phate of  copper  combines  with  more  oxide  of  copper  to  produce  a 
corresponding  basic  salt.  The  salts  of  water  possess  the  most  com- 
plete similarity  with  those  of  zinc  and  copper,  and  it  is  from  their 
comparative  study  that  the  evidence  in  favour  of  the  view  inculca- 
ted already,  of  hydrogen  being  a  volatile  metal,  has  been  in  greatest 
part  derived. 

Water  combines  also  with  bases :  the  majority  of  metallic  oxides 
combine  with  water,  often  with  the  evolution  of  considerable  heat. 
The  slacking  of  lime,  which  is  the  act  of  combination  of  dry  lime 
with  water,  produces  so  much  heat  as  to  ignite  gunpowder,  and^ 
when  in  large  quantity,  to  become  red  hot.  Ships  laden  Avith  lime 
Have  often  been  burned  at  sea,  from  water  getting  into  the  hold 
among  the  lime,  and  so  much  heat  being  evolved  as  to  set  the  ship 
on  fire.  Barytes  and  strontia  produce,  in  slacking,  still  more  heat^ 
Potash  retains  water  so  strongly  that  it  can  only  be  obtained  free 
from  it  by  the  direct  combustion  of  the  metal,  potassium,  in  dry 
oxygen  gas  or  air.  In  relation  to  these  powerful  bases,  water  ap- 
pears, therefore,  to  act  the  part  of  a  feeble  acid. 

The  compounds  of  water  have  been  generally  termed  by  chemists 
hydrates ;  thus,  hydrate  of  lime,  hydrated  oxide  of  copper,  hydrated 
sulphuric  acid,  hydrated  sulphate  of  zinc.  The  very  different  func- 
tions performed  by  water,  in  the  various  modes  of  combination  it 
affects,  render  it  necessary  to  adopt  a  definite  principle  of  nomen- 
clature in  this  respect.  In  the  subsequent  pages  I  shall  employ  the 
wovdJiydrate  only  where  the  water  is  combined  with  a  base,  such 
as  a  metallic  oxide ;  thus,  hydrate  of  lime,  hydrate  of  potash,  hy- 
drated oxide  of  lead.  Where  the  water  is  united  to  an  acid,  I  shall, 
in  all  cases  in  which  the  true  chemical  nature  of  the  compound 
comes  into  play,  term  it  a  salt  ;  as  sulphate  of  u^ater,  oxalate  of 
water,  &c. ;  but  where  no  strict  theoretical  explanation  is  involved, 
I  shall  continue  to  use  the  common  name,  as  oil  of  vitriol,  strong 
sulphuric  acid,  oxalic  acid,  aquafortis,  &c.  There  is  no  name  pecu- 
liarly applicable  to  the  form  of  compounds  which  contains  constitu- 
tional water,  but  it  will  serve  as  well  to  characterize  the  absence  or 
deprivation  of  this  water  by  the  word  anhydrous,  the  ordinary 
name  of  the  substance  being  supposed  to  include  the  combined  wa- 
ter j  thus,  common  sulphate  of  zinc,  freed  from  water  of  crystalliza- 
tion, is  Zn.O. .  S.O3 .  H.O. ',  anhydrous  sulphate  of  zinc  is  Zn.O. .  S.O3. 
When  there  exists  water  of  crystallization  in  a  salt,  it  is  of  course 
included  when  the  salt  is  spoken  of  as  crystallized.  In  formula?, 
for  the  purpose  of  distinguishing  between  water  of  crystallization 
and  water  more  closely  united,  the  latter  will  always  be  marked  by 
the  symbols  of  its  constituents,  the  former  by  the  two  initial  letters 
of  the  Latin  word  aqua,  aq. ;  thus  the  crystallized  oxalic  acid  is 
CA  .  H.0.4-2Aq.  The  phosphate  of  soda  is  PA+^Na.O. .  H.0.+ 
24Aq. 

Water  does  not  exist  in  nature  in  a  perfectly  pure  condition.  It 
contains  dissolved  a  small  portion  of  atmospheric  air  and  of  carbonic 
acid,  and  also  certain  quantities  of  solid  impurities,  of  which  com 

K  K 


258    MINERAL     WATERS. PEROXIDE     OP    HYDROGEN. 

mon  salt,  sulphates  and  carbonates  of  lime,  and  chloride  of  magne- 
sium, are  the  most  important.  In  particular  localities,  the  water  is- 
suing from  the  earth  contains  iron,  and  often  sulphuretted  hydrogen  ; 
also  traces  of  iodine  and  bromine  j  and  occasionally  the  quantity  of 
these  foreign  matters  present  is  so  great  as  to  confer  upon  the  wa- 
ter medicinal  properties,  and  to  make  such  springs,  under  the  name 
of  mineral  springs,  spas,  be  resorted  to  for  the  purpose  of  preserving 
or  recovering  health.  These  impurities  arise  from  the  water,  in 
percolating  through  the  porous  rocky  strata,  of  which  the  mount- 
ains and  general  crust  of  the  earth  are  composed,  dissolving  in  small 
quantity  almost  all  the  substances  it  meets.  Hence  rain-water  or 
snow-water,  collected  at  a  distance  from  houses,  is  the  purest  water 
which  can  be  obtained  in  nature.  It  contains  only  some  carbonic 
acid  and  air  dissolved.  The  sea  being  the  general  reservoir  into 
which  all  the  rivers  of  the  earth  discharge  their  waters,  contains 
in  a  concentrated  form  all  the  materials  which  the  river  waters  had 
carried  down.  Although  not  of  absolutely  the  same  constitution  all 
over  the  globe,  yet  it  varies  so  little  that  the  deviation  may  be  ex- 
plained by  local  circumstances.  It  is  in  many  countries  the  source 
from  which  common  salt  and  sulphate  of  magnesia  are  derived. 
When  sea-water  freezes,  the  ice  contains  scarcely  a  trace  of  saline 
matter,  so  that,  when  melted,  it  forms  a  sweet,  drinkable  wafer. 
Hence,  in  voyages  in  the  Northern  Seas,  supplies  of  fresh  water  are 
obtained  by  chopping  blocks  of  ice  from  the  frozen  surface  of  the 
ocean.  To  obtain  water  pure  for  chemical  purposes,  it  is  necessary 
to  distil  it.  The  saline  and  fixed  impurities  remain  behind,  the  pure 
water  passes  over.  Its  purity  may  be  ascertained  by  means  of  the 
reagents  fitted  to  detect  the  most  important  impurities.  Thus,  if 
free  from  common  salt,  it  will  give  no  precipitate  with  a  solution  of 
nitrate  of  silver  j  if  free  from  lime,  it  will  not  be  affected  by  oxalic 
acid  5  and  if  it  be  not  rendered  turbid  by  nitrate  of  barytes,  it  can 
not  contain  sulphuric  acid. 

From  the  inactivity  of  water,  and  the  facility  with  which  it  may 
be  obtained  pure,  as  well  as  the  important  part  which  it  plays  in  the 
economy  of  nature,  it  is  taken  as  the  standard  with  which  the  prop- 
erties of  other  bodies,  when  numerically  determined,  are  compared. 
Thus  the  specific  heats  of  solids  and  liquids  are  reduced  to  a  scale, 
water  being  taken  as  I'OOO.  The  specific  gravities  of  liquids  and 
solids  are  also  taken  in  numbers,  that  of  water  being  the  standard. 
If,  however,  the  specific  gravities,  and  heats  of  gases  and  vapours 
were  reduced  to  the  standard  of  water,  the  fractions  by  which  they 
should  be  expressed  would  be  inconveniently  small  j  and  hence,  for 
this  class  of  bodies,  a  better  suited  standard  substance  is  found  in 
atmospheric  air. 

Of  Oxygenated  Water.     Peroxide  of  Hydrogen, 
H.O.  +  O.,  or  H.O,. 
This  singular   substance  was  first  discovered  by  Thenard ;  its 
preparation  is  somewhat  circuitous  and  indirect,  oxygen  and  hydro- 
gen not  combining  \/ith  each  other  directly  in  any  other  proportions 
but  those  which  form  water. 
For  its  preparation,  peroxide  of  jarium  must  be  first  procured ;  this  is  prepared 


PEROXIDE    OF    HYDROGEN,    PREPARATION,    ETC.    259 

by  placing  pure  barytes  (oxide  of  barium)  in  a  porcelain  tube,  which  is  heated  to 
redness  in  a  charcoal  furnace,  and  then  a  stream  of  pure  oxygen  gas  passed  over  it 
as  long  as  it  is  absorbed ;  the  barytes  absorbs  as  much  more  oxygen  as  it  already 
contained,  and  from  Ba.O.  becomes  Ba.02 

This  substance  may  be  still  more  easily  prepared  by  mixing  pure  barytes  with 
its  weight  of  chlorate  of  potash,  and  heating  it  nearly  to  redness ;  when  the  disen- 
gagement of  oxygen  from  the  chlorate  of  potash  has  set  in,  the  mass  becomes 
glowing  red  at  one  point,  and  this  appearance  spreads  over  the  whole  mass  like  tinder. 
The  barytes  burns,  as  it  were,  in  the  atmosphere  of  oxygen,  and  forms  the  deutox- 
ide  of  barium.  If,  then,  the  residual  mass  be  washed  with  water,  the  chloride  of 
potassium,  which  remains  from  the  chlorate  of  potash,  is  dissolved,  and  the  deutox- 
ide  of  barium,  combining  with  an  equivalent  of  water  to  form  a  bulky,  white,  insol- 
uble hydrate,  remains  behind,  and  may  be  collected  on  a  filter. 

The  best  mode  of  obtaining  peroxide  of  hydrogen  from  this  substance  is  that  pro- 
posed by  Pelouze.  To  dilute  hydrofluoric  acid  (fluoride  of  hydrogen),  the  peroxide 
of  barium  is  added  until  the  acidity  of  the  liquor  is  completely  neutralized.  The 
reaction  is  very  simple  ;  the  fluorine  combines  with  the  barium,  while  all  the  oxy- 
gen is  transferred  to  the  hydrogen,  which  the  fluoric  acid  abandons ;  thus, 
H.F.-l-Ba.02=Ba.F.-|-H.02. 

The  fluoride  of  barium  is  insoluble,  and  may  be  collected  on  a  filter  along  with 
the  excess  of  peroxide  of  barium ;  the  liquor  contains  only  pure  oxygenated  water. 
Fluosilicic  acid,  which  is  cheaper,  and  more  convenient  than  the  fluoric  acid,  may 
also  be  used  in  this  decomposition.  The  fluosilicate  of  barium  separates  as  an  in- 
soluble white  powder,  and  the  peroxide  of  hydrogen  remains  dissolved. 

Thenard's  plan  consisted  in  dissolving  the  peroxide  of  barium  in  dilute  muriatic 
acid,  and  then  precipitating  the  barytes  by  sulphuric  acid.  The  muriatic  acid 
which  became  free  was  then  neutralized  by  another  portion  of  peroxide  of  barium, 
and  this  again  precipitated  by  sulphuric  acid.  When  the  liquor  had  become  strong 
enough,  the  free  muriatic  acid  was  removed  by  the  cautious  addition  of  sulphate  of 
silver,  and  the  sulphuric  acid  then  evolved  was  precipitated  by  the  addition  of  pure 
barytes,  carefully  avoiding  an  excess. 

The  weak  solution  of  peroxide  of  hydrogen  thus  obtained  must  be  placed,  along 
with  a  capsule  of  sulphuric  acid,  under  the  exhausted  receiver  of  the  air-pump. 
The  water  being  more  volatile,  evaporates  first,  and  the  hquor  gradually  becomes 
more  concentrated,  until,  finally,  the  peroxide  of  hydrogen  remains  pure  behind.  If 
left  too  long  in  the  exhausted  vessel,  it  evaporates  itself  without  alteration. 

Peroxide  of  hydrogen  is  a  thick,  colourless  liquid.  Its  specific  gravity  is  1-452. 
It  has  a  nauseous  taste,  and  irritates  the  skin.  It  bleaches  and  destroys  all  vegeta- 
ble colours.  Its  reactions  are  generally  so  violent  that  it  must  be  diluted  with 
many  times  its  volume  of  water  before  they  can  be  accurately  observed. 

Its  most  curious  property  is,  that  by  being  put  in  contact  with  any  one  of  a  great 
number  of  solid  substances,  it  is  decomposed  with  great  rapidity,  being  resolved 
into  oxygen  and  water.  Black  oxide  of  manganese  is  one  of  the  most  active.  If  a 
little  of  this  substance,  in  powder,  be  introduced  ipto  strong  peroxide  of  hydrogen,  in 
a  graduated  tube,  over  mercury,  the  latter  is  decomposed  almost  explosively,  disen- 
gaging 475  times  its  volume  of  oxygen,  the  oxide  of  manganese  remaining  perfectly 
unaltered.  Platinum,  gold,  silver,  quicksilver,  particularly  if  the  metal  be  in  the 
form  of  leaf  or  sponge,  produce  the  same  effect ;  and  if  the  peroxide  of  hydrogen 
be  put  into  contact  with  an  oxide  of  these  metals,  as  oxide  of  silver,  it  is  not  mere- 
ly decomposed  itself,  but  the  oxide  is  also  decomposed,  the  oxygen  and  metal  both 
becoming  free.  In  the  dark,  and  with  strong  peroxide  of  hydrogen,  a  flash  of  light  is 
seen  to  accompany  its  decomposition,  and  the  mbe  becomes  red  hot.  The  decompo- 
sition of  the  oxide  of  silver  cannot,  however,  be  referred  to  the  great  heat  produced, 
as,  even  if  the  peroxide  of  hydrogen  be  diluted  with  fifty  times  its  volume  of  water, 
oxide  of  silver  produces  complete  decomposition,  evolution  of  oxygen,  and  separa- 
tion of  metallic  silver ;  yet  the  effervescence  is  not  very  energetic,  and  the  liquor 
does  not  become  sensibly  warm  to  the  hand. 

With  other  metals,  the  oxygen,  in  place  of  becoming  free,  enters  into  combinatipn, 
forming  an  oxide  of  a  higher  degree ;  thus,  with  the  oxides  of  lead  and  bismuth 
there  are  formed  peroxides  of  those  metals ;  with  arsenic  there  is  formed  arsenic 
acid.  The  animal  substances  fibrine  and  albumen,  which  are  so  similar  in  most 
respects,  are  distinguished  from  each  other  by  their  action  on  this  body,  fibrine  de- 
composing it  with  rapidity,  while  albumen  is  without  effect.  It  is  highly  probable, 
that  in  the  decomposition  of  water  by  the  voltaic  pile,  some  of  this  compound  may 


260  PREPARATION     OF     NITROGEN     GAS. 

be  formed,  as  the  quantity  of  oxygen  collected  is  frequently  smaller  than  it  should 
be  ;  and  a  portion  of  the  process  of  bleaching,  by  exposing  the  wetted  cloth  to  the 
action  of  light  and  air,  may  possibly  be  carried  on  by  the  formation  and  subsequent 
decomposition  of  this  substance. 

Peroxide  of  hydrogen,  when  kept  for  any  length  of  time,  even  in  a  dilute  condi- 
tion, gradually  decomposes,  oxygen  being  given  off,  and  water  remaining  behind. 
The  presence  of  an  acid  in  the  liquor  retards  this  action  very  much,  while  the  pres- 
ence of  an  alkah  accelerates  it.  It  w^as  in  great  part  from  the  remarkable  charac- 
ters of  this  body  that  Berzelius  derived  his  evidence  in  favour  of  the  existence  of  a 
catalytic  force  influencing  chemical  action,  which  has  been  described  already. 

Of  JVitrogen. 
N. 
It  has  been  already  noticed,  that  the  substance  by  which  the  ox- 
ygen is  diluted  in  atmospheric  air,  so  as  to  render  it  suitable  to  the 
respiration  of  animals,  is  called  nitrogen,  from  its  being  the  basis 
of  nitric  acid  and  nitre  (the  nitre  former).     It  is  also  called  by  some 
chemists  azote,  from  its  incapability  of  supporting  life  ;  but,  as  a 
great  number  of  gases  resemble  it  in  that  respect,  the  former  name 
is  the  more  characteristic,  and  it  alone  will  be  hereafter  used. 
As  nitrogen  exists  in  great  quantity  in  the  air  we  breathe,  it  is 
most  easily  obtained  by  acting  upon  a  con- 
fined portion  of  the  air  so  as  to  abstract  the 
oxygen,  when  the  residual  gas  is  found  to 
be  nitrogen  almost  completely  pure.     Thus, 
if  a  small  piece  of  phosphorus,  laid  in  a  cup 
c/,  floating  on  water,  be  set  on  fire,  and  a  bell 
glass,  a,  be  inverted  over  it,  the  phosphorus, 
in  burning,  unites  with  the  oxygen  of  the 
air,  and  forms  white  fumes  of  phosphoric 
acid.     At  first,  from  the  great  expansion  of 
the  air  caused  by  the  high  temperature  of  the  flame,  some  bubbles 
escape  from  under  the  edge  of  the  glass  ;  but  soon,  even  before  the 
phosphorus  has  ceased  to  burn,  the  water  begins  to  rise  in  the  bell, 
and,  finally,  the  clouds  of  phosphoric  acid  gradually  dissolving  in  the 
water,  the  residual  gas  will  be  found  to  occupy  about  four  fifths  of 
the  original  volume  of  the  air,  and  to  be  colourless  as  the  air  had 
been  before.     Any  other  burning  body  would  answer  the  same  pur- 
pose, although  not  so  perfectly  as  the  phosphorus.     Thus,  if  spirit 
of  wine,  or  pyroxylic  spirit,  or  ether,  which  burn  without  smoke,  be 
placed  in  the  little  cup,  and  set  on  fire  under  the  bell  glass,  as  in 
the  former  instance,  the  inflammable  constituents,  carbon  and  hy- 
drogen, combine  with  the  oxygen  of  the  air,  forming  carbonic  oxide 
and  water,  the  nitrogen  remaining  behind.     The  gas  thus  obtained 
must  be  washed  well  with  water,  or,  better,  a  little  solution  of  pot- 
ash, to  remove  the  carbonic  acid,  and  even  then  the  nitrogen  con- 
tains some  oxygen  unconsumed  ;  for  in  every  case  where  carbonic 
acid  is  formed  by  a  burning  body,  the  combustion  ceases  before  all 
the  oxygen  present  has  been  consumed,  the  carbonic  acid  exercising 
on  combustion  a  positively  impeding  power,  similar  to  that  which  it 
has  on  respiration.     The  purest  nitrogen  is  consequently  obtained 
by  means  of  phosphorus. 

Independent  of  this  source  of  nitrogen  in  atmospheric  air,  it  mav 


PREPARATION     OF      NITROGEN     GAS. 


261 


be  obtained  indirectly  from  a  great  number  of  substances.  Thus 
most  animal  substances  contain  nitrogen  in  large  quantity,  united  to 
carbon,  hydrogen,  and  oxygen.  If,  therefore,  some  pieces  of  muscle, 
or  albumen,  or  gelatine,  be  boiled  in  a  retort  with  some  nitric  acid, 
the  oxygen  of  the  nitric  acid  combines  with  the  carbon  and  hydroge* 
of  the  animal  substance,  forming  different  compounds  according  to 
the  temperature  and  the  proportions,  while  the  nitrogen  of  both  is 
disengaged. 

If  a  gas,  termed  nitrous  oxide,  which  will  be  described  in  a  sub- 
sequent section,  be  put  into  contact  with  a  slip  of  metallic  zinc,  at 
the  moment  of  its  formation  the  zinc  deprives  it  of  its  oxygen,  form- 
ing oxide  of  zinc,  and  the  nitrogen  is  set  free.  The  apparatus  used 
for  this  purpose  consists  of  a  tubulated  retort,  into  which  is  intro- 
duced the  salt  (nitrate  of  ammonia),  which,  when  heated,  yields  ni- 
trous oxide.  Into  the  tubulure  is  fitted  a  cork,  through  which  passes 
a  copper  wire,  to  the  end  of  which  a  slip  of  zinc  is  fastened.  To 
the  neck  of  the  retort  a  bent  tube  is  adapted,  passing  to  the  pneu- 
matic trough.  Heat  being  applied  to  the  retort  by  means  of  a  lamp, 
the  salt  melts,  and  then  begins  to  emit  gas.  At  this  moment  the 
copper  wire  is  depressed,  so  that  the  slip  of  zinc  may  touch  the  sur- 
face of  the  melted  mass.  The  effervescence  immediately  becomes 
much  more  violent,  white  clouds  of  oxide  of  zinc  are  formed,  and 
the  gas,  which  passes  over,  is  nitrogen  quite  pure.  The  theory  of 
the  formation  of  the  nitrous  oxide  will  be  noticed  under  the  proper 
head.  Its  decomposition  by  the  zinc  is  simple:  nitrous  oxide  is  N. 
0.,  and  acted  on  by  Zn.  their  products  are  N.  and  Zn.O. 

If  ammonia  dissolved  in  water  be  exposed  to  the  action  of  a  cur- 
rent of  chlorine,  it  is  decomposed,  sal  ammoniac  is  formed,  and  ni- 
trogen gas  is  disengaged.  The  solu- 
tion of  ammonia  may  be  contained  in 
a  bottle  with  a  wide  neck,  g,  to  which 
a  cork  is  fitted,  perforated  to  admit 
two  tubes,  the  one,  /,  conveying  the 
chlorine  from  the  vessel  a,  in  which 
it  is  disengaged,  and  opening  under 
the  surface  of  the  liquid  near  the  bot- 
tom, the  other  projecting  but  little 
under  the  cork,  and  leading  to  the 
pneumatic  trough.  The  action  of  the 
chlorine  upon  the  ammonia  is  accompanied  by  the  formation  of  white 
fumes  and  the  evolution  of  much  heat.  If  the  solution  be  strong,  a 
flash  of  light  is  seen  at  the  entrance  of  each  bubble  of  chlorine  gas; 
but  these  are  not  attended  with  any  danger.  The  ammonia,  how- 
ever, must,  all  through  the  process,  be  kept  in  excess,  as,  were  the 
chlorine  in  excess,  it  might  produce  a  body,  chloride  of  amidogene, 
possessed  of  the  most  eminently  dangerous  explosive  properties. 

The  reaction  which  here  takes  place  may  be  simply  shown.  Am- 
monia consists  of  one  equivalent  of  nitrogen  and  three  of  hydrogen  ; 
by  the  action  of  three  equivalents  of  chlorine  there  are  formed  three 
of  chloride  of  hydrogen  (muriatic  acid),  which  unite  then  with  three 
equivalents  of  ammonia  to  form  three  of  sal  ammoniac  (muriate  of 
ammonia).     Thus  (N.+3H.)  and  3C1.  give  N.  and  (3C1.H.),  which 


262    PROPERTIES    OF   NITROGE  N. A  T  M  O  S  P  H  E  R  I  C    AIR. 

combine  with  3N.H3  to  form    3(C1.H.  .  N.H3),  one  equivalent  of  ni- 
trogen becoming  free. 

Nitrogen,  when  obtained  by  any  of  these  processes,  is  a  perma- 
nent gas,  colourless  and  transparent ;  it  is  absorbed  by  water  only 
Jti  very  small  quantity.  It  is  lighter  than  atmospheric  air,  its  specific 
gravity  being  976,  air  being  1000.  It  is  characterized  by  the  com- 
plete absence  of  the  positive  properties  which  distinguish  other 
gases.  Thus,  it  does  not  support  combustion  or  respiration  ;  it  ex- 
tinguishes a  taper,  and  animals  are  suffocated  in  it ;  but  these  ef- 
fects appear  to  be  due  only  to  the  absence  of  oxygen. 

Although  nitrogen  is  thus  incapable  of  combining  directly  with 
oxygen,  yet  by  indirect  methods  they  may  be  made  to  unite,  and 
the  compounds  formed  of  these  elements  are  surpassed  in  number 
and  importance  by  few  series  of  binary  combinations.  When  oxy- 
gen and  nitrogen  combine,  their  result  is  almost  universally  that 
which  contains  most  oxygen,  nitric  acid  ;  their  union  may  be  effect- 
ed by  the  electric  spark,  provided  water,  or  a  solution  of  an  alkali 
be  present ;  hence  rain-water  often  contains  traces  of  nitric  acid, 
particularly  if  its  deposition  has  been  preceded  by  discharges  of 
lightning  between  the  clouds ;  and  lime  or  potash  contained  in  old 
walls  are  found,  after  a  certain  time,  to  be  neutralized  by  nitric  acid. 
A  mixture  of  ammonia  and  oxygen  may  be  converted  into  nitric 
acid  and  water,  likewise,  by  spongy  platinum  at  a  temperature  of 
572^ 
,  The  combining  proportion  of  nitrogen  is,  on  the  hydrogen  scale, 
14*0,  and  on  the  oxygen  scale,  175.  In  a  great  number  of  instances, 
however,  it  appears  to  enter  into  combination  with  one  third  of  its 
ordinary  equivalent,  and  I  have  found  this  peculiarity  to  extend  to 
arsenic  and  phosphorus,  which  are  so  closely  assimilated  to  it 
throughout  their  chemical  relations. 

Before  entering  upon  the  history  of  the  compounds  of  nitrogen 
with  oxygen,  I  shall  describe  more  particularly  the  properties  and 
composition  of  atmospheric  air,  which,  being  of  so  much  importance 
in  the  majority  of  chemical  reactions  which  occur  on  a  large  scale, 
and  being  assumed  as  the  standard  of  properties  for  gaseous  and 
vaporous  bodies,  deserves  minute  attention. 

Of  the  Atmosphere. 
The  analysis  of  atmospheric  air  was  the  first  important  problem 
in  the  chemistry  of  gaseous  bodies  with  which  chemists  occupied 
themselves,  and  hence  the  names  of  instruments  originally  devised 
for  examining  atmospheric  air  became  generally  used  to  indicate 
those  employed  in  the  analysis  of  gaseous  mixtures  or  compounds 
of  any  kind.  The  word  eudiometer  signifies  a  measurer  of  the  good- 
ness of  the  air  j  and  from  the  interest  which  the  problem  presented, 
numerous  methods  were  early  invented,  although  it  is  only  recently 
that  very  great  precision  has  been  obtained.  It  was  at  first  believed 
that  the  relative  salubrities  of  districts,  and  even  of  different  local- 
ities in  the  same  neighbourhood,  could  be  determined  by  the  pro- 
portions of  oxygen  and  nitrogen  whicn  the  air  of  these  places  might 
contain;  and  that  the  admixture  of  pernicious  substances,  exhaling 
from  a  marsh,  or  generated  within  the  ill-ventilated  apartments  oi 


ANALYSIS     OF     AIR.  263 

an  hospital  or  of  a  jail,  might  be  recognised,  and  means  discov- 
ered of  removing  them,  or  of  destroying  their  activity,  when  their 
nature  had  become  determined  by  the  analysis  of  the  air  in  which 
they  had  been  contained.  The  differences  between  the  results  of 
various  chemists,  on  which  these  expectations  had  been  founded, 
have  gradually  disappeared  by  the  use  of  better  methods,  and  the 
constitution  of  atmospheric  air  is  now  recognised  as  being  almost 
absolutely  the  same  throughout  its  entire  mass  5  but  from  other 
sources,  the  very  results  which  had  been  originally  sought  after 
now  appear  to  form  a  legitimate  and  promising  subject  of  inquiry. 

In  addition  to  oxygen  and  nitrogen,  its  principal  constituents,  at- 
mospheric air  contains  some  carbonic  acid  and  watery  vapour ;  the 
quantitjr  of  the  latter  is  determined  by  methods  almost  entirely 
physical,  and  forms  a  practical  department  in  the  theory  of  vapours, 
termed  hygrometry.  I  shall,  thereifore,  not  touch  upon  it  here,  refer- 
ring to  what  has  been  already  noticed  of  it  in  the  sections  upon 
water  and  upon  heat. 

The  determination  of  the  quantity  of  carbonic  acid  present  in  at- 
mospheric air  has  been  made  accurately  by  Saussure,  who  found 
that,  in  general,  10,000  volumes  of  air  contain  4*15  of  carbonic  acid  j 
the  maximum  of  carbonic  acid  he  found  to  be  5*74,  and  the  minimum 
3*15.  Over  the  surface  of  lakes,  as  that  of  Geneva,  the  quantity  of 
carbonic  acid  is  smaller,  but  in  cities  greater,  amounting  to  4*46  in 
the  average  :  the  quantity  is  somewhat  greater  by  night  than  by  day, 
and  in  the  higher  regions  of  the  air  than  on  the  surface  of  the  low 
ground  ;  it  is  diminished  also  during  and  for  some  time  after  rain. 
To  determine  the  quantity  of  the  carbonic  acid,  a  large  globe  or 
bottle  containing  air  is  taken,  and  a  solution  of  barytes  is  introduced, 
until,  after  having  been  well  agitated  with  the  air,  it  is  found,  by 
browning  turmeric  paper,  to  be  present  in  excess.  The  carbonic 
acid  combines  with  barytes  to  form  a  white  powder,  carbonate  of 
barytes,  which,  being  collected  on  a  filter  and  weighed,  gives,  by  a 
simple  calculation^  the  volume  of  the  carbonic  acid  in  the  air. 

The  experiments  of  Saussure  and  of  Boussingault  have  made  it 
probable  that  carbon  combined  with  hydrogen  (probably  as  the  gas 
of  marshes)  exists  in  very  small  quantity  in  atmospheric  air.  Thus, 
when  Saussure,  after  having  removed  all  carbonic  acid  by  barytes, 
detonated  the  residual  air  with  pure  hydrogen,  he  obtained  a  quan- 
tity of  carbonic  acid  equal  to  nearly  one  part  in  2000  of  the  air  em- 
ployed ;  and,  although  employing  other  methods,  the  results  of  Bous» 
singault  strongly  corroborate  the  same  idea :  he  found  sulphuric  acid 
to  be  blackened  when  exposed  to  air,  although  all  access  of  dust  or 
accidental  impurities  was  removed,  and  that  when  air,  previously 
freed  from  carbonic  acid,  was  passed  over  red-hot  oxide  of  copper, 
a  perceptible  quantity  of  water  and  of  carbonic  acid  was  produced. 

But  the  most  important  portion  of  the  analysis  of  atmospheric  air 
is  to  ascertain  the  proportions  of  the  oxygen  and  nitrogen.  To  ef- 
fect this,  any  one  of  a  great  variety  of  bodies  which  are  capable  of 
uniting  with  oxygen  may  be  used ;  thus,  if  a  solution  of  sulphuret 
of  potassium  be  exposed  to  air,  it  absorbs  oxygen,  and  gradually 
passes  to  the  state  of  hyposulphite  of  potash,  and  by  the  amaunt  of 
absorption  the  quantity  of  oxygen  may  be  ascertained.     Thi&  isth.e 


264  COMPOSITION     OP     THE     ATMOSPHERE. 

method  of  Scheele.  One  proposed  by  Sir  Humphrey  Davy  consisted 
in  agitating  the  deep  olive  liquor  formed  by  passing  nitric  oxide 
gas  into  a  solution  of  green  sulphate  of  iron,  with  a  measured  quan- 
tity of  atmospheric  air ;  but  it  is  now  abandoned.  An  excellent 
mode  of  using  these  bodies  as  eudiometers  is  to  fill  with  the  liquid 
a  small  caoutchouc  bottle,  holding  about  two  fluid  ounces,  and  then 
tie  it  securely  on  the  tube  of  air  which  passes  pretty  closely  in  at 
the  neck  ;  the  mass  of  air  and  fluid  can  thus  be  brought  extensively 
int©  contact,  and  the  absorption  is  shown  by  the  gradual  rise  of  the 
liquid  in  the  tube,  the  soft  parietes  of  the  bottle  yielding  to  the  press- 
ure of  the  external  air. 

Nitric  oxide  gas  possesses  the  property  of  combining  with  the 
oxygen  of  the  air,  and  forming  deep  red  fumes  of  nitrous  acid,  which 
dissolve  in  water.  By  this  means,  using  an  excess  of  the  nitric  ox- 
ide, all  oxygen  may  easily  be  removed  from  atmospheric  air,  but 
the  composition  of  the  nitrous  acid  fumes  is  not  always  the  same, 
and  hence  the  quantity  of  oxygen  which  the  air  contained  is  liable 
to  be  mistaken.  This  mode,  therefore,  from  the  great  precaution 
necessary  in  its  use,  has  been  quite  laid  aside. 

The  use  of  the  hydrogen  gas  eudiometer,  whether  the  combination 
of  that  substance  with  the  oxygen  be  accomplished  by  the  agency 
of  the  electric  spark,  or  by  means  of  spongy  platina,  has  been  already 
noticed.  It  is  one  of  the  most  accurate  and  easy  methods  that  can 
be  used,  and  hence  has  been  most  generally  employed.  The  risk 
of  accident  from  the  violence  of  the  explosion  by  the  electric  spark 
is  much  diminished  by  using  the  form  proposed  by  Ure.  The  tube, 
which  need  not  be  at  all  so  stout  as  in  the  common  form,  is  taken 
about  twice  as  long,  and  bent  into  the  form  of  a  U.  Having  been 
tilled  with  mercury,  the  mixture  of  air  and  hydrogen  is  transferred 
to  the  sealed  leg,  and  then,  the  open  leg  being  about  half  occupied 
by  air,  it  is  to  be  firmly  closed  by  the  thumb  or  by  a  cork.  When 
the  explosion  follows,  the  air  in  the  open  leg  yields  to  the  pressure 
and  graduates  the  shock ;  no  portion  of  the  exploded  mixture  can 
be  projected. 

Slips  of  copper  foil,  moistened  with  muriatic  acid,  absorb  oxygen 
with  great  avidity,  and  have  been  proposed  by  Gay  Lussac  for  the 
analysis  of  atmospheric  air.  Saussure  has  used  in  his  accurate  re- 
searches thin  filings  or  turnings  of  lead,  which  combine  with  oxygen 
very  rapidly,  and  remove  it  totally  from  the  air. 

Phosphorus,  which  burns  in  oxygen  and  in  air  so  brightly,  may 
also  be  employed  to  form  a  eudiometer.  It  may  be  used  either  by 
slow  or  by  rapid  combustion.  In  the  former  mode,  a  stick  of  moist- 
ened phosphorus,  placed  in  a  graduated  tube  of  air,  deprives  it  com- 
pletely of  its  oxygen  in  about  twenty  hours  5  the  residue  is  nitro- 
gen, which  has  the  smell  of  phosphorus,  and  requires  a  correction 
for  a  small  quantity  of  vapour  of  that  substance  which  is  diffused 
through  it.  The  rapid  combustion  of  phosphorus  is  too  violent,  and 
exposes  the  vessels  to  too  much  risk  of  breaking,  to  be  made  use  of 
for  accurate  experiment. 

All  of  these  methods  are,  however,  liable  to  error  to  the  amount 
of  nearly  1  per  cent.,  which  is  to  be  in  great  part  attributed  to  the 
small  quantity  of  air  which  the  apparatus  allows  to  be  experimented 


CONSTITUENTS     OF     ATMOSPHERIC     AIR.  265 

on.  This  disadvantage  has  been  obviated  by  the  mode  proposed  by 
Brunner,  and  used  by  him  in  some  determinations  lately  made,  in 
which  the  liability  to  error  has  been  reduced  to  0*20  per  cent.  In 
the  figure,  a,  Z>,  c  is  a  tube,  consisting  of  a  wide  por- 
tion, bj  and  a  narrower,  c ;  the  wider  part  being 
drawn  in  a  to  a  capillary  opening.  Into  it  is  intro- 
duced a  quantity  of  loose  cotton  and  some  bits  of 
phosphorus,  and  being  then  warmed,  the  melted 
phosphorus  is  allowed  to  spread  over  the  fibres  of 
the  cotton  so  as  to  expose  a  very  great  surface. 
The  tube  at  c  fits  air-tight  to  the  orifice  of  the  ves- 
sel c?,  which  is  graduated  and  filled  with  mercury ; 
a  cock  at  e  allows  the  mercury  to  flow  out  on  oc- 
casion. To  use  this  apparatus,  the  tube  a,  6,  c  is 
weighed,  and  then  attached  to  the  vessel  d ;  the 
cock  e  is  then  slig^itly  opened  j  the  mercury  issues 
out  in  a  properly  graduated  stream,  and  its  place  is  supplied  by  air, 
which,  entering  at  the  capillary  orifice  a,  streams  over  the  surface 
of  the  phosphorus,  by  which  all  its  oxygen  is  removed,  and  the  re- 
sidual nitrogen  passing  into  the  graduated  vessel,  its  volume  can  be 
easily  read  off;  or  the  mercury  which  flows  ofl*  being  caught  in  a 
graduated  glass,  its  volume  is  equal  to  that  of  the  nitrogen  which 
has  passed  in.  Besides  extending  the  surface  of  the  phosphorus, 
and  thus  quickening  the  absorption  of  the  oxygen,  the  mass  of  cot- 
ton serves  as  a  filter  to  collect  the  white  fumes  or  flakes  of  phos- 
phorous acid  formed.  When  a  sufficient  quantity  of  air  has  passed 
through  the  apparatus,  the  tube  a,  6,  c  is  to  be  weighed  again  ;  the 
increase  of  weight  is  the  quantity  of  oxygen  absorbed,  from  which 
the  volume  may  be  known,  and  the  mercury  measured  is  the  volume 
of  the  nitrogen,  from  whence  its  weight  may  be  calculated.  The 
air  must  be  of  course  dry.  This  is  eflected  by  securing  to  the  tube 
a,  bj  c,  by  means  of  a  caoutchouc  connector,  a  small  tube  contain- 
ing fragments  of  fused  chloride  of  calcium,  through  which  the  air 
streaming  deposites  the  moisture  it  may  contain. 

The  result  of  all  these  methods  indicates  that  atmospheric  air  con- 
tains from  20-79  to  21-08  of  oxygen  gas  in  100  volumes  ;  and  from 
experiments  of  Gay  Lussac  on  air  brought  down  by  him  from  a 
height  of  21,735  feet,  to  which  he  had  ascended  in  a  balloon,  and 
those  of  Brunner  for  the  air  on  the  summit  of  the  Faulhorn,  8020 
feet  above  the  level  of  the  sea,  the  constitution  appears  to  be  iden- 
tical at  all  heights.  By  weight,  the  constituents  of  the  atmospheric 
air  in  100  parts  are,  omitting  carbonic  acid  and  water. 

Oxygen  gas =23-04 

Nitrogen  gas =76-96 

.Too^o"o 

This  permanency  of  constitution  of  atmospheric  air,  together 
with  many  other  circumstances  which  I  shall  briefly  notice,  led  to 
the  opinion  among  many  chemists  of  its  being  a  compound,  and  not 
a  mere  mixture  of  its  constituents.  The  analysis  not  being  then  so 
accurately  made,  it  was  supposed  to  consist  of  one  volume  of  oxy- 
gen united  to  four  volumes  of  nitrogen,  a  simplicity  of  proportion 

Ll 


26Q  VELOCITY     OF     DIFFUSION     OF     GASES. 

which  characterizes  chemical  union  among  gases.  It  was  also  re 
marked,  that  if  the  nitrogen  and  oxygen  were  merely  mixed,  their 
different  densities  should  cause  them  to  separate ;  the  heavier  oxy- 
gen accumulating  near  the  earth,  while  the  lighter  nitrogen  should 
occupy  the  higher  regions  of  the  air.  The  former  ground  has  been 
completely  disproved  by  later  research,  and  the  elements  of  air  are 
separated  from  one  another  by  such  feeble  means,  thus,  by  nitric 
oxide,  by  metallic  lead,  by  agitation  with  water,  &c.,  as  would  be 
unexampled  in  chemistry  among  substances  of  a  constitution  such 
as  it,  if  a  true  compound,  should  be  supposed  to  have.  Besides, 
its  density,  its  refractive  power,  its  specific  heat,  are  the  mean 
qualities  of  the  oxygen  and  nitrogen  which  form  it ;  circumstances 
which  necessarily  occur  if  it  be  a  mixture,  but  which  do  not  take 
place  in  any  case  of  chemical  combination.  An  artificial  mixture, 
also,  of  oxygen  and  nitrogen  possesses  all  the  properties  of  atmo- 
spheric air. 

It  is  also  not  the  fact  that  gases  of  different  densities  tend,  when 
mixed  together,  to  separate,  and  form  different  layers,  in 
^  accordance  with  their  specific  gravities.  On  the  contrary, 
if  two  bottles,  containing,  the  one,  a,  a  lighter,  and  the  other, 
e,  a  heavier  gas,  be  connected  by  stopcocks,  6,  c,  c/,  and  al- 
lowed to  stand  for  a  few  hours,  the  bottle  containing  the 
heavy  gas  being  lowest,  they  will  be  found  to  mix,  the  light- 
er gas  finding  its  way  to  the  lower  bottle,  and  the  heavy 
gas  ascending  to  the  bottle  which  is  above.  In  this  process 
the  gases  evince  a  positively  active  power  of  penetrating 
into  the  spaces  occupied  by  each  other  ',  and  this  occurs 
even  when  they  are  separated  by  membranes,  or  by  masses 
of  porous  earthy  substances.  This  peculiar  property  of 
gases  was  first  recognised  by  Dobereiner,  and  then  studied 
by  Mitchell,  but  finally  examined,  and  its  laws  accurately  assigned, 
by  Graham.  When  gases  of  unequal  densities  are  placed  in  con- 
tact with  each  other,  they  tend  to  mix  ultimately  in  a  uniform 
manner ;  but  the  rapidity  with  which  they  penetrate  each  other's 
volume,  or,  as  it  is  termed  bjr  Graham,  the  velocity  of  diffusion  of 
the  gases,  is  unequal,  and  depends  upon  their  densities ;  the  lighter 
gases  diffusing  themselves  most  rapidly,  the  heavier  more  slowly. 
Thus,  if  a  tube  be  closed  at  the  top  by  a  plug  of  plaster  of  Paris, 
which,  when  dry,  is  very  porous,  and  filled  with  hydrogen  gas,  the 
plug  being  kept  dry,  the  hydrogen  and  the  external  air  tend  to  mix 
across  the  porous  plug  ;  but  the  hydrogen  comes  out  more  rapidly 
than  the  air  gets  in,  and  hence  the  water  rises  considerably  in  the 
tube.  In  a  similar  way,  if  a  glass  be  filled  with  hydrogen  gas,  and, 
the  top  being  closed  by  a  sheet  of  India  rubber,  a  bell  glass  of  air 
be  inverted  over  it,  the  hydrogen  passing  out  of  the  glass  more  rap- 
idly than  air  enters  to  supply  its  place,  the  sheet  of  India  rubber 
is  gradually  bent  into  the  glass,  and  ultimately  burst  by  the  external 
pressure.  On  the  contrary,  if  the  small  glass  contain  air  and  the 
bell  glass  hydrogen,  the  membranous  cover  is  gradually  forced  up- 
ward by  means  of  the  excess  of  hydrogen  which  passes  in,  and 
which  finally  breaks  through  it  by  the  elasticity  thus  produced  in- 
side. 


LAW     OF     DIFFUSION     OF     GASES.  267 

The  exact  law  of  the  diffusion  of  gases  is,  that  the  velocity  of  diffusion  is  inverse- 
ly proportional  to  the  square  roots  of  the  specific  gravities  of  the  gases.  This  is  ex- 
hibited in  the  following  table. 


Specific  Gravities.  Square  Roots  of  S.  G.  DiflFusion  Velum* 

Hydrogen    ....  00688     ....  02623     .  . 

Ammonia    ....  05898     ....  07681     .  . 

Air 10000     ....  10000     .  . 


Carbonic  acid  .     .     .  1-6239     .     .  .  1-2345 

Chlorine      ....  2-4700     ....  15716 


457 
130 
100 
81 
64 


By  this  table  it  will  be  seen,  that  in  the  same  time  in  which  100  volumes  of  at- 
mospheric air  escape  from  a  vessel  through  a  membranous  or  porous  plug,  457 
volumes  of  hydrogen  pass  in ;  and  if  the  vessel  were  previously  full  of  hydrogen, 
457  volumes  will  escape  from  it  during  the  entrance  of  100  volumes  of  atmospheric 
air.  If  the  vessel  contained  carbonic  acid,  the  result  would  be  the  passage  of  81 
volumes  in  the  same  time,  and  so  of  the  other  gases. 

[This  law  is,  however,  entirely  departed  from  when  the  gases  are  separated 
from  one  another  by  a  plug  or  barrier  which  exerts  upon  them  a  condensing  action, 
and  the  diffusion  volumes  are  found  to  be  other  than  those  indicated  in  the  forego- 
ing table.  A  plug  of  stucco  exerts#)ut  little  condensing  effect  upon  the  gases,  and 
hence  their  diffusion  takes  place  into  one  another  with  a  velocity  inversely  propor- 
tional to  the  square  roots  of  their  densities  ;  but  a  thin  lamina  of  India  rubber,  ef- 
fecting a  powerful  condensation,  presents  the  two  gases  to  each  other  with  densi- 
ties that  are  abnormal,  and  hence  disturbs  their  rate  of  diffusion. 

Phenomena  of  this  kind  may  be  very  beautifully  shown  by  means  of  soap-bub- 
bles. If  a  vial  that  has  had  a  film  of  soap- water  spread  over  its  mouth  be  exposed 
under  a  jar  to  an  atmosphere  of  ammonia  or  protoxide  of  nitrogen,  its  horizontality 
is  instantly  disturbed,  and  it  begins  to  assume  a  spherical  convexity,  and  continues 
expanding  until,  after  passing  through  a  series  of  brilliant  colours,  it  may  become 
so  thin  as  to  be  almost  invisible.  To  show  the  great  rapidity  with  which  a  gas  or 
vapour  will  pass  through  such  barriers,  if  a  soap-bubble  be  expanded  in  a  vial  con- 
taining a  little  aqua  ammonias,  and  the  air  from  its  interior  be  immediately  with- 
drawn into  the  mouth,  the  strong  caustic  taste  of  the  ammonia  will  be  immediately 
perceived. 

Through  thin  pieces  of  India  rubber  gases  will  diffuse  into  each  other,  though 
resisted  by  any  given  pressure.  I  have  found  that  sulphuretted  hydrogen  will  thus 
pass  into  atmospheric  air  against  a  pressure  of  more  than  fifty  atmospheres.] 

This  law  of  the  passage  of  gases  through  each  other  is  the  same  as  that  for  the 
passage  of  a  gas  into  a  perfectly  empty  space.  If  the  different  gases  be  allowed  to 
strain  through  a  porous  plug  into  a  vessel  from  which  the  air  has  been  removed  by 
the  air-pump,  they  will  enter  with  different  velocities,  regulated  by  their  specific 
gravities,  precisely  as  in  the  former  instance ;  and  hence  it  is  experimentally  de- 
monstrated that  different  gases  are  ultimately  permeable  to  each  other,  precisely  as 
the  spaces  they  occupy  would  be  if  entirely  empty ;  that  the  gases,  in  fact,  form 
vacua  to  each  other,  but  that  so  far  as  the  law  of  mixture  and  the  final  effect  are- 
concerned,  the  mixture  taking  place  more  slowly,  in  consequence  of  the  mechani- 
cal obstruction. 

This  general  principle  had,  however,  been  laid  hold  of  by  the  keen  intellect  of 
Dalton,  and  announced  long  before  its  truth  had  been  accurately  proved  in  the  man- 
ner that  has  been  now  described ;  to  him  we  are  indebted  for  the  first  philosophical 
view  of  the  molecular  constitution  of  the  atmosphere ;  he  proposed  to  consider  the 
different  gases  which  exist  in  the  atmosphere  as  being  in  all  points  independent  of 
each  other,  mixed  uniformly  in  virtue  of  the  diffusive  power  which  he  had  been 
the  first  to  recognise,  and  exercising  pressures  upon  the  surface  of  the  earth  pro- 
portional to  their  quantities.  Thus,  if  we  suppose  100  parts  of  atmospheric  air  to 
consist  by  weight  of, 

Nitrogen  gas    .  .              ...  75-88  "\ 

Oxygen  gas      .  ...  23041  ,„^.^^ 

Watery  vapour  ...     103  f^"""" 

Carbonic  acid  .  ....       05^ 

the  pressure  of  the  air  being  taken  at  thirty  inches  of  mercurj',  the  respective 
pressures  of  the  independent  atmospheres  will  be  as  follows : 


268    CONSTITUTION  OF   THE    ATMOSPHERE   PERMANENT. 

Pressure  of  the  nitrogen  gas 22  764  inches, 

"  oxygen  gas 6912       " 

"  watery  vapour 0309       " 

"  carbonic  acid  gas 0015      " 

30  000 

The  different  constituents  of  air  are  thus  in  the  state  best  suited 
to  the  purposes  for  which  the  atmospliere  is  destined ;  no  one  gas 
can  interfere  with,  or  retard  the  others'  action  j  there  are  no  affini- 
ties to  be  overcome,  or  existing  combinations  to  be  broken  up,  before 
the  agency  of  watery  vapour,  of  carbonic  acid,  and  of  oxygen  can 
be  brought  into  the  extended  alternations  on  which  the  continu- 
ed and  happy  existence  of  animal  and  vegetable  life  depends,  from 
which  arises  the  diversity  of  aspect  of  our  ever  varying  sky,  and 
the  gradual  detrition  of  the  solid  rocky  materials  of  the  earth's  sur- 
face giving  a  fruitful  soil. 

By  the  processes  of  combustion  and  of  respiration  which  are  in  ac- 
tion on  the  surface  of  the  earth,  the  'Oxygen  of  the  atmosphere  is 
continually  removed,  and  an  equal  volume  of  carbonic  acid  gener- 
ally substituted  for  it.  This  carbonic  acid  is  absolutely  a  narcotic 
poison,  and  the  air  becomes  unfitted  for  the  support  of  life  before 
one  half  of  the  quantity  of  oxygen  it  contains  has  been  consumed. 
A  healthy  man  spoils  in  twenty-four  hours,  by  respiration,  720  cubic 
feet  of  atmospheric  air,  that  is,  a  mass  of  air  eleven  feet  square  and 
six  feet  thick.  The  burning  of  three  ounces  of  charcoal  produces 
the  same  effect.  In  many  factories  there  are  burned  daily  ten  tons 
of  coal,  which  deteriorate  at  least  as  much  air  as  the  same  weight 
of  charcoal,  and  hence  each  day,  by  such  a  factory,  there  is  render- 
ed unfit  for  respiration  3,185,760  cubic  yards  of  air,  which  would 
cover  to  the  depth  of  six  feet  a  space  a  quarter  of  a  mile  square. 
Nevertheless,  it  has  been  already  mentioned,  that  even  in  cities,  the 
relative  proportions  of  oxygen,  nitrogen,  and  carbonic  acid  in  the 
air  are  but  little  altered,  and  it  becomes  an  object  of  great  interest 
to  ascertain  in  what  manner  that  permanency,  on  which  the  stabili- 
ty, in  truth,  of  all  organized  nature  seems  ultimately  to  depend,  has 
been  secured. 

In  the  first  place,  from  the  frequent  occurrence  of  storms  and  vio- 
lent currents,  which  agitate  vast  tracts  of  air,  accumulation  of  nox- 
ious gases  or  corrupted  portions  cannot  take  place,  except  in  some 
rare  and  limited  localities,  which  do  not  affect  the  condition  of  the 
atmosphere  even  near  at  hand  ;  and  although  the  numbers  which 
have  been  shown  as  indicating  the  amount  of  air  destroyed  become 
enormous  when  multiplied  by  the  number  of  breathing  beings  and 
the  quantity  of  fuel  burned  on  the  earth's  surface,  they  yet  bear  but 
a  trifling  proportion  to  the  immensity  of  the  aerial  ocean  in  which 
we  live.  The  atmosphere  may  be  considered  as  being,  if  brought 
throughout  to  its  usual  density  at  the  surface  of  the  earth,  about 
five  miles  deep  j  and  Prevost  has  calculated  that  the  loss  of  all  the 
oxygen  employed  in  respiration  and  combustion  for  100  years  could 
not  diminish  its  quantity  by  ,  2V0  part,  a  quantity  too  trifling  to  be 
detected  by  our  methods,  even  had  the  exact  sciences  flourished 
for  such  a  period  as  to  allow  a  comparison  to  be  made. 

But,  independent  of  this  negative  proof  of  permanence  of  com- 


ATMOSPHERIC     PRESSURE.  269 

positior.,  science  has  pointed  out,  in  the  peculiar  relations  of  the 
lunctions  of  vegetable  and  aninnal  beings,  a  provision  of  adaptation 
to  each  other's  wants,  which  retains  the  atmosphere  in  a  condition 
practically  of  eternal  identity  of  constitution.  A  healthy  growing 
plant,  exposed  to  sunlight,  is  found  to  absorb  carbonic  acid,  and  to 
emit  oxygen  from  the  surfaces  of  its  green  leaves.  In  the  dark,  an 
inverse  effect  takes  place,  oxygen  being  absorbed,  and  carbonic 
acid  formed.  The  coloured  parts  of  plants,  as  flowers  and  fruits, 
absorb  likewise  oxygen,  and  emit  carbonic  acid ;  but  as  the  green 
surfaces  preponderate  so  much  throughout  the  vegetable  world,  and 
the  stimulus  of  light  is  active  throughout  the  greater  portion  of  the 
twenty-four  hours,  the  ultimate  effect  is,  that  an  action  the  opposite 
of  that  which  animals  exercise  upon  the  atmosphere  is  constantly 
going  on.  That  which  the  plant  rejects  is  to  the  animal  the  source 
of  energy  and  of  all  vital  powers,  while  the  same  element  which  the 
plant  absorbs,  and  from  which  it  forms  its  tissues,  has  been  thrown 
out  as  useless  by  the  animal,  and  would,  if  not  removed,  accumulate 
in  the  end,  and  destroy  all  animal  existence. 

The  most  accurate  experiments  have  determined  that  100  cubic 
inches  of  atmospheric  air,  freed  from  moisture  and  carbonic  acid, 
weigh  31,0117  grains;  the  barometer  being  at  30  inches,  and  the 
thermometer  at  60°.  Its  specific  gravity  is  taken  as  the  standard 
for  gases  and  vapours,  and  is  hence  1000.  It  is  about  780  times 
lighter  than  water  at  40*5°  Fahrenheit,  when  water  is  at  its  gre9test 
density,  and  is  then  also  10,600  times  lighter  than  quicksilver. 

The  weight  of  the  atmosphere  pressing  upon  the  surface  of  the 
earth  is  equivalent  to  about  fifteen  pounds  on  each  square  inch  of 
surface.  The  existence  of  this  pressure  may  be  shown  in  many 
ways  :  a  bladder  or  a  thin  plate  of  glass  may  be  burst  if  the  pressure 
of  the  air  be  removed  from  one  side  by  the  air-pump  while  it  is  al- 
lowed to  act  against  the  other ;  a  pair  of  brass  hemispheres,  which 
are  easily  separated  while  filled  by  air,  are  pressed  most  firmly  to- 
gether if  the  air  be  removed  from  their  interior.  This  pressure  is 
equivalent  to  that  exercised  by  a  column  of  mercury  in  a  tube  about 
thirty  inches  high,  and,  accordingly,  an  instrument,  the  common  ba- 
rometer^ or  pressure  measurer,  is  thus  constructed,  to  register,  at  ev- 
ery moment,  the  pressure  which  the  atmosphere  exercises.  A  tube 
closed  at  one  end,  and  about  thirty-two  inches  long,  is  to  be  care- 
fully filled  with  pure  mercury ;  it  is  then  inverted  in  a  basin  of  mer- 
cury, and  being  placed  in  a  vertical  position,  the  column  of  mercury 
sinks  to  a  certain  height  in  the  tube,  generally  between  twenty-nine 
and  thirty  inches,  leaving  above  it  a  space  which  is,  at  low  temper- 
atures, the  most  perfectly  empty  that  can  be  experimentally  pro- 
cured. From  the  name  of  the  inventor  of  this  instrument,  it  is  called 
the  Torricellian  vacuum.  If  the  external  pressure  varies,  the  height 
of  the  column  of  mercury  alters  likewise,  rising  when  the  pressure 
increases,  descending  when  it  is  diminished;  and  as  considerable 
changes  in  the  amount  of  pressure  generally  depend  on  violent  mo 
tions  in  the  air,  which  produce  changes  fn  the  weather  also,  the 
barometer  is  popularly  regarded  as  a  weather-glass,  although  no  ac- 
curate indications  of  approaching  changes  can  be  at  all  reckoned  on 
from  its  use. 


270    PRESSURE    AND    EXTENT    OP    THE    ATMOSPHERE. 

If  the  atmosphere  preserved  throughout  its  entire  mass  the  same 
density  and  elasticity  which  it  possesses  at  the  surface  of  the  earth, 
its  height  would  be  about  five  miles.  But  such  is  not  the  case  j 
the  lower  portions  of  the  air,  which  press  upon  the  earth,  are  pressed 
upon  by  the  portions  next  over  them,  these  again  by  those  still 
higher  up,  so  that  the  amount  of  pressure,  and,  consequently,  the 
density  of  the  air,  decreases  continually  as  we  ascend  through  its 
mass.  The  rate  of  diminution  is  even  very  rapid,  forming  a  geo- 
metrical proportion  when  the  heights  are  taken  in  an  arithmetic 
series  j  and  on  this  principle  is  founded  one  of  the  most  accurate 
modes  of  estimating  heights  that  has  been  yet  discovered.  If  a 
barometer  be  carried  to  the  summit  of  a  mountain,  the  column  of 
quicksilver  will  be  observed  to  be  shorter  than  it  had  been  upon  the 
plain,  and  the  difference  being  marked,  the  height  corresponding  to 
it  is  determined,  from  a  knowledge  of  the  law  just  stated.  In  prac- 
tice there  are  corrections  depending  on  temperatures  and  other 
causes,  to  which  it  is  not  necessary  to  allude.  So  rapid  is  this  dimi- 
nution of  density,  that  one  half  of  the  w^hole  mass  of  the  atmosphere 
lies  within  three  miles  of  the  surface  of  the  earth,  and  four  fifths  of 
it  within  eight  miles.  Hence,  in  those  elevated  regions,  the  lungs 
receive,  even  in  a  deep  inspiration,  but  little  oxygen,  and  the  blood 
not  being  well  arterialized,  causes  the  headaches,  lassitude,  and 
faintness  which  those  who  ascend  high  mountains  or  in  balloons  feel 
so  severely.  The  lakes  in  the  mountainous  valleys  of  Switzerland 
and  the  Andes  are,  for  the  like  reason,  destitute  of  fish  j  the  water 
holds  no  air  dissolved  to  fit  it  for  their  respiration,  precisely  as 
one  may  kill  a  fish  in  water  by  placing  it  under  the  receiver  of  an 
air-pump  and  abstracting  the  atmospheric  air. 

The  question  of  how  far  the  atmosphere  really  extends  in  space, 
possesses,  in  relation  to  the  views  of  the  ultimate  constitution  of 
matter,  already  noticed,  considerable  interest.  If  the  particles  of 
atmospheric  air  were  capable  of  division  to  an  infinite  degree,  then 
the  attenuation  which  occurs  in  the  higher  regions  of  the  air  should 
have  no  limit,  and  we  should  look  upon  all  space  as  occupied  by  the 
elements  which  form  our  atmosphere,  rarefied  to  an  inconceivably 
great  degree,  and  our  earth  as  having  provided  itself,  in  its  course 
through  space,  with  as  much  of  this  circumambient  matter  as,  from 
its  attractive  power,  it  was  able  to  keep  round  it.  If,  on  the  other 
hand,  the  oxygen  and  nitrogen  of  the  air  consist  of  molecules  of  defi- 
nite form  and  size,  these,  being  in  the  gaseous  form,  are  subjected  to 
the  simultaneous  action  of  two  forces  :  one,  the  mutual  repulsion 
which  characterizes  the  gaseous  condition,  and  which  causes  their 
elasticity,  but  which,  diminishing  with  this  elasticity,  must  become 
very  small  in  the  upper  strata  of  our  atmosphere  ;  the  other,  the 
general  attraction  of  the  earth,  which,  though  much  inferior  at  the 
surface,  must,  since  it  diminishes  but  very  little  in  ascending  so  far, 
at  a  certain  point  become  equal  to  the  former,  and  then  all  farther 
expanding  tendency  bein^  overcome,  the  atmosphere  should  be  ter- 
minated by  a  definite  surffce,  similar  in  form  to  that  of  the  solid  earth, 
having  its  tides  and  currents  like  those  of  our  great  oceans,  and 
from  these  various  fluctuations  in  its  depth,  produce  the  regular 
variations  in  the  height  of  the  barometer,  which,  though  involved 
by  the  irregular  motions  of  much  larger  amount,  have  been  detected 


S    ATMOSPHERIC     THEORY.  271 

The  amount  of  refraction  proves  that  the  sensible  atmosphere 
does  not  extend  beyond  45  miles ;  at  least,  if  it  exist  higher  up,  it 
must  be  so  rare  as  to  have  no  effect  in  deflecting  a  ray  of  light. 
But  other  considerations  prove  that  the  air  does  not  extend  through 
space.  If  we  had  obtained  our  atmosphere  by  gathering  up,  in  vir- 
tue of  our  attracting  force,  the  thin  air  which  pervades  all  space,  the 
other  bodies  of  our  system  should  also  possess  atmospheres  whose 
densities  should  represent  the  masses  of  the  bodies  they  include. 
However,  exact  observation  has  shown  that  even  the  largest  bodies 
of  our  system  possess  no  atmospheres.  A  ray  of  light  suffers  no 
bending  in  its  course,  although  it  passes  by  the  edge  of  Jupiter ; 
yet,  from  the  immense  size  of  that  planet,  it  should  have  collected 
round  it  an  atmosphere  so  dense,  that  by  its  refraction  a  star  should 
become  visible  to  us  upon  one  side  of  it  before  it  had  disappeared 
at  the  other.  The  sun,  likewise,  the  gravitating  centre  of  our  sys- 
tem, does  not  possess  a  trace  of  atmosphere  sufficient  to  cause  a 
sensible  refraction. 

Poisson  has  recently  suggested  a  view  of  the  constitution  of  our  atmosphere, 
upon  grounds,  however,  so  little  connected  with  experiment  that  it  would  not  be 
a  subject  for  notice  here,  had  it  not  been  introduced  to  the  notice  of  chemists 
under  the  sanction  of  Dumas's  eloquent  discourses.  I  will,  therefore,  briefly  describe 
the  theory  he  has  put  forward. 

The  atmosphere,  as  we  ascend,  grows  colder.  The  source  from  which  the  at- 
mosphere derives  its  heat  is  not  the  sun,  but  the  solid  earth ;  the  solar  rays  passing 
through  the  air  as  they  pass  through  glass  and  all  transparent  bodies,  without  com- 
municating much  of  their  heat.  These  heating  rays  are  absorbed  by  the  dark  and 
rugged  surface  of  the  earth.  From  this  the  layer  of  air  next  to  it  derives  its  warmth, 
and  hence,  the  farther  from  the  earth  the  air  is  taken,  the  colder  it  is  found  to  be. 
Hence,  even  under  the  glare  of  a  tropical  sun,  there  exists  an  elevation  where  the 
temperature  never  rises  above  32°,  the  melting  point  of  ice  ;  above  that  height  all  is 
eternal  snow.  Farthest  from  the  level  of  the  sea  at  the  equator,  being  15,000  feet, 
this  line  of  perpetual  congelation  gradually  descends,  until  at  the  poles  it  sinks  below 
the  surface  of  the  earth.  In  these  countries  we  have  no  mountains  with  perpetual 
snow,  the  line  of  congelation  being  6000  feet  above  the  surface. 

From  this  source,  also,  are  derived  the  various  phenomena  of  fog  and  cloud,  the 
production  of  snow,  of  hail  and  rain.  The  vapour  forming  at  the  surface  of  a  pond 
IS  generated  with  an  elasticity  proportional  to  its  temperature  ;  and  when  the  air, 
thus  mixed  with  vapour,  rises  to  a  higher  and  colder  stratum,  the  elasticity  of  the 
vapour  is  diminished,  and  a  portion  separates  either  as  cloud  or  rain.  Thus,  if  air 
becomes  loaded  with  vapour  at  the  surface  having  a  temperature  of  80°,  and,  on 
ascending,  it  becomes  cooled  to  40°,  the  quantity  of  water  separated  is  thus  found  • 

The  elasticity  at  60°  is  0524  inch  of  mercury. 
40°  is  0263 

the  difference  is      .     .  0.261  " 

But  524  :  261  :  :  100  :  498,  or  nearly  50,  and  hence  almost  exactly  one  half  of  the 
quantity  of  vapour  carried  up  is  deposited  under  the  form  of  cloud  ;  in  addition  to 
this,  another  portion  of  vapour  is  deposited  as  liquid  water,  from  the  circumstance 
of  the  diminution  in  volume  of  the  mixture  of  gas  and  vapour  produced  by  the  low- 
ering of  its  temperature ;  this  is  equal  to  about  four  per  cent.,  so  that  there  remains 
as  invisible  vapour  only  about  forty-six,  while  fifty-four  per  cent,  are  engaged  in  the 
production  of  the  cloudy  masses.  The  farther  properties  of  clouds,  the  circum- 
stances which  determine  the  production  of  rain,  snow,  or  hail,  are  of  so  httle  refer- 
ence to  chemistry  that  I  shall  pass  from  them  without  remark. 

Reasoning  from  the  principle  that  all  gases  ma^by  suitable  reduction  of  their 
temperature,  be  reduced  to  the  sohd  form,  Poisson  proposes  to  consider  the  atmo- 
sphere as  being  extended  above  the  earth,  gradually  becoming  more  attenuated  and 
more  cold,  until  it  arrives  at  a  point  at  which  it  freezes ;  there  then  should  be  a 
shell  of  transparent  colourless  air-ice,  lined  on  its  concave  surface  with  a  sea  of 


272 


NITROUS    OXIDE, 


liquid  oxygen  and  nitrogen  mixed  or  combined  together.  From  such  assumption, 
Poisson  proposes  to  render  the  theory  of  astronomical  refractions  more  definite  and 
exact  than  it  had  before  been,  but  those  grounds  can  scarcely  be  deemed  sufficient 
to  justify  the  adoption  of  that  idea  as  a  physical  reality.  So  far,  in  fact,  as  collat- 
eral evidence  can  be  found,  the  fundamental  idea  of  Poisson's  theory  is  disproved  ; 
for  it  results  from  Fourier's  researches  on  the  distribution  of  Heat,  that  the  tem- 
perature of  the  planetary  spaces  cannot  be  below  — 57°  of  Fahrenheit,  a  degree  of 
cold  which  is  met  with  in  Melville  Island  during  winter,  and  which  has  been  far 
exceeded  by  artificial  means.  At  this  temperature  air  shows  no  sign  of  even  be- 
coming liquid,  far  less  solid ;  and  hence  the  supposition  of  such  a  hollow  sphere 
of  frozen  air  cannot  be  granted. 

Compounds  of  Jfitrogen  and  Oxygen. 
Nitrous  oxide       .     .     .     N.  =  14-0-{-  0.=-  8=N.O  =22-0 


Nitric  oxide  .  . 
Hyponitrous  acid 
Nitrous  acid  .  . 
Nitric  acid  .     .     . 


N.=:14-0H-2O.  =  16=N.O2=30-0 
N.  =  14-0+3O.=24=N.O3=38-0 
N.  =  14-0+4O.=32=--N.O4=46-0 
N.==14-0+5O.=40=N.O5=54-0 


JVitrous  Oxide.     Protoxide  of  Jfitrogen. 

This  substance,  which  exists,  under  ordinary  pressure,  in  the  gab 
eous  form,  is  best  and  most  easily  prepared  by  heating  to  about  350° 
Fah.  the  crystallized  nitrate  of  ammonia.  This  salt  melts  at  300° 
Fah.  into  a  colourless  liquid,  without  being  at  all  decomposed  or 
losing  water ;  but  when  the  temperature  is  raised  to  350^,  a  lively 
effervescence  occurs,  and  the  salt  is  totally  resolved  into  vapour  of 
water  and  nitrous  oxide  gas,  an  equivalent  of  nitrate  of  ammonia 
producing  two  equivalents  of  the  gas  and  four  of  water,  thus: 

N.O,+N.H40.=2(N.O.)+4(H.O.) 

The  nitrate  of  ammonia  may  be  placed  in  the  flask  a,  imbedded 

in  the  little  cup  of  sand. 
A  bent  tube  conducts  the 
gas  evolved  to  the  pneu- 
matic trough,  as  in  the 
figure,  or  to  the  gasom- 
eter, if  the  quantity  be 
large.  In  this  process 
the  temperature  should 
not  be  allowed  to  rise  be- 
yond the  point  at  which 
the  effervescence  is  mod- 
erately brisk ;  for  when 
the  salt  becomes  much 
hotter,  the  decomposi- 
'"ii'wii"H'i'"i"iiii'ii;iy'  ^     ^  ^^tion  is  tumultuously  rap- 

id, and  the  gas  obtained  may  not  be  at  all  pure. 

The  nitrous  oxide  gas  so  obtained  is  perfectly  colourless  and 
transparent ;  it  is  absorbed  by  water  in  moderate  quantity,  and  hence 
the  water  over  which  it  i# collected  should  always  be  heated  to  about 
90^  in  order  to  diminish  the  loss  of  gas  thus  suffered.  It  is  heavier 
than  air,  its  specific  gravity  being  1-527. 

A  lighted  taper  burns  with  increased  brilliancy  in  this  gas  j  and  if 


ITS     PROPERTIES     AND     COMPOSITION.  273 

blown  out,  may  be  relighted,  provided  a  pretty  large  portion  of  the 
wick  remains  bright  red.  If  the  gas  be  mixed  with  its  own  volume 
of  hydrogen,  it  may  be  inflamed  by  a  taper  or  by  an  electric  spark, 
and  then  burns  with  a  loud  explosion.  If  phosphorus  be  heated  in 
this  gas,  it  inflames  and  burns  with  almost  as  much  brilliancy  as  in 
pure  oxygen. 

In  none  of  these  instances  does  the  nitrous  oxide  enter  into  com 
bination.  It  is  decomposed  by  the  high  temperature  of  the  burning 
body  and  the  affinity  of  this  last  for  oxygen,  and  the  combustion  is 
maintained  by  means  of  the  oxygen  which  is  thus  disengaged.  After 
the  process  is  completed,  the  nitrogen  of  the  nitrous  oxide  remains 
free. 

In  this  manner  nitrous  oxide  may  be  analyzed.  If  a  little  bit  of  potassium  or  of 
phosphorus  be  heated  in  a  measured  quantity  of  the  gas  until  the  decomposition  is 
complete,  and  then  the  apparatus  be  cooled  to  its  original  temperature,  it  will  be 
found  that  a  quantity  of  nitrogen  remains  exactly  equal  in  volume  to  the  nitrous 
oxide  used,  and  the  quantity  of  oxygen  absorbed  is  such,  that  in  its  gaseous  form 
it  had  exactly  half  that  volume.  The  nitrous  oxide  consists,  therefore,  of  two  vol- 
umes of  nitrogen  and  one  of  oxygen  condensed  to  two  volumes,  and  hence  its  spe- 
cific gravity  may  be  calculated  thus : 

Two  volumes  of  nitrogen  976x2=19520 
One  volume  of  oxygen  .  .  .  1102-6 
give  two  volumes  of  nitrous  oxide  3054-6 
and  one  volume  weighs,  therefore  1527.3 

By  weight,  the  composition  of  nitrous  oxide  and  its  equivaletit 
number  on  each  scale  are  expressed  as  follows : 

Nitrogen,  63*9  One  equivalent,  140  or  175 

Oxygen,    36-1  «  _8^  "   100 

"100^  22-0       275 

and  its  formula  is  N.O. 

The  most  singular  property  of  this  gas  is,  that  when  breathed 
pure  for  a  few  minutes  it  produces  a  lively  and  agreeable  into'xica- 
tion,  which  does  not  leave  any  lassitude  or  disagreeable  sensation 
when  it  goes  off*.  To  prepare  gas  for  being  breathed,  it  is  necessa- 
ry to  attend  to  the  purity  of  the  nitrate  of  ammonia  used,  as  very 
frequently  the  salt  found  in  commerce  contains  muriate  of  ammo- 
nia, in  which  case  the  gas  obtained  may  be  contaminated  by  nitrous 
acid  and  chlorine,  and  prove  very  irritating  to  the  lungs.  To  ob- 
tain the  full  effects  of  the  gas  upon  the  system,  four  or  five  quarts 
must  be  introduced  into  an  air-tight  bag  or  bladder,  and  inspired 
through  a  pretty  wide  glass  tube.  About  two  ounces  of  nitrate  of 
ammonia  yield  sufficient  gas  to  intoxicate  one  person. 

J^itric  Oxide.     Deutoxide  of  Kitrogen. 

This  substance  exists  naturally  under  the  form  of  a  gas,  which 
chemists  have  not,  as  yet,  been  able  to  reduce  to  the  liquid  form.  It 
is  very  easily  prepared,  being  almost  always  the  principal  product 
of  the  decomposition  of  nitric  acid  by  the  metals. 

If  a  small  quantity  of  quicksilver,  or  of  cd^per  cut  into  small  bits, 
be  placed  in  the  gas  bottle  in  the  figure,  and  diluted  nitric  acid,  pre- 
pared by  mixing  equal  volumes  of  the  aquafortis  of  commerce  and  of 
water,  be  poured  in  by  the  funnel  a,  efl!ervescence  is  immediately  pro- 

Mm 


274        PREPARATION,     ETC.,     OF     NITRIC     OXIDE. 


duced,  even  without  the 
application  of  heat,  and 
the  metal  dissolves  in  the 
acid,  which  becomes  pale 
green-coloured  if  quicksil- 
ver had  been  employed, 
but  of  a  rich  blue  if  cop- 
per had  been  used.  From 
greater  economy,  the  lat- 
ter metal  is  almost  always 
that  employed.  For  some 
time  after  the  action  commences,  the  space  in  the  bottle  over  the 
liquid  is  occupied  by  reddish  fumes  ;  but  these  gradually  pass  away, 
and  the  gas  may  be  collected  when  the  upper  part  of  the  generating 
flask  is  occupied  by  it  completely  colourless. 

The  theory  of  this  process  is  very  simple :  a  quantity  of  nitric 
acid  gives  off  three  fifths  of  its  oxygen  to  the  copper,  and  the  ni- 
trogen is  evolved  in  combination  with  the  remainino-  two  fifths, 
forming  nitric  oxide.  The  copper,  being  thus  oxidized,  combines 
with  another  portion  of  nitric  acid  to  form  a  fine  blue  salt,  nitrate 
of  copper,  which  exists  in  the  blue  liquor,  and  may  be  obtained  crys- 
tallized. For  complete  decomposition,  four  equivalents  of  nitric 
acid  and  three  of  copper  are  required,  and  the  action  may  be  then 
expressed  as  follows :  4N.O5  and  3Cu.  give  SrN.Og .  Cu.O.)  and 
(N.O,). 

By  the  action  of  organic  substances,  such  as  starch  or  sugar,  upon 
nitric  acid,  nitric  oxide  may  also  be  formed  in  abundance,  but  it  is 
not  then  so  uniformly  pure  as  when  obtained  by  means  of  mercury 
or  copper. 

This  gas  is  colourless  and  transparent ;  it  is  scarcely  absorbed  by 
water,  and  may  hence  be,  on  all  occasions,  collected  over  it.  It  is 
a  little  heavier  than  air,  its  sp.  gr.  being  1039  ;  its  refractive  index 
is  0*876 1.  A  lighted  taper  plunged  into  this  gas  is  extinguished,  and 
a  red-hot  wire  maybe  applied  to  phosphorus  in  it  without  inflaming 
it ;  but  if  the  phosphorus  be  already  set  on  fire,  it  not  only  continues 
to  burn  when  plunged  into  the  nitric  oxide  gas,  but  the  combustion 
is  almost  as  brilliant  as  in  pure  oxygen.  In  this  case,  it  is  indeed  in 
oxygen,  and  not  in  nitric  oxide,  that  the  combustion  actually  occurs ; 
for  the  gas  is  decomposed  by  the  high  temperature  of  the  burning 
phosphorus,  and,  being  resolved  into  its  constituents,  the  oxygen  is 
the  body  with  which  the  phosphorus  combines,  and  the  nitrogen  re- 
mains untouched. 

In  this  way  nitric  oxide  may  be  analyzed,  and  is  found  to  consist  of  equal  vol- 
umes of  nitrogen  and  oxygen  united  without  any  condensation.  From  this  its  spe- 
cific gravity  may  be  calculated : 

One  volume  of  nitrogen  .  .  .=976  0 
One  volume  of  oxygen  .  .  .  rr=ll02  6 
give  two  volumes  of  nitric  oxide  2078  6 
of  which  one  is  found  to  weigh     .      1039  3 

Its  equivalent  volume  is  therefore  4,  and  its  composition  by  weight 
and  its  equivalent  number  on  each  scale  are  as  follows: 


HYPONITROUSACID.  275 

Nitrogen,  46-95         One  equivalent,     =175  or  14-0 
Oxygen,    53-05         Two  equivalents,  =200  or  16-0 
loFOO  375       30^ 

and  Its  formula  is  N.O2. 

Nitric  oxide  may  be  deprived  of  one  half  of  its  oxygen,  and  so  be 
reduced  to  the  state  of  nitrous  oxide,  by  remaining  in  contact  for 
some  days  with  moist  iron  or  zinc  filings  5  in  this  case  its  volume 
is  reduced  to  one  half. 

The  most  remarkable  property  of  nitric  oxide  is  its  tendency  to 
unite  with  oxygen  when  this  last  is  uncombined.  Nitric  oxide 
cannot  take  oxygen  from  any  other  substance  ;  but  when  it  is  mixed 
with  air,  or  with  any  mixture  of  gases,  of  which  oxygen  is  one,  it 
unites  with  this,  forming  deep  red  fumes.  It  is  this  which  causes 
the  red  fumes  in  the  flask  in  which  the  nitric  oxide  is  generated. 
The  oxygen,  in  combining  with  the  nitric  oxide,  may  form  either 
hyponitrous  acid  (N.O3)  or  nitrous  acid  (N.O4),  and  they  are  both 
generally  formed  in  uncertain  proportions.  Hence  we  cannot  ex- 
actly calculate  the  quantity  of  oxygen  that  had  been  present ;  and 
this  process  does  not  answer  well  for  gaseous  analysis,  but  it  is 
useful  for  removing  oxygen  from  a  gaseous  mixture,  which  it  effects 
completely  if  the  nitric  oxide  be  added  in  excess.  The  red  fumes 
so  formed  are  soluble  in  water,  and,  by  washing  the  mixed  gases 
with  water,  may  therefore  be  completely  removed. 

Nitric  oxide  combines  with  a  great  number  of  salts  and  with  some 
acids  to  form  compounds,  which  in  some  respects  possess  consid- 
erable interest :  these  shall  be  noticed  under  those  heads  to  which 
their  history  more  particularly  belongs. 

Hyponitrous  Acid. 

The  red  fumes  which  are  formed  when  niiric  oxide  is  mixed  with 
atmospheric  air  or  oxygen,  consist  in  great  part  of  hyponitrous  acid, 
particularly  when  the  nitric  oxide  is  in  excess.  To  obtain  it  pure, 
four  volumes  of  nitric  oxide  should  be  mixed  with  one  volume  of 
oxygen,  and  the  vessel  containing  the  hyponitrous  acid  vapour  form- 
ed, exposed  to  a  cold  of  about  40  degrees  below  the  freezing  point 
of  water.  The  acid  then  condenses  into  a  deep  green-coloured 
liquid,  which  is  excessively  volatile. 

When  hyponitrous  acid,  either  in  the  state  of  liquid  or  of  vapour,  is  brought*iiito 
contact  with  water,  it  is  in  great  part  decomposed,  being  resolved  into  nitric  oxide 
and  nitric  acid,  three  equivalents  of  hyponitrous  acid  (SN.Og)  giving  2(N.02)  and 
N.O5.  The  same  occurs  when  it  is  acted  on  by  bases  dissolved  in  water,  and 
hence  the  salts  of  this  acid  can  only  be  prepared  by  indirect  means. 

When  nitre  has  been  kept  melted  for  some  time,  so  as  to  have  parted  with  a  portion 
of  its  oxygen,  it  is  reduced  to  the  state  of  hyponitrite  of  potash,  N.O5 .  K.O.  giving  off 
20.,  and  leaving  N.O3  .  K.O.  This  is  known  by  the  hyponitrite  being  decomposed 
by  acetic  acid,  and  giving  off  copious  red  fumes,  while  the  nitrate  of  potash  is  unal- 
terable by  acetic  acid.  The  hyponitrite  of  potash  cannot  be  crystallized  so  as  to 
free  it  from  the  excess  of  unaltered  nitre,  but  it  may  be  converted  into  sparingly 
soluble  salts,  as  those  of  silver  and  of  lead,  and  so  pure  salts  of  hyponitrous  acid 
formed. 

The  specific  gravity  of  the  vapour  of  this  acid  has  not  been  experimentally  deter- 
mined. It  consists  of  two  volumes  of  nitrogen  united  to  three  of  oxygen,  but  of 
their  condensation  we  know  nothing. 

Its  composition  by  weight  and  its  equivalent  constitution  are, 


S76       PREPARATION,     ETC.,     OF     NITROUS     ACID. 

Nitrogen,  37*11  One  equivalent,        =175  or  14*0 

.    Oxygen,    62-89  Three  equivalents,  =300  or  24-0 

iOO-00  -  475       38^ 

JSTitrous  Jicid.     Jfitroso-nitric  Acid. 

This  substance  presents  itself,  like  the  last,  under  the  form  of  deep 
red  fumes,  and  is  produced  when  the  oxygen  is  in  excess  with  regard 
to  the  nitric  oxide.  By  a  cold  of  about  0°  on  Fahrenheit's  scale,  it 
raay  be  rendered  liquid.  To  form  it  directly,  four  volumes  of  nitric 
oxide  are  to  be  mixed  with  two  volumes  of  oxygen,  and  the  mixture 
exposed  to  a  great  cold ;  but  it  is  more  conveniently  prepared  by 
means  of  the  decomposition  of  nitrate  of  lead  byiieat. 

A  quantity  of  finely-powdered  and  dry  nitrate  of  lead  is  to  be  pla- 
ced in  an  earthenware  or  hard  glass  retort,  and  heated  to  full  red- 
hess.  The  red  vapours  that  are  produced  are  to  be  conducted  into 
a  receiver,  carefully  cooled  by  a  mixture  of  snow  and  salt.  They 
then  condense  into  a  liquid,  while  a  quantity  of  oxygen  gas  escapes, 
and  oxide  of  lead  remains  behind  in  the  retort.  The  nitric  acid  of 
the  nitrate  of  lead  is  decomposed  into  nitrous  acid  and  oxygen,  as 
follows  :  N.O5 .  Pb.O.  gives  Pb.O.,  free  N.O4  and  O. 

The  liquid  nitrous  acid  is  nearly  colourless  at  zero,  at  60°  it  is 
orange  yellow,  and  at  — 40^  it  solidifies  into  a  white  crystalline 
mass.  It  boils  at  82°,  and  its  vapour,  which  is  ruddy  red  at  that 
temperature,  is  almost  perfectly  black  at  212°.  In  these  various 
coloured  states,  it  exercises  remarkable  absorbing  power  on  light. 
The  specific  gravity  of  the  liquid  acid  is  1*451. 

Nitrous  acid  is  the  most  stable  compound  of  nitrogen  and  oxy- 
gen; it  is  not  decomposed  by  a  red  heat;  it  is  decomposed  in  great 
part  by  water,  nitric  acid  being  formed,  and  nitric  oxide  being  given 
off  as  gas.  Thus,  3(N.04)  give  N.O^  and  2(N.05).  The  nitric  acid 
formed  always  protects'a  portion  of  the  nitrous  acid  from  this  reac 
tion. 

When  the  nitrous  acid  is  formed  by  the  direct  union  of  nitric  oxide  and  oxygen, 
it  is  found  that  the  six  volumes  of  gas  are  condensed  by  combination  into  two ; 
hence  the  specific  gravity  of  nitrous  acid  vapour  should  be  3181-2 ;  thus, 

One  volume  of  nitrogen 976  0 

Two  volumes  of  oxygen 2205  2 

One  volume  of  nitrous  acid    ....  31812 

Its  composition  by  weight  and  the  constitution  of  its  equivalent 
are  as  follows : 

Nitrogen,  =30*33         One  equivalent,     =175  or  14*0 

Oxygen,    =69.67         Four  equivalents,  =400  or  32*0 

100*00  575       4^0 

Considerable  doubt  has  been  thrown  upon  the  nature  of  this  substance,  for  many 
chemists  regard  it  as  incapable  of  uniting  with  bases,  and  hence  look  upon  it  as  a 
kind  of  acid  salt,  consisting  of  nitric  and  hyponitrous  acids  combined  together ; 
2(N.04)=N.05-4-N.03.  But  late  researches  have  shown  that  it  does  produce  true 
salts,  and  that  even  many  saline  compounds  which  had  been  supposed  to  be  salts 
of  hyponitrous  acid  really  contain  this  substance ;  thus,  the  yellow  basic  salt,  formed 
'^y  boiling  a  solution  of  nitrate  of  lead  on  metallic  lead,  is  a  true  nitrite,  I  retain, 
therefore,  for  this  body  the  old  name  of  nitrous  acid,  the  more  as  that  of  peroiude 
of  nitrogen,  proposed  for  it  by  Graham,  is  frequently  applied  to  nitric  oxide 


NITRIC     ACID.  277 

Mitric  Acid. 
N.O3. 

It  IS  found  that  when  nitric  oxide  is  brought  into  contact  with  a 
great  excess  of  oxygen  over  water,  they  combine  in  the  proportion 
of  four  volumes  of  the  first  to  three  of  the  second ;  and  when  the 
red  fumes  which  are  produced  have  dissolved  in  the  water,  that  is 
found  to  be  a  solution  of  pure  nitric  acid.  Looking  to  the  compo- 
sition of  nitric  oxide,  we  find  in  this  manner  that  the  nitric  acid 
consists  of  two  volumes  of  nitrogen  gas  united  with  five  volumes 
of  oxygen. 

Although  nitrogen  and  oxygen  do  not  unite  at  once  when  directly 
brought  into  contact  with  each  other,  yet  they  are  capable  of  com- 
bining under  certain  circumstances  ;  and  there  is  no  doubt  but  that 
the  great,  if  not  the  only  source  of  nitric  acid  in  nature,  is  the  union 
of  the  nitrogen  and  oxygen  of  the  atmosphere.  Although  nitrogen 
is  not  strictly  inflammable,  yet,  if  some  of  it  be  mixed  with  hydro- 
gen, and  this  mixture  be  set  on  fire,  the  flame  is  coloured  green, 
and  the  water  formed  is  found  to  contain  nitric  acid ;  if  a  series  of 
electric  sparks  be  passed  through  a  quantity  of  air  confined  over  a 
strong  solution  of  potash,  this  gradually  loses  its  alkaline  reaction, 
and  after  a  time  crystals  of  saltpetre  (nitrate  of  potash)  form  in  it. 
This  may  be  shown,  also,  by  simply  moistening  some  litmus  paper 
with  a  solution  of  an  alkali,  and  taking,  by  means  of  it,  a  succession 
of  sparks  from  a  strong  electrical  machine  ;  at  the  point  where  the 
spark  passes,  the  paper  becomes  reddened,  and  that  nitric  acid  has 
been  formed  is  shown  by  its  burning  like  touch  paper  when  dried 
and  set  on  fire.  Rain-water,  particularly  that  which  falls  after  a 
thunder  storm,  contains  a  certain  quantity  of  nitrate  of  ammonia ; 
the  lightning  forming,  as  the  electric  spark  does,  nitric  acid  in  pass- 
ing through  the  air,  and  this  uniting  with  the  ammonia  which  is  al- 
ways present  in  our  atmosphere  from  decomposing  animal  remains. 

In  warm  climates,  where  the  abundance  of  organic  matter  and  its 
rapid  decomposition  pour  into  the  atmosphere  a  copious  supply  of 
ammonia,  the  formation  of  nitric  acid  proceeds  with  extraordinary 
energy,  and  the  nitrate  of  ammonia  being  washed  down  by  the  rains 
into  the  porous  limestone  soils,  the  ammonia  is  again  given  ofl*,  while 
the  ground  becomes  coated  with  an  efflorescence  of  earthy  nitrates 
when  it  dries  on  the  cessation  of  the  ram  \  a  small  quantity  of  ni- 
trate of  potash  is  also  thus  formed,  but  the  nitrate  of  lime,  of  which 
the  crude  produce  of  nitre  principally  consists,  is  converted  into 
saltpetre  by  means  of  carbonate  of  potash.  In  this  way  there  is 
formed  in  the  East  Indies  a  quantity  of  nitrate  of  potash  sufficient 
to  supply  the  wants  of  Europe.  On  the  Continent,  this  process  is 
imitated  in  artificial  nitre-beds,  and  large  quantities  of  home-made 
saltpetre  are  used  in  France  and  Germany  for  the  manufacture  of 
gunpowder.  In  South  America,  particularly  in  Chili  and  Peru,  there 
are  found  immense  deposites  of  nitrate  of  soda  upon  the  surface  of 
the  soil,  and  it  is  now  extensively  imported  into  these  countries; 
the  source  of  the  nitric  acid  is,  in  this  case  also,  the  union  of  the 
elements  of  the  atmosphere,  although  the  circumstances  which  sup- 
plied the  alkali  cannot  be  distinctly  seen. 


278 


PREPARATION     OF     NITRIC     ACID. 


It  is  from  the  nitrates  of  soda  or  potash  so  produced  that  the 
nitric  acid  is  always  obtained.  True  nitric  acid  has  never  been  iso- 
lated ;  that  substance  which  is  generally  spoken  of  as  nitric  acid, 
and  which  I  shall,  unless  especially  remarked  otherwise,  be  under- 
stood to  mean  in  the  following  account  of  its  properties  and  prepar- 
ation, is  a  compound  of  it  with  water ;  it  is  a  nitrate  of  water,  or,  as 
it  is  popularly  termed,  liquid  nitric  acid,  or  aquafortis. 

To  prepare  liquid  nitric  acid  from  nitrate  of  potash,  equal  weights 

of  this  salt  and  of  oil  of  vit- 
riol are  mixed  in  a  glass  re- 
tort, A,  which  is  placed  in 
a  furnace,  supported  in  a 
sand  bath,  as  in  the  figure. 
The  oil  of  vitriol  consists 
of  sulphuric  acid  and  wa- 
ter, and  by  the  reaction 
which  ensues,  the  sulphu- 
ric acid  combines  with  the 
potash  of  the  nitre,  while 
the  water  of  the  oil  of  vit- 
riol uniting  with  the  nitric 
acid,  forms  the  liquid  nitric  acid,  which  distils  over,  and  is  conden- 
sed in  the  receiver,  B.  To  render  the  condensation  more  complete, 
this  is  surrounded  by  a  net,  and  placed  in  a  trough,  c  c  ;  a  stream  of 
cold  water  flows  continually  on  it  from  the  pipe  «,  and  being  dis- 
tributed evenly  over  the  surface  by  the  network,  flows  out  by  the 
exit  pipe  of  the  trough,  /,  and  escapes  into  d  e.  Using  the  propor- 
tions just  noticed  (equal  weights),  the  quantity  of  sulphuric  acid 
present  is  double  that  necessary  to  neutralize  the  potash  of  the  ni- 
tre, and  completely  expel  the  nitric  acid ;  for 


The  nitre  consists  of 
One  atom  nitric  acid,  54*0 
One  atom  potash     .      -iT'S 

loTs 


Oil  of  vitriol  consists  of 
One  atom  sulph.  acid,  40*1 
One  atom  water  .     9*0 

49^ 


These,  reacting  upon  each  other,  should  produce, 

Sulphate  of  potash  consisting  of     Liquid  nitric  acid  formed  of 
One  atom  sulph.  acid,  40*1  One  atom  nitric  acid,  54*0 

One  atom  potash     .     47-3  One  atom  water        .     9*0 

And  hence  nitre  might  be  decomposed  by  half  its  weight  of  oil  of 
vitriol ;  but  the  following  reasons  prevent  those  proportions  being 
employed  in  practice.  r 

When  oil  of  vitriol  acts  upon  nitre,  there  is  at  first  but  one  half  of 
the  sulphuric  acid  taken  by  the  potash,  and  the  sulphate  of  potash 
so  produced  unites  with  the  remaining  oil  of  vitriol  (sulphate  of 
water)  to  form  bisulphate  of  potash,  thus,  2(S.03 .  H.O.)  and  K.O. . 
N.O5  give 

(S.O3 .  H.O.+K.O. .  S.O3)  and  H.O.  N.O5. 

If  there  be  oil  of  vitriol  enough,  the  nitre  is  thus  perfectly  decom- 


PREPARATION     OF     NITRIC     ACID. 


279 


posed  at  a  temperature  not  exceeding  260°  F.,  and  the  bisulphate  of 
potash  which  remains  is  very  easily  soluble  and  fusible,  and  may 
hence  be  removed  from  the  retort  without  inconvenience.  But  if 
the  nitre  and  oil  of  vitriol  be  used  in  the  proportion  of  an  equiva- 
lent of  each,  or  by  weight  in  round  numbers  of  two  parts  of  nitre 
to  one  of  oil  of  vitriol,  then  one  half  of  the  nitre  remains  at  first 
totally  unacted  on,  and  the  retort  contains,  when  the  process  is  half 
finished,  a  pasty  mass  of  bisulphate  of  potash  and  of  nitre,  which 
do  not  fully  act  on  each  other  until  the  temperature  rises  to  400°. 
The  nitre  is  then  decomposed;  the  nitric  acid  distils  over,  and 
there  remains  in  the  retort  a  mass  of  neutral  sulphate  of  potash, 
which  can  seldom  be  removed  from  glass  vessels  with  success.  The 
high  temperature  necessary  also  increases  very  much  the  risk  of 
the  apparatus  breaking. 

The  scientific  chemist  and  the  apothecary,  however,  do  not  prepare  nitric  acid ;  it 
IS  made  on  the  large  scale  for  the  purposes  of  the  arts,  and  the  processes  of  purify- 
ing the  acid  of  commerce  is  so  simple  that  no  other  source  is  required.  On  the 
great  scale  the  nitric  acid  is  prepared,  not  in  glass  retorts,  but  in  iron  cylinders, 
connected  with  condensers,  as  represented  in  the  figures,  one  being  a  section  per- 
pendicular to  the  axes  of  the  cylinders,  and  the  other  a  section  paraUel  to  the  axes  : 
the  same  letters  apply  to  both. 


a  is  the  grate,  and  d  the  ashpit  of  the  furnace,  h.  In  each  furnace  two  cast  iron 
cylinders,  c,  c,  are  set,  of  such  capacity  that  about  li  cwt.  of  the  nitrate  used  may 
be  decomposed  at  once.  The  ends  of  the  cylinders  are  closed  by  covers,  e,  e,  in 
one  of  which  is  fixed  a  tube,/,  for  introducing  the  oil  of  vitriol,  and  to  the  other  is 
adapted  a  tube  of  glazed  earthenware,  g,  h,  by  which  the  vapours  of  the  nitric  acid 
are  conducted  to  the  range  of  condensing  jars  of  earthenware,  fitted  with  safety 
tubes,  of  which  the  first  is  seen  in  the  figure,  as  h,  I,  k.  The  flues,  w,  m,  m,  pass 
from  the  furnaces  to  the  chimney,  n.  As  in  this  apparatus  the  temperature  can  be 
raised  to  dull  redness  without  injury,  and  as  the  residuum  can  be  removed  in  the 
solid  form,  a  smaller  quantity  of  oil  of  vitriol  may  suffice,  and  is  generally  used. 

Since  the  introduction  of  nitrate  of  soda  into  commerce,  it  has  almost  completely 
superseded  nitrate  of  potash  for  making  nitric  acid.  It  is  much  cheaper,  and  it 
yields  a  larger  product.  It  does  not  require,  either,  so  much  sulphuric  acid  nor  so 
high  a  temperature.    The  nitrate  of  soda  consists  of 

One  equivalent  of  nitric  acid 540 

One  equivalent  of  soda 31-3 

and  hence  100  parts  of  it  yield  about  74  parts  of  liquid  nitric  acid,  while  100  parts 
of  nitrate  of  potash  yield  but  62. 

In  making  nitric  acid,  there  always  occurs  at  the  commencement 
of  the  process  a  disengagement 'of  red  fumes,  which  dissolve  in  the 
liquid  acid  which  comes  next,  and  tinge  it  yellow.  This  arises  from 
the  oil  of  vitriol  in  excess  abstracting  the  water  from  some  of  the 
nitric  acid,  which  then  is  decomposed  into  nitrous  acid,  and  some 
oxygen  becomes  free.     At  the  termination  of  the  process,  if  the  tem- 


280    PR  OPE  R  TIE  S,     ETC.,     OF     LIQUID     NITRIC     ACID. 

perature  pass  much  beyond  300°,  there  is  a  new  evolution  of  red 
fumes,  for  the  nitric  acid  is  then  similarly  decomposed  into  N.O4 
and  O. 

The  strongest  nitric  acid  that  can  be  thus  made  is  of  specific  gravity  1-521,  and 
consists  of  N.Os-f-H.O. 

One  equivalent  of  nitric  acid    .     .     .  540  or  per  cent.  8571 
One  equivalent  of  water      ....    90  "  14  29 

63^  10000 

It  boils  at  187°  F.,  but  cannot  be  distilled  without  partial  decomposition.  The 
acid  is  very  seldom  obtained  of  this  strength.  In  general,  the  specific  gravity  of 
the  strong  liquid  acid  is  1-500,  and  it  consists  of  2N.05-|-3H.O. 

Two  equivalents  of  nitric  acid    .    .  1080  or  per  cent.  8000 
Three  equivalents  of  water    .    .     .     270  "  20  00 

1350  100  00 

When  the  nitric  acid  is  gradually  mixed  with  water,  the  boiling  point  rises  until 
when  the  specific  gravity  is  1-420,  it  boils  at  248°.  If  it  be  farther  diluted,  the 
boiling  point  is  again  lowered.  At  this  point  the  acid  has  a  definite  chemical  con- 
stitution ;  it  consists  of  N.05-{-4H  0. 

One  equivalent  of  nitric  acid  .    .    .    540  or  per  cent.  6022 
Four  equivalents  of  water  ....    360  "  39  78 

900  10000 

The  liquid  nitric  acid  is,  when  pure,  completely  colourless  ;  it 
fumes  when  exposed  to  the  air,  and  if  exposed  to  the  direct  solar 
light,  very  soon  becomes  deep  yellow,  while  oxygen  gas  is  disen- 
gaged j  the  same  decomposition  into  nitrous  acid  and  oxygen  gas 
may  be  instantly  effected  by  passing  the  vapours  of  the  acid  through 
a  red-hot  porcelain  tube.  In  a  great  variety  of  processes  where 
substances  are  to  be  oxidized,  nitric  acid  is  employed.  It  acts  with 
remarkable  rapidity  on  the  generality  of  the  metals  and  of  organic 
bodies,  supplying  oxygen  for  the  constitution  of  a  variety  of  new 
compounds,  and  being  itself  reduced  to  the  state  of  nitric  or  nitrous 
oxide,  or  even  pure  nitrogen. 

If  the  organic  body  do  not  contain  nitrogen,  it  is  generally  ulti- 
mately converted  into  the  oxalic  and  carbonic  acids ;  with  animal 
substances,  new  bodies  are  formed  of  a  deep  yellow  colour,  and 
hence  the  stains  produced  upon  the  nails  and  fingers  where  nitric 
acid  touches,  and  it  is  hence  used  for  stamping  the  yellow  patterns 
on  woollen  table  covers.  The  decomposition  of  the  acid  is  gener- 
ally accompanied  by  the  production  of  red  fumes. 

In  its  action  on  the  metals,  nitric  acid  presents  some  remarkable 
anomalies ;  when  of  the  specific  gravity  of  1*48,  it  may  be  put  into 
contact  with  tin  or  iron  without  acting  on  those  metals,  although, 
if  a  little  stronger  or  weaker,  its  action  is  very  great ;  and  this  inac 
tive  acid  may  be  brought  into  activity  by  various  means,  as  by  touch- 
ing the  immersed  metal  with  another  different  one.  These  phenom- 
ena appear  to  involve  conditions  probably  electrical,  which  are  not, 
as  yet,  completely  understood. 

The  nitric  acid  prepared  by  decomposing  nitre  by  half  its  weight 
of  oil  of  vitriol,  is  always  of  a  deep  red  or  orange  colour,  owing  to 
a  quantity  of  the  acid  having  been  decomposed  into  nitrous  acid, 
which  remains  dissolved.     This  deep-coloured  acid  is  frequently 


DETECTION     OF     NITRIC     ACID.  281 

useful,  as  it  gives  off  oxygen  still  more  easily  than  the  pure  acid, 
and  is  hence  sometimes  applicable  as  an  oxidixing  agent  where  the 
colourless  acid  fails.  A  deep  red  fuming  acid  may  be  prepared  by 
passing  a  stream  of  nitric  oxide  gas  through  the  colourless  acidj  it 
is  absorbed  in  great  quantity,  and  the  liquor  assumes  successively 
various  shades  of  yellow,  green,  and  red,  according  to  its  state  of 
dilution.  The  nitric  oxide  (N.O2)  decomposes  the  nitric  acid  (N.O5), 
and  forms  nitrous  acid  (N.O4),  which  dissolves  in  the  excess  of  liquid 
acid.  If  it  be  required  to  obtain  a  colourless  acid,  it  is  sufficient 
that  the  coloured  acid  should  be  boiled  for  a  few  minutes;  all  the 
nitrous  acid  fumes  pass  off,  and  the  nitric  acid  remains  colourless, 
though  somewhat  weaker. 

I  have  mentioned  that  the  nitric  acid  is  not  prepared  on  the  small 
scale,  as  the  commercial  aquafortis  is  easily  purified.  The  impuri- 
ties of  it  are,  generally,  chlorine,  arising  from  the  nitre  employed 
having  contained  common  salt ;  sulphuric  acid,  from  some  having 
been  distilled  over  by  too  great  heat  j  and  some  iron,  arising  from 
the  cylinders  or  stoneware  bottles  in  which  the  acid  is  preserved. 
These  may  be  easily  detected  ;  on  mixing  a  few  drops  of  the  com- 
mercial acid  with  half  an  ounce  of  distilled  water,  a  drop  of  solution 
of  nitrate  of  barytes  will  give  a  precipitate  if  sulphuric  acid  be  pres- 
ent ;  nitrate  of  silver  will  indicate,  by  a  precipitate,  the  presence  of 
chlorine ;  while  a  little  solution  of  yellow  prussiate  of  potash  will 
form  Prussian  blue  if  the  acid  contained  any  iron.  From  these  im- 
purities the  acid  may  be  freed  by  being  redistilled  3  the  chlorine 
passes  off  along  with  the  portions  which  first  come  over,  and  by 
thus  testing  from  time  to  time  the  acid  which  is  thus  obtained,  it 
will  be  found  no  longer  to  precipitate  the  nitrate  of  silver,  and  may 
then  be  considered  pure  ;  the  iron  and  sulphuric  acid  remain  behind 
in  the  retort,  provided  the  distillation  be  not  pushed  too  far.  I  have 
found  that  from  twelve  pounds  of  commercial  aquafortis  there  can 
be  obtained  eight  quite  pure,  three  being  allowed  to  come  over  first 
to  carry  off  the  chlorine,  and  one  being  left  in  the  retort  with  the 
fixed  impurities. 

The  detection  of  nitric  acid  is  not  difficult;  it  cannot  be  recog- 
nised by  forming  precipitates,  as  all  its  neutral  salts  are  soluble,  but 
its  properties  are  very  marked.  1st,  The  production  of  red  fumes 
by  nitric  oxide  when  it  is  brought  into  contact  with  a  metal,  is  char- 
acteristic of  it.  2d,  When  a  drop  of  nitric  acid  is  added  to  water 
tinged  blue  by  sulphate  of  indigo,  and  the  mixture  boiled,  it  is 
bleached  by  the  oxidizement  of  the  indigo  by  the  acid.  3d,  When 
a  small  crystal  of  protosulphate  of  iron  is  placed  in  contact  with 
water  containing  nitric  acid,  a  ring  of  deep  olive-coloured  liquid 
forms  round  it,  according  as  it  dissolves  ;  from  one  portion  of  the 
protosulphate  reducing  the  acid  to  the  state  of  nitric  oxide,  which 
then  combines  with  the  remaining  protosulphate.  4th,  Nitric  acid 
confers  upon  muriatic  acid  the  power  of  dissolving  gold  leaf,  but 
this  test  is  not  of  such  distinctness  as  the  others,  from  the  same 
effect  being  produced  by  the  chloric  and  some  other  acids.  5th, 
Nitric  acid  may  also  be  distinguished  by  the  deep  red  colour  it  pro- 
duces with  a  crystal  of  morphia. 

For  the  detection  of  a  small  quantity  of  nitric  acid,  the  best  plan 

Nn 


282  SOURCES,  PROPERTIES,  AND 

is  to  neutralize  the  liquor,  if  it  be  acid,  by  a  solution  of  potash,  and 
to  evaporate  to  dryness.  The  salt  so  obtained  crystallizes  in  sharp 
needles,  and  deflagrates  when  placed  on  ignited  charcoal ;  heated  with 
a  little  bisulphate  of  potash  and  some  copper  filings,  it  evolves  copious 
red  fumes,  and  with  a  drop  of  sulphuric  acid  and  a  crystal  of  pro- 
tosulphate  of  iron,  produces  the  olive-coloured  liquor  already  noticed. 
All  solid  compounds  of  nitric  acid,  such  as  the  basic  nitrates,  may 
be  recognised  in  this  way. 

The  nitric  acid  not  being  isolable,  we  do  not  know  the  state  of 
condensation  of  its  elements,  which  are  united  in  the  proportion  of 
two  volumes  of  nitrogen  to  five  of  oxygen.  Its  composition  by 
weight  and  its  equivalent  numbers  are  as  follows : 

Nitrogen,  26-15  One  equivalent,     =175  or  14-0 

Oxygen,    73-85  Five  equivalents,  =500  or  40.0 

100^0  675       54^ 

The  specific  gravity  of  the  vapour  of  the  liquid  nitric  acid,  H.O. .  N.O5,  is  not  known ; 
but  Bineau  has  found  the  sp.  gr.  of  the  vapour  of  the  liquid  acid,  which  boils  at  248*^, 
H.O.  .  N.Os+SH.O.,  to  be  1243,  which  might  result  from 

Two  volumes  of  nitrogen 976x2=19520 

Five  volumes  of  oxygen 1102  6x5=55130 

Eight  volumes  of  watery  vapour    ....      6201X  8=4960  8 

condensed  into  ten  volumes 12425  8 

of  which  one,  therefore,  should  weigh 1242-6 

This  result  requires  confirmation. 

Sulphur. 

This  substance  exists  in  large  quantity  in  nature  in  combination 
The  most  important  ores  of  copper,  lead,  silver,  mercury,  antimony, 
and  many  other  metals,  are  their  sulphurets  5  and  a  great  quantity 
of  the  sulphur  at  present  used  in  commerce  is  derived  from  the  iron 
pyrites,  bisulphuret  of  iron.  Sulphur  is  exhaled  in  large  quantity 
also  from  volcanoes,  partly  uncombined,  partly  in  the  state  of  sul- 
phuret  of  hydrogen,  arising  probably  from  the  decomposition  of  me- 
tallic sulphurets  by  the  high  temperature  in  the  interior  of  the  earth. 
The  native  sulphur  so  produced,  condensing  in  fissures,  constitutes 
the  great  deposites  of  volcanic  sulphur  of  Sicily  and  other  places, 
which  supply  a  large  proportion  of  that  employed  in  commerce.  It 
exists  also  native,  combined  with  oxygen  and  various  metallic  oxides, 
forming  native  sulphates,  of  which  those  of  lime  and  of  barytes  are 
the  most  abundant.  In  many  organic  bodies,  also,  sulphur  exists  as 
a  constituent,  as  in  the  white,  and  particularly  the  yolk  of  egg^  the 
hair,  the  horns,  and  hoofs  of  animals,  and  in  the  black  mustard-seed 
it  exists  in  considerable  quantity. 

At  ordinary  temperatures  sulphur  exists  generally  as  an  opaque 
solid,  sp.  gr.  1-98.  When  heated,  it  melts  at  226°  into  an  amber- 
coloured  thin  liquid ;  if  the  temperature  be  then  raised  to  about 
400°,  it  becomes  dark  brown,  opaque,  and  so  thick  that  the  vessel 
containing  it  may  be  inverted  without  its  pouring  out ;  but  when  heat- 
ed farther  it  becomes  thinner,  until  at  601°,  its  boiling  point,  it  is  as 
thin  and  limpid  as  when  first  it  began  to  melt.  If  the  sulphur,  when 
just  melted,  be  allowed  to  cool  slowly,  and  the  internal  liquid  be 


PREPARATION     OF     SULPHUR. 


28£ 


poured  out  when  the  outer  crust  has  solidified,  the 
interior  will  be  found  lined  with  crystals,  as  in  the 
figure,  which  have  the  form  of  the  oblique  rhombic 
prism,  of  which  a  common  modification  with  second- 
ary faces,  and  the  surfaces  of  the  octohedron,  which 
determines  the  height  of 
the  principal  axis  of  the 
crystal,  is  given.  These  crystals,  when 
first  obtained,  are  transparent  and  amber- 
coloured,  but  after  a  few  days  they  be- 
come opaque,  sulphur  yellow,  and  friable, 
being  then  changed  into  the  dimorphous 
state. 

If  the  thick  tenacious  sulphur  at  400^  be  suddenly  cooled  by  im- 
mersion in  a  large  quantity  of  water,  it  forms  a  soft  and  transparent 
mass  of  considerable  elasticity,  and  may  be  drawn  out  into  long 
threads  like  India  rubber  j  after  some  time,  however,  it  changes 
into  the  ordinary  state. 

Sulphur  is  used  in  pharmacy  under  two  forms,  that  of  roll  and 
flowers ;  the  former  is  made  by  melting  the  rough  native  sulphur, 
and  pouring  it  into  slightly  conical  moulds,  in  which  it  solidifies. 
The  flowers  of  sulphur  are  formed  by  the  condensation  of  the  va- 
pour of  sulphur  so  rapidly  that  the  molecules  have  not  time  to  form 
crystals  of  any  perceptible  size,  so  that  the  condensed  sulphur,  al- 
though really  crystalline,  appears  to  the  sight  and  touch  as  an  im- 
palpable soft  powder. 

For  the  manufacture  of  flowers  of  sulphur,  the  apparatus  is  arranged  as  in 
the  subjoined  figures,  in  which  A  is  a  vertical  and  B  a  horizontal  section,  to  which 


the  same  letters  refer.  In  an  apartment  and  shed,  M,  M,  a  chamber,  A,  is  con 
structed,  which  must  have  at  least  2000  cubic  feet  capacity.  Outside  T)f  this  cham- 
ber is  an  iron  pan,  c,  in  which,  by  a  fire  at  o,  the  sulphur  is  kept  gently  boiling.  The 
boiler  and  fireplace  must  be  completely  surrounded  by  brickwork,  so  that  as  little 
heat  as  possible  may  be  communicated  to  the  vaulted  chamber,  A ;  the  draught 
from  the  fire  passes  to  the  chimney,  g ;  the  pan  is  supplied  with  sulphur  by  the 
door,  n,  which  can  be  closed  air-tight ;  the  vapour  of  sulphur  mixes  with  the  air  in 
the  wide  space,  d,  over  the  boiler,  and,  passing  through  the  aperture  b,  rises  into 
the  chamber,  where,  mixing  with  the  large  mass  of  cold  air,  the  sulphur  is  con- 
densed, and  falls  like  a  fine  snow  shower  upon  the  floor  underneath.  When  a  sul- 
ficient  quantity  of  the  flowers  of  sulphur  have  been  thus  formed,  they  are  removed 
by  the  door  at  p.  If,  at  the  commencement  of  the  process,  the  mixture  of  sulphur- 
vapour  and  air  should  inflame,  the  explosion  opens  the  valve  at  e,  the  gases  escape 
at  t,  and  all  danger  is  avoided. 

The  form  of  crystal  of  sublimed  sulphur  is  the  right  rhombic  oc- 
tohedron, of  which  a  common  modification  is  represented  in  the 


284  RELATIONS     OF     SULPHUR     TO     OXYGEN. 

margin.  Sulphur  is  found  crystallized  in  this  form  on 
the  edges  of  the  craters  of  most  volcanoes,  the  crys- 
tals being  transparent,  and  sometimes  of  considerable 
size.  When  sulphur  is  deposited  from  its  solution  in 
chloride  of  sulphur  or  in  sulphuret  of  carbon,  it  is  in 
this  form  also  that  its  particles  arrange  themselves. 

Sulphur  may  be  obtained,  however,  in  a  state  of 
much  more  minute  division,  and  destitute  of  all  crys- 
talline structure,  by  precipitation  from  solution.  Thus,  if  the  per- 
sulphuret  of  potassium,  K.S^,  be  decomposed  by  muriatic  acid,  four 
equivalents  of  sulphur  are  set  free,  and  separate  as  a  milk-white 
powder.  This  constitutes  the  Sulphur  Precipitatum  of  pharmacy. 
In  all  cases  where  sulphur  is  precipitated  from  a  cold  solution,  it  is 
pure  white. 

Sulphur  is  not  soluble  in  water  or  in  alcohol  -,  it  dissolves  in  the 
oils,  still  more  in  those  liquids  mentioned  above.  It  dissolves  in 
alkaline  solutions,  or  in  milk  of  lime  ;  but  there  then  occur  complex 
reactions,  which  will  be  studied  hereafter. 

When  sulphur  is  boiled  it  forms  a  deep  yellow  vapour,  the  specific 
gravity  of  which  is  6648.  Sulphur  evaporates,  however,  very  rap- 
idly long  before  it  boils,  and  even  forms  some  vapour  below  ita 
melting  point.  At  a  temperature  of  about  300°  it  takes  fire,  burning 
with  a  bluish  violet  flame,  and  forming  sulphurous  acid  (S.Og). 

The  resemblance  of  sulphur  to  oxygen  in  its  chemical  relations  is  very  striking , 
by  combining  with  the  same  bodies,  according  to  the  same  proportions,  they  gener 
ate  completely  parallel  classes  of  acids,  bases,  and  salts.  Thus,  with  carbon  and 
potassium,  there  are  formed 


C.O2  Carbonic  acid. 

K.O.  Oxide  of  potassium. 

K.O.  .  C.O2  Carbonate  of  potassium. 

and  with  arsenic  and  potassium, 
As.Qs  Arsenic  acid. 
K.O.   Oxide  of  potassium. 
K.O.  .  AS.O5  Arseniate  of  potassium. 


C.S2  Sulpho-carbonic  acid. 
K.S.  Sulphuret  of  potassium. 
K.S.  .C.S2  Sulpho-carbonate  of  potaf*- 
sium. 

As.Ss  Sulpharsenic  acid. 
K.S.    Sulphuret  of  potassium. 
K.S.  .  As.So  Sulpharseniate  of  potas- 
sium. 

In  like  manner,  the  similar  compounds  Fe304  and  Fe3S4  are  not  altered  by  heat, 
but  are  magnetic,  while  Fe.Sa  and  Mn.Os  give  out  oxygen  and  sulphur,  and  are  re- 
duced to  Fe3S4  and  Mn304.  I  shall  have  frequent  occasion  to  revert  to  these  con- 
siderations, which  have  already  been  noticed  under  another  point  of  view  (p.  238). 

The  equivalent  number  of  sulphur  is  16*1  or  201*2,  and  its  com- 
bining volume  one  third  that  of  oxygen. 

Sulphur  combines  with  oxygen,  forming 

Sulphurous  acid    ......  S.O2. 

Sulphuric  acid S.O3,  or    S.O2 .  O. 

Hyposulphurous  acid     ....  S2O2,  or    S.O2 .  S. 

Hyposulphuric  acid        ....  S2O5,  or  2S.O2 .  O. 

Sulphurous  Acid. 

Sulphurous  acid  exists  at  ordinary  temperature  and  pressure  in 

the  gaseous  form ;  it  is  one,  however,  of  the  most  easily  liquefied 

gases.     It  is  produced  always  when  sulphur  burns  either  in  air  or 

m  pure  oxygen,  sulphur  not  being  capable  of  passing  directly  to  a 


PREPARATION,  ETC.,  OF  SULPHUROUS  ACID.  285 

higher  degree  of  oxidation.  In  the  burning  of  sulphur,  the  volume 
of  sulphurous  acid  gas  formed  is  exactly  equal  to  that  of  the  oxygen 
consumed. 

When  required  pure,  it  is  prepared  generally  by  decomposing 
sulphuric  acid  by  means  of  a  metal  not  very  easily  oxidized,  as 
mercury  or  copper.  The  metal  combines  with  one  atom  of  the  ox- 
ygen of  the  sulphuric  acid,  and  the  sulphur,  with  the  remaining  two 
atoms  of  oxygen,  pass  off  as  sulphurous  acid  gas  ;  the  oxide  formed 
unites  with  the  remaining  sulphuric  acid  to  form  a  salt.  Thus,  if 
mercury  be  used,  S.O3  and  Hg.  give  S.O2  and  Hg.O.,  and  Hg.O.  unites 
with  S.O3  to  form  sulphate  of  mercury.  If  the  heat  be  not  raised 
beyond  200°  in  this  process,  it  is  black  oxide  of  mercury  which  is 
produced  (Hg20.),  but  above  that  degree  the  red  oxide  (Hg.O.)  alone 
is  formed. 

Sulphurous  acid  gas  may  also  be  very  simply  prepared  by  heating 
three  parts  of  flowers  of  sulphur  with  four  of  peroxide  of  manga- 
nese. The  reaction  is  very  simple ;  one  part  of  the  sulphur  uniting 
with  the  metal,  and  another  with  the  oxygen,  form  sulphuret  of  man- 
ganese and  sulphurous  acid  ;  thus,  Mn.Oi  and  2S.  give  Mn.S.  and 
S.O2.  The  apparatus  used  in  these  processes  may  be  that  figured 
under  the  heads  of  oxygen  (p.  244)  or  nitrous  oxide  (p.  272). 

Sulphurous  acid  gas  is  absorbed  by  water ;  and  hence,  in  order 
to  examine  its  properties  in  that  state,  it  must  be  collected  over 
mercury.  It  is  colourless  and  transparent,  possessing  an  odour  pe- 
culiarly irritating  (the  smell  of  burning  sulphur),  and  cannot  be 
breathed.  It  is  not  combustible,  nor  does  it  support  combustion. 
It  bleaches  a  variety  of  vegetable  and  animal  bodies,  and  is  hence 
used  in  the  arts  to  whiten  straw  bonnets,  corn,  silk,  sponges,  and 
other  substances.  The  bleaching  is  produced  by  the  sulphurous 
acid  combining  with  the  coloured  substance,  and  forming  a  white 
compound,  from  which  the  gas  gradually  escapes  on  exposure  to 
air,  and  hence  such  bleaching  is  not  permanent.  The  sulphurous 
acid  may  be  expelled,  also,  from  this  kind  of  compound  by  a  stronger 
acid,  .and  the  colour  generally  restored  ;  thus,  if  a  red  rose  be  ex- 
posed to  the  fumes  of  burning  sulphur,  it  becomes  completely  white  5 
but  if  washed  in  dilute  sulphuric  acid,  its  red  colour  is  perfectly 
renewed. 

TJie  specific  gravity  of  sulphurous  acid  gas  is  2210'6,  and  it  is 
formed  by 

One  volume  of  sulphur-vapour 6648*0 

Six  volumes  of  oxygen 6615*6 

The  seven  volumes  condensed  to  six,  give  .     .  13263.6 
Weight  of  one  volume  of  S.O2 2210-6 

When  this  gas  is  exposed  to  a  cold  of  0°  F.,  it  condenses  into 
liquid  heavier  than  water,  which  boils  at  14°,  and  produces  by  its 
evaporation  a  very  intense  cold  ;  it  ^^,„„-,.^^ 

is  easily  obtained  in  the  liquid  form        ^    ^.^^-^^"'^l^^^^^'''^^^^^^^^^-^  i 

by  putting  a  quantity  of  mercury  and   ^^^^^^j^^""^"''^       ^n./^x 
oil  of  vitriol  into  a  tube,  and  sealing   ^^^^"'^  ^^ 

up  the  ends,  as  in  the  figure ;  on  applying  heat  to  the  extremity  a, 


286 


PROPERTIES,  ETC.,  OF  SULPHUROUS  ACID. 


containing  those  materials,  and  cooling  the  other  end  by  means  of 
ether,  the  gas  evolved  is  liquefied  by  its  own  pressure,  and  collects 
in  quantity  at  b. 
When  a  large  quantity  of  sulphurous  acid  is  required  dissolved  in  water,  or  wheu 

it  is  to  be  employed  to  form  com- 
pounds with  bases,  it  may  be  pro- 
duced in  a  much  cheaper  way  than 
those  described  above.  Into  a  mat- 
rass, a,  placed  in  a  furnace,  is  in- 
troduced a  quantity  of  well-burned 
charcoal,  in  bits  about  the  size  of  a 
hazel-nut,  and  by  means  of  the  safe- 
ty-funnel I,  as  much  oil  of  vitriol  is 
poured  in  as  that  the  mixture  shall 
half  fill  the  vessel ;  a  tube  passes  to 
a  bottle,  i,  containing  some  water  to 
v.'ash  the  gas  from  any  adhering  sul- 
phuric acid,  and  it  is  then  conduct- 
ed by  the  tube  /,  which  passes  to 
the  bottom  of  the  vessel  h,  contain- 
ing the  liquor  in  which  the  gas  is  to 
be  dissolved.  On  applying  heat,  the 
carbon  of  the  charcoal  abstracts 
from  the  sulphuric  acid  one  third  of  its  oxygen,  so  that  with  C.  and  2S.O3  there  are 
formed  C.O2  and  2S.O2  ;  there  is  produced  a  mixture  of  two  volumes  of  sulphur- 
ous acid  and  one  of  carbonic  acid,  which  last  cannot  enter  into  combination,  and 
passes  off  from  the  apparatus  without  change. 

Water  dissolves  about  thirty-seven  times  its  volume  of  sulphurous 
acid  ;  the  solution  possesses  the  properties  of  the  gas  in  a  very  high 
degree,  and  bleaches  vegetable  colours  with  great  power  j  when 
kept  for  some  time,  it  gradually  absorbs  oxygen,  and  the  sulphurous 
becomes  changed  into  sulphuric  acid. 

The  sulphurous  acid  is  one  of  the  feeblest  acids,  and  is  e:^pelled 
from  its  combinations  by  almost  all  but  the  carbonic  acid.  Of  its 
salts,  those  which  are  soluble,  all  possess  alkaline  reaction. 

The  sulphurous  acid  passes  into  the  state  of  sulphuric  acid  by 
absorbing  oxygen  from  many  bodies  ;  thus,  when  it  is  heated  with  a 
solution  of  gold  or  silver,  or  of  mercury,  these  metals  are  reduced 
to  the  metallic  state  j  others  yield  but  a  part  of  their  oxygen ;  thus 
the  peroxide  of  iron  abandons  a  third,  and  the  black,  oxide  of  copper 
one  half  of  that  constituent. 

The  salts  of  sulphurous  acid  possess  the  same  deoxidizing  power. 
The  composition  and  equivalent  of  sulphurous  acid  are  as  follows : 


Sulphur,  50-14 

Oxygen,  J^-86 

100^ 


One  equivalent, 
Two  equivalents, 


=  201-2  or  16-1 

=2000  or  16-0 

40F2        32-1 


Sulphuric  Acid. 
S.O3. 
Sulphuric  acid,  one  of  the  most  important  compound  bodies,  from 
the  energy  of  its  action,  and  the  variety  of  combinations  which  it 
forms,  is  not  produced  by  the  direct  union  of  oxygen  and  sulphur 
in  any  case,  but  arises  from  the  combination  of  sulphurous  acid  with 
another  quantity  of  oxygen.  Thus,  by  the  action  of  sulphurous  acid 
on  the  easily  reducible  metallic  oxides,  sulphuric  acid  is  produced. 
This  principle  is  beautifully  shown  by  passing  a  mixture  oi  sulphur- 


PREPARATION  OF  SULPHURIC  ACID. 


287 


ous  acid  gas  and  air  through  a  tube  filled  with  spongy  platinum, 
and  heated  to  dull  redness,  when  there  issues  from  the  extremity  a 
mixture  of  vapour  of  sulphuric  acid,  mixed  with  the  residual  nitro- 
gen of  the  air  j  by  such  processes,  however,  it  could  not  be  formed 
in  quantities  suited  to  the  purposes  of  commerce. 

The  preparation  of  sulphuric  acid  is  effected  upon  the  large  scale 
by  bringing  sulphurous  acid,  produced  by  the  burning  of  sulphur, 
into  contact  with  watery  vapour  and  nitrous  acid  fumes  ',  these  unite 
to  form  a  white  crystalline  solid,  which  appears  to  be  a  compound 
of  sulphurous  acid  and  nitrous  acid  (S.02H-N.04),  united  with  a  quan- 
tity of  sulphuric  acid  and  water  which  is  not  constant.  The  forma- 
tion of  this  substance  may  be  shown  by  the  arrangement  in  the 
figure.  The  central  vessel,  the  inner  surface  of  which  is  slightly 
moistened,  contains  atmospheric 
air  ;  by  means  of  the  tubes,  sul- 
phurous acid  gas  generated  in  the 
flask  a,  and  nitric  oxide  formed  in 
6,  are  introduced,  to  the  latter  of 
which  the  oxygen  is  supplied  by 
the  air  to  form  nitrous  acid  fumes ; 
the  interior  of  the  vessel  becomes 
gradually  covered  with  a  deposite 
like  hoar-frost,  consisting  of  this 
substance;  and,  in  order  that  its 
production  may  proceed  without 
interruption,  the  vessel  may  be  filled  with  fresh  atmospheric  air  by 
blowing  through  one  of  the  tubes  c,  d,  while  the  residual  gases  are 
expelled  through  the  other. 

This  crystalline  substance  is  decomposed  by  a  larger  quantity  of 
water ;  hence,  if  the  bottom  of  the  central  vessel  be  covered  by  a  layer 
of  water,  the  crystalline  substance  falling  into  it  according  as  it  is 
generated,  is  resolved  into  sulphuric  and  hyponitric  acids  j  thus  S. 
Oa+N.Ot  gives  S.O3  and  N.O3,  which  last  is  decomposed  by  the 
water  into  nitric  acid  and  nitric  oxide,  SN.Og  giving  N.O5  and  2 
N.O2;  the  nitric  acid  remains  combined  with  the  water  along  with 
the  sulphuric  acid,  while  the  nitric  oxide  escaping  with  effervescence, 
generates,  on  arriving  at  the  air,  a  new  quantity  of  red  fumes,  and 
oxidizes  a  new  quantity  of  sulphurous  acid. 

It  was  supposed  that  a  certain  quantity  of  water  was  necessary  to  the  existence 
of  this  solid  body,  although  a  larger  quantity  decomposed  it ;  but  it  has  been  found 
that  a  similar  substance  may  be  formed  which  contains  no  water.  Sulphurous  and 
nitrous  acids  do  not  act  on  each  other  when  in  the  gaseous  form,  unless  water  be 
present;  but  they  combine  if  placed  in  contact  under  considerable  pressure,  and 
liquid,  even  when  completely  dry.  A  portion  of  the  nitrous  acid  converts  an  equiv- 
alent of  the  sulphurous  acid  into  sulphuric  acid,  it  being  itself  reduced  to  the  state 
of  hyponitrous  acid,  while  another  quantity  of  nitrous  and  sulphurous  acid  unites 
directly ;  there  are  thus  formed  from  2S.O2  and  2N.O4  a  white  crystalline  solid 
S.O2  .  N.O4-I-S.O3,  and  a  quantity  of  N.O3,  which  is  given  off  on  the  tube  in 
which  the  combination  is  produced  being  opened. 

It  may  be  questioned,  however,  whether  this  substance,  for  the  discovery  and 
analysis  of  which  we  are  indebted  to  M.  de  Prevostaye,  interferes  in  the  formation 
of  sulphuric  acid  on  the  large  scale,  where  the  nitrous  and  sulphurous  acids  act  on 
one  another  in  the  gaseous  forms. 

In  the  manufacture  of  sulphuric  acid,  the  apparatus  consists  of  a  long  leaden 
chamber  consisting  of  two  portions  ;  the  lower  a  tray  of  about  li  feet  deep,  the 


288 


MANUFACTURE     OF     OIL     OF     VITRIOL. 


Other  a  quadrangular  bell,  which,  being  suspended  on  a  wooden  framework,  h,  6, 
rests  with  its  edges  immersed  in  the  liquid,  with  which  the  tray  is  filled,  like  the 
cylinder  of  a  bell  gasometer.  The  bottom  of  the  chamber,  which  is  supported  at  a 
certain  distance  from  the  ground  on  pillars,  a,  a,  a,  slants  from  before,  so  that  the 


liquid  which  occupies  it  increases  in  depth  towards  the  end.  Under  the  front  is 
placed. a  furnace,  d,  on  the  floor  of  which,  e,  the  sulphur  is  burned,  and  the  sulphur- 
ous acid  passes  into  the  chamber  by  the  chimney/;  the  heat  necessary  is  supplied 
by  the  fireplace  under  e ;  the  nitrous  acid  is  obtained  by  placing  over  the  burning 
sulphur  in  g  a  pan  containing  a  quantity  of  nitrate  of  soda  and  oil  of  vitriol,  the  ni- 
tric acid  evolved  from  which  directly  oxidizes  a  portion  of  sulphurous  acid,  and 
then,  being  brought  to  the  state  of  N.O4,  acts  on  the  mass  of  sulphurous  acid  as  has 
been  just  described :  ^  is  a  boiler,  by  which  steam  is  driven  into  the  chamber  at  h, 
and  thus,  in  the  interior,  are  provided  the  conditions  for  the  reunion  of  steam,  sul- 
phurous acid  gas  and  nitrous  acid  fumes,  which  produce,  as  in  the  apparatus  figured 
already,  the  white  crystalline  solid,  by  which,  when  decomposed  by  the  water  at 
the  bottom  of  the  chamber,  the  sulphurous  acid  is  produced,  and  nitric  oxide  gas 
evolved.  This  nitric  oxide,  mixing  with  the  atmospheric  air,  which  is  always 
present  in  large  excess  in  the  interior  of  the  chamber,  is  reconverted  into  nitrous 
acid,  which  combines  with  a  new  quantity  of  sulphurous  acid,  generating  another 
proportion  of  the  solid  body,  from  whose  decomposition  by  the  water  the  nitric  oxide 
is  again  evolved  with  little  loss  ;  and  thus  the  oxygen  of  the  air  is  gradually  trans- 
ferred to  the  sulphurous  acid  by  the  intermediate  agency  of  the  nitrous  acid  fumes. 
Were  there  no  nitric  acid  formed,  the  same  quantity  of  nitric  oxide  might  convert 
an  infinite  quantity  of  sulphurous  acid  into  sulphuric  acid  ;  but  as  the  oil  of  vitriol 
produced  always  retains  a  certain  proportion  of  the.  nitric  acid,  it  is  necessary  to 
supply  its  loss,  and  to  send  into  the  chamber  a  continued  current  of  nitrous  acid  fumes. 
This  is  secured  by  the  construction  already  described,  about  one  part  of  nitrate  of  soda 
"being  decomposed  for  every  eight  or  nine  parts  of  sulphur  burned  in  the  furnace  d, 
e.  The  draught  is  regulated  by  the  chimney  c,  which  is  fitted  with  a  valve,  by  the 
position  of  which  a  current  of  air  is  established  through  the  chamber  sufficient  to 
bring  the  gases  into  complete  mixture  inside,  and  in  due  proportions,  but  which 
does  not  carry  them  away  until  their  action  is  completed. 

The  inclination  given  to  the  bottom  of  the  chamber  is  for  the  purpose  of  allow- 
ing the  water,  which,  having  dissolved  most  of  the  sulphuric  acid,  and  become 
heavy,  to  flow  down  to  the  farthest  end  ;  and  thus  there  is,  on  the  surface  has  next 
the  front,  a  layer  of  the  weakest  acid,  ready  to  absorb  and  decompose  the  great 


MANUFACTURE    OF     OIL     OP     VITRIOL.  289 

^jntity  of  the  crystalline  body  formed  when  the  mixed  sulphurous  and  nitrous 
acid  gases  meet  the  damp  atmosphere  of  the  chamber. 

Ttie  water  in  the  chamber  is  allowed  to  remain  unchanged  until  it  has  attained 
a  specific  gravity  of  about  1600  ;  it  is  then  removed  by  leaden  pipes,  and  concen 
traled  by  evaporation  in  leaden  cisterns,  until  its  specific  gravity  is  increased  to 
about  1-76.  At  this  strength  it  begins  to  act  upon  the  lead,  and  must  be  transferred 
to  vessels  of  glass,  or,  still  better,  of  platinum,  in  which  the  concentration  may  be 
finished.  In  the  strongest  form  in  which  it  can  be  so  obtained,  its  specific  gravity 
is  1-847,  and  it  contains  81  54  of  real  acid  in  100. 

Thus  is  the  oil  of  vitriol  of  commerce  manufactured.  At  present,  a  midification 
of  the  process  has  been  introduced,  in  consequence  of  the  extensive  use  of  the  iron 
pyrites  (bisulphuret  of  iron,  Fe.Sa)  in  place  of  sulphur,  as  the  source  of  the  sul- 
phurous acid.  Instead  of  the  furnace  e,  f,  there  is  built  in  front  of  the  chamber  a 
kiln,  somewhat  like  a  limekiln,  except  that  it  is  narrowed  at  top  into  a  chimney 
passing  into  the  chamber.  At  the  bottom  of  the  kiln  is  placed  a  layer  of  coal  or 
wood,  on  it  the  pyrites  in  small  pieces.  The  fire  is  lighted,  and  the  ignition  being 
communicated  to  the  pyrites,  the  sulphur  burns,  forming  sulphurous  acid,  which  is 
conducted  into  the  chamber,  while  the  iron  remains  behind  as  peroxide.  The  pan 
with  nitre  and  oil  of  vitriol  is  supported  in  the  kiln  at  such  a  height  above  the  mass 
of  burning  pyrites  as  that  the  temperature  may  not  be  too  great.  As  the  combus- 
tion proceeds,  new  quantities  of  pyrites  are  introduced  by  apertures  high  up  in  the 
kiln,  while  the  residue  of  adherent  rock  and  oxide  of  iron  is  raked  out  from  the 
ashpits  at  the  bottom. 

A  form  of  sulphuric  acid  is  prepared  upon  the  Continent,  and 
known  as  German  oil  of  vitriol,  or  fuming  sulphuric  acid,  which  is 
much  stronger  than  can  be  made  by  the  combustion  of  sulphur,  as 
has  been  described. 

It  is  obtained  by  exposing  sulphate  of  iron  to  a  red  heat,  in  earthen  retorts.  If 
the  sulphate  of  iron,  perfectly  dry,  be  strongly  heated,  the  sulphuric  acid  is  driven 
off,  and  oxide  of  iron  remains  behind ;  but  the  acid  is  mostly  resolved  into  sulphur- 
ous acid  and  oxygen,  and  consequently  lost.  But  if  the  sulphate  of  iron  be  not 
completely  dried,  the  sulphuric  acid  combines  with  the  water,  and,  distilling  over  in 
combination  with  it,  forms  a  dark-coloured  liquid  of  a  thick,  oily  consistence,  spe- 
cific gravity  about  19,  and  consisting  generally  of  about  90  of  real  acid  and  10  of 
water  in  100,  approaching  closely  to  the  formula  2S.03-J-H.O.  At  the  same  time, 
a  quantity  (one  half)  of  the  acid  is  decomposed,  the  iron  becoming  peroxidized, 
and  sulphurous  acid  gas  being  evolved.  Thus  4(S.03+Fe.O.)  and  H.O.  give 
2S.03-J-H.0.  and  2S.O2,  leaving  behind  ZFejOa,  known  in  commerce  as  colcothar 
of  vitriol. 

This  process  is  carried  on  in  a  long  furnace,  in  which  are  ranged  about  120 

earthen  retorts,  as  I,  in  rows  of  20,  containing  the  ^.-— ^ — — ~-^ 

partially-dried  sulphate  of  iron.     They  are  gradu-  f   I      ^  "^    J 

ally  heated  until  the  fumes  of  sulphuric  acid  begin        — ""^  —  "-^ 

to  appear,  and  the  receiver  A  is  then  attached,  in  which  the  acid  is  condensed  by 
means  of  cold  applied  externally. 

When  this  fuming  sulphuric  acid  is  heated,  it  is  resolved  into  or- 
dinary oil  of  vitriol  and  real  sulphuric  acid.  This  last,  being  very 
volatile,  distils  over  in  colourless  vapours,  which,  on  coming  into 
contact  w^ith  moist  air,  form  dense  white  fumes  of  liquid  acid.  If 
the  colourless  vapour  be  received  in  a  dry  vessel,  cooled  by  a  freez- 
ing mixture,  it  condenses  in  beautiful  white  satiny  fibres,  consti- 
tuting the  dry  sulphuric  acid.  This  acid  melts  at  77^,  and  very 
little  above  that  temperature  it  boils.  The  specific  gravity  of  its 
vapour  is  2762,  formed  by 

One  volume  of  vapour  of  sulphur =6648  0 

Nine  volumes  of  oxygen 1102-6x9=  99234 

The  ten  volumes  forming  six =16571-4 

Of  which  one  weighs,  therefore 2761  9 

When  this  dry  sulphuric  acid  in  vapour  is  brought  into  contact 

Oo 


290      SULPHURIC     ACID. H  Y  P  O  S  U  L  P  H  U  R  O  U  S     ACID. 

with  dry  barytes,  lime,  or  magnesia,  they  combine  with  brilliant 
combustion,  forming  sulphates  of  those  earths.  When  a  mass  of 
the  crystals  is  thrown  into  water,  it  hisses  as  on  the  immersion  of 
red-hot  iron,  and  ordinary  liquid  sulphuric  acid  is  produced. 

There  exist  several  definite  compounds  of  sulphuric  acid  with 
water,  of  which  the  most  remarkable  are  two  :  the  first  is  the  strong- 
est oil  of  vitriol  made  in  this  country,  and  contains  an  equivalent 
of  acid  united  to  one  of  water  ;  its  formula  is  S.O3  +  H.O.  ;  its  most 
important  properties  have  been  already  described.  The  other  con- 
tains twice  as  much  water  ;  its  formula  being  S.03-J-2H.O. ;  its  spe 
cific  gravity  is  1780.  When  exposed  to  the  temperature  of  melting 
ice,  this  acid  forms  large  and  regular  crystals,  while  the  stronger 
or  weaker  acids  require  very  intense  cold  to  solidify  them.  When 
oil  of  vitriol  is  mixed  with  water,  the  great  heat  which  is  produced 
results  from  the  formation  of  definite  compounds  j  and  it  has  been 
already  shown  (page  185)  that,  no  matter  what  combination  a  cer- 
tain quantity  of  sulphuric  acid  forms,  it  evolves  the  same  quantity 
of  heat  on  entering  into  union. 

Sulphuric  acid,  formed  by  the  combustion  of  sulphur,  as  described, 
in  leaden  chambers,  is  liable  to  be  contaminated  by  the  presence  of 
some  nitric  acid  and  lead  ;  from  these  it  may  freed  by  redistilla- 
tion, which  should,  however,  be  conducted  with  great  care,  as  the 
vapour  of  the  acid  forms  interruptedly  and  by  sudden  bursts,  which 
might  endanger  the  apparatus.  On  diluting  common  oil  of  vitriol, 
a  white  powder  is  generally  seen  to  form,  which  is  sulphate  of  lead, 
that  had  been  held  in  solution  by  the  strong  acid,  but  which  precip- 
itates from  the  diluted  acid.  The  acid  now  formed  from  the  iron 
pyrites  is  found  to  contain  frequently  arsenic  and  selenium :  the 
presence  of  the  former  may  become  of  great  importance  in  medico- 
legal investigations,  and  the  detection  of  it  will  be  fully  described 
in  its  proper  place. 

Sulphuric  acid  is  very  easily  detected  by  means  of  a  solution  of 
nitrate  of  barytes.  If  the  smallest  quantity  of  sulphuric  acid  be 
present,  a  white  precipitate  is  formed,  which  is  insoluble  in  muriatic 
acid,  even  when  boiled. 

Sulphuric  acid  appears  to  dissolve  certain  bodies  in  small  quantity, 
which  are  not  soluble  without  alteration  in  any  other  medium. 
These  are  sulphur,  carbon,  tellurium,  and  selenium.  These  solu- 
tions are  not,  however,  of  any  independent  interest. 

Hyposulphurous  Acid. 
SA,  or  S.O,-fS. 

When  a  stream  of  sulphurous  acid  gas  (S.O2)  is  passed  into  a  sohition  of  sul- 
phuret  of  calcium,  it  is  absorbed,  a  quantity  of  sulphur  is  precipitated,  and  the  liquor, 
when  filtered,  is  found  to  be  a  solution  of  hyposulphite  of  lime.  The  reaction 
which  occurs  is  simple.  Half  of  the  oxygen  of  the  sulphurous  acid  passes  to  the 
calcium  to  form  lime,  reducing  the  sulphurous  to  the  state  of  hyposulphurous  acid, 
and,  at  the  same  time,  the  sulphur  which  had  been  combined  with  the  calcium  is 
set  free,  2Ca.S.  and  2S.O2  giving  2Ca.0.4-S202,  while  2S.  is  precipitated. 

This  acid  is  also  formed  when  sulphur  is  boiled  with  an  alkaline  liquor  or  with 
milk  of  lime.  Thus,  when  soda  and  sulphur  are  boiled  in  water,  the  liquor  contains 
hyposulphite  of  soda  and  sulphuret  of  sodium,  produced  by  3Na.O.  and  4S.  giving 
Na.O.-f-SzOa  and  2Na.S. 

This  acid  itself  is  very  easily  decomposed  ;  it  may,  however,  be  obtained,  at 


HYPOSULPHURIC     ACID.  291 

least  fot  a  time,  in  a  free  state,  by  adding  to  any  of  its  salts  a  stronger  acid,  or,  bet- 
ter, by  bringing  sulphurous  acid  and  sulphuretted  hydrogen  gas  to  meet  in  water ; 
the  reaction  which  occurs  is  that  4S.O2  and  2S.H.  give  3S2O2  and  20. H.  The 
water  gradually  becomes  intensely  sour,  but  after  some  time  this  acid  resolves  itself 
into  sulphur  and  sulphurous  acid. 

The  most  remarkable  character  which  the  compounds  of  hyposulphurous  acid 
possess  is,  that  they  dissolve  those  compounds  of  silver  which  are  insoluble  in 
water,  as  the  chloride  and  iodide,  and  form  a  solution  possessing  an  intensely  sweet 
taste ;  upon  this  property  is  founded  their  use  in  Daguerreotype  and  photogenic  draw- 
ing. This  acid  is  also  recognised  by  its  silver  salt  being  decomposed,  when  boiled, 
into  black  sulphuret  of  silver  and  free  sulphuric  acid,  SaOa+Ag.O.  giving  S.O3  and 
Ag.S.  It  is  an  important  fact,  also,  in  the  history  of  the  hyposulphuric  acid,  that 
its  salts  do  not  always  contain  metaUic  oxides,  but  that  it  may  form  salts  with  me- 
tallic sulphurets ;  thus  there  are  two  hyposulphites  of  sodium,  of  which  one  con- 
tains oxide  of  sodium  (soda),  the  other  sulphuret  of  sodium.  Their  formulae  are 
S202-}-Na.O.,  and  SzOa-l-Na.S  Each  of  these,  in  crystallizing,  combines  with  ten 
atoms  of  water,  like  common  sulphate  of  soda  ;  they  possess,  like  it,  a  point  of  max- 
imum solubility,  and  the  crystals  of  all  three  appear  to  be  isomorphous.  There 
are,  therefore,  three  salts, 

S.O2  .  S.+Na.S.-[-10H.O., 
S.O2  .  S.-l-Na.O.-flOH.O., 
S.O2  . 0.-i-Na.O.+lOH.O., 

the  similar  constitution  of  which  evidences  the  relation  of  sulphur  and  oxygen  in  a 
remarkable  degree,  and  will  furnish  the  ground  of  speculations  of  great  interest,  to 
which  I  shall  again  recur. 

Hyposulphuric  Acid. 

S2O5,  or  S2O4+O. 

When  sulphurous  acid  gas  is  passed  through  water  in  which  pure  peroxide  of 
manganese  is  diffused,  this  dissolves,  and  the  solution  contains  neutral  hyposul- 
phate  of  manganese.  The  reaction  by  which  it  is  produced  is  simply  that  the  sec- 
ond atom  of  oxygen  of  the  peroxide  of  manganese  converts  two  equivalents  of  sul- 
phurous acid  into  hyposulphuric  acid,  which  is  exactly  neutralized  by  the  protoxide 
of  manganese  that  is  evolved,  Mn.Oa  and  2S.O2  giving  Mn.O.-}-S205. 

When  a  salt  of  hyposulphuric  acid  is  heated,  it  is  resolved  into  sulphurous  acid, 
which  passes  off  as  gas,  and  a  neutral  sulphate  which  remains  behind,  S2  05-J-R.O. 
giving  S.O2  and  S-Og-j-RO-  The  acid  may  be  obtained  free  by  decomposing  its 
barytes  salt  by  sulphuric  acid,  but  it  cannot  be  kept  long.  When  heated,  it  gives 
off  sulphurous  acid,  and  sulphuric  acid  remains ;  and  even  when  cold  it  rapidly 
forms  stilphuric  acid  by  absorbing  oxygen. 

Remarks  on  the  Constitution  of  the  Compounds  of  Oxygen  and  Sulphur, 
The  progress  of  science  has  gradually  brought  into  view  a  num- 
ber of  facts,  by  which  it  is  now  very  nearly  fully  established,  that 
of  the  bodies  just  now  described,  we  must  look  upon  the  sulphurous 
acid  as  the  only  direct  compound  of  sulphur  and  oxygen,  and  that 
in  the  others,  sulphurous  acid  must  be  considered  as  pre-existing. 
The  reasons  for  this  are  very  numerous.  By  the  direct  union  of 
sulphur  and  oxygen  we  can  never  obtain  any  other  ^compound  than 
sulphurous  acid ;  the  others  being  always  formed  from  it,  prepared 
either  perfectly  distinctly,  or  at  the  moment  of  the  reaction,  and 
then  presented  to  other  elements  with  which  it  may  unite. 

On  this  view  the  necessity  of  the  indirect  process  of  manufacture 
of  sulphuric  acid  becomes  evident.  The  sulphur,  when  it  forms  sul- 
phurous acid,  is  fully  saturated  with  oxygen,  and  cannot  combine 
with  any  more ;  but  the  sulphurous  acid  (S.O2)  acts  as  a  compound 
radical,  like  cyanogen,  as  described  in  p.  233,  and  may  unite  with 


\ 

292  PREPARATION     AND     PROPERTIES 

any  of  the  simple  and  compound  bodies.  It  does  not  unite  directly 
with  oxygen,  but  it  does  so  with  nitrous  acid,  and  the  body  so  form- 
ed is  decomposed  by  water,  producing  sulphuric  acid,  as  has  been 
fully  described.  In  like  manner,  to  form  hyposulphurous  acid,  the 
radical,  sulphurous  acid,  combines  with  sulphur  ;  the  compound  is 
a  sulphur  acid,  S.02-}-S.,  and  combines  with  sulphur  bases  to  form  a 
distinct  class  of  salts.  The  hyposulphuric  acid  contains  also  sul- 
phurous acid  as  its  basis ;  but  there  are  two  equivalents  of  the  rad- 
ical to  one  of  oxygen  :  it  is  28.02  +  0.  This  hypothesis  is  render- 
ed still  stronger  by  the  fact  that  sulphurous  acid  combines  with 
chlorine  and  with  iodine  to  form  the  chloro-sulphurous  acid  S.O^ 
-j-Cl.,  and  the  iodo-sulphurous  acid  S.O^+I.  It  combines  also 
with  nitric  oxide  to  form  the  nitro-sulphurous  acid  S.O2+N.O2. 
The  chloro-sulphurous  acid  is  produced  by  the  direct  combination 
of  chlorine  and  sulphurous  acid,  when  exposed  to  strong  sunlight. 
The  iodo-sulphurous  acid  is  formed  by  passing  sulphurous  acid  gas 
through  a  solution  of  iodine  in  pyroxylic  spirit,  and  the  nitro-sul- 
phuric  acid,  which  exists  only  combined  with  bases,  by  placing  a 
solution  of  sulphite  of  potash  in  contact  with  nitric  oxide,  which  it 
gradually  absorbs.  The  sulphurous  acid  forms,  therefore,  an  exten- 
sive range  of  combinations,  in  which  it  serves  as  a  compound  radi- 
cal, and  of  which  the  formulae  are  as  follows : 

Sulphuric  acid S.Oa-f-O. 

Hyposulphuric  acid gSOj-j-O. 

Hyposulphurous  acid S.Og-j-S. 

Chloro-sulphurous  acid S.O2-J-CI. 

Iodo-sulphurous  acid S.02-|-I- 

Nitro-sulphurous  acid S.Oa-f-N.Oa. 

The  ordinary  salts  of  sulphurous  acid,  the  Sulphites^  I  rank  along 
with  the  compounds  of  chlorine  with  the  metallic  oxides  and  with 
peroxide  of  hydrogen,  which  bodies  they  resemble  also  in  their 
bleaching  powers. 

Compounds  of  Sulphur  and  Hydrogen. 

Sulphur  unites  with  hydrogen  in  two  proportions,  forming  a  gas, 
Sulphuretted  Hydrogen^  by  an  equivalent  of  each  element,  and  a  heavy 
liquid  when  in  the  proportion  of  one  equivalent  of  hydrogen  to  two 
of  sulphur. 

To  prepare  sulphuretted  hydrogen,  the  protosulphuret  of  iron 
(Fe.S.)  is  acted  on  by  dilute  sulphuric  acid,  in  the  apparatus  figured 
in  p.  24'7.  A  lively  effervescence  occurs  from  the  escape  of  sul- 
phuretted hydrogen  gas,  and  the  solution  contains  sulphate  of  pro- 
toxide of  iron  ;  a  gentle  heat  may  be  applied  to  favour  the  reaction 
of  the  materials.  In  this  process  water  is  decomposed,  its  oxygen 
being  transferred  to  the  iron,  and  its  hydrogen  to  the  sulphur  j  the 
result  may  be  expressed  as  follows :  Fe.S.  and  S.Oj-f-jfl.O.  give 
H.S.  and  S.Og+Fe.O.  This  gas  may  also  be  obtained  by  acting  on 
sulphuret  of  potassium  by  dilute  sulphuric  or  muriatic  acid,  in  which 
case  the  theory  is  the  same  as  that  already  given.  Sulphuret  of 
antimony  and  liquid  muriatic  acid  produce,  when  heated,  very  pure 
sulphuretted  hydrogen,  the  reaction  being  that  Sb^Sg  and  3(H.C1.) 
give  Sb^Cla  and  3(H.S.). 


OF     SULPHURETTED     HYDROGEN.  293 

The  sulphuretted  hydrogen  gas,  being  absorbed  by  water,  cannot 
be  well  collected  over  it,  except  it  be  saturated  with  common  salt, 
or  be  heated  to  above  90^,  in  which  case  its  solvent  power  is  very 
much  diminished.  It  cannot  be  kept  long  over  the  mercurial  pneu- 
matic trough,  for  the  lead  and  tin  always  present  in  the  mercury  of 
commerce  gradually  decompose  it,  combining  with  the  sulphur,  and 
leaving  the  hydrogen  free  j  the  volume  of  the  gas  remains  the  same 
during  this  decomposition. 

This  gas  is  colourless  and  transparent :  it  is  characterized  by  its 
fetid  odour,  that  of  rotten  eggs,  which,  indeed,  owe  their  peculiar 
odour  to  the  formation  of  this  gas  during  their  putrefaction.  Its 
specific  gravity  is  1177.     It  consists,  therefore,  of 

One  volume  of  vapour  of  sulphur 66480 

Six  volumes  of  hydrogen 688x6=    412-8 

the  seven  volumes  are  condensed  to  six 70608 

of  which  one  weighs,  therefore 1176-8 

The  sulphuretted  hydrogen  gas  dissolves  in  water,  forming  a  so- 
lution which  is  extensively  used  as  a  reagent  for  the  metals,  from 
the  solutions  of  most  of  which  it  precipitates  metallic  sulphurets  of 
various  colours,  by  which  many  metals  may  be  recognised.  Thus 
antimony  gives  an  orange,  manganese  a  flesh  red,  arsenic  and  cad- 
mium a  canary  yellow,  and  several,  as  lead,  mercury,  and  bismuth, 
black  or  brown  precipitates. 

Sulphuretted  hydrogen  is  highly  inflammable  ;  if  burned  in  a  lim- 
ited quantity  of  air,  the  hydrogen  is  consumed,  while  most  of  the 
sulphur  is  deposited.  By  means  of  nitric  acid  or  chlorine  it  may  be 
completely  decomposed  j  hence  chlorine  acts  as  a  disinfectant  and 
purifier  of  sewers  or  rooms  impregnated  with  the  odour  of  sulphu- 
retted hydrogen.  This  gas  is  very  poisonous ;  air  being  capable  of 
producing  death  to  large  animals,  if  respired,  though  it  may  not  con- 
tain more  than  ^i^  of  this  gas.  Many  of  the  metals  decompose  sul- 
phuretted hydrogen,  particularly  when  heated  in  this  gas,  combining 
with  the  sulphur,  and  setting  the  hydrogen  free.  This  occurs  slow- 
ly, even  at  common  temperatures  ;  and  hence  metals,  as  gold  and 
silver,  which  are  not  oxidized  by  the  air,  are  gradually  tarnished  by 
the  sulphuretted  hydrogen,  which,  exhaled  from  decomposing  animal 
matter,  is  always  present  in  the  atmosphere.  This  gas,  evolved 
probably  by  the  action  of  water  on  the  native  sulphurets  of  iron,  at 
high  temperatures,  is  a  frequent  constituent  of  mineral  springs,  and 
forms  the  class  of  spas  termed  sulphureous,  such  as  those  of  Har- 
rowgate,  Lucan,  and  Golden-bridge.  They  are  easily  recognised 
by  the  fetid  odour,  by  blackening  a  silver  spoon,  or  by  giving  a  black 
or  brown  precipitate  with  a  solution  of  acetate  of  lead. 

In  its  chemical  relations,  sulphuretted  hydrogen  assimilates  it- 
self closely  to  water ;  its  composition  and  equivalent  numbers  are 
as  follows : 

Sulphur,      94-18  One  equivalent,  =201-2  or  16-1 

Hydrogen,   5-82  One  equivalent,  =    12-5  or    1-0 

100-00  ns^     Wl 

Bisulphuret  of  Hydrogen. — To  prepare  this  substance,  bisulphuret  of  potassium 
ia  to  be  dissolved  in  water,  and  the  solution  gently  poured  into  dilute  muriatic  acid ; 


294  SELENIUM,    ITS    COMPOUNDS    WITH    OXYGEN,    ETC. 

the  potassium  combines  with  the  chlorine,  and  the  hydrogen  unites  with  the  sul- 
phur, K.S2  and  H.Cl.  giving  K.Cl.  and  H.S2 ;  the  latter  sinlis  to  the  bottom  of  the 
vessel  as  a  heavy  yellow  liquid,  insoluble  in  water,  but  decomposed  rapidly  by  con- 
tact with  it,  unless  free  acid  be  present.  It  is  not  easily  obtained  pure,  as  the  sul- 
phuret  of  potassium,  formed  by  melting  salt  of  tartar  and  sulphur  together,  or  by 
dissolving  sulphur  in  a  solution  of  caustic  potash,  always  contains  an  excess  of  sul- 
phur beyond  two  atoms,  which,  precipitating  along  with  this  true  compound,  dis- 
solves in  it,  and  modifies  its  properties  and  composition. 

This  oily  liquid  is  characterized  by  separating,  with  great  ease,  into  sulphuretted 
hydrogen  gas  and  solid  sulphur ;  indeed,  the  best  way  of  obtaining  sulphuretted  hy- 
drogen condensed  into  a  hquid,  is  to  seal  up,  in  a  strong  tube,  a  quantity  of  this  bi- 
sulphuretted  hydrogen,  which,  after  a  short  time,  is  decomposed ;  the  gas,  not  being 
able  to  escape,  is  liquefied  by  the  pressure  it  exercises,  \vhile  the  sulphur  separates 
in  octohedral  crystals. 

This  body  is  decomposed  by  all  substances  which  decompose  deutoxide  of  hydro- 
gen. Black  oxide  of  manganese,  or  oxide  of  silver  put  in  contact  with  it,  evolve 
sulphuretted  hydrogen  gas,  and  often  with  the  appearance  of  hght  and  heat ;  it 
corrodes  the  skin,  and  appears  to  possess  bleaching  properties. 

Sulphurets  of  Nitrogen  have  been  discovered  and  described ;  they  are  solid  and 
crystallizable,  but  are  of  no  importance. 

Of  Selenium. 

Selenium  was  discovered  by  Berzelius,  and  accompanies,  although 
in  exceedingly  small  quantity,  the  native  metallic  sulphurets,  existing 
as  seleniurets  of  the  same  metals.  It  remains  even  still  a  very  rare 
substance  :  it  has  not  been  introduced  into  the  arts  or  into  medicine, 
and  it  will  hence  be  necessary  to  touch  upon  its  history  but  very 
slightly. 

When  extracted  from  its  native  combinations,  selenium  is  a  solid 
of  a  dark  brown  colour,  and  when  smooth,  with  metallic  lustre.  Its 
density  is  4-32 ;  its  fracture  is  crystalline ;  it  melts  a  little  above 
the  boiling  point  of  water,  and  boils  at  650^  5  its  vapour  is  of  a  deep 
yellow  colour,  like  that  of  sulphur.  In  its  manner  of  combination 
It  resembles,  almost  completely,  sulphur. 

In  one  respect,  however,  they  differ ;  when  selenium  is  burned  in  air,  it  combines 
with  but  one  equivalent  of  oxygen,  forming  oxide  of  selenium  (Se.O.),  a  colourless 
gas,  which  is  remarkable  for  its  pungent  odour  of  horseradish.  By  this  means 
selenium  may  be  recognised,  even  when  present  in  exceedingly  small  quantity. 
Sulphur  does  not  appear  to  form  a  similar  compound. 

When  selenium  is  boiled  with  nitric  acid,  it  unites  with  two  equivalents  of  oxy- 
gen, and  forms  selenious  acid,  Se.Og-  This  may  be  also  produced  by  burning  se- 
lenium in  oxygen  gas  at  a  high  temperature.  It  is  solid,  white,  volatile,  and  may 
be^  obtained  crystaUized  by  sublimation,  or  from  its  watery  solution.  Selenious 
acid  may  be  deprived  of  its  oxygen  by  contact  with  zinc  or  iron  filings,  or  by  sul- 
phurous acid :  selenium  is  set  free  as  a  crimson  precipitate.  When  selenite  of  am- 
monia is  heated,  it  gives  water,  nitrogen,  and  free  selenium. 

If  a  current  of  chlorine  gas  be  passed  through  a  solution  of  selenious  acid,  or  if 
selenium  be  melted  with  nitre,  the  selenic  acid  is  formed  (Se.Oa),  which  has  the 
most  remarkable  analogy  with  sulphuric  acid.  All  their  similar  salts  are  isomorph- 
ous,  and  almost  identical  in  properties.  Indeed,  to  distinguish  them,  it  is  necessary 
to  boil  the  salt  with  muriatic  acid,  which  has  no  action  on  the  sulphate,  but  gives 
with  the  seleniate,  chlorine,  and  selenious  acid. 

Seleniurctted  Hydrogen  is  formed  by  the  action  of  acids  upon  metallic  seleniurets, 
in  precisely  the  same  manner  as  that  described  under  the  head  of  sulphuretted  hy- 
drogen. It  is  a  colourless  gas,  of  an  extremely  fetid  odour,  irrespirable,  soluble 
in  water,  and  precipitating,  from  the  solutions  of  many  of  the  metals,  metallic  sel- 
eniurets ;  these  are  generally  black  or  brown  ;  but  the  seleniuret  of  manganese  is, 
like  the  sulphuret,  flesh-red,  and  that  of  zinc  is  white. 

When  sulphuret  of  hydrogen  is  passed  into  a  solution  of  selenious  acid,  water  is 
formed,  and  a  sulphuret  of  selenium  is  produced  analogous  to  selenious  acid,  its 
formula  being  Se.^-Sa-     It  is  a  canary  yellow  powder,  insoluble  in  water. 


PHOSPHORUS,  ITS  PREPARATION,  ETC. 


295 


Of  Phosphorus. 

Phosphorus  exists  in  nature,  principally  in  the  animal  kingdom, 
in  the  bones  of  the  vertebrated  animals,  in  the  fluids  of  the  body, 
and  also  in  the  pulpy  material  of  the  brain  and  nerves.  It  is  found 
in  small  quantity  in  many  vegetables,  and  is  a  constituent  of  some 
minerals.  It  is  prepared  as  an  article  of  manufacture  in  large  quan- 
tity in  London  and  Paris.  In  the  latter  city  it  is  computed  that 
about  200,000  lbs.  of  phosphorus  are  annually  obtained. 

The  principal  source  of  pliosphorus  is  the  earthy  material  of  bones  (phosphate  of 
lime).  The  bones  are  first  burned  until  they  become  completely  white,  and  then 
ground  to  powder.  To  three  parts  of  this  powder  are  added  thirty  parts  of  water 
and  two  of  oil  of  vitriol.  The  sulphuric  acid  unites  with  a  portion  of  the  lime  of 
the  bone  ashes,  while  the  remainder  forms,  with  the  whole  of  the  phosphoric  acid, 
a  soluble  salt,  which  is  obtained  in  the  hquor,  when  the  insoluble  sulphate  of  lime  is 
separated  by  straining  through  a  cloth.  The 
liquor  is  evaporated  to  the  consistence  of  a  sirup, 
and  gradually  mixed  with  a  quantity  of  powdered 
charcoal,  about  one  fourth  the  weight  of  the 
bones  that  had  been  used,  and  the  whole  com- 
pletely dried  at  a  temperature  just  below  redness. 
The  niass  is  introduced,  in  powder,  into  an 
earthen  retort,  a,  which  is  placed  in  a  furnace, 
as  in  the  figure.  To  the  neck  of  the  retort  is 
adapted  a  copper  tube,  6,  the  other  extremity  of 
which  dips  a  little  into  the  water  in  the  bottle 
which  serves  as  a  receiver.  The  retort  being 
gradually  heated,  the  excess  of  the  phosphoric 
acid  is  decomposed  by  the  charcoal,  the  carbon 
of  which  combines  with  the  oxygen  to  form  car- 
bonic acid,  while  the  phosphorus  becomes  free ; 
this  being  volatilized  by  the  high  temperature, 
passes  in  the  state  of  vapour  into  the  copper 
tube,  where  it  is  condensed,  and,  flowing  down 
in  the  liquid  form  into  the  bottle,  collects  under  the  surface  of  the  water.  The  cop- 
I)er  tube  must  dip  so  little  under  the  water,  that  by  no  condensation  could  this  be 
forced  back  into  the  retort. 

The  phosphorus  so  obtained  is  again  melted  under  the  surface  of  the  water, 
and  poured  into  glass  tubes,  where  it  is  allowed  to  solidify.  It  thus  gets  the  cylin- 
drical form  in  which  it  is  found  in  commerce. 

Phosphorus,  when  pure,  is  transparent  and  colourless  j  but,  as 
generally  found,  it  is  of  a  pale  yellow,  or  even  of  a  reddish  col- 
our. At  ordinary  temperatures  it  is  soft,  so  that  it  may  be  bent  or 
cut  with  a  knife ;  but  at  32^  it  becomes  quite  brittle  and  crystalline 
in  its  fracture.  It  is  insoluble  in  water,  but  it  dissolves  in  the  vol- 
atile oils,  in  ether,  and  in  sulphuret  of  carbon,  from  which  last  it 
may  be  obtained  in  crystals  of  considerable  size, 
which  are  regular  dodecahedrons,  as  in  the  figul'e. 
It  has  also  been  obtained  crystallized  by  fusion, 
under  the  form  of  octohedrons.  At  108^  phos- 
phorus melts  into  a  colourless  liquid,  and  at  550° 
it  boils,  forming  a  colourless  vapour,  the  sp.  gr. 
of  which  is  4327.  Phosphorus  appears  to  assume 
an  anomalous  condition  like  that  of  sulphur  ;  when 
strongly  heated  and  suddenly  cooled,  it  becomes  jet  black  and 
opaque,  but  gradually  returns  to  its  ordinary  aspect. 

Phosphorus  is  exceedingly  inflammable.     Even  at  ordinary  tem- 
peratures, when  exposed  to  the  air,  it  burns  slowly,  forming  phos- 


296    COMPOUNDS     OF     PHOSPHORUS     AND     OXYGEN. 

phorous  acid,  and  emitting  light  visible  in  the  dark,  from  whence 
its  name  (^o)^  0epw,  I  bring  light).  It,  at  the  same  time,  emits  a 
remarkable  and  penetrating  garlic  smell.  It  is  hence  that  phospho- 
rus is  used  to  analyze  atmospheric  air,  and  that  it  must  always  be 
preserved  under  water.  When  heated  to  120^  phosphorus  bursts 
into  brilliant  flame,  and  unites  with  oxygen  to  form  phosphoric  acid. 
The  combustibility  of  phosphorus  is  influenced  by  the  presence  of 
various  gaseous  bodies  in  a  very  remarkable  degree.  Thus,  in 
pure  oxygen,  phosphorus  does  not  burn  nor  give  any  light  until  the 
temperature  is  raised  to  80"^ ;  and  if  the  oxygen  or  air  be  mixed 
with  small  quantities  of  olefiant  gas,  or  the  vapours  of  ether  or  of 
oil  of  turpentine,  its  slow  combustion  may  be  totally  prevented. 
This  influence  even  extends,  under  some  circumstances,  to  much 
higher  temperatures. 

The  atomic  weight  of  phosphorus  had  been  formerly  taken  as 
15*7  (H.  =  l)  in  consequence  of  some  views  of  the  constitution  of 
its  compounds,  which  are  now  generally  abandoned,  and  I  consider 
the  true  equivalent  number  to  be  31'4,  double  the  former. 

Phosphorus  combines  with  oxygen  in  four  proportions,  forming  an  oxide  anr* 
Uiree  acid  compounds,  the  constitution  of  which  follows : 

Oxide  of  phosphorus  .  .  .  =2P.+0.=62  8-f-  80=70  8 
Hypophosphorous  acid  .  .  .  =  P.-i-0.=31-4-|-  80=39-4 
Phosphorous  acid  .  .  .  .  =  P.4-03=31 -44-24  0=55-4 
Phosphoric  acid =  P.-i-O5=31-4-|-400=71-4 

Oxide  of  Phosphorus. — When  phosphorus  is  exposed  to  light,  in  water  containing 
air  dissolved,  it  gradually  becomes  covered  with  a  white  powder,  which  is  a  com- 
pound of  phosphorus  with  water ;  but  there  forms,  at  the  same  time,  a  reddish  sub- 
stance, which  is  oxide  of  phosphorus.  It  is  generated,  also,  whenever  phosphorus 
is  incompletely  burned,  and  may  be  formed  in  large  quantity  by  melting  phosphorus 
under  water,  and  bringing  a  stream  of  oxygen  gas  to  act  upon  it  by  means  of  a  tube 
pjissing  to  the  bottom  of  the  vessel ;  the  phosphorus  burns  brilliantly,  but,  being 
present  in  great  excess,  it  passes  principally  only  to  the  lowest  degree  of  combina- 
tion that  it  can  form.  It  may  be  obtained  purer  by  other  processes,  which  are,  how- 
ever, too  complicated  to  be  introduced  in  this  place. 

The  oxide  of  phosphorus  so  formed  is  a  red  or  yellow  powder,  insoluble  in  water ; 
it  is  exceedingly  inflammable  in  some  forms,  but  in  others  does  not  take  fire  until 
heated  to  near  the  boiling  point  of  mercury.  It  is  not  probable  that  the  red  and 
yellow  substances  which  are  called  oxide  of  phosphorus  are  really  identical,  as  they 
differ  in  their  most  striking  characters  besides  in  colour.  The  formula  P2O.  is  that 
obtained  from  the  yellow  matter ;  Pelouze  considers  the  reddish  matter  to  be  ex- 
pressed by  P3O2. 

Hypophosphorous  Acid. — This  acid  is  very  little  known ;  it  is  formed  when  phos 
phorus  is  heated  in  a  solution  of  an  alkali  or  earth  :  water  is  decomposed  ;  one  por- 
tion of  phosphorus  combining  with  the  hydrogen,  and  another  with  the  oxygen, 
produce  phosphuretted  hydrogen  gas,  which  passes  off,  and  hypophosphorous  acid, 
which  remains  combined  with  the  alkali  or  earth  employed ;  the  reaction  may  be 
shown  thus  with  phosphorus  and  solution  of  barytes  :  4P.,  3H.0.,  and  3Ba.O.,  give 
3(P.O.+Ba.O.)  and  P.H3. 

The  hypophosphite  of  barytes,  so  obtained,  may  be  decomposed  by  sulphuric  acid, 
and  the  sulphate  of  barytes  being  removed  by  filtration,  the  hypophosphorous  acid 
remains  uncombined  ;  its  solution  may  be  evaporated  to  the  consistence  of  a  sirup, 
but  it  cannot  l^e  obtained  solid ;  it  is  decomposed,  by  continuing  the  heat,  into 
phosphuretted  hydrogen,  phosphoric  acid,  and  some  phosphorus  is  set  free. 

Its  salts  are  all  soluble  in  water,  and  most  of  them  crystallize  and  contain  water 
of  crystallization ;  when  heated  strongly,  they  give  phosphuretted  hydrogen  and  a 
phosphate  of  the  base. 

Phosphorous  Acid. — This  acid  is  the  principal  product  of  the  slow  combustion  of 
phosphorus,  but,  to  obtain  it  pure,  it  is  necessary  to  avoid  carefully  an  excess  of 
oxygen ;  for  this  purpose,  a  glass  tube  of  ten  inches  long  and  half  an  inch  bore  ia 


PHOSPHORIC    ACID^    ITS    PREPARATION,    ETC.    297 

drawn  out  at  one  end  to  a  point,  with  an  aperture  large  enough  to  admit  a  pin,  and 
bent  at  an  obtuse  angle  about  two  inches  from  the  point ;  at  the  bend  is  laid  a  piece 
of  phosphorus,  which  is  heated  until  it  takes  fire,  but  the  temperature  must  not  rise 
so  high  as  to  sublime  any  of  it.  As  there  is  a  great  excess  of  phosphorus  present, 
the  principal  product  of  the  combustion  is  phosphorous  acid,  which,  being  formed  in 
exceedingly  light  flakes,  is  carried  by  the  current  of  air  to  the  upper  part  of  the 
tube,  where  it  is  deposited.  These  flakes  are  volatile,  and  may  be. sublimed  from 
one  part  of  the  tube  to  another ;  they  attract  water  so  powerfully,  that  the  heat 
evolved  is  sometimes  great  enough  to  inflame  the  phosphorous  acid,  which  then 
combines  with  more  oxygen,  and  forms  phosphoric  acid. 

Phosphorous  acid  is  more  easily  prepared  in  the  Uquid  form ;  for  this  purpose,  a 
quantity  of  phosphorus  is  placed  in  a  thin  glass  vessel,  covered  with  water  to  the 
depth  of  some  inches  ;  a  current  of  chlorine  is  then  conducted  by  a  tube  to- the 
phosphorus,  which  inflames  and  forms  protochloride  of  phosphorus  ;  this  substance 
is  immediately  decomposed  by  the  water,  phosphorous  acid  and  muriatic  acid  being 
produced ;  the  P.CI3  and  3H.0.  giving  P.O3  and  3H.C1. ;  both  acids  dissolve  in  the 
water,  but  by  evaporating  the  solution  to  the  consistence  of  a  sirup,  the  muriatic 
acid  passes  off  as  gas,  and  the  hydrate  of  phosphorous  acid,  P.Og-j-SH.O.,  remains 
behind.  This  hydrated  acid  cannot  be  freed  from  water  by  farther  heat,  it  being 
then  decomposed  into  phosphoric  acid,  and  the  variety  of  phosphuretted  hydrogen 
which  is  not  spontaneously  inflammable.  Thus  4(P.03-l-3H.O.)give  BP.Os-j-SH.O.) 
and  P.H3. 

The  solution  of  phosphorous  acid  absorbs  oxygen  rapidly  from  the  air,  and,  with 
the  assistance  of  heat,  reduces  to  the  metalUc  state  the  salts  of  mercury,  silver, 
gold,  and  platina.    It  is  hence  occasionally  used  as  a  deoxidizing  agent. 

Phosphoric  Acid, 

When  this  acid  is  required  in  large  quantity,  it  is  generally  pre- 
pared from  the  earth  of  bones,  which  are  acted  on  by  sulphuric  acid, 
as  was  described  for  the  preparation  of  phosphorus.  The  acid  so- 
lution of  superphosphate  of  lime  is  decomposed  by  carbonate  of  am- 
monia, by  which  the  lime  is  thrown  down  in  combination  with  car- 
bonic acid,  and  the  phosphoric  acid  remains  in  solution  as  phosphate 
of  ammfinia.  This  salt  may  be  crystallized,  but  it  is  generally 
evaporated  to  dryness,  and  ignited ;  the  ammonia  passes  off,  and 
the  phosphoric  acid  remains  behind  melted,  and  solidifies  on  cool- 
ing into  a  colourless  glass,  the  glacial  phosphoric  acid. 

It  may  also  be  obtained  by  acting  on  phosphorus  with  dilute  nitric 
acid.  This  supplies  oxygen  to  the  phosphorus,  and  nitric  oxide  is 
evolved.  When  the  action  has  terminated,  the  solution  is  to  be 
evaporated  to  dryness,  and  the  residual  phosphoric  acid  ignited,  to 
expel  all  traces  of  nitric  acid.  This  process  is  somewhat  danger- 
ous, as  sometimes  fragments  of  phosphorus  are  projected  by  the 
effervescence  out  of  the  liquid,  and  burning  in  the  nitric  oxide  gas, 
may  burst  the  retort.  The  phosphoric  acid  may  also  be  prepared 
very  simply,  and  in  a  pure  and  dry  state,  by  setting  fire  to  some 
phosphorus  in  a  little  cup,  and  covering  it  with  a  large  bell  glass. 
The  oxygen  of  the  contained  air  forms  phosphoric  acid,  which  is 
deposited  in  white  flakes  on  the  inside  of  the  glass  and  on  the  sup- 
porting plate.  In  all  these  cases,  the  acid  so  obtained  is  destitute 
of  water  ;  it  is  anhydrous. 

The  phosphoric  acid  has  a  great  affinity  for  water,  combining 

with  it  almost  explosively.     It  may  form  three  distinct  compounds, 

phosphates  of  water  ^  the  constitution  of  which  is  as  follows: 

Monobasic  phosphate  of  water     .     .     P.O54-  H.O. 

Bibasic  phosphate  of  water      .     .     .     P.O,-f-2H.O. 

Tribasic  phosphate  of  water    .     .     .     P.Os-f-SH  O. 

Pp 


298  PHOSPHATES     OF     WATER. 

This  relation  was  first  established  by  the  researches  of  Graham, 
whose  admirable  memoir  on  the  arseniates  and  phosphates  formed 
an  important  epoch  in  science.  The  phosphoric  acid  combines  not 
only  with  water  in  these  three  proportions,  but  each  of  them  is  a 
type  of  a  series  of  salts  which  the  phosphoric  acid  is  capable  of 
forming.  Thus  there  is  a  class  of  monobasic  phosphates^  another 
class  oi  bihasic phosphates^  and  a  third,  which  is  the  most  common,  of 
tribasic  phosphates  ;  the  water  contained  in  the  phosphates  of  water 
being  replaced  to  a  greater  or  less  extent  by  means  of  equivalent 
proportions  of  ammonia  or  metallic  oxides. 

A  solution  of  phosphoric  acid  in  water  may  contain  any  one  of 
the  three  phosphates  of  water  that  have  been  described,  and,  when 
neutralized  by  bases,  may  hence  produce  totally  different  salts. 
The  properties  of  a  solution  of  phosphoric  acid  may  therefore  be 
totally  different,  according  to  the  manner  in  which  it  had  been  pre- 
pared, and  hence  this  acid  was  at  one  time  ranked  as  a  remarkable 
instance  of  isomerism  j  but  Graham  has  beautifully  shown  that  the 
difference  of  properties  is  only  the  result  of  the  existence  of  the 
different  states  of  combination  in  which  the  phosphoric  acid  actually 
exists.  It  will  consequently  be  necessary  to  study  separately  the 
properties  of  the  three  compounds  of  phosphoric  acid  with  water. 

Monobasic  Phosphate  of  Water. — A  solution  of  this  body  reacts  pow- 
erfully acid  ;  it  precipitates  albumen  (white  of  egg)  in  white  curds ; 
when  neutralized  by  a  base,  it  gives  salts  which  contain  but  one 
atom  of  base,  their  formula  being  P.O5-I-R.O.,  and  a  soluble  salt  of  it 
produces,  in  solutions  of  silver,  a  white,  soft  precipitate,  P.Oj-f- 
Ag.O.  This  is  the  least  stable  of  the  phosphates  of  water;  it  grad- 
ually passes  into  the  other  forms,  particularly  when  its  solution  is 
boiled. 

Bibasic  Phosphate  of  Water. — This  form  of  the  acid  may  be  pre- 
pared by  decomposing  bibasic  phosphate  of  lead  by  sulphuretted 
hydrogen-.  It  is  characterized  by  combining  always  with  two  equiv- 
alents of  base,  forming  salts,  whose  formula  is  P.O5  +  2R.O.  ;  its 
salts  give,  with  nitrate  of  silver,  a  white  precipitate,  P.Oj-fSAg.O., 
which  is  not  pasty  like  the  monobasic  phosphate.  The  salts  of  this 
acid  may  contain  only  one  equivalent  of  fixed  base,  the  other  being 
water,  and  may  hence,  at  first  sight,  appear  to  be  constituted  like 
the  monobasic  salts  ;  the  basic  water  is,  however,  easily  known  to  be 
present,  by  its  not  being  expelled  by  a  moderate  heat  with  the  water 
of  crystallization,  but  requiring  a  temperature  approaching  to  igni- 
tion for  its  expulsion. 

Tribasic  Phosphate  of  Water. — This  is  the  form  of  phosphoric  acid 
which  represents  the  class  of  salts  most  generally  known ;  it  is 
characterized  by  not  precipitating  albumen,  and  by  combining  with 
three  equivalents  of  base  when  fully  neutralized.  In  the  majority 
of  cases,  of  the  three  equivalents  of  base,  one  is  water  ;  thus  the  com- 
mon phosphate. of  soda  is  a  tribasic  phosphate,  its  formula  being 
(P.05H-2Na.O.H.O.)-f  24-Aq. ;  when  moderately  heated,  or  even  by 
long  exposure  to  dry  air,  it  loses  the  24.Aq.,  but  it  requires  to  be 
melted  at  a  red  heat  in  order  to  drive  off  the  twenty-fifth  atom  of 
water  ;  and,  if  this  be  done,  on  redissolving  the  fused  mass  in  water, 
it  crystallizes  in  a  totally  different  form,  and  is  found  to  have  been 


PHOSPHURETTED     HYDROGEN. 


299 


changed  into  bibasic  phosphate  of  soda,  the  formula  of  which  is 
(P.O5  f  2Na.0.)+ lOAq.  The  difference  is  remarkably  shown  by 
the  action  of  these  salts  on  solution  of  silver ;  common  phosphate 
of  soda  precipitates  nitrate  of  silver  of  a  canary  yellow,  and  the  so- 
lution becomes  acid ;  one  equivalent  of  tribasic  phosphate  of  soda 
decomposing  three  equivalents  of  nitrate  of  silver,  producing  one 
equivalent  of  tribasic  phosphate  of  silver,  two  of  nitrate  of  soda, 
and  one  of  nitrate  of  water ;  this  last  being  liquid  nitric  acid,  of 
course,  renders  the  liquor  acid.  The  reaction  may  be  simply  ex- 
pressed : 

P.05+2Na.O.H.O.  and  3(N.05-LAg.O.) 
give  R05+3Ag.O. . .  2(N.O,+Na.O.)  and  N.O5+H.O. 
If,  on  the  other  hand,  bibasic  phosphate  of  soda  be  used,  the  liquor 
remains  neutral,  for  P.05  +  2Na.O.  and  2(N.05-f  Ag.O.)  give  P.O5  + 
2Ag.O.  and  2(^0^  +  Na.O.). 

In  the  tribasic  phosphates  it  frequently  occurs  that  there  is  but 
one  equivalent  of  fixed  base,  the  other  two  being  water ;  such  salts 
have  frequently  an  acid  reaction,  and  were  formerly  termed  biphos- 
phates.  Thus  one  tribasic  phosphate  of  soda  is  P.Os  +  Na.O. .  2H. 
O. ;  the  biphosphate  of  ammonia  is  tribasic,  its  formula  beinff  P.Os 
+  N.H,0..2H.O. 

These  salts  of  phosphoric  acid  were  originally  designated  by 
Graham  metaphosphates,  pyrophosphates,  and  common  phosphates, 
but  the  systematic  names  which  he  has  since  proposed  should  be 
universally  adopted. 

In  the  general  remarks  on  the  constitution  of  salts,  and  on  some 
other  occasions,  I  shall  have  opportunities  to  return  to  the  consid- 
eration of  this  subject. 

Compounds  of  Phosphorus  and.  Hydrogen. 

Although  it  is  probable  that  there  exist  at  least  two  compounds 
of  phosphorus  and  hydrogen,  yet  I  shall  describe  only  that  which 
is  gaseous  (P.H3),  as  of  it  alone  do  we  possess  accurate  knowledge. 

The  modes  of  preparing  this  gas  have  been  already  noticed.  It 
may  be  formed,  1st,  when  phosphorus  is  heated  in  a  solution  of 
potash  or  barytes,  or  with  milk  of  lime  ;  the  water  being  decom- 
posed, gives  its  oxygen  to  one  portion  of  the  phosphorus  to  form 
hypophosphorous  acid,  and  its  hydrogen  to  another,  forming  phos- 
phuretted  hydrogen  gas:  2d,  when  the  hydrated  phosphorous  acid 
is  heated,  the  water  is  decomposed,  and  phosphoric  acid  and  phos- 
phuretted  hydrogen  are  produced.  The  gas,  prepared  in  these  ways, 
possesses  very  different  properties;  I  shall  term  that  obtained  by 
the  first  process  the 
A,  and  that  by  the 
second  the  B  variety. 
If  the  A  gas,  evolved 
from  the  retort  a, 
be  allowed  to  bub- 
ble through  the  wa- 
ter of  the  pneumatic 
trough,  each  bubble 
of  gas,  as  it  bursts  in 


300  PHOSPHURETTED     HYDROGEN. 

the  air,  takes  fire  spontaneously,  and,  burning  with  a  beautiful  white 
flame,  forms  a  ring  of  phosphoric  acid  smoke,  which,  widening  as 
it  rises,  may  ascend  to  a  considerable  height,  if  the  air  of  the  apart- 
ment be  still,  without  its  form  being  broken  up.  The  structure  of 
this  ring  is  exceedingly  curious  and  pretty ;  it  consists  of  an  ama- 
zing number  of  small  rings,  which  revolve  with  great  rapidity  on 
their  axis,  and  whose  plane  is  perpendicular  to  that  of  the  general 
ring  which  they  produce.  This  is  spontaneously  inflammable  phos- 
phuretted  hydrogen :  if  the  gas  bubbles  be  received  in  a  jar  of  pure 
oxygen,  the  combustion  is  excessively  brilliant  and  explosive.  The 
B  variety  of  the  gas  is  not  spontaneously  inflammable,  but  if  set  on 
fire  it  burns  with  the  same  appearance  as  the  other. 

On  analysis,  the  two  varieties  give  exactly  the  same  result ;  they 
are  colourless  and  transparent,  and  of  a  very  disagreeable  garlic 
smell  J  but  slightly  absorbed  by  water,  and  precipitating  the  generali- 
ty of  metallic  salts,  giving  insoluble  phosphurets.  The  specific  grav- 
ity is  the  same  for  both,  being  1185,  which  arises  from 

One  volume  of  phosphoms- vapour =43270 

and  six  volumes  of  hydrogen 68-8x6=  412-8 

being  condensed  to  four 4739-8 

of  which  one  weighs,  therefore 1184-9 

Their  constituents  by  weight,  and  equivalent  numbers,  are  as  fol- 
lows: 

Phosphorus,  =91-29  One  equivalent,        =392-3  or  31-4? 

Hydrogen,  8-71  Three  equivalents,  =  37-5  or    3-0 

100-00  429^        34¥ 

These  two  varieties  were  naturally  looked  upon  as  isomeric,  but 
Graham  has  shown  that  the  difference  of  properties  may  arise  from 
the  presence  of  a  small  quantity  of  foreign  substance,  as  such  may 
change  the  one  variety  into  the  other.  Thus  a  very  small  quantity 
of  the  vapour  of  ether  removes  altogether  the  power  of  spontaneous 
inflammability  from  the  A  variety ;  the  vapour  of  the  essential  oils, 
and  even  carbon,  phosphoric  acid,  and  potassium,  produce  the  same 
effect.  On  the  other  hand,  an  exceedingly  small  quantity  of  vapour 
of  nitrous  acid  or  nitric  oxide  converts  the  variety  B  into  A,  and 
makes  it  spontaneously  inflammable.  Graham  considers  that,  in 
obtaining  the  gas  from  phosphorus  and  milk  of  lime,  &c.,  it  is  accom- 
panied by  a  very  minute  trace  of  some  compound  of  phosphorus  and 
oxygen,  probably  the  same  as  is  formed  by  nitrous  acid  with  the  B 
variety,  which  is  really  spontaneously  inflammable,  and,  acting  as  a 
match,  inflames  the  general  mass  of  gas  (see  p.  296.) 

Phos2)huret  of  Nitrogen. — Tliis  compound  has  been  discovered  and  described  by 
Rose,  but  possesses  no  important  properties. 

Sulphur et  of  Phosphorus  is  formed  by  melting  together  sulphur  and  phosphorus  in 
equivalent  weights.  It  appears  that  these  elements  unite  in  more  proportions  than 
one.  The  compound  is  much  more  inflammable  than  phosphorus,  and  is  the  mate- 
rial used  in  the  phosphorus  match-boxes. 

Of  Chlorine, 
Chlorine  exists  in  large  quantity  in  nature,  principally  combined 
with  sodium,  forming  immense  deposites  of  rock-salt  (chloride  of 


CHLORINE,  ITS  PREPARATION. 


301 


8odmm)  in  England,  in  Poland,  and  elsewhere  j  and  in  the  same 
state  it  communicates  the  saltness,  and  constitutes  the  chief  ingre- 
dient of  sea- water.  It  is  found  also  combined  with  calcium,  mercury, 
lead,  silver,  and  some  other  metals  ;  but  these  compounds  are  rare, 
and  exist  only  in  small  quantity.  The  only  source  of  chlorine 
practically  useful  in  chemistry  and  in  the  arts  is  from  common  salt* 

To  obtain  chlorine  in  large  quantity,  the  common  salt  is  mixed  with  peroxide  of 
manganese,  and  then  decomposed  by  sulphuric  acid  ;  the  half  of  the  oxygen  of  tht 
peroxide  of  manganese  passes  to  the  sodium,  the  chlorine  being  expelled,  and  the 
soda  and  protoxide  of  manganese  both  unite  with  the  sulphuric  acid.  Thus  Mn.Oj 
and  Na.Cl.,  treated  with  2S.O3,  produce  S.O3  .  Na.O.-f-SOg  .  Mn.O.,  and  CI.  i& 
evolved.  By  weight,  about  six  parts  of  oxide  of  man- 
ganese and  eight  of  chloride  of  sodium  are  employed 
with  thirteen  of  oil  of  vitriol ;  and  as  the  manufactu- 
rers of  chloride  of  lime  are  generally  makg;rs  of  oil  of 
vitriol  also,  a  proportionate  quantity  of  acid  of  1  600 
from  the  chamber  (p.  289)  is  generally  used  in  place 
of  strong  oil  of  vitriol,  the  expense  of  concentration 
being  thus  saved.  Into  a  leaden  still,  h,  h,  such  as  is 
represented  in  the  figure,  the  mixed  salt  and  manga- 
nese are  introduced  at  the  aperture  z,  which  is  then 
tightly  closed ;  the  sulphuric  acid  enters  by  the  bent 
funnel  b,  and  these  materials  are  well  mixed  by  means 
of  the  agitator,  turned  by  the  cross  handle  n ;  the  gas 
evolved  escapes  by  the  tube  a,  which  conducts  it  to  its 
destination.  At  first  the  operation  does  not  require 
heat,  but  the  still  sits  in  an  iron  jacket,  e,  e,  into  which  steam  is  conducted  by  the 
tube  /,  and  thus  the  heat  necessary  for  the  decomposition  is  kept  up  ;  a  waste-pipe, 
g-,  serves  for  running  out  the  residue  of  one  process,  in  order  to  clear  the  still  for 
another. 

When  chlorine  is  required  in  small  quantity  in  the  laboratory,  it 
may  be  more  conveniently  prepared  from  the  muriatic  acid  of  com- 
merce, which  is  a  solution  of  chloride  of  hydrogen  gas  in  water. 
This  is  completely  decomposed  by  peroxide  of  manganese  at  very 
moderate  temperatures,  the  hydrogen  of  the  muriatic  acid  combining 
with  the  oxygen  of  the  peroxide  of  manganese  to  form  a  deuto- 
chloride  of  manganese,  which  is  completely  resolved  by  a  very 
moderate  heat  into  protochloride  and  free  chlorine.  Thus,  at  first, 
Mn.Oa  and  2C1.H.  give  Mn.Cl^  and  2H.0.,  and  then  Mn.Cla  sep- 
arates into  Mn.Cl.  and  CI.,  which  is  evolved  as  gas.  For  this  it  is 
only  necessary  to  introduce  about  one  part  of  peroxide  and  three  of 
muriatic  acid  into  an  apparatus,  such  as  those  already  often  figured, 
and  the  gas  may  be  obtained. 
The  collection  of  the  chlorine 
requires  some  remark.  It  is  ab- 
sorbed rapidly  by  cold  water, 
and  it  cannot  be  collected  over 
mercury,  as  it  combines  rapid- 
ly with  it,  forming  calomel;  wa- 
ter heated  to  above  90°  should 
therefore  be  used  ;  but  it  is  still 
better  to  take  advantage  of  the 
great  density  of  chlorine  for  its 
collection. 

If  the   tube   conducting  the 
chlorine   from  the   flask  a,  in 


302  BLEACHING     POWER     OF     CHLORINE. 

which  it  is  generated,  be  brought  to  the  bottom  of  a  dry  glass,  c,  the 
chlorine  issues  there,  and,  being  much  heavier  than  the  air,  pushes 
the  air  up  out  of  its  way,  and  gradually  fills  the  jar  completely,  pre- 
cisely as,  by  conducting  a  stream  of  water  to  the  bottom  of  a  vessel 
containing  oil,  this  might  be  perfectly  expelled,  and  the  vessel  filled 
with  water.  The  colour  of  the  chlorine  allows  the  gradual  filling  of 
the  bottle  to  be  seen,  and  by  stopping  its  aperture  Avith  a  greased 
stopple,  the  gas  may  be  preserved  unaltered  for  a  long  time. 

The  chlorine,  when  thus  prepared,  is  a  greenish  yellow  gas, 
whence  its  name  (^/Iwpoc) ;  of  an  extremely  suffocating  odour,  ir- 
ritating the  air  passages  when  respired,  even  very  much  diluted,  in 
an  intolerable  degree.  Its  specific  gravity  is  2470.  On  plunging 
a  lighted  taper  into  chlorine,  it  burns  for  a  moment  with  a  red,  smoky 
flame,  but  is  soon  extinguished.  Many  bodies  burn,  however,  more 
readily  in  chlorine  than  in  air,  or  even  in  oxygen  gas.  If  some 
powdered  antimony  or  arsenic  be  thrown  into  a  bottle  of  chlorine, 
they  take  fire,  with  bright  scintillations.  Tin  or  brass  foil  burns 
spontaneously,  as  also  phosphorus,  although  with  little  light.  A 
paper  dipped  in  oil  of  turpentine  takes  fire  spontaneously,  the  hy- 
drogen burning,  and  the  carbon  being  deposited  as  a  thick  black 
smoke.  The  affinity  of  chlorine  for  hydrogen  is  very  great :  when 
mixed,  these  gases  gradually  unite,  even  at  common  temperatures, 
and  suddenly,  with  explosion  if  set  on  fire  by  a  taper  or  by  the 
electric  spark.  In  consequence  of  this  affinity  for  hydrogen,  chlo- 
rine decomposes  most  organic  substances,  one  half  of  the  chlorine 
removing  an  equivalent  quantity  of  hydrogen,  and  the  other  half 
going  in  its  place  j  thus  ether  and  chlorine  give  chloride  of  hydro- 
gen and  chlorine  ether,  C4H5O.  and  lOCl.  giving  C4CI5O.  and  5H.C1. 
Very  often,  however,  the  action  of  chlorine  is  much  more  complex. 

Perhaps  the  most  important  character  of  chlorine,  and  certainly 
that  upon  which  its  value  in  the  arts  depends,  is  its  power  of  re- 
moving the  colour  of  organic  substances  ;  its  bleaching  properties. 
Formerly  it  was  considered  that  water  was  necessary  for  this  bleach- 
ing, and  that  the  chlorine  combined  with  the  hydrogen,  while  the 
oxygen  of  the  water,  being  thus  thrown  upon  the  organic  substance, 
oxidized  it,  and  formed  a  new  body,  which  was  colourless.  I  have 
shown,  however,  that  this  is  not  the  case,  but  that  the  chlorine  enters 
into  the  constitution  of  the  new  substance  formed,  sometimes  repla- 
cing hydrogen,  at  others  simply  combining  with  the  coloured  body, 
and  in  some,  the  reaction  being  so  complex  that  its  immediate  stages 
cannot  be  completely  traced.  I  shall  notice  this  agency  of  chlorine 
again  when  describing  the  chloride  of  lime,  and  also  when  discuss- 
ing its  relations  to  organic  chemistry. 

From  this  action  on  organic  bodies,  chlorine  is  extensively  em- 
ployed as  a  disinfectant,  to  remove  the  miasmata  and  infectious  im- 
purities by  which  the  atmosphere  of  an  hospital  may  be  contaminated. 
For  this  purpose,  it  is  desirable  to  evolve  the  gas  slowly,  but  con- 
tinuously ;  in  order  to  do  so,  some  chloride  of  lime,  diffused  through 
water,  may  be  placed  in  a  capsule  or  teacup,  and  by  a  funnel,  the 
throat  of  which  is  partly  stopped,  dilute  sulphuric  acid  be  allowed 
to  drop  down  on  it.  The  acid  takes  the  lime,  and  the  chlorine  is 
set  free. 


OXIDIZING     POWER     OF     CHLORINE.  303 

When  chlorine  is  brought  into  contact  with  water  at  32°,  they 
combine,  forming  a  hydrate  which  crystallizes  in  plates,  and  which, 
when  heated  to  about  45^,  is  decomposed.  If  a  quantity  of  these 
crystals  be  sealed  up  in  a  strong  glass  tube,  the  chlorine,  when  lib- 
erated, exercises  so  much  pressure  as  to  condense  itself  into  a  liquid. 
This  was  the  first  instance  in  which  the  liquefaction  of  the  gases 
was  successful.  Water  holding  chlorine  in  solution  possesses  the 
colour,  odour,  taste,  and  bleaching  properties  of  the  gas  itself,  and 
may  hence  be  used  for  the  purposes  of  the  arts,  although  not  so 
manageable  or  convenient  as  many  other  forms.  When  chlorine 
water  is  exposed  to  the  light,  it  is  gradually  decomposed,  chloride 
of  hydrogen  being  formed,  and  oxygen  set  free;  the  solution  be- 
comes colourless,  loses  its  bleaching  powers,  and  acquires  an  acid 
reaction.  In  contact  with  other  bodies,  chlorine  may  decompose 
water  much  more  rapidly,  and  is  hence  frequently  employed  as  an 
oxidizing  agent,  substances  being  frequently  oxidized  by  chlorine 
to  a  higher  degree  than  by  nitric  acid.  This  results,  probably,  from 
the  chlorine  first  combining  with  the  body,  and  the  compound  then 
decomposing  water ;  thus,  when  chlorine  converts  selenious  acid 
into  selenic  acid,  it  is  probable  that  it  is  not  that  the  chlorine  decom- 
poses water,  but  that  it  unites  with  the  selenious  acid,  forming  chlo 
ro-selenious  acid,  Se.O^  .  CL,  which,  in  contact  with  water,  is  resolv- 
ed into  Se.Og  .  O.  and  Cl.H.  Very  frequently  chlorine  oxidizes  a 
metal  to  a  higher  degree  by  combining  with  one  portion  of  it,  and 
hence  throwing  all  of  the  oxygen  upon  the  remainder ',  thus  pro- 
toxide of  iron  is  converted  into  peroxide  by  chlorine,  because  6Fe. 
0.,  acted  on  by  3C1.,  produce  Fe2Cl3  and  2Fe203.  The  direct  decom- 
position of  water  by  chlorine  I  consider  to  occur  very  seldom. 

The  combinations  of  chlorine  form,  perhaps,  next  to  those  of  ox- 
ygen, the  most  complete  series  which  exists  in  chemistry.  Its  af- 
fiirities  are  so  varied  that  it  unites  with  almost  all  the  simple  bodies, 
metallic  and  non-metallic,  and  in  most  cases  it  forms  more  than  one 
compound  with  the  other  body.  Its  metallic  compounds  are  gener- 
ally constituted  like  the  oxides  of  the  same  metals,  but  in  its  union 
with  the  non-metallic  bodies  it  does  not  appear  to  follow  so  closely 
the  analogies  of  oxygen. 

Chlorine  possesses  also  the  property  of  combining  with  metallic 
oxides,  apparently  without  decomposition  in  many  cases,  and  form- 
ing compounds  resembling  peroxides,  in  which  a  portion  of  the  ox- 
ygen is  replaced  by  chlorine.  Thus,  w4th  lime  it  forms  Ca.O. .  CI., 
with  protoxide  of  lead  Pb.O.  .  CI.,  withbarytes  Ba.O. .  CI.,  which  cor- 
respond probably  to  Pb.Oa  and  Ba.Oa.  In  the  hydrate  of  chlorine, 
which  is  Cl.  +  IOH.O.,  it  is  likely  that  a  compound  corresponding  to 
peroxide  of  hydrogen  may  exist,  and  that  the  constitution  of  the 
crystals  may  be  H.O.  .  Cl.  +  QH.O.,  and  that  bleaching  compounds  in 
general  may  have  that  type. 

Chlorine  is  easily  recognised,  when  free,  by  its  peculiar  odour,  by 
its  bleaching  powers,  and  by  producing  with  a  solution  of  nitrate  of 
silver  a  white  curdy  precipitate,  which  is  insoluble  in  acids,  soluble 
inwater  of  ammonia,  and  is  rapidly  blackened  by  exposure  to  the  sun's 
rays.  When  in  combination  with  a  metal,  its  solution  gives  the 
same  kind  of  precipitate  of  chloride  of  silver,  but  the  bleaching  prop- 
erties and  smell  are  absent. 


304  HYPOCHLOROUS     ACI  D. C  ULORIC    ACID. 

Compounds  of  Chlorine  with  Oxygen. 
These  are  four,  constituted  as  follows  : 

Hypochlorous  acid    ....     =C1.4-  0.r:r35-4-|-8  =434 

Chlorous  acid =Cl.-|-40.=35  4-|-32=67-4 

Chloric  acid =C1.4-50.=35  4-1-40=75  4 

Percliloric  acid    .....     =Cl.-j-70.=354-j-56=91-4 

Hypochlorous  Acid. 

If  red  oxide  of  mercury,  diffused  through  a  small  quantity  of  wa- 
ter, be  introduced  into  bottles  containing  chlorine,  and  the  whole 
be  agitated,  the  gas  is  rapidly  absorbed,  and,  combining  with  both 
constituents  of  the  oxide,  forms  chloride  of  mercury  and  hypochlo- 
rous acid.  Thus  Hg.O.  and  2C1.  give  Hg.Cl.  and  Cl.O.  As  there  is 
always  an  excess  of  oxide  of  mercury  employed,  the  chloride  of 
mercury  combines  with  it,  forming  the  insoluble  brown  oxychloride 
of  mercury  Hg.Cl.  4- 3Hg.O.,  which  separates,  and  the  hypochlorous 
acid  remains  nearly  pure  in  solution  in  the  water.  By  a  very  mod- 
erate heat  it  may  be  distilled  in  a  dilute  form,  and  so  obtained  quite 
pure  from  sublimate,  but  at  212^  the  acid  is  rapidly  decomposed 
into  chlorine  and  oxygen. 

A  solution  of  hypochlorous  acid  is  yellow  ;  its  odour  is  like  that 
of  chlorine ;  it  bleaches  powerfully  j  it  decomposes  spontaneously 
even  in  the  cold,  forming  chlorine  and  chloric  acid  ;  it  oxidizes  most 
bodies  with  extreme  energy.  To  obtain  it  in  the  gaseous  form,  it 
is  sufficient  to  introduce  a  small  quantity  of  the  solution  into  a  tube 
over  mercury,  and  to  add  pieces  of  dry  nitrate  of  lime  ;  the  water  is 
absorbed  by  this  deliquescent  salt,  and  the  acid  remains  as  a  green- 
ish yellow  gas,  very  similar  to  chlorine  in  all  respects  ;  water  ab- 
sorbs 100  volumes  of  it  j  by  raising  its  temperature  even  slightly,  it 
explodes,  and  its  volume  is  increased  by  one  half:  100  volumes  of 
it  produce  100  of  chlorine  and  fifty  of  oxygen.  Its  specific  gravity 
is  by  theory  3021*3,  and  its  equivalent  numbers  542-6  or  43.4:  its 
formula  is  Cl.O. 

The  hypochlorous  acid  combines  with  bases  to  form  salts,  hypo- 
chlorites, which  possess  the  bleaching  properties  of  the  acid  in  a 
great  degree  ;  but  their  nature  is  involved  so  much  in  the  general 
history  of  the  bleaching  compounds  of  chlorine,  that  I  shall  not  enter 
upon  any  notice  of  them  here. 

Chloric  Acid. 
When  chlorine  is  brought  into  contact  Avith  an  alkaline  solution, 
it  is  absorbed  with  great  avidity,  and  the  liquor  acquires  powerful 
bleaching  properties.  Concerning  the  nature  of  the  reaction,  the 
opinions  of  chemists  are  not  completely  settled  j  it  may  be  sup- 
posed, on  the  one  hand,  that  the  chlorine  unites  directly  with  the 
alkali,  forming  simply,  if  potash  be  employed,  chloride  of  potassa, 
K.O.  .  CI.  But,  on  the  other  hand,  it  is  possible  that  a  quantity  of 
alkali  may  be  decomposed,  as  certainly  occurs  with  oxide  of  mer- 
cury, and  that  chloride  of  potassium  and  hypochlorite  of  potash  may 
coexist  in  the  liquor;  thus,  that  2K.0.  and  2C1.  should  produce  K. 
CI.  and  Cl.O.-j-K.O.  The  majority  of  chemists  incJine  to  the  latter 
view,  but  the  subject  will  hereafter  receive  detailed  consideration. 


CHLORIC     ACID. CHLOROUS     ACID.  305 

In  any  case,  this  bleaching  alkaline  liquor  is  completely  decomposed 
by  boiling,  particularly  if  it  be  very  concentrated.  Oxygen  is  then 
evolved  in  considerable  quantity,  while  chloride  of  potassium  and 
chlorate  of  potash  are  produced:  thus  9(K.0.-}-C1.0)  evolve  120., 
and  form  8K.C1.  and  K.O.-f-Cl.O^.  It  is  in  this  way  that  the  chlorate 
of  potash  of  commerce  is  obtained,  and  from  it  the  chemist  prepares 
chloric  acid. 

A  solution  of  this  acid  is  readily  prepared  by  decomposing  a  so 
lution  of  chlorate  of  barytes  by  sulphuric  acid.  It  cannot  be  obtained 
solid,  as,  when  a  concentrated  solution  of  it  is  heated,  it  is  resolved 
into  chlorine,  oxygen,  and  perchloric  acid.  It  does  not  bleach ;  it  does 
not  precipitate  a  solution  of  nitrate  of  silver :  when  in  its  strongest 
form,  of  a  thick,  oily  consistence,  it  sets  fire  to  many  organic  bodies, 
and  is  a  powerful  oxidizing  agent. 

The  compounds  of  chloric  acid  are  easily  recognised,  by  yielding, 
when  heated,  oxygen  and  a  metallic  chloride  ;  thus  the  chlorate  of 
potash  is  used  in  the  preparation  of  oxygen  (p.  244),  CI.O5+K.O. 
giving  Cl.K.  and  60.  When  mixed  with  sulphur  and  rubbed  in  a 
warm  mortar,  they  explode,  and  if  thrown  upon  an  ignited  coal,  they 
deflagrate  with  violence. 

The  chlorate  of  potash  is  of  very  great  commercial  importance, 
from  its  utility  in  making  matches,  and  is  the  source  from  whence 
the  chemist  obtains  the  remaining  compounds  of  chlorine  and  ox- 
ygen. 

The  constitution  and  equivalent  numbers  of  chloric  acid  are  as 
follows :  by  weight. 

Chlorine,  46-95         One  equivalent,   =442'6  or  35-4 

Oxygen,    53-05         Five  equivalents,  =500-0  or  40-0 

iWoO  942-6       75^ 

its  formula  is  CI.O5,  and,  like  the  nitric  acid,  which  it  resembles  m 
so  many  other  properties,  it  consists  of  five  volumes  of  oxygen  uni- 
ted to  two  of  the  other  element. 

Chlorous  Acid. — When  chlorate  of  potash  in  fine  powder  is  decom- 
posed by  moderately  strong  sulphuric  acid,  the  chloric  acid,  at  the 
moment  of  being  set  free,  breaks  up  into  two  other  compounds,  one 
containing  more,  and  the  other  less  oxygen,  the  former  being  the 
chlorous,  and  the  latter  the  perchloric  acid,  3CI.O5  giving  2(C1. 
Oj)  and  CI.O7.  This  process  must  be  conducted  very  cautiously,  and 
the  retort  warmed  very  gently  in  a  water  bath.  The  chlorous  acid 
may  be  collected  over  mercury,  or,  from  its  great  density,  like  chlo- 
rine, in  a  dry  jar  ;  there  remains  in  the  retort  a  mixture  of  bisul- 
phate  and  of  perchlorate  of  potash. 

This  acid  gas  is  of  a  rich  yellowish-green  colour,  and  an  aromatic 
odour  ;  it  is  rapidly  absorbed  by  water  ;  it  bleaches  strongly,  and  is 
u  powerful  oxidizing  agent,  its  elements  separating  from  the  slightest 
causes.  If  it  be  heated  above  212^,  it  explodes  with  a  flash  of  light ; 
phosphorus  immersed  in  it  takes  fire  spontaneously,  and  burns  brill- 
iantly in  the  mixture  of  chlorine  and  oxygen  which  results  from  its 
decomposition.  This  may  be  very  well  shown  by  placing  some 
crystals  of  chlorate  of  potash  and  some  phosphorus  together,  at 

Qq 


306  PERCHLORICACID. 

the  bottom  of  a  tall  glass  filled  with  water,  and  conducting  to  the 
mixture,  by  means  of  a  long  glass  funnel,  some  oil  of  vitriol ;  the 
phosphorus  burns  in  each  bubble  of  chlorous  acid  gas  which  forms, 
and  a  brilliant  combustion  under  water  results. 

When  this  gas  is  decomposed,  100  volumes  produce  150,  of  which 
50  are  chlorine  and  100  oxygen ;  its  specific  gravity  may  therefore 
be  calculated  to  be  2337-5. 

The  chlorous  acid  combines  with  bases  to  form  salts,  chlorites, 
which  possess  bleaching  properties,  but  are  not  of  much  importance, 
as  they  do  not  enter  into  practical  use. 

Perchloric  Acid. — This  acid  is  formed  in  the  process  for  obtaining 
chlorous  acid,  as  already  described,  and  is  obtained  by  washing  the 
saline  residue  with  cold  water.  The  bisulphate  of  potash  readily 
dissolves,  leaving  behind  the  perchlorate  of  potash,  which  is  but 
sparingly  soluble  therein ;  this  may  then  be  dissolved  in  boiling 
water,  from  which  it  crystallizes  as  the  solution  cools.  When  the 
object  is  only  the  preparation  of  perchloric  acid,  and  not  of  chlorous 
acid,  the  process  becomes  easier  by  heating  chlorate  of  potash  with 
dilute  nitric  acid  ;  the  elements  of  the  chlorous  acid  are  then  sep- 
arated, merely  mixed  together,  and  the  explosions  and  sputtering 
which  occur  with  sulphuric  acid  are  avoided. 

In  the  process  of  obtaining  oxygen  from  chlorate  of  potash,  there 
occurs  a  period  at  which  it  is  necessary  to  elevate  the  temperature 
very  much  in  order  to  keep  up  the  evolution  of  gas  j  this  arises 
from  the  salt  being  at  first  decomposed  into  oxygen,  chloride  of 
potassium,  and  perchlorate  of  potash,  3(K.O.C1.05)  giving  2(C1.K.) 
and  K.O.CI.O7,  while  80.  are  evolved  as  gas.  This  is  exactly  half 
of  the  oxygen  which  the  salt  contains.  If  the  saline  mass  then  re- 
maining be  washed  with  a  small  quantity  of  water,  the  chloride  of 
potassium  dissolves,  and  the  perchlorate  of  potash  remains  behind. 

Perchloric  acid  may  be  prepared  from  this  potash  salt  by  mixing 
it  in  a  retort  with  half  its  weight  of  oil  of  vitriol,  and  as  much  wa- 
ter, and  distilling  ;  the  acid  passes  over  Avith  the  water.  If  it  be 
distilled  with  an  excess  of  oil  of  vitriol,  it  may  be  obtained  free  from 
water,  and  is  then  a  white  crystalline  mass,  very  deliquescent,  and 
evolving  great  heat  when  mixed  with  water.  In  this  process,  how- 
ever, a  great  part  of  the  acid  is  decomposed. 

The  perchloric  acid  is  the  most  stable  compound  of  chlorine  and 
oxygen.  It  is  not  decomposed  by  muriatic  acid,  by  which  the  chlo- 
ric acid  is  immediately  decomposed,  a  mixture  of  chlorous  acid  and 
chlorine  being  evolved  ;  CI.O5  and  Cl.H.  giving  H.O.  and  a  mixture 
of  CI.O4  with  CI.,  which  was  described  by  Sir  Humphrey  Davy  as  a 
peculiar  gas,  Euchlorine.  By  this  means  the  salts  of  perchloric  and 
of  chloric  acid  may  be  distinguished.  It  is  not  decomposed  by  al- 
cohol, nor  has  it  any  spontaneous  action  on  organic  bodies.  It  is 
well  characterized  by  the  very  sparing  solubility  of  its  potash  salt 
whence  it  has  been  employed  as  a  reagent  to  detect  that  alkali. 

The  constitution  and  equivalent  numbers  of  perchloric  acid  are  as 
follows : 

Chlorine,  38-74         One  equivalent,       =442-6  or  35-4 

Oxygen,    61-26         Seven  equivalents,  =700-0  or  56-0 

100-00  ll4¥6       9F4 


CHLORIDE     OF     HYDROGEN.  307 

Compound  of  Chlorine  and  Hydrogen. 

This  compound  exists  naturally  as  a  gas,  of  which  a  solution  m 
water  has  been  known  since  a  very  early  period  in  chemistry  under 
the  names  of  spirit  of  salt,  marine  acid,  muriatic  acid,  hydrochloric 
acid,  and,  more  properly,  chloride  of  hydrogen.  In  speaking  of  it 
under  ordinary  circumstances,  I  shall  use  the  common  names  of  li- 
quid or  gaseous  muriatic  acid,  according  as  it  is  free  or  combined 
with  water  ;  but  in  cases  where  its  functions  in  combination  are  dis- 
cussed, I  shall  term  it  chloride  of  hydrogen. 

To  prepare  the  gaseous  muriatic  acid,  a  sigfiall  quantity  of  the  com 
mercial  spirit  of  salt  may  be  placed  in  a  flask  or  retort  connected 
with  the  mercurial  pneumatic  trough,  and  the  gas,  which  passes  off 
on  the  application  of  heat,  collected.  It  may  also  be  prepared  by 
the  action  of  oil  of  vitriol  on  common  salt ;  water  being  decomposed, 
its  oxygen  unites  with  the  sodium,  forming  soda,  which  combines 
with  the  sulphuric  acid,  while  its  hydrogen,  uniting  with  the  chlo 
rine,  produces  the  chloride  of  hydrogen,  which  is  given  off  as  a  gas ; 
the  reaction  may  be  thus  expressed:  S.O3H.O.  and  Na.Cl.  give  S. 
OaNa.O.  and  H.Cl. 

This  gas  may  also  be  formed  by  putting  together  chlorine  and  hy- 
drogen in  equal  volumes.  Even  in  diffuse  light  they  combine 
completely  in  some  hours,  but  in  the  direct  sunshine  the  union 
is  instant  and  explosive.  The  mixture  may  also  be  fired  by  the  ta- 
per or  by  the  electric  spark ,  the  colour  of  the  chlorine  disappears, 
and  the  resulting  muriatic  acid  gas  occupies  the  same  volume  as 
its  ingredients.  In  almost  all  cases  of  the  action  of  chlorine  on  or- 
ganic matters,  this  substance  is  also  formed  j  indeed,  the  agency  of 
chlorine  in  bleaching,  and  in  decomposing  organic  compounds,  ap- 
pears generally  to  result  from  its  disposition  to  unite  with  hydro- 
gen. 

The  chloride  of  hydrogen  is  a  colourless  and  invisible  gas.  "When 
completely  dry  it  has  no  action  on  vegetable  colours,  but  if  a  trace 
of  moisture  be  present  it  reddens  litmus  paper,  and  restores  the 
colour  of  turmeric  paper  that  has  been  browned  by  an  alkali  5  hence 
it  is  generally  looked  upon  as  a  powerful  acid.  When  mixed  with 
damp  air  it  forms  heavy  white  fumes  by  uniting  with  the  wa- 
tery vapour,  and  condensing  in  minute  drops  of  liquid  acid.  It  may 
be  liquefied  by  great  pressure.  It  cannot  be  breathed,  but  does  not 
produce  anything  like  the  suffocating  effects  of  chlorine. 

When  muriatic  acid  gas  is  put  in  contact  with  a  metallic  oxide, 
both  are  decomposed,  a  metallic  chloride  and  water  being  produced  5 
thus  Cu.O.  and  H.Cl.  give  Cu.Cl.  and  H.O.  If  any  of  the  more  oxi- 
dable  metals,  as  iron,  zinc,  or  potassium,  be  heated  in  a  current  of 
the  gas,  it  is  decomposed,  a  metallic  chloride  being  formed  and  hy- 
drogen gas  evolved.  This  occurs,  also,  when  these  metals  are  im- 
mersed in  the  liquid  acid  ;  a  copious  effervescence  is  produced  by 
the  escape  of  hydrogen,  and  the  water  holds  a  chloride  of  the  metal 
in  solution.  In  this  way  muriatic  acid  may  be  proved  to  consist  of 
equal  volumes  of  hydrogen  and  chlorine  united  without  condensa 
tion.     Its  specific  gravity  is,  by  theory, 


308 


PREPARATION  AND  PROPERTIES  OP 


One  volume  of  chlorine =2470  0 

One  volume  of  hydrogen =    68-8 

give  two  volumes  of  muriatic  acid   ....    =2538  8 
of  which  one  weighs,  therefore 12694 

Its  constitution  and  equivalent  numbers  are  therefore, 

Chlorine,     97-26       One  equivalent,     =442-6  or  35-4 

Hydrogen,    2*74        One  equivalent,     =   12-5  or     1-0 

100^ 


455-1 


36-4 


This  gas  is  distinguished  by  its  great  affinity  for  water.  If  a  jar 
of  it  be  opened  under  water,  this  fluid  rushes  in,  as  if  it  were  into  a 
vacuum.  If  a  fragment  of  ice  be  introduced  into  a  bell  glass  of  the 
gas,  over  mercury,  the  ice  instantly  melts,  and  the  mercury  rises 
in  the  tube,  the  gas  being  totally  absorbed.  The  solution  of  the 
gas  in  water  is  one  of  the  most  valuable  agents  in  chemical  re- 
search. 

To  prepare  liquid  muriatic  acid  in  the  laboratory,  chloride  of  sodium  is  to  be  in- 
troduced into  a  glass  globe,  placed  in  a  sand-bath  on  the  furnace,  and  then  an  equal 
weight  of  sulphuric  acid  and  water,  mixed  together,  are  to  be  introduced  by  the  fun- 
nel :  the  decomposition  proceeds  as  already  explained,  and  the  gas  evolved  passes 


»y  the  tube  into  the  first  of  a  range  of  three-necked  bottles,  as  in  the  figure.  Eact 
bottle  is  about  half  full  of  water.  When  that  in  the  first  has  become  completely  sat- 
urated with  the  gas,  this  passes  into  the  second,  and  when  it  has  been  saturated, 
into  the  third.  The  vertical  tube  in  the  central  neck  of  each  bottle  is  a  safety-tube, 
the  action  of  which  is  as  follows.  If  a  sudden  condensation  occurred  in  the  first 
bottle,  the  acid  in  the  second  might,  by  the  greater  pressure  on  its  surface,  be 
forced  back  into  it ;  but,  before  it  can  rise  so  high  as  to  pass  through  the  connecting 
tube,  the  external  air  enters  by  the  safety-tube,  being  driven  in  by  the  difference  of 
pressure  inside  and  outside,  and  thus  restores  the  equilibrium.  Pure  muriatic  acid 
may  be  much  more  conveniently  prepared  for  laboratory  use  by  rectifying  the  spir- 
its of  salt  of  commerce.  When  this  is  placed  in  a  distilling  apparatus,  arranged  as 
that  figured  in  p.  278,  and  about  one  fourth  as  much  water  is  introduced  into  the 
receiver  to  condense  the  quantity  of  gas  which  is  first  expelled,  the  distillation  may 
be  carried  on  until  the  retort  is  nearly  empty,  and  an  acid  so  obtained  completely 
pure,  and  of  a  very  convenient  strength  for  the  general  range  of  applications. 

The  manufacture  of  this  acid  is  carried  on  on  a  very  large  scale  more  generally 
with  a  view  to  the  extraction  of  the  alkali  from  the  residual  sulphate  of  soda  than  foi 
the  sake  of  the  muriatic  acid,  the  great  difficulty  in  a  soda  factory  being  how  to  get  rid 
of  tlic  muriatic  acid  which  is  produced.     When  the  object  is.  however,  to  prepare  the 


MURIATICACID.  309 

liquid  acid,  precisely  the  same  apparatus  is  employed  as  for  the  manufacture  of  nitric 
acid,  which  has  been  already  figured  and  described  (p.  278),  the  cylinders  being 
somewhat  larger,  as  from  four  to  five  cwts.  of  common  salt  are  generally  decom- 
posed in  each  cylinder  at  a  charge ;  the  upper  part  of  the  cylinder  is  generally,  both 
in  this  operation  and  in  the  making  of  nitric  acid,  protected  from  the  too  corrosive 
action  of  the  acid  vapours  by  being  lined  internally  with  thin  fire-tiles,  and  the 
heads  e  e  in  the  figure  are  very  fi-equently  constructed,  not  of  metal,  but  of  free- 
stone or  of  granite.  In  the  decomposition  of  the  salt  upon  this  large  scale,  the  oil 
of  vitriol  is  employed  of  the  strength  to  which  it  is  brought  in  the  chambers,  without 
concentration,  and  in  such  quantity  that  for  each  equivalent  of  chloride  of  sodium 
an  equivalent  of  real  sulphuric  acid  is  employed.  The  strongest  liquid  muriatic 
aci^,  thus  prepared,  possesses  a  specific  gravity  of  1-211.  In  order  to  obtain  water 
fully  saturated  with  the  gas,  it  must  be  kept  near  the  freezing  point  by  artificial 
cold ;  it  then  absorbs  480  times  its  volume,  and  increases  in  bulk  by  about  one  fifth. 
Its  constitution  is  quite  definite,  for  in  this  state  it  consists  of  H.C1.-J-6H.0.,  or  in 
numbers, 

Muriatic  acid    .  40  27        One  equivalent    .  =4551  or  364 

Water      .     .     .  59  73         Six  equivalents    .  =6750  or  54  0 

10000  11301       904 

When  this  concentrated  acid  is  heated,  it  evolves  a  large  quantity  of  gas,  and 
the  boiUng  point  gradually  rises  to  230°,  at  which  temperature  the  residual  acid 
distils  over  unchanged ;  it  then  has  a  specific  gravity  of  1.094,  and  consists  of 
H.C1.-J-16H.0.,  or  in  numbers, 

Muriatic  acid    .  2013        One  equivalent      .    .     .  =  4551  or    36-4 

Water     .     .    .  79  87        Sixteen  equivalents   .     .  =18000 or  144.0 

100  00  22551       180l 

Graham  has  found  that  the  strong  acid,  when  evaporated  in  the  open  air,  aban- 
dons a  quantity  of  gas,  while  the  remaining  liquid  becomes  H.Cl.-|-12H.O. 

The  metallic  character  of  hydrogen,  and  the  analogy  of  its  combinations  with 
those  of  zinc,  are  completely  shown  by  comparing  the  formulae  of  the  compounds 
of  oxide  and  chloride  of  hydrogen  with  the  compounds  of  oxide  and  chloride  of  zinc, 
and  their  combinations  with  water.  Thus  I  have  shown  that  the  hydrates  of  oxy- 
chloride  of  zinc  are  as  follows : 

Zn.Cl.-|-6Zn.O. 
Zn.Cl.-f6Zn.0.4-  6Aq. 
Zn.Cl.-l-6Zn.O.4-10Aq. 

and  the  definite  states  of  liquid  muriatic  acid  are 

H.Cl.-f6H.O. 
H.Cl.-f  6H.0.-f  6Aq. 
H.Cl.-i-6H.O.-|-10Aq. 

As  we  proceed,  other  similar  proofs  of  the  electro-positive  and  metallic  character 
of  hydrogen  will  be  found. 

The  other  degrees  of  strength  of  the  liquid  muriatic  acid  are  solutions  in  water 
of  one  or  other  of  these  definite  compounds  ;  a  table  of  them  will  be  found  in  the 
appendix. 

The  muriatic  acid  of  commerce  frequently  contains  sulphuric  acid, 
find  always  a  trace  of  iron,  derived  from  the  metal  cylinders  in 
which  it  is  fabricated.  Occasionally,  sulphurous  acid  is  formed  in 
it  in  small  quantity.  These  impurities  are  detected  thus  :  by  dilu- 
ting the  muriatic  acid  with  water,  and  adding  nitrate  of  barytes,  a 
white  precipitate  is  formed  if  sulphuric  acid  be  present ;  yellow 
ferroprussiate  of  potash  indicates  the  existence  of  iron  ;  while  solu- 
tion of  protochloride  of  tin  produces  a  brown  precipitate  of  sulphuret 
of  tin  if  sulphurous  acid  had  been  present. 

Muriatic  acid  is  easily  recognised,  as  a  gas,  by  its  action  on  moist 
litmus  paper,  its  fuming  in  the  air,  its  forming  with  ammonia  dense 


310 


NITRO-MURIATIC     ACID. 


white  clouds  of  sal  ammoniac,  and  in  solution,  by  giving  with  nitrate 
of  silver  a  curdy  white  precipitate,  which  blackens  on  exposure  to 
light,  is  totally  insoluble  in  nitric  acid,  but  dissolves  easily  in  water 
of  ammonia. 

Mitromuriatic  Acid.  Aqua  Hegia. — When  nitric  and  muriatic 
acids,  both  colourless,  are  mixed  together,  the  mixture  becomes 
deep  yellow,  and  exhales  a  strong  smell  of  chlorine  and  of  nitrous 
acid,  H.Cl.  and  N.O5  giving  CI.  and  N.O4,  with  formation  of  H.O. 
This  decomposition,  however,  proceeds  only  so  far  as  to  saturate 
the  liquid  with  chlorine  \  but  if  a  metal  be  placed  in  the  liquid  it 
unites  with  the  chlorine,  and  new  quantities  of  the  acid  are  decom- 
posed. Thus  the  nitromuriatic  acid  is  a  source  of  chlorine  in  a 
very  concentrated  state,  and  is  hence  employed  to  dissolve  gold 
and  platina,  which  are  not  soluble  in  nitric  acid,  and  to  oxidize  some 
bodies  (metallic  sulphurets)  which  resist  the  action  of  nitric  acid. 
The  name  aqua  regia  was  given  to  it  from  its  power  of  dissolving 
gold,  the  ancient  rex  metallorum. 

Chloride  of  Sulphur. — In  order  to  obtain  this  body,  a  quantity  of  sulphur  is  placed 
in  a  tubulated  retort,  into  which  a  current  of  chlorine  gas  is  conducted  by  means 

of  the  bent  tube  e,  in  the  figure. 

The  chlorine  and  sulphur  unite  to 
form  a  volatile  reddish  yellow  li- 
quid, which  distils  over,  and  con- 
denses in  the  receiver  /,  which 
must  be  kept  very  cool ;  any  uncon- 
densed  gas  is  conducted  away  by 
the  tube  I.  The  chloride  of  sul- 
phur, thus  obtained,  has  always 
an  excess  of  sulphur  dissolved  in 
it,  from  which  it  may  be  freed  by 
a  second  distillation.  Its  specific 
gravity  is  1  687.  When  exposed  to  the  air  it  gives  off  very  acrid  fumes  ;  it  boils 
at  280°  ;  the  specific  gravity  of  its  vapour  is  4686.  It  consists  of  one  equivalent  of 
chlorine  united  to  two  of  sulphur,  S2CI.,  and  in  contact  with  water,  muriatic  acid, 
sulphur,  and  hyposulphurous  acid  are  formed  by  mutual  decomposition. 

It  is  probable  that  there  is  another  chloride  of  sulphur  consisting  of  one  equiva- 
lent of  each,  S.Cl. 

Chlorides  of  Phosphorus. — Chlorine  unites  with  phosphorus  in  two  proportions, 
forming  a  liquid  protochloride,  P. CI 3,  and  a  solid  perchloride,  P.CI5.  These  may 
be  prepared  in  a  simple  apparatus,  like  that  used  for  chloride  of  sulphur ;  but  as  a 


more  complex  arrangement  is  necessary  for  examining  the  action  of  chlorine  upon 
many  substances  that  will  be  described  hereafter,  I  will  introduce  the  description 


CHLORIDES     OF     PHOSPHORUS. IODINE.         311 

of  it  here.  The  chlorine  is  generated  by  hquid  muriatic  acid  and  peroxide  of  man- 
ganese, in  the  flask  a,  supported  on  a  sand-bath  over  the  lamp  ;  from  it  a  bent  tube 
passes  to  the  receiver  b,  in  which  a  quantity  of  watery  vapour  is  condensed,  and 
serves  to  absorb  any  muriatic  acid  gas  that  might  escape  decomposition.  The  pure 
chlorine  passes  then  through  the  tube  c,  which  is  filled  with  fragments  of  fused 
cliloride  of  calcium,  which,  from  its  great  affinity  for  water,  dries  the  gas  completely. 
In  the  bulb  e  is  contained  the  substance  to  be  acted  on  by  the  chlorine,  and  the 
product  of  the  reaction,  if  volatile,  distils  over  into  the  receiver  k,  in  which  it  conden- 
ses ;  the  excess  of  chlorine  escapes  by  the  tube  I,  and  a  stream  of  water  from  the 
reservoir  i  h  retains  the  receiver  k  at  the  tempeiature  proper  for  condensation. 

The  phosphorus  being  placed  in  the  bulb  e,  takes  fire  on  the  arrival  of  the  chlorine 
gas,  and  continues  burning  until  it  is  all  converted  into  the  liquid  chloride  which 
collects  in  k.  While  there  is  an  excess  of  phosphorus,  the  protochloride  is  princi- 
pally formed ;  but  after  all  the  phosphorus  has  been  consumed,  if  the  current  of 
chlorine  be  continued,  it  is  absorbed  by  the  liquid  in  k,  which  changes  into  the  solid 
perchloride. 

The  Protochloride  of  Phosphorus  is  obtained  pure  by  stopping  the  process  before 
all  the  phosphorus  has  been  consumed,  and  rectifying  the  colourless  liquid  by  dis- 
tilling it  in  a  retort  containing  some  bits  of  phosphorus,  which  bring  back  any  per- 
chloride it  might  contain  dissolved,  to  the  state  of  protochloride.  This  body  is 
heavier  than  water,  by  which  it  is  completely  decomposed,  P.CI3  and  3H.0.  giving 
P.O3  and  3H.C1.  It  is  thus  that  the  liquid  phosphorous  acid  is  obtained,  as  de- 
scribed in  p.  297. 

The  Perchloride  of  Phosphorus  is  a  white  solid,  volatile  under  212°,  and  conden- 
sing in  a  crystalline  form.  In  contact  with  water,  it  is  decomposed  with  the  evo- 
lution of  great  heat,  producing  phosphoric  acid  and  muriatic  acid,  P.CI5  and  5H.0. 
giving  P.O5  and  5H.0. ;  the  sp.  gr.  of  its  vapour  is  4788,  consisting  of  ten  volumes 
of  chlorine  and  one  of  vapour  of  phosphorus,  the  eleven  being  condensed  to  six. 

There  is  a  Chloride  of  Selenium  analogous  in  general  properties  to  the  chloride 
of  sulphur. 

Iodine. 

Iodine  is  found  principally  in  sea- water,  associated  'wjth  chlorine, 
combined  with  sodium  and  magnesium.  It  has  been  also  discover- 
ed in  the  mineral  kingdom,  united  with  silver.  For  the  purposes  of 
commerce  it  is  always  extracted  from  kelp^  which  is  a  semifused 
mass  of  saline  ashes  remaining  after  the  burning  of  various  species 
of  fiici  (sea-weed). 

For  this  purpose,  the  powdered  kelp  is  lixiviated  in  water,  to 
which  it  yields  about  half  its  weight  of  salts.  The  solution  is  evap- 
orated down  in  an  open  pan,  and  Avhen  concentrated  to  a  certain 
point,  begins  to  deposite  its  soda-salts,  namely,  common  salt,  car- 
bonate and  sulphate  of  soda,  which  are  removed  from  the  boiling 
liquid  by  means  of  a  shovel  pierced  with  holes  like  a  colander. 
The  liquid  is  afterward  run  into  a  shallow  pan  to  cool,  in  which 
It  deposites  a  crop  of  crystals  of  chloride  of  potassium  j  the  same 
operations  are  repeated  on  the  mother-ley  of  these  crystals  until  it 
is  exhausted.  A  dense,  dark-coloured  liquid  remains,  which  con- 
tains the  iodine,  in  the  form,  it  is  believed,  of  iodide  of  sodium,  but 
mixed  with  a  large  quantity  of  other  salts,  and  this  is  called  the 
iodine  ley. 

To  this  ley,  sulphuric  acid  is  gradually  added  in  such  quantity 
as  to  leave  the  liquid  very  sour,  which  causes  an  evolution  of  car- 
bonic acid,  sulphuretted  hydrogen,  and  sulphurous  acid  gases,  with 
a  considerable  deposition  of  sulphur.  After  standing  for  a  day  or 
two,  the  ley  so  prepared  is  heated  with  peroxide  of  manganese,  to 
separate  the  iodine.    This  operation  is  conducted  in  a  leaden  retort, 


;u2 


PREPARATION    OF     IODINE. 


fl,  of  a  cylindrical  form, 
supported  in  a  sand-bath, 
which  is  heated  by  a 
small  fire  below.  The 
retort  has  a  large  open 
ing,  to  which  a  capital, 
b^  c,  resembling  the  head 
of  an  alembic,  is  adapt- 
ed, and  luted  with  pipe- 
clay. In  the  capital  it- 
self there  are  two  open- 
ings, a  larger  and  a  small- 
er, at  b  and  c,  closed  by 
leaden  stoppers.  A  se- 
ries of  bottles,  J,  having 
each  two  openings,  con- 
nected together,  as  rep- 
resented in  the  figure, 
and  with  their  joinings  luted,  are  used  as  condensers.  The  prepa- 
red ley  being  heated  to  about  140°  in  the  retort,  the  manganese  is 
then  introduced,  and  b  c  luted  to  a.  Iodine  immediately  begins  to 
come  off,  and  proceeds  on  to  the  condensers,  in  which  it  is  collect- 
ed ',  the  progress  of  its  evolution  is  watched  by  occasionally  re- 
moving the  stopper  at  c  ;  and  additions  of  sulphuric  acid  or  man- 
ganese are  made  by  ^,  if  deemed  necessary.  This  description  of 
the  manufacture  of  iodine  iipon  the  large  scale  at  Glasgow  is  due 
to  Professor  Graham. 

In  this  operation,  the  peroxidvs  i)f  manganese  will  be  in  contact 
at  once  with  hydriodic,  hydrochloric,  and  sulphuric  acids ;  but  for 
success,  the  quantity  of  sulphuric  acid  must  be  sufficient  only  to  de- 
compose the  iodides,  but  not  the  chlorides.  If  both  were  decom- 
posed, the  chlorine  and  iodine  simultaneously  evolved  would  unite 
to  form  chloride  of  iodine,  by  which  the  iodine  would  be  lost  j  but 
as  the  chlorine  remains  combined,  the  action  becomes  simply,  that 
the  metal  of  the  iodide  present  is  oxidized  by  the  oxide  of  manga- 
nese, and  the  iodine  set  free  ;  thus,  with  iodide  of  sodium,  S.O,-f- 
Mn.02  and  Na.I.  give  Mn.O. .  S.O3 .  Na.O.  and  I. 

Another  mode  of  preparing  iodine  consists  in  adding  to  the  solu- 
tion containing  iodide  of  sodium,  a  solution  of  sulphate  of  copper, 
in  which  the  copper  is  reduced  to  the  state  of  sub-oxide  (CU2O.)  bv 
means  of  protosulphate  of  iron  dissolved  along  with  it.  By  the  in- 
terchange of  elements,  sulphate  of  soda  is  formed,  and  a  sub-iodid« 
of  copper  of  a  very  pale  yellow  colour,  and  quite  insolubl<» 
in  water,  is  produced,  S.Og+CuaO.  and  Na.I.  giving  S.Og-h 
Na.O.  and  Cugl.  This  last  is  then  decomposed  by  peroxide 
of  manganese  and  sulphuric  acid,  as  in  the  former  process  -• 
in  this  way  the  various  crystallizations  described  above? 
may  be  avoided. 

Iodine  exists  generally  in  crystalline  sca.es  of  a  bluish 
black  colour  and  metallic  lustre.     It  may  also  be  obtained 
from  solution,  in  the  form  of  oblique  octohedrons  with  a 
rhomboidal  base,  as  in  the  figure,  or  in  prisms.     The  density  of 


PROPERTIES     OF     IODINE. IODIC     ACID.  313 

iodine  is  4948 ;  it  fuses  at  225°,  and  boils  at  347°  j  but  it  evaporates 
at  the  usual  temperature,  and  more  rapidly  when  damp  than  when 
dry,  diffusing  an  odour  having  considerable  resemblance  to  chlorine, 
but  easily  distinguished  from  it.  Iodine  stains  the  skin  of  a  yellow 
colour,  which,  however,  disappears  in  a  few  hours.  Its  vapour  is  of 
a  splendid  violet  colour,  which  is  seen  to  great  advantage  when  a 
scruple  or  two  of  iodine  is  thrown  at  once  upon  a  hot  brick.  Hence 
its  name,  from  loeidTjg,  violet-coloured.  The  vapour  of  iodine  is 
one  of  the  heaviest  of  gaseous  bodies,  its  density  being  8707*7,  ac- 
cording to  calculation  from  its  atomic  weight. 

Pure  water  dissolves  about  l-7000th  of  its  weight  of  iodine,  and 
acquires  a  brown  colour.  In  general,  iodine  comports  itself  like 
chlorine,  but  its  affinities  are  much  less  powerful.  Iodine  is  soluble 
in  alcohol  and  ether,  with  which  it  forms  dark  reddish-brown  liquors ; 
solutions  of  iodides,  too,  all  dissolve  much  iodine. 

A  solution  of  starch  forms  an  insoluble  compound  with  iodine,  of 
a  deep  blue  colour,  the  production  of  which  is  an  exceedingly  deli- 
cate test  of  iodine.  If  the  iodine  be  free,  starch  produces  at  once 
the  blue  precipitate  ;  but  if  it  be  in  combination  as  a  soluble  iodide, 
no  change  takes  place  till  chlorine  is  added  to  liberate  the  iodine. 
If  more  chlorine,  however,  be  added  than  is  necessary  for  that  pur- 
pose, the  iodine  is  withdrawn  from  the  starch,  chloride  of  iodine 
formed,  and  the  blue  compound  destroyed.  The  iodide  of  starch,  in 
water,  becomes  colourless  when  heated,  but  recovers  its  blue  colour 
if  immediately  cooled.  The  soluble  iodides  give,  with  nitrate  of 
silver,  an  insoluble  iodide  of  silver,  of  a  pale  yellow  colour,  insoluble 
in  ammonia;  with  salts  of  lead,  an  iodide  of  a  rich  yellow  colour; 
and  with  corrosive  sublimate,  a  fine  scarlet  iodide  of  mercury. 

Iodine  combines  with  most  of  the  non-metallic  bodies,  and  with 
all  the  metals,  forming  compounds  which  possess  the  closest  sim- 
ilarity to  the  analogous  compounds  of  chlorine.  It  is  employed  in 
the  laboratory  for  many  chemical  preparations,  and  as  a  test  of  starch 
and  for  several  metals. 

Compounds  of  Iodine  and  Oxygen. 

Iodine  appears  to  combine  with  oxygen  in  three  proportions,  form 
ing  the  iodous  acid^  the  iodic  acid,  and  the  periodic  acid.  Of  the  con- 
stitution of  the  first  there  is  nothing  positively  known;  it  has  not 
been  isolated,  and  the  substances  that  have  been  supposed  to  contain 
it  may  also  be  considered  as  compounds  of  an  iodide  with  an  iodate. 
The  description  of  these  compounds  will  be  found  in  the  chapter 
on  the  salts;  and  I  shall,  therefore,  at  present,  only  notice  the  other 
two  acids. 

Iodic  Acid. — This  acid  may  be  very  easily  prepared  by  boiling 
iodine  in  fuming  nitric  acid  until  it  is  all  dissolved,  and  then  distil 
ling  off  the  excess  of  acid;  the  iodic  acid  remains  as  a  white  crys 
talline  mass,  which  deliquesces  in  the  air.  If  the  quantity  of  iodine 
be  large,  this  process  would  occupy  a  very  long  time ;  and  a  much 
shorter,  though  more  complex  method  is  the  following  :  The  iodine 
being  diffused  through  water,  a  current  of  chlorine  is  passed  through 
it  until  all  iodine  is  dissolved ;  the  acid  liquor  so  obtained  is  to  be 
neutralized  by  carbonate  of  soda,  by  which  a  quantity  of  iodine  ia 


314     PROPERTIES     OF     IODIC     ACID. PERIODIC     ACID. 

precipitated ;  the  chlorine  is  then  passed  through  until  this  iodine 
disappears,  and  then  more  carbonate  of  soda  added,  and  this  alter- 
nation continued  until  the  addition  of  the  carbonate  of  soda  produces 
no  deposite  of  iodine ;  the  solution  contains  then  iodate  of  soda  and 
chloride  of  sodium,  generated  by  the  decomposition  of  the  soda  by 
the  chloride  of  iodine  first  formed.  Thus  5C1.  and  I.  produce  I.CI5, 
which,  with  6Na.O.,  give  5Na.Cl.  and  Na.O.  -I-I.O5.  This  solution  is 
then  mixed  with  a  solution  of  a  salt  of  barytes,  and  iodate  of  barytes 
precipitates,  which  may  be  decomposed  by  boiling  it  for  some  time 
with  one  fourth  its  weight  of  oil  of  vitriol  and  1^  times  its  weight 
of  water  j  the  sulphate  of  barytes  may  be  then  separated  by  the  fil- 
ter, and  the  solution  of  iodic  acid  evaporated  gently  to  dryness. 

Iodic  acid  is  very  soluble  in  water;  from  a  strong  solution  it  crys 
tallizes  in  rhombic  plates  and  octohedrons.  When  heated  strongly, 
it  separates  into  iodine  and  oxygen.  It  first  reddens,  and  then 
bleaches  litmus  paper.  It  acts  as  powerfully  as  nitric  acid  in  oxi- 
dizing the  metals.  When  mixed  with  solution  of  sulphurous  acid, 
water  and  sulphuric  acid  are  formed,  and  iodine  is  set  free  ;  with 
sulphuretted  hydrogen  it  gives  water  and  iodide  of  sulphur.  By  an 
excess  of  these  agents,  the  iodine  is  finally  converted  into  iodide  of 
hydrogen.  By  these  means  the  iodic  acid  may  be  recognised,  and 
also  by  its  peculiar  action  upon  morphia,  which  it  decomposes,  io- 
dine being  set  free.  This  is  more  valuable  as  a  character  of  mor- 
phia than  of  iodic  acid. 

The  salts  of  iodic  acid  resemble  the  chlorates  in  most  respects, 
and,  like  them,  when  heated,  separate  into  oxygen  and  a  metallic 
iodide.  One  mode  of  preparing  the  iodide  of  potassium  of  com- 
merce is  founded  on  this  property.  Iodine  is  dissolved  in  a  solution 
of  potash,  and,  when  dried  down,  gives  a  mixture  of  5K.I.  and  I.O5 . 
K.O.  When  this  mass  is  fused,  oxygen  is  given  off  in  abundance, 
and  ultimately  pure  K.I.  remains.  The  commercial  salt  prepared  in 
this  way  has  been  shown  by  Mr.  Scanlan  frequently  to  contain  iodate 
of  potash,  either  fradulently  or  accidentally,  left  undecomposed. 

The  composition  and  equivalent  numbers  of  the  iodic  acid  are  as 
follows,  its  formula  being  I.O5 : 

Iodine,      75-96  One  equivalent,     =1579-5  or  126-6 

Oxygen,    24-04  Five  equivalents,  -■  500-0  or    40-0 

100^  ■2079^      166^ 

Its  elements  are  united  in  the  proportion,  by  volume,  of  two  vol- 
umes of  vapour  of  iodine  to  five  volumes  of  oxygen. 

Periodic  Acid,  I.O7. — If  a  solution  of  iodate  of  soda  be  mixed  with  a  great  excess 
of  caustic  soda,  and  acted  upon  by  a  current  of  chlorine,  a  quantity  of  the  soda  is 
decomposed ;  its  sodium  combining  with  the  chlorine,  while  its  oxygen,  being  added 
to  the  iodic  acid,  converts  it  into  the  periodic  acid,  which  combines  with  two  equiv- 
alents of  soda.  Thus,  2C1.  acting  on  3Na.O.  and  I.Os-f-Na.O.,  produce  2Na.Cl.  and 
1.07-f  2Na.O.  On  adding  to  the  solution  of  this  salt  nitrate  of  silver,  a  basic  peri- 
odate  of  silver  is  produced,  which,  being  dissolved  in  nitric  acid,  gives  yellow  crys- 
tals of  neutral  periodate  of  sil\^r  When  put  in  contact  with  water,  these  crystals 
are  decomposed,  half  of  the  periodic  acid  precipitating  with  the  whole  of  the  oxide 
of  silver  as  the  insoluble  salt,  I.07-}-2Ag.O.,  while  the  other  half  of  the  acid  remains 
in  solution  quite  pure,  and  by  evaporation  may  be  obtained  as  a  white  crystallized 
mass. 

This  acid  is  more  stable  than  the  iodic  acid ;  it  resists  a  higher  temperature 


HYDRIODIC     ACID,     ITS     PREPARATION.  ^±0 

without  decomposition.    All  its  important  characters  may  be  inferred  from  the 
method  of  preparation. 
Its  composition  and  equivalent  numbers  are, 

Iodine,      69-31  One  equivalent,       =15795  or  126-6 

Oxygen,  30 -69  Seven  equivalents,  =  700-0  or    56  0 

100  00  "2279^       182^6 

Compound  of  Iodine  and  Hydrogen.     Hydriodic  Acid. 

There  is  but  one  compound  of  iodine  with  hydrogen  :  this  exists 
under  ordinary  temperatures  and  pressure  as  a  colourless  gas,  which 
may  be  best  generated  in  the  following  manner :  Some  iodine  and 
small  fragments  of  phosphorus  are  to  be  put  together  at  the  bottom 
of  a  glass  tube,  then  covered  with  pounded  glass,  and  gently  heated, 
so  as  to  produce  combination.  Iodide  of  phosphorus  is  thus  formed. 
If  a  little  water  be  now  poured  on  the  pounded  ^^^^~a\ 
glass,  it  filters  through  to  the  bottom,  and  there, 
acting  violently  on  the  iodide  of  phosphorus,  is 
decomposed  j  from  P.I.  and  H.O.  there  are  pro- 
duced P.O.  and  H.I.  To  the  mouth  of  the  tube 
may  be  adapted,  by  a  cork,  a  smaller  tube,  bent 
as  in  the  figure,  and  the  hydriodic  acid  gas  issu- 
ing from  it  may  be  collected.  This  gas  is  obtain-  Jn 
ed  by  the  method  of  displacement,  as  has  been 
described  for  chlorine  (p.  302)  ;  and  as  it  fumes 
like  muriatic  acid  in  contact  with  the  air,  it  can 
easily  be  recognised  when  the  bottle  is  full.  ^ 

The  specific  gravity  of  this  gas  is  4385,  produced  by 

One  volume  of  vapour  of  iodine =87010 

One  volume  of  hydrogen =    68  8 

united  without  condensation 8769-8 

and  one  volume  weighing,  therefore 4384  9 

To  obtain  hydriodic  acid  dissolved  in  water,  the  simplest  process 
is  to  act  on  iodine,  diffused  through  water,  by  sulphuretted  hydrogen 
gas.  The  iodine  combines  with  the  hydrogen,  and  the  sulphur  is 
set  free.  When  the  iodine  has  all  disappeared,  the  liquor  should  be 
well  boiled,  to  drive  off  the  excess  of  sulphuretted  hydrogen,  and 
then  filtered  ;  the  liquid  hydriodic  acid  may  be  evaporated  to  a  sp. 
gr.  of  1*700  :  it  is  then  in  its  strongest  form,  and  may  be  distilled 
unaltered.  Liquid  hydriodic  acid  reddens  litmus  paper  strongly ; 
it  dissolves  iodine  in  large  quantity ;  it  is  decomposed  by  all  the 
oxidable  metals,  and  even  by  mercury  ;  and  hence  the  gaseous  acid 
cannot  be  collected  over  mercury.  Exposed  to  the  air,  it  rapidly 
absorbs  oxygen,  water  being  formed,  and  iodine  being  set  free.  It  is 
decomposed  by  sulphuric  acid,  sulphurous  acid  and  iodine  being  pro- 
duced ;  also  by  nitric  acid  and  by  chlorine. 

Hydriodic  acid  may  also  be  obtained  by  acting  on  iodide  of  barium 
with  dilute  sulphuric  acid. 

Its  composition  and  equivalent  numbers  are  as  follows : 

Iodine,        99-22  One  equivalent,  =1579-5  or  126-6 

Hydrogen,    0-78  One  equivalent,  =     12-5  or       1-0 

100-00  Y592^0      l27^ 


316  lODO-PH  O  SPHURE  T     OF     HYDROGEN. 

A  solution  of  hydriodic  acid  or  of  a  metal  produces,  with  nitrate 
of  silver,  a  curdy  pale  yellow  precipitate,  which  is  insoluble  in  acids 
and  in  water  of  ammonia  j  by  this  character  the  iodides  are  distin- 
guished from  the  chlorides,  even  without  the  aotion  of  starch  upon 
the  iodine  when  set  free. 

Iodine  and  sulphur  may  be  melted  together  in  equivalent  proportions,  and,  on 
cooling,  form  a  steel-gray  crystalline  mass,  iodide  of  sulphur,  which  is  decomposed 
gradually  by  exposure  to  the  air,  and  appears  to  be  rather  a  mixture  than  a  true 
compound  of  its  elements. 

When  iodine  and  phosphorus  are  warmed  together  very  gently,  they  combine, 
evolving  considerable  heat,  and  forming  iodides  of  phosphorus,  the  constitution  of 
which  depends  on  the  proportions  used ;  there  appears  to  be  at  least  three :  the 
first  fuses  at  212°,  is  orange  coloured,  and  gives,  when  decomposed  by  water,  hy- 
driodic and  hypophosphorous  acids  ;  its  composition  is  therefore  P.I.  :  the  second  is 
gray ;  it  fuses  at  84°,  and  gives,  with  water,  hydriodic  and  phosphorous  acids ;  its 
formula  is  hence  P.I3.  The  third,  which  produces,  when  decomposed  by  water, 
hydriodic  acid  and  phosphoric  acid,  consists  of  P.I5,  is  black,  and  melts  at  114^. 

Hydriodic  acid  combines  with  phosphuretted  hydrogen,  forming  a  white  sohd 
compound,  the  constitution  of  which  is  of  considerable  interest.  It  cannot  be  pre- 
pared directly,  as  the  gases  are  without  action  on  each  other  except  when  in  their 
nascent  form.  It  is  best  prepared  by  introducing  eight  parts  of  iodine,  two  of  phos- 
phorus, and  one  of  water,  into  a  retort,  mixed  with  some  coarsely-powdered  glass  ; 
to  the  neck  of  the  retort  is  adapted  a  wide  glass  tube  with  a  cork,  through  which  a 
small  tube  passes  and  dips  into  some  water.  On  applying  heat,  the  phosphorus 
and  iodine  unite,  and  the  iodide  of  phosphorus  being  instantly  decomposed  by  the 
water,  hydriodic  acid  and  hypophosphorous  acid  are  produced,  which  last  is  re- 
solved, by  contact  with  the  water  at  that  temperature,  into  phosphorous  acid  and 
phosphuretted  hydrogen.  This  last  immediately  unites  with  the  hydriodic  acid,  and 
the  compound  formed  condenses  in  the  neck  of  the  retort  in  well  shaped  crystals, 
which,  by  a  proper  management  of  the  heat,  may  be  driven  into  the  wide  glass  tube 
to  be  preserved.  The  excess  of  hydriodic  acid  gas  is  conducted  off  by  the  small 
tube,  and  condensed  in  the  water. 

This  body  was  supposed  to  crystallize  in  cubes,  and  to  be  isomorphous  with  hy- 
driodate  of  ammonia,  to  which  this  formula,  in  one  way,  might  assimilate  it, 
H.I.-f-P-Hg  corresponding  to  H.I.-j-N.Hg,  the  difference  being  only  that  phosphorus 
replaced  nitrogen.  It  will,  however,  be  shown  fully,  in  the  division  on  organic 
chemistry,  that  ammonia  is  not  mere  nitruret  of  hydrogen,  N.Hg,  but  that  it  con- 
tains amidogene  (N.H2),  being  amidide  of  hydrogen,  Ad.H.  It  has  been  also  shown 
that  the  crystals  of  the  body  H.I.-j-PHg  are  not  cubes,  but  belong  to  a  rhombic 
system.  When  I  come  to  describe  the  compounds  of  mercury,  I  shall  show  that 
there  exist  similar  bodies  containing  phosphuret  of  mercury  and  nitruret  of  mercury, 
and  that  the  constitution  of  phosphuretted  hydrogen  may,  with  great  reason,  be 
supposed  to  be,  not  P.H3,  but  that  a  quantity  of  phosphorus  equal  to  one  third  of 
its  ordinary  atomic  weight  unites  with  an  equivalent  of  hydrogen,  its  formula  being 
3.H.,  and  the  commonly  received  equivalent  of  phosphuretted  hydrogen  being  in 
reality  three  equivalents,  =3.?.H.  I  therefore  consider  the  compound  which  I  have 
just  described  as  having  for  its  true  constitution  H.I.-[-3-.H.,  as  there  will  be  here- 
after described  the  bodies  Hg.Cl.-|-3.|.,Hg.,  and  2Hg.Cl.-{-3.j.Hg. :  the  equiva- 
lent of  nitrogen  being  capable  of  the  same  subdivision  by  three. 

This  Hydriodate  of  Phosphuretted  Hydrogen  is  decomposed  by  water,  hydriodic 
acid  and  phosphuretted  hydrogen  being  given  off,  the  last  in  the  B  variety.  But  if 
a  little  oxide  of  silver  be  sprinkled  on  the  salt,  the  gas  is  evolved  in  its  spontane- 
ously inflammable  condition.  It  burns  when  heated  in  air,  but,  in  a  dry  tube  con- 
taining no  oxygen,  it  may  be  sublimed  from  place  to  place  unaltered. 

Chlorides  of  Iodine. — I  have  shown  that  chlorine  and  iodine  unite  in  three  pro- 
portions, forming  bodies  having  the  formulae  I.-fCl.,  I.-}-3Cl.,  and  I.-f 5C1.  By 
much  water  the  first  and  second  are  decomposed,  producing  muriatic  and  iodic 
acids,  and  iodine  becoming  free.  The  third,  which  was  long  ago  discovered  by 
Humphrey  Davy,  gives  muriatic  and  iodic  acids  without  separation  of  iodine. 
These  bodies  are  interesting  only  as  being  employed  to  obtain  the  iodic  and  psriodic 
acids,  as  already  noticed. 


PROPERTIES     OF     BROMINE.  317 

Of  Bromine. 

This  substance,  which  is  intermediate  in  almost  all  chemical  prop- 
erties to  chlorine  and  iodine,  exists  associated  with  those  bodies  in 
sea-water,  in  many  varieties  of  sea-weeds,  and  in  some  of  the  brine- 
springs  belonging  to  the  deposites  of  rock-salt  in  the  earth.  In  these 
cases  it  is  generally  combined  with  sodium  or  with  magnesium, 
forming  very  soluble  salts,  which  remain  behind  when  the  common 
salt  crystallizes  out  by  evaporation  from  sea-water.  When  a  cur- 
rent of  chlorine  gas  is  passed  through  the  mother  liquor  so  obtained, 
which  is  called  bittern^  the  bromine  is  set  free,  and  tinges  the  solution 
yellow.  On  agitating  this  liquor  with  some  ether,  the  bromine  is 
completely  taken  up  by  it,  and  an  ethereal  solution  of  bromine,  of  a 
fine  hyacinth-red  colour,  is  produced  ;  when  this  is  acted  on  by  pot- 
ash, there  is  formed  a  mixture  of  bromide  of  potassium  and  bromate 
of  potash,  which  by  fusion  gives  off  oxygen,  and  pure  bromide  of 
potassium  remains ;  this  is  mixed  with  peroxide  of  manganese  and 
sulphuric  acid,  and  precisely  as  in  the  preparation  of  chlorine  or  of 
iodine,  the  bromine  is  set  free  and  may  be  distilled  over.  It  is  ne- 
cessary to  condense  the  bromine  with  great  care,  and  to  receive  it 
in  water,  to  the  bottom  of  which  it  sinks ;  the  reaction  that  occurs 
is  that  2S.O3,  Mn.02,  and  K.Br,  produce  (S.O3 .  Mn.O+K.O. .  S.O3) 
and  Br. 

Bromine  is  a  liquid  at  ordinary  temperatures,  but  at  4°  it  solidi- 
fies ;  it  is  deep  red  by  transmitted,  but  black  by  reflected  light ;  it  is 
much  heavier  than  water,  its  specific  gravity  being  2-97  ]  its  odour 
is  like  that  of  chlorine,  but  much  more  disagreeable,  whence  its 
name  (from  BpWjUOf).  It  is  very  volatile,  boiling  at  116^  ',  but  even 
at  common  temperatures  it  forms  copious  fumes,  which  have  the 
same  orange-red  colour  as  those  of  nitrous  acid ;  the  specific  grav 
ity  of  its  vapour  is  5-393 ;  it  does  not  conduct  electricity ;  it  must 
be  preserved  under  water,  as  otherwise  the  quantity  of  vapour  it 
would  form  might  burst  the  vessel  containing  it.  It  dissolves  spa- 
ringly in  water,  but  copiously  in  alcohol  and  ether.  A  taper  is  ex- 
tinguished by  its  vapour,  but  not  immediately,  burning  for  a  moment 
with  a  green  flame  and  much  smoke.  Some  of  the  metals  in  fine 
powder  or  leaf  burn  spontaneously  in  its  vapour,  as  in  chlorine  5  a 
drop  of  liquid  bromine,  put  in  contact  with  a  globule  of  potassium, 
unites  with  it  explosively  and  with  brilliant  ignition.  It  bleaches 
vegetable  colours,  but  leaves  itself  a  yellowish  stain,  less  intense 
than  that  of  iodine  ;  it  is  poisonous. 

Bromine  unites  with  water,  forming  a  crystalline  hydrate  like  that 
of  chlorine. 

With  starch,  bromine  produces  a  fine  yellow  colour,  which  is  not 
intense  if  the  solution  be  very  much  diluted. 

Bromine  is  easily  recognised  by  the  peculiar  colour  and  odour 
of  its  vapour,  which  can  only  be  confounded  with  that  of  nitrous 
and  hyponitrous  acid,  from  which  its  other  characters  completely 
separate  it.  A  solution  containing  bromine  or  a  metallic  bromide 
gives,  Avith  nitrate  of  silver,  a  white,  curdy  precipitate,  insoluble  in 
nitric  acid,  but  dissolved  by  ammonia.  This  precipitate  is  distin- 
guished from  the  chloride  of  silver  by  giving  vapours  of  bromine 
when  heated  with  a  little  chlorine  water 


318  B  R  O  M  I  C     A  C  I  D. H  YDROBROMIC     ACID. 

The  equivalent  numbers  of  bromine  are  978-2  on  the  oxygen 
scale,  and  78-4,  hydrogen  being  unity. 

Bromic  Acid. — There  is  known  only  one  compound  of  bromine 
and  oxygen,  the  bromic  acid,  the  history  of  which  is  still  very  im- 
perfect. When  bromine  is  dissolved  in  a  solution  of  potash,  bro- 
mide of  potassium  and  bromate  of  potash  are  formed,  6Br.  and 
6K.0.  giving  5K.Br.  and  Br.O^+K.O.  On  adding  a  solution  of  a 
salt  of  barytes  to  the  liquor  so  obtained,  bromate  of  barytes  is  pre- 
cipitated, and  this  may  be  decomposed  by  sulphuric  acid,  which 
forms  sulphate  of  barytes,  leaving  the  bromic  acid  in  solution. 

The  bromic  acid  has  not  been  obtained  solid  j  it  is  still  more 
easily  decomposed  by  deoxidizing  agents  than  the  chloric  acid  \  thus 
the  sulphurous  acid  and  the  phosphorous  acid  liberate  bromine.  The 
same  effect  is  produced  by  sulphuretted  hydrogen.  Its  salts  have 
not  been  much  examined,  but  appear  to  resemble  the  chlorates  and 
iodates. 

Its  formula  is  Br.05,  its  composition  by  weight  and  equivalent 
numbers  being, 

Bromine,  66-18  One  equivalent,    =978-2  or  78-40 

Oxygen,    33-82  Five  equivalents,  ^500-0  or  40-00 

100^0  1478-2     11840 

These  elements  are  united  by  volume  in  the  ratio  of  two  vol- 
umes of  bromine-vapour  to  five  volumes  of  oxygen. 

Hydrobromic  Acid. — The  processes  for  obtaining  the  bromide  of 
hydrogen  are  precisely  the  same  as  those  described  for  preparing 
hydriodic  acid  in  the  liquid  or  in  the  gaseous  form,  to  which  I  shall 
therefore  refer  (p.  315),  bromine  being  substituted  for  iodine  in 
every  case.  This  gas  is  colourless ;  it  is  rapidly  absorbed  by  wa 
ter,  the  solution  reacting  acid  ;  it  is  not  decomposed  by  oxygen, 
nor  does  bromine  decompose  water,  so  that  it  stands  between  iodine 
and  chlorine  in  that  respect.  It  resembles  muriatic  acid  in  almost 
all  its  reactions,  but  is  at  once  distinguished  from  it  by  evolving 
bromine  on  contact  with  chlorine  or  nitric  acid.  If  bromide  of  po- 
tassium be  acted  on  by  oil  of  vitriol,  the  result  is  partly  as  occurs 
with  a  chloride,  water  being  decomposed  and  hydrobromic  acid 
evolved,  and  partly  as  occurs  with  an  iodide,  bromine  and  sulphur- 
ous acid  being  evolved  together  ;  hence  hydrobromic  acid  cannot 
be  prepared  pure  in  that  way. 

The  sp.  gr.  of  hydrobromic  acid  gas  is  2731,  being  produced  by- 
One  volume  of  bromine- vapour  .     .     .  53930 

One  volume  of  hydrogen 68  8 

united  without  condensation      ....  5461  8 
and  hence  one  volume  weighs  ....  2730-9 

The  Bromide  of  Sulphur  is  a  heavy  reddish  liquid,  like  chloride  of  sulphur,  prob- 
ably SaBr. 

There  are  two  Bromides  of  Phosphorus,  one  liquid,  P.Brn,  and  the  other  solid, 
P.Brs,  which  present  complete  analogy  with  the  chlorides  of  phosphorus.  Neither 
of  these  bodies  presents  particular  interest. 

The  bromide  of  hydrogen  unites  with  phosphuretted  hydrogen,  forming  a  com- 
pound similar  to  that  already  noticed,  containing  hydriodic  acid.  It  is  sufficient  to 
mix  the  two  gases  together  over  mercury  ;  a  dense  white  cloud  forms,  which  con- 
denses on  the  sides  of  the  glass  in  small  crystals,  which  appear  to  be  cubes,  but  are 


OF     FLUORINE.  319 

not  so  really.  This  substance  can  also  be  formed  in  the  indirect  manner  described 
for  the  iodine  compound.  It  consists  of  an  equivzdent  of  each  element,  its  for- 
mula being  H.Br.-j-P.Hg,  or,  as  I  prefer  to  write  it,  for  the  reasons  already  stated, 
H.Br.-f3|.H. 

This  body  is  volatile,  and  may  be  sublimed,  provided  neither  oxygen  nor  water 
be  present ;  heated  in  oxygen,  it  takes  fire,  and  with  water  it  is  instantly  decom- 


The  Chloride  of  Bromine  and  the  Bromides  of  Iodine  resemble  in  general  charac 
ters  the  compounds  of  chlorine  and  iodine.  The  first,  when  decomposed  by  water^ 
produces  hydrochloric  and  bromic  acids ;  the  latter,  on  the  contrary,  gives  hydro- 
bromic  and  iodic  acids.    These  bodies  are  not  otherwise  of  interest. 

Of  Fluorine. 

Although  the  existence  of  this  body  is  rendered  exceedingly  prob- 
able by  analogical  reasoning,  and  recent  experiments  have  gone 
very  far  in  establishing  its  distinctive  characters,  yet  it  cannot 
be  prepared  in  an  isolated  form,  or  exhibited  like  all  the  simple 
bodies  as  yet  described ;  for  such  is  the  intensity  and  variety  of  its 
affinities,  that  no  sooner  is  it  liberated  from  combination  with  one 
substance,  than  it  enters  into  union  with  some  other,  attacking  the 
materials  of  which  the  apparatus  used  may  be  constructed.  The 
most  successful  experiments  made  for  examining  it  in  its  isolated 
form  are  due  to  two  talented  Irish  chemists,  the  Messrs.  Knox. 

The  only  substances  on  which  fluorine  is  incapable  of  acting  be- 
ing such  as  already  are  fully  saturated  with  it,  Messrs.  Knox  had 
vessels  constructed  of  fluor  spar  (fluoride  of  calcium),  which  were 
filled  with  pure  dry  chlorine  gas.  Into  these  vessels  was  then  in- 
troduced fluoride  of  mercury,  and  the  whole  carefully  warmed.  The 
chlorine  decomposed  the  fluoride  of  mercury,  forming  chloride  of 
mercury,  and  the  fluorine  was  disengaged,  Hg.F.  and  CI.  giving 
Hg.Cl.  and  F.  There  was  in  this  way  obtained  a  colourless  gas, 
which  acted  with  violence  on  the  fragments  of  metallic  foils,  that 
by  means  of  a  very  ingenious  arrangement  were  submitted  to  its 
action.  The  small  quantity  of  material  on  which  the  experiments 
were  conducted  did  not  allow  of  the  metallic  compounds  so  formed 
being  analyzed  ;  and  the  only  doubt  that  can  exist  of  the  isolation 
of  fluorine  in  this  process  is  that,  as  it  was  liberated,  it  might  have 
combined  with  the  excess  of  chlorine  present,  and  that  the  colour- 
less gas  may  have  been  chloride  of  fluorine,  and  not  the  mere  fluo 
rine  itself. 

The  specific  gravity  of  gaseous  fluorine,  calculated  from  the 
analogy  of  its  compounds  to  those  of  chlorine,  is  1289  3  its  equivalent 
number  is  233-8,  or  18.7. 

Fluorine  does  not  combine  with  oxygen. 

The  most  important  compound  of  fluorine  that  is  known  is  the 
Fluoride  of  Hydrogen^  or  Hydrofluoric  Acid.  To  prepare  it,  pure 
fluor  spar,  which  consists  of  fluorine  and  calcium,  is  reduced  to 
powder,  and  distilled  in  a  leaden  retort  with  twice  its  weight  of  the 
strongest  oil  of  vitriol.  The  receiver  must  also  be  of  lead,  and  be 
kept  cool  by  ice.  An  acid  liquor  distils  over,  of  an  excessively  suf- 
focating odour,  and  so  intensely  corrosive,  that  a  drop  let  fall  upon 
the  hand  produces  a  sore  very  difficult  to  heal.  This  liquid  is  hy- 
drofluoric acid,  the  reaction  be  ng  that  H.O.  .S.O3  and  Ca.F.  give 
Ca.O. .  S.O3  and  H.F.     Sulphate     f  lime  remains  in  the  retort. 


320  HYDROFLUORIC     ACID. 

The  hydrofluoric  acid,  which  is  thus  obtained  in  an  anhydrous 
form,  is  very  volatile,  boiling  at  60^.  It  is  heavier  than  water,  and 
becomes  still  more  so  when  diluted  to  a  certain  degree.  It  dissolves 
the  more  oxidable  metals  rapidly  with  the  escape  of  hydrogen  gas, 
and  the  formation  of  a  metallic  fluoride.  The  only  metals  which  it 
does  not  act  upon  are  gold,  platina,  silver,  and  lead.  There  must 
be  no  solder  about  the  leaden  vessels  in  which  the  acid  is  kept,  as 
it  is  acted  on  very  violently.  It  is  dangerous  to  have  much  to  do 
with  the  anhydrous  acid,  from  its  corrosive  power;  and  as  a  dilute 
acid  answers  for  all  practical  purposes,  a  quantity  of  water  is  gener- 
ally put  into  the  receiver,  into  which  the  acid  is  distilled. 

The  most  remarkable  property  of  hydrofluoric  acid  is  its  action 
upon  glass,  which  it  corrodes  and  dissolves.  The  glass  contains 
silica,  which  the  hydrofluoric  decomposes,  Si.Og  and  3H.F.  producing 
3H.0.  and  Si.Fg.  This  fluoride  of  silicon  is  a  gas,  decomposed  by 
water  in  a  way  that  will  be  soon  described.  Patterns  or  designs 
may  therefore  be  etched  upon  glass  by  means  of  this  hydrofluoric 
acid.  There  are  two  modes  in  which  this  operation  may  be  con- 
ducted: 1st,  by  the  liquid  acid  j  2d,  by  the  acid  in  vapour.  For  the 
first,  the  glass  plate  being  covered  with  a  uniform  coating  of  wax, 
the  design  is  traced  on  it  with  the  point  of  a  needle  or  graving  tool, 
taking  care  that  the  surface  of  the  glass  shall  be  laid  bare  through- 
out the  whole  extent  of  each  line  ;  a  rim  of  wax  being  then  formed 
round  the  edge  of  the  plate,  the  liquid  acid,  the  strength  of  which 
must  be  regulated  by  the  depth  of  engraving  required,  is  poured  on 
the  plate  to  the  depth  of  two  or  three  lines,  and  left  for  a  time  de- 
pendant on  the  judgment  of  the  operator.  When  it  has  remained 
long  enough,  the  remaining  acid  is  poured  ofl*,  and  the  wax  cleared 
away.  The  etched  portions  of  the  glass  are  equally  transparent 
with  the  others,  and  the  design  is  therefore  indistinct  except  in  cer- 
tain incidences  of  the  light.  A  glass  plate  so  prepared  may  be  used 
as  a  copper  plate  to  print  from,  but  the  risk  of  breaking  is  too  great 
to  allow  of  its  introduction  into  practice. 

To  etch  by  the  second  mode,  the  plate  of  glass  is  prepared  exactly 
ah  described  for  the  first,  except  that  there  need  not  be  any  raised 
edge.  A  flat  leaden  basin,  of  the  size  of  the  plate,  is  used  to  hold 
the  mixture  of  powdered  fluor  spar  and  oil  of  vitriol,  and  the  glass 
plate  is  laid  upon  it,  with  the  waxed  side  down ;  the  basin  is  then 
heated  ao  gently  as  not  to  melt  the  wax  or  injure  the  accuracy  of 
the  design  3  the  hydrofluoric  acid,  which  rises  in  vapour,  acts  upon 
the  surface  of  glass  exposed,  and  decomposes  the  silica,  forming 
fluoride  of  silicon ;  but  a  sufficient  quantity  of  watery  vapour  rises 
to  decompose  this  substance,  and  a  quantity  of  silica  is  regenerated 
and  deposited  upon  the  corroded  surface,  giving  it  a  rough  and  white 
appearance,  so  as  to  be  easily  visible  in  every  direction.  When  the 
action  has  continued  long  enough,  the  plate  is  removed  from  the 
basin,  and  the  wax  cleared  off'by  means  of  some  spirits  of  turpentine. 
Other  uses  of  the  hydrofluoric  acid,  such  as  in  mineral  analysis,  will 
be  described  hereafter. 

The  composition  and  equivalent  numbers  of  the  hydrofluoric  acid 
ire  as  follows: 


OF     SILICON.  321 

Fluorine,      94-93         One  equivalent,  =233-8  or  18-7 

Hydrogen,     5-07  One  equivalent,  =   12-5  or    1-0 

'lOO^O  246-3       l9^ 

There  are  no  other  combinations  known  of  fluorine  with  any  of  the  simple  bodies 
as  yet  described,  except  sulphur  and  phosphorus :  these  are  dense  volatile  liquids. 
The  Fluoride  of  Phosphorus,  when  decomposed  by  water,  produces  hydrofluoric  acid 
and  phosphorous  acid  ;  it  is,  therefore,  P.F3.  When  heated  in  the  air,  it  bums,  but 
the  product  of  the  combustion  has  not  been  examined. 

Of  Silicon. 

This  substance  is  one  of  the  most  extensively  distributed  of  the 
undecomposed  bodies,  constituting,  probably,  a  sixth  of  the  total 
weight  of  the  mineral  crust  of  the  globe.  It  never  exists  free,  but 
always  in  nature  combined  with  oxygen,  forming  silicic  acid,  or,  as 
it  is  termed  in  popular  language,  the  earth  silica.  Quartz,  in  the 
state  of  rock  and  crystallized,  flints,  agate,  sand,  and  many  other 
mineral  substances,  are  silica  completely  or  nearly  pure,  and  when 
combined  Vith  various  metallic  oxides,  it  forms  the  great  family  of 
silicates,  which  includes  the  majority  of  earthy  minerals. 

It  is  exceedingly  difficult  to  deprive  silicic  acid  of  its  oxygen  j 
even  by  ignition  with  potassium  it  is  but  imperfectly  decomposed. 
To  prepare  silicon,  therefore,  a  somewhat  complex  body  is  selected 
to  be  acted  on,  the  double  fluoride  of  silicon  and  potassium  (2Si.Fj 
4-3K.F.),  which  is  a  white  powder  like  starch,  very  sparingly  soluble 
in  water ;  a  quantity  of  this  substance  is  to  be  mixed  with  nearly 
its  own  weight  of  potassium,  cut  into  little  bits, 
and  placed  in  an  iron  cylinder,  or  in  a  tube  of 
hard  glass,  which  may  be  held,  as  in  the  figure, 
over  the  flame  of  a  spirit-lamp.  As  soon  as  the 
bottom  of  the  tube  has  been  heated  to  redness, 
vivid  ignition  occurs  by  the  decomposition,  which 
spreads,  with  little  need  of  external  heat,  through- 
out the  entire  mass ;  when  cool,  the  residual 
brown  matter  is  to  be  washed  carefully  with  wa- 
ter:  fluoride  of  potassium  dissolves,  and  the  silicon  remains  behind  j 
the  2Si.F3+  3K.F.,  acted  on  by  6K.,  give  9K.F.  and  2Si.  To  have  the 
silicon  quite  pure,  numerous  precautions  are  necessary,  which  need 
not  be  detailed  here. 

The  silicon  so  obta:ined  is  a  dull  brown  powder,  which  when 
heated  in  air  or  in  oxygen,  takes  fire  and  burns,  forming  silicic 
acid.  If  it  be  ignited  in  a  closely  covered  vessel,  it  shrinks  in  vol- 
ume, increases  very  much  in  density,  and  becomes  insoluble  in 
acids  or  alkalies,  Avhich,  in  its  original  form,  it  would  dissolve  in, 
with  evolution  of  hydrogen  gas  ;  it  then  also  cannot  be  made  to 
burn  in  oxygen  gas  ;  it  burns  in  the  vapour  of  sulphur  and  in  chlo- 
rine, combining  with  these  bodies.  When  ignited  with  carbonate 
of  potash,  the  silicon  burns  brilliantly,  setting  carbon  free,  and  form- 
ing, with  the  oxygen  of  the  carbonic  acid,  silicic  acid,  which  com- 
bines with  the  potash.  The  equivalent  number  of  silicon  is  277-31 
or  22-22,  according  as  the  oxygen  or  the  hydrogen  standard  may  be 
adopted. 

S  s 


322  SILICIC     ACID. 

Silicic  Jlcid.  Silica. — This,  the  only  compound  of  silicon  and 
oxygen,  exists  in  nature  completely  pure,  in  masses  constituting 
quartz  rock,  and  in  crystals  which  belong  to  the  rhombohedral  sys- 
tem 5  their  ordinary  form  is  represented  in  the  mar- 
gin. It  is  exceedingly  hard,  and,  in  order  to  be  re- 
duced to  powder,  requires  to  be  heated  first  to  red- 
ness, and  then  thrown  into  a  large  mass  of  cold  water. 
The  piece  of  quartz  cracks  in  every  direction  by  be- 
ing so  suddenly  cooled,  and  is  then  easily  reduced 
to  powder  in  an  agate  mortar.  It  may  be  obtained 
in  a  state  of  much  more  minute  division,  by  melting, 
in  a  platinum  crucible,  a  mixture  of  equal  weights  of 
carbonate  of  potash  and  of  carbonate  of  soda,  and  ad- 
ding thereto  powdered  flint,  by  small  quantities  at  a 
time  ;  the  silica  dissolves  in  the  melted  alkali,  while  carbonic  acid 
gas  is  given  off.  When  the  alkaline  silicates,  so  formed,  are  dis- 
solved in  water,  and  a  stronger  acid  added,  the  silicic  acid  is  pre- 
cipitated as  a  gelatinous  hydrate,  which,  when  completely  dried, 
forms  a  white  powder,  still  somewhat  gritty  to  the  feel.  When  the 
gaseous  fluoride  of  silicon  comes  into  contact  with  water,  a  portion 
of  it  is  decomposed,  fluoride  of  hydrogen  and  silicic  acid  being 
produced  ;  this  last  separates  in  the  gelatinous  form,  but,  on  drying, 
becomes  an  exceedingly  fine  light  powder. 

Silica,  even  when  prepared  by  precipitation,  feels  gritty  between 
the  teeth  ;  when  in  mass,  it  is  exceedingly  hard,  scratching  glass 
and  the  generality  of  minerals.  Its  specific  gravity  is  2*66  j  it  is 
fusible  only  by  the  oxyhydrogen  blowpipe,  in  the  flame  of  which 
it  melts  into  a  colourless  glass  ;  when  once  dried  it  is  totally  in- 
soluble in  water,  but  in  its  gelatinous  form  it  is  soluble  to  a  small  ex- 
tent ;  hence  many  mineral  waters  contain  silica,  which,  being  grad- 
ually precipitated  in  the  substance  of  decomposed  organic  matter, 
produces  the  silicious  petrifactions  in  which  the  most  delicate  vege- 
table tissues  are  so  beautifully  preserved.  The  differences  between 
silica  in  its  dry  and  in  its  hydrated  condition  are  so  great,  that  we 
can  scarcely  suppose  them  to  be  satisfactorily  accounted  for  by  the 
presence  of  a  substance  for  which  the  silica  appears  to  have  so  lit- 
tle affinity.  When  a  dilute  alkaline  solution  of  silica  is  decomposed 
by  an  acid,  there  is  no  precipitation,  the  silica  remaining  dissolved; 
but  on  evaporating  the  liquor  to  dryness,  the  silica  assumes  the  in- 
soluble condition,  and  remains  behind  when  the  saline  constituent 
is  dissolved.  On  the  other  hand,  by  the  presence  of  an  alkali,  the 
insoluble  silica  is  made  to  assume  the  soluble  state. 

There  is  some  difference  of  opinion  as  to  whether  the  compounds 
of  silica  and  water  are  truly  definite,  but  I  look  upon  the  existence 
of  at  least  one,  having  the  formula  2Si.03  +  H.O.,  as  being  certain ; 
I  have  found  the  light  spongy  masses  of  silica  deposited  from  vol- 
canic springs,  and  on  the  edges  of  volcanic  craters  from  Iceland  and 
Tenerifl^e,  to  have  accurately  that  constitution. 

It  is  probable  that  a  great  deal  of  the  silica  which  exists  in  nature 
has  been  originally  deposited  in  the  soluble  condition.     The  struc 
ture  of  the  agates,  chalcedony,  and  many  other  minerals,  proves 
that  they  Avere  formed  by  a  solution  of  silica  having  penetrated 


CHLORIDE     OP     SILICON. 


323 


into  a  cavity  in  the  surrounding  rock,  and  having  then  gradually- 
dried  down  or  crystallized.  It  is  even  pretty  certain  that  the  crys- 
tallized  quartz  is  also  of  this  aqueous  origin. 

In  the  arts,  silica  is  of  exceeding  importance,  being  an  essential 
constituent  of  glass,  porcelain,  and  every  kind  of  delft  and  earthen- 
ware. For  purely  chemical  purposes,  it  is  only  of  interest  from 
the  compound  which  silicon  forms  with  fluorine ;  the  hydrofluoric 
acid  being  the  only  acid  capable  of  dissolving  silica. 

The  composition  of  silica  and  its  equivalent  numbers  are  as  fol- 
lows, its  formula  being  Si.Og. 

Silicon,   48-04         One  equivalent,       =277-3  or  22-22 

Oxygen,  51-96         Three  equivalents,  =3000  or  24-00 

100-00  5773       46-22 

Silicon  does  not  combine  with  hydrogen  nor  with  nitrogen :  there 
exists  a  sulphuret  of  silicon,  which  is  probably  Si.Sg,  as  when  acted 
on  by  water  it  produces  soluble  silica  and  sulphuretted  hydrogen. 

Chloride  of  Silicon. — This  substance,  Eilthough  not  itself  important,  is  yet  inter- 
esting from  the  fact  that  the  method  of  preparing  it  is  one  by  which  a  number  of 
remarkable  compounds  of  chlorine  have  been  discovered,  and  hence  it  deserves  to 
be  described.  Chlorine  has  no  action  on  silica  at  any  temperature ;  but  if  finely- 
divided  silica  be  mixed  with  powdered  charcoal,  and  heated  to  redness  in  a  porcelain 
tube,  a,  c,  inserted  in  the  furnace,  as  in  the  figure,  and  by  means  of  a  glass  tube  at 


tached  at  h,  a  current  of  dry  chlorine  be  made  to  stream  over  the  ignited  mixture, 
decomposition  ensues,  the  oxygen  of  the  silica  combining  with  the  carbon  to  form 
carbonic  oxide  gas,  while  the  chlorine  and  sihcon  unite,  producing  the  chloride  of 
sihcon,  which,  being  a  very  volatile  liquid,  requires  to  be  carefully  condensed  ;  for 
this  purpose,  the  tube  c  /  is  wrapped  up  in  a  cloth,  or  a  paper  kept  constantly  wetted 
by  a  stream  of  water  from  the  reservoir  e,  and  the  liquid  produced  then  collects 

in  the  bottle  /,  while  the  oxide 
of  carbon  and  the  excess  of 
chlorine  pass  off  by  the  tube 
m.  In  this  process  the  reac- 
tion is  such,  that  3C1.  acting 
on  Si.Og  and  3C.,  give  rise  to 
3C.0.  and  Si.Cls- 

The  stream  of  dry  chlorine 
may  be  very  conveniently  ob- 
tained by  the  apparatus  here 
figured ;  the  muriatic  acid  and 
peroxide  of  manganese  are 
placed  in  the  flask  a,  arid  the 
gas  evolved,  depositing  the  ac- 
companying liquid  in  the  re- 
ceiver b,  passes  through  the 
tube  c,  which,  being  filled  with 


324 


FLUORIDE     OF      SILICON. 


fragments  of  recently-fused  chloride  of  calcium,  absorbs  all  the  watery  vapoui 
The  gas  issues  dry  from  the  extremity,  where  it  is  connected  with  the  end  b  of  the 
porcelain  tube  in  the  preceding  figure. 

The  chloride  of  silicon  is  a  colourless  liquid,  denser  than  water ;  it  boils  at  124° ; 
in  contact  with  water,  it  is  resolved  into  siUca  and  hydrochloric  acid,  from  whence 
its  formula  must  be  Si.Cls. 

Fluoride  of  Silicon. — This  is  the  most  remarkable  compound  of 
silicon  after  silicic  acid  j  it  is  a  gas  colourless  and  transparent ;  to 
prepare  it,  fluor  spar  and  sand,  or  glass  in  powder,  are  mixed  together, 
and  heated  in  contact  with  oil  of  vitriol;  the  mass  swells  up  very- 
much,  so  that  a  large  vessel  must  be  employed.  In  this  reaction 
we  may  look  upon  water  as  being  decomposed  or  not,  as  the  results 
maybe  explained  in  either  way.  Thus  the  oxygen  of  the  silica  may 
combine  with  the  calcium,  forming  lime,  and  this  with  the  sulphuric 
acid,  while  the  silicon  unites  with  the  fluorine  of  the  fluor  spar.  Or, 
water  being  decomposed,  hydrofluoric  acid  and  lime  may  be  first 
produced,  and  the  former,  reacting  on  the  silica,  may  reproduce  wa- 
ter, and  form  fluoride  of  silicon.  I  prefer  to  omit  here,  as  I  did 
when  describing  the  formation  of  chlorine,  all  the  unnecessary  the- 
oretic agency  of  the  water,  and  to  express  the  decomposition  as 
3(S.03 .  H.O.)  with  Si.Oa  and  3(Ca.F.)  give  SrS.Og .  Ca.O. .  H.O.)  and 
Si;F3. 

This  gas  must  be  collected  over  mercury,  and  in  vessels  dried 
with  .the  greatest  care.  When  it  mixes  with  air,  it  forms  dense 
white  fumes,  which  arise  from  the  formation  of  silica  by  the  watery 
vapour  present  being  decomposed. 

It  is  colourless  and  transparent ;  its  specific  gravity  is  3600.  Its 
composition  and  equivalent  numbers  are  as  follows,  its  formula  being 

Si.Fg. 

Silicon,     28-32  One  equivalent,       =277-3  or  22-22 

Fluorine,  71-68  Three  equivalents,  =701-4  or  ,56-22 

lOCHOO  978^7       78^4" 

The  hydrofluosilicic  acid,  or  the  double  fluoride  of  hydrogen  and 
silicon,  cannot  be  obtained  free  from  water,  but  its  solution  is  of 
considerable  importance  as  a  chemical  reagent,  and  hence  its  prep- 
aration requires  to  be  described. 

The  mixture  of  powdered  fluor  spar  and  sand  is  introduced  into 
the  matrass  a,  which  is  imbedded  in  a  sand- 
bath,  as  in  the  figure.  By  means  of  the 
siphon  funnel  /,  the  oil  of  vitriol  is  then 
poured  in,  and  the  gas  evolved  is  conduct- 
ed by  the  tube  to  the  water  in  the  ves- 
sel d  e.  If  the  tube  opened  into  the  wa- 
ter directly,  so  much  silica  would  be  de- 
posited at  its  orifice  as  to  stop  it  up  every 
moment;  and  hence  a  quantity  of  mer- 
cury, e,  is  placed  at  the  bottom,  and  the 
end  of  the  tube  dips  into  it.  The  gas  bub- 
ble, therefore,  does  not  touch  the  water 
until  completely  separated  from  the  tube : 
it  escapes  from  the  surface  of  the  mercu- 
ry, and  then  it  becomes  invested  with  a 


OF     BORON.  325 

coating  of  silica,  like  a  bag  of  tissue  paper,  of  which  many  preserve 
their  form  for  a  certain  time.  The  passage  of  the  gas  is  to  be  con- 
tinued until  the  water  becomes  thick  from  the  quantity  of  silica  sep- 
arated j  it  is  then  to  be  poured  on  a  fine  linen  cloth,  and  the  silica 
removed  by  straining  and  pressure.  In  this  process,  one  third  of 
the  fluoride  of  silicon  is  decomposed  by  the  water  forming  silica 
and  hydrofluoric  acid,  which  last  unites  with  the  remaining  fluoride 
of  silicon  to  form  the  hydrofluosilicic  acid,  the  formula  of  which  is 
2(Si.F3)-f3H.F. 

When  a  solution  of  this  acid  is  heated,  fluoride  of  silicon  is  given 
ofl*,  and  hydrofluoric  acid  remains.  Hence,  although  the  hydrofluo- 
silicic acid  is  without  action  upon  glass,  glass  vessels  in  which  it  is 
evaporated  are  corroded. 

The  property  of  this  acid  which  is  of  most  interest  to  the  chemist 
is,  that  it  forms,  by  acting  on  the  salts  of  potassium  and  barium, 
compounds,  Jluosilicates,  or  double  fluorides  of  those  metals  which 
are  very  sparingly  soluble  in  water ;  and  hence  it  is  used  to  detect 
the  presence  of  these  substances  in  solution.  The  precipitate  so 
obtained  is  remarkable  for  being  at  first  so  gelatinous  and  transpa- 
rent that  it  can  be  recognised  in  the  liquor  only  by  the  play  of  colours 
in  the  light  reflected  from  its  upper  surface.  When  collected  on  a 
filter  and  dried,  these  compounds  appear  like  powdered  starch.  The 
constitution  of  the  salts  of  the  hydrofluosilicic  acid  resembles  that 
of  the  acid  itself,  the  hydrogen  being  replaced  by  a  metal;  thus 
the  fluosilicate  of -potassium,  already  described  as  used  for  preparing 
silicon,  is  expressed  by  the  formula  2Si.F3-f3K.F. 

The  composition  of  hydrofluosilicic  acid  is  easily  known  from  that 
of  the  hydrofluoric  acid  and  fluoride  of  silicon.  Its  equivalent  num- 
ber is  2696-4.  or  216-2. 

Of  Boron. 

The  history  of  this  substance  presents  a  very  close  analogy  with 
that  of  silicon.  It  was  first  obtained  by  decomposing  boracic  acid  by 
galvanism,  but  is  best  prepared  by  acting  on  the  fluoborate  of  pot- 
ash by  metallic  potassium,  exactly  as  has  been  described  under  the 
head  of  silicon.  That  salt  consists  of  fluoride  of  boron  united  to 
fluoride  of  potassium  ;  by  the  reaction,  all  the  fluorine  passes  to  the 
potassium,  and  the  boron  is  set  free. 

Boron  is  a  dark  olive  substance,  which  does  not  conduct  electri- 
city. It  is  insoluble  in  water  and  all  other  neutral  fluids.  When 
heated  to  600^  in  the  air  or  oxygen,  it  takes  fire,  and  burning,  forms 
boracic  acid  ;  the  same  eflect  is  produced  by  boiling  with  nitric  acid, 
or  by  ignition  with  nitrate  or  with  carbonate  of  potash. 

This  element  is  not  extensively  distributed  in  nature,  and  only 
found  combined  with  oxygen,  forming  boracic  acid.  This  exists  in 
certain  springs  in  India,  combined  with  soda,  and,  being  crystallized 
in  an  imperfect  way,  was  brought  into  commerce  under  the  name 
of  tinkal,  or  crude  borax.  The  boracic  acid  is  also  found,  and  in 
much  larger  quantity,  free,  or  combined  only  with  a  small  quantity 
of  ammonia,  in  the  small  volcanic  lakes  or  lagoons  of  Tuscany.  It 
accompanies  the  watery  vapour  which  gushes  out  of  fissures  in  the 
earth,  and  which  contains  also  muriatic  acid.     The  water  of  these 


326  BORACIC     ACI  D. C  HLORIDE      OF     BORON. 

lakes  is  evaporated,  and  the  boracic  acid  being  crystallized,  is  im- 
ported into  these  countries  for  the  manufacture  of  borax  (borate  of 
soda)  and  other  salts. 

The  boracic  acid  is  the  only  compound  of  boron  and  oxygen  ,•  it 
may  be  obtained  quite  pure  from  the  native  acid  by  boiling  this 
with  eight  parts  of  water  and  a  little  white  of  egg,  and  filtering  the 
solution.  On  cooling  slowly,  the  boracic  acid  crystallizes  in  large 
brilliant  plates,  soft  and  unctuous  to  the  feel,  and  of  an  irregular 
crystalline  form.  It  may  be  also  produced  from  borax  by  dissolving 
it  in  four  times  its  weight  of  boiling  water,  and  adding  sulphuric 
acid  until  the  liquor  becomes  sour  to  the  taste.  On  cooling,  the 
boracic  acid  crystallizes  ;  but  as  it  retains  a  little  sulphuric  acid  and 
sulphate  of  soda,  a  second  solution  and  crystallization  is  necessary 
to  have  it  pure. 

The  crystals  of  boracic  acid,  so  prepared,  contain  water,  the  oxy- 
gen of  which  is  equal  to  the  oxygen  of  the  acid;  when  heated,  this 
water  passes  off,  and  the  acid  melts  ;  on  cooling,  it  forms  a  colourless 
glass  5  when  completely  dry  it  is  fixed,  but  in  the  presence  of  wa- 
ter it  is  carried  ofi'  by  the  vapour  in  great  quantity.  The  glacial 
acid,  when  exposed  to  the  air,  absorbs  water,  swells,  and  becomes 
opaque.  The  boracic  acid  is  much  more  soluble  in  hot  than  in  cold 
water,  the  crystals  requiring  twenty-six  parts  of  water  at  60^,  and 
only  three  at  212^  for  their  solution.  Alcohol  dissolves  boracic  acid 
copiously  ;  and  the  solution,  when  set  on  fire,  burns  with  a  beauti- 
ful green  flame,  by  which  this  body  may  easily  be  recognised.  The 
boracic  acid  possesses  but  very  feeble  acid  properties  ;  many  of  its 
soluble  salts  possess  alkaline  reaction,  and  all  are  decomposed  by 
the  weakest  acids.  It  does  not  redden  litmus,  but  gives  it  a  port- 
wine  colour,  and  a  strong  solution  of  it  browns  turmeric  paper  like 
an  alkali.  At  high  temperatures,  however,  boracic  acid  may  decom- 
pose the  salts  of  the  nitric,  or  even  of  the  sulphuric  acids,  from  the 
principles  that  have  been  already  explained  in  the  chapter  on  Affin- 
ity (p.  169). 

The  composition  and  equivalent  numbers  of  boracic  acid  are  as 
follows,  its  formula  being  B.O3 : 

Boron,     31-22        One  equivalent,       ==136  2  or  10-9 

Oxygen,  6878        Three  equivalents,  =  300*0  or  24-0 

lOO^O  436^        34^ 

Boron  does  not  combine  with  hydrogen  or  nitrogen  j  its  com- 
pounds with  sulphur  and  selenium  are  not  important. 

Chloride  of  Boron. — Boron  burns  spontaneously  in  chlorine  gas,  but  the  best  way 
to  prepare  the  compound  of  chlorine  and  boron  is  to  proceed  as  described  for  ma- 
king chloride  of  silicon,  substituting  boracic  acid  for  the  silica.  The  product  is  a  gas, 
colourless  and  transparent,  but  producing  dense  white  fumes  in  contact  with  damp 
air,  owing  to  its  decomposition,  and  the  formation  of  boracic  and  hydrochloric  acids. 
The  presence  of  this  last  in  the  volcanic  lagoons  would  render  it  probable  that  by 
some  subterraneous  action  chloride  of  boron  is  generated,  and  is  decomposed  when 
mixed  with  the  watery  vapour  simultaneously  exhaled.  The  chloride  of  boron  is 
rapidly  absorbed  and  decomposed  by  water  ;  its  specific  gravity  is  4079  ;  it  contains 
1^  times  its  volume  of  chlorine  ;  its  formula  is  B.CI3. 

Fluoride  of  Boron. — This  substance  is  prepared  in  exactly  the 
same  way  as  fluoride  of  silicon,  substituting  the  boracic  acid  for 
the  silicic  acid.     It  is  a  gas,  rapidly  absorbed  and  decomposed  by 


GENERAL     CHARACTERS     OF     THE     METALS.      327 

water,  and  generating  hydrofiuoboric  acid,  which  is  perfectly  anal- 
ogous to  the  hydrofluosilicic  acid.  It  hence  forms  dense  white 
fumes  when  mixed  with  damp  air.     Its  specific  gravity  is  2362. 

The  hydrofiuoboric  acid  is  obtained  by  precisely  the  same  plan 
as  that  described  for  the  hydrofluosilicic  acid.  The  boracic  acid  is 
deposited  in  crystals  according  as  the  gas  is  absorbed.  If  the  li- 
quor be  evaporated  without  the  acid  deposited  being  removed,  it  is 
all  again  taken  up  and  carried  off  as  gaseous  fluoride  of  boron. 
The  liquid  hydrofluoboric  acid  resembles,  in  the  combinations  that 
it  forms,  the  hydrofluosilicic  acid,  and  is  similar  to  it  also  in  con- 
stitution, its  formula  being  2(B.F3)-f-3H.F. 

No  other  compound  of  boron  of  any  interest  is  known. 

The  history  of  carbon  involves  so  many  considerations  regarding  the  constitution 
and  properties  of  organic  substances,  that  I  shall  postpone  entering  upon  it  until 
after  the  description  of  the  metals  and  their  salts,  and  other  compounds  with  the 
non-metallic  bodies.  I  will  then  commence  the  study  of  the  chemistry  of  organic 
substances  with  that  of  their  most  constant  ingredient,  carbon. 

The  compound  of  nitrogen  with  hydrogen  (ammonia)  has  not  been  introduced 
among  those  of  the  non-metallic  bodies  with  each  other,  because  all  the  details  of 
its  history  attach  it  to  organic  chemistry,  under  which  head  it  will  consequently  be 
found.  The  hypothetical  compounds  of  nitrogen  and  hydrogen  (amidogene  and  am- 
monium) will  be  associated  with  it. 

The  substances  hitherto  described  as  chloride  and  iodide  of  nitrogen  having  been 
found  to  contain  hydrogen,  and  to  range  themselves  in  an  important  series  of  or- 
^  ganic  combinations,  have  not  been  noticed  in  the  chapter  now  closed,  but  will  be 
' ''  found  in  their  true  position  hereafter. 


CHAPTER  XII.* 

OF  THE   GENERAL  CHARACTERS  OF  THE   METALS,  AND  OF  THEIR  COMPOUNDS 
WITH  THE  NON-METALLIC  BODIES, 

Although,  as  has  been  already  noticed,  the  metals  cannot  be  con- 
sidered as  forming  a  class  of  bodies,  united  by  such  analogies  of 
chemical  properties  and  laws  of  combination  as  would  constitute  a 
natural  family,  yet  in  their  physical  characters,  and  the  most  prom- 
inent facts  of  their  technical  history,  they  have  so  much  in  common 
as  to  render  a  notice  of  the  conditions  in  which  they  exist  in  na- 
ture, the  methods  by  which  they  are  extracted  upon  the  large  scale, 
and  the  physical  and  chemical  properties  by  which  they  are  distin- 
guished as  a  great  division  of  the  elementary  bodies,  necessary,  be 
fore  proceeding  to  the  detailed  history  of  the  individual  metals. 

The  metals  are  forty-two  in  number  ;  their  names  have  been  al- 
ready given  in  more  than  one  place  (p.  150  and  189).  They  reflect 
light  powerfully,  and  hence  possess  what  is  termed  metallic  lustre. 
If  the  incident  light  be  plane  polarized,  it  undergoes  a  remarkable 
change,  produced  only  by  the  metals  and  by  diamond,  becoming 
elliptically  polarized  on  reflection.  The  metals  are  characterized 
very  completely  by  their  power  of  conducting  heat  and  electricity, 
in  which,  although  they  differ  among  each  other,  yet  the  worst 
excels  all  non-metallic  bodies.     Lists  of  their  relative  eonducting 


328   GENERAL  CHARACTERS  OF   THE   METALS. 

powers  in  these  respects  have  been  already  given  (p.  92,  109,  and 
137).  By  the  combination  of  these  characters,  the  histre  and  con- 
ducting- power,  the  metallic  or  non-metallic  nature  of  a  body  is  al- 
ways determined. 

In  the  other  properties  of  the  metals  there  is  found  remarkable 
diversity  j  thus  in  colour,  although  silver  is  purely  white,  the  major- 
ity of  the  metals  are  of  various  shades  of  bluish-white  or  gray, 
while  copper  and  titanium  are  reddish  coloured,  and  gold  is  yellow. 
In  specific  gravity,  the  metals  include  some  of  the  lightest  along 
with  the  heaviest  solids  that  we  know  ;  the  density  of  platinum  being 
21  times,  of  gold  19  times,  and  of  potassium  only  -^^  that  of  water. 

Some  of  the  most  important  applications  of  the.  metals  in  the  arts 
depend  on  their  malleability  and  ductility.  Those  metals  are  malle- 
able which  admit  of  being  rolled  or  beaten  out  into  thin  leaves ; 
tho§e  being  ductile  which  can  be  drawn  into  wire.  Gold  is  the 
most  malleable  of  metals ;  gold  leaf  may  be  obtained  of  -j^-^-  of 
an  inch  in  thickness,  and  is  hence  the  only  metal  in  which  any  trace 
of  transparency  has  been  found  j  silver,  copper,  tin,  rank  next  in 
malleability.  The  most  malleable  metals  are  not  at  all  the  most 
ductile  ;  platinum,  and  even  iron,  can  be  obtained  in  finer  wire  than 
gold  j  platinum  wire  was  made  by  Wollaston  of  3  q^^^  o  ^^^^  diame- 
ter ;  but  a  met^l  which  is  not  malleable  cannot  be  ductile,  and  vice 
versa  ;  thus  antimony,  arsenic,  and  bismuth,  the  brittle  metals,  may 
be  powdered  in  a  mortar,  but  give  neither  leaves  nor  wire.  The 
texture  of  the  metals  which  produces  the  malleable  and  ductile  con- 
ditions, depends  closely  upon  temperature.  Thus  zinc  is  malleable 
and  ductile  at  300^ ;  it  loses  this  power,  but  remains  tough,  at  GO"', 
while  at  600^  it  becomes  so  brittle  that  it  powders  as  easily  as  bis- 
muth. In  the  drawing  of  lead  pipe,  and  in  making  most  of  the  me- 
tallic wires,  there  is  a  peculiar  temperature  required  for  the  most 
perfect  execution,  by  which  is  regulated  the  rapidity  with  which  the 
process  is  carried  on. 

In  strength  and  tenacity  the  metals  differ  also  ;  iron  is  the  strong- 
est metal ;  an  iron  wire  of  a  given  thickness  will  support  a  greater 
weight  than  a  similar  wire  of  any  other  metal ;  copper  is  next  to  iron, 
but  only  about  one  half  so  strong  j  then  platinum,  silver,  and  gold : 
tin  and  lead  are  the  weakest  of  the  metals.  The  tenacity  depends 
also  on  the  molecular  structure ;  if  the  wires  had  been  annealed,  so 
as  to  allow  of  an  approach  to  internal  crystallization,  the  tenacity 
is  often  found  to  be  reduced  to  one  half. 

In  their  relations  to  heat  the  metals  exhibit  remarkable  variety  t 
but  one  metal  is  liquid  at  ordinary  temperatures.  All  the  metal? 
are  fusible,  but  they  require  for  their  liquefaction  the  greatest  range 
of  temperature  which  can  be  produced;  thus  mercury  melts  at — 39^. 
potassium  and  sodium  below  the  heat  of  boiling  water  ;  tin,  lead, 
zinc,  antimony,  and  tellurium  below  a  red  heat,  and  manv  metals 
as  platinum,  are  infusible  in  the  most  intense  heat  of  a  blast  furnace 
and  yield  only  to  the  flame  of  the  oxyhydrogen  blowpipe.  In  the 
history  of  each  individual  metal,  its  point  of  fusion  will  be  given,  so 
far  as  it  is  known. 

The  majority  of  the  metals  are  fixed  at  the  greatest  heat  of  our 
furnaces ;  but  mercury,  zinc,  cadmium,  arsenic,  tellurium,  potassium, 
and  sodium  may  be  volatilized. 


CLASSIFICATION     OF     THE     METALS. 


329 


The  generality  of  metals,  when  exposed  to  the  air,  particularly 
when  damp,  absorb  oxygen  and  form  oxides  j  some  becoming  mere- 
ly tarnished  upon  the  surface,  others  becoming  thoroughly  oxidized. 
Some  metals,  however,  as  gold,  silver,  platinum,  palladium,  and 
mercury,  are  not  liable  to  this  action.  Those  metals  which  oxidize 
when  exposed  to  air,  unite  with  oxygen  at  a  higher  temperature 
with  great  rapidity,  many  with  actual  combustion.  Thus  zinc,  when 
heated  to  full  redness,  takes  fire  and  burns  brilliantly  with  a  white 
flame,  and  the  combustion  of  iron  wire  in  oxygen  is  one  of  the  pret- 
tiest lecture  experiments.  Mercury  also,  which  does  not  tarnish 
when  exposed  to  oxygen  at  common  temperatures,  becomes  oxi- 
dized when  heated  to  near  its  boiling  point,  but  the  oxide  is  resolv- 
ed again  at  a  red  heat  into  oxygen  and  metallic  mercury. 

It  is  owing  to  their  affinity  for  oxygen  that  many  of  the  metals 
decompose  water,  and  one  of  the  most  convenient  classifications 
that  have  been  proposed  for  ordinary  use  is  founded  on  the  fact  of 
the  different  degrees  of  facility  with  which  this  decomposition  pro- 
ceeds. Thus, 
Potassium, 


Sodium, 

liithium, 

Barium, 

Strontium, 

Calcium, 

Magnesium, 

Aluminum, 

Glucinum, 

Thorium, 

Yttrium, 

Zirconium, 

Lanthanum, 

Cerium, 

Manganese, 

Iron, 

Nickel, 

Cobalt, 

Zinc, 

Cadmium, 

Tin, 

Chromium, 

Vanadium, 

Tungsten, 

Molybdenum, 

Osmium, 

Columbium, 

Titanium, 

Arsenic, 

Antimony, 

Tellurium, 

I    Uranium, 
Copper, 
Lead, 
Bismuth, 
Silver, 
Mercury, 
Gold, 

Palladium, 
Platinum, 
Rhodium, 
Iridium, 


.     The  first  class  consists  of  metals  which  decompose  water  with 
^lively  effervescence,  even  at  32°. 


The  second  class  consists  of  metals  which  do  not  decompose  watei 
>with  lively  effervescence,  except  at  about  212°,  but  very  far  below  a 
red  heat. 


The  third  class  consists  of  metals  which  do  not  decompose  water 
>  except  at  a  red  heat,  or  at  common  temperatures  in  contact  with 
strong  acids. 


The  fourth  class  consists  of  metals  which  decompose  vapour  of 
>  water  energetically  at  a  red  heat,  but  which  do  not  decompose  it  at 
common  temperature,  even  in  contact  with  strong  acids. 


"v  The  fifth  class  consists  of  metals  which  decompose  water  at  a  red 
Vheat  but  very  feebly,  but  whose  oxides  are  not  reducible  to  the  me- 
J  tallic  state  by  heat  alone. 


The  sixth  class  consists  of  metals  whose  oxides  are  decomposea 
>  alone  at  a  high  temperature,  and  which  do  not  decompose  water 
under  any  circumstances. 


Tt 


\ 

330  CLASSIFICATION     OF     THE     METALS. 

This  kind  of  classification  was  first  proposed  by  Thenard,  and  has 
been  adopted  by  Graham  in  a  form  differing  very  slightly  from  that 
now  given. 

The  following  classification,  although  old,  and  founded  solely  on 
popular  considerations,  is  yet  so  far  consonant  with  the  simplest 
characters  of  the  metals  as  to  be  frequently  referred  to,  and  hence 
to  be  worthy  of  notice. 

Those  metals  which  do  not  tarnish  on  exposure  to  the  air,  and 
the  oxides  of  which  are  reduced  by  heat  alone,  were  termed  the 
noble  or  perfect  metals  ;  at  the  head  of  this  list  stood  gold,  and  at  the 
bottom  mercury. 

All  the  otHer  metals  known  to  the  older  chemists  were  termed 
ordinary  or  imperfect  metals.  Of  the  metals  of  the  first  and  second 
class,  none  had  been  then  discovered  j  and  of  their  oxides,  only 
potash,  soda,  barytes,  lime,  magnesia,  and  alumina  were  known. 
From  the  old  name  of  potash,  Kali^  with  the  Arabic  prefix  a/,  potash 
and  soda,  at  one  time  confounded  together,  were  termed  alkalies^ 
and  ammonia,  resembling  them  very  much  when  dissolved  in  water 
or  combined  with  acids,  was  also  called  an  alkali ;  it  was  the  vol- 
atile alkali,  potash  and  soda  being  fixed  alkalies  ;  it  was  also  termed 
the  animal  alkali,  while  soda  was  the  mineral  alkali,  being  derived 
from  rock-salt  or  from  the  ocean ;  and  potash  received  the  name  of 
the  vegetable  alkali,  from  its  source  being  the  ashes  of  plants  grow- 
ing upon  land.  The  alkalies  are  characterized  by  being  very  soluble 
in  water,  and  by  neutralizing  the  strongest  acids.  They  hence  re- 
store the  blue  colour  of  reddened  litmus  paper,  and  change  the 
vegetable  colours  in  general :  the  yellows  to  brown,  the  reds  and 
blues  to  green. 

Paper  tinged  yellow  by  turmeric  is  a  delicate  test  of  the  presence 
of  an  alkali,  by  which  it  is  browned. 

Magnesia  and  alumina  were  termed  earths^  and  silica  was  classed 
with  them ;  these  bodies,  the  earths  proper,  are  insoluble  in  water, 
and  have  no  action  on  turmeric  paper. 

Barytes,  lime,  and  strontia  were  termed  alkaline  earths  ;  they  are 
soluble  in  water,  but  much  less  so  than  the  alkalies ;  these  solutions 
brown  turmeric  paper,  and  neutralize  acids  ;  but  they  are  complete- 
ly distinguished  from  the  alkalies  by  their  combinations  with  car- 
bonic acid,  which  are  insoluble  in  water,  while  the  alkaline  carbon- 
ates are  very  soluble  in  that  liquid.  These  phrases  of  alkalies  and 
earths  are  of  constant  recurrence  in  descriptions  of  chemical  pro- 
cesses and  results,  and  are  thus  seen  to  be  founded  on,  and  express- 
ive of,  some  of  the  most  important  characters  in  those  bodies. 

Most  of  the  metals  combine  with  oxygen  in  more  than  one  pro- 
portion, and  the  characters  of  the  oxides  are  found  to  be  regulated 
in  a  great  degree  by  their  composition.  All  protoxides  (R.O.)  (R. 
representing  an  equivalent  of  any  metal)  appear  capable  of  combi- 
ning with  acids  to  form  neutral  salts  ;  they  constitute,  properly,  the 
metallic  basis,  but  in  many  cases  suboxides,  (RaO*)?  such  as  those 
of  copper  and  mercury,  form  well-characterized  salts,  and  sesqui- 
oxides,  (R2O3),  as  those  of  iron,  manganese,  aluminum,  and  chrome, 
produce  well-defined  classes  of  salts  also,  which,  however,  in  solu- 
tion always  possess  an  acid  reaction.     Peroxides,  (R.O^),  as  those 


AFFINITY     OF     METALS     FOR     CHLORINE,    ETC.    331 

of  manganese,  tin,  titanium,  and  lead,  are  either  indifferent  or  feebly 
acid,  and  the  higher  degrees  of  oxidation  lose  all  basic  character, 
and  become  true  acids,  as  the  manganic  acid,  Mn.Og,  and  the  chro- 
mic acid  (Cr.Og). 

The  different  oxides  of  the  same  metal  frequently  unite  with  each 
other,  producing  compounds  wWch  have  great  similarity  to  salts. 
Examples  of  this  will  be  found  under  the  heads  of  manganese,  of 
iron,  and  of  lead. 

The  affinity  of  the  metals  for  chlorine  is,  in  many  cases,  even 
more  remarkable  than  that  which  they  manifest  for  oxygen  ;  thus 
gold  and  platinum,  which  resist  even  nitric  acid,  at  once  combine 
with  chlorine  ;  and  tin,  copper,  mercury,  antimony,  arsenic,  and 
bismuth,  which  require  a  high  temperature  to  effect  their  rapid 
combination  with  oxygen,  burn  spontaneously  when  introduced  into 
chlorine  gas  in  a  state  of  minute  division.  Most  metallic  oxides 
are  decomposed  by  chlorine  also  at  a  high  temperature  ;  thus,  if  a 
stream  of  chlorine  gas  be  passed  over  lime  heated  to  redness  in  a 
porcelain  tube,  oxygen  gas  is  expelled,  and  the  calcium  remains 
combined  with  chlorine.  On  this  account,  the  chlorides  are  gener- 
ally, after  the  oxides,  the  most  important  metallic  compounds. 
Towards  iodine,  bromine,  and  fluorine,  the  metals  are  related  near- 
ly as  to  chlorine,  the  affinities  being,  however,  much  weaker  towards 
bromine,  and  still  more  so  towards  iodine :  of  fluorine  we  do  not 
as  yet  possess  much  positive  knowledge,  but  its  affinities  appear  to 
be  at  least  as  intense  of  those  of  chlorine. 

The  compounds  of  sulphur  with  the  metals  constitute  a  very  ex- 
tensive and  important  series,  which,  as  has  been  more  fully  noticed 
in  p.  284,  resembles  in  a  very  striking  manner  the  series  of  oxides 
of  the  same  metal.  Many  metals,  at  a  high  temperature,  combine 
with  sulphur  with  brilliant  combustion ;  and  even  at  common  tem- 
peratures, if  iron  filings  and  sulphur  be  mixed  together  with  a  little 
water,  they  will,  in  uniting,  produce  so  much  heat  as  to  burst  into 
flame,  if  the  mass  be  moderately  large.  The  metallic  sulphurets, 
like  the  metallic  oxides,  are  some  acids  and  some  bases,  and  these, 
by  uniting,  form  the  extensive  classes  of  sulphur-salts.  The  metals 
combine  with  selenium  and  with  phosphorus,  subject  to  nearly  the 
some  conditions  as  in  forming  sulphurets,  but  the  history  of  those 
compounds  is  not  nearly  so  complete.  As  yet  but  very  little  has 
been  done  towards  the  history  of  the  compounds  of  the  metals  with 
nitrogen,  silicium,  or  boron. 

Some  of  the  metals,  tellurium,  arsenic,  and  antimony,  combine 
with  hydrogen,  forming  gaseous  compounds,  which  resemble  very 
closely  the  sulphurets  and  phosphurets  of  hydrogen  in  properties 
and  constitution.  In  these  bodies  the  hydrogen  is  the  positive  ele- 
ment, the  metal  playing  the  part  of  the  sulphur  or  of  oxygen. 

The  circumstances  under  which  the  metals  are  found  in  nature 
are  exceedingly  diverse.  Some  are  found  native,  or  only  alloyed 
with  other  metals,  as  gold,  silver,  tellurium,  bismuth,  and  some  oth- 
ers. Many  exist  combined  with  arsenic,  the  sources  of  cobalt  and 
nickel  being  almost  exclusively  their  native  arseniurets.  Some  me- 
tallic chlorides  and  iodides  exist  also  native,  but  the  most  abundant 
forms  in  which  the  metals  are  to  be  found  are  combinations  with 


332  GENERAL     PRINCIPLES     OF     THE 

oxygen  and  sulphur.  There  are  few  of  the  metals  that  do  not  exist 
naturally  in  the  state  of  oxides,  which  are  either  free  or  else  com- 
bined with  acids,  forming  salts.  Thus  lead,  copper,  iron,  zinc,  tin, 
manganese,  antimony,  are  all  found  in  abundance  as  native  oxides, 
or  as  native  sulphates,  carbonates,  arseniates,  phosphates,  silicates, 
&c.  The  majority  of  the  metals  exist  also  in  nature  combined  with 
sulphur.  The  sulphurets  of  lead,  of  zinc,  and  of  copper  are  the 
sources  from  whence  the  supplies  of  those  metals  are  obtained ;  and 
the  sulphuret  of  iron  exists  in  great  abundance,  and,  although  not 
used  for  the  extraction  of  the  metal,  is  of  great  importance  in  the 
manufacture  of  green  vitriol,  of  alum,  and  of  sulphuric  acid.  These 
native  compounds  of  the  metals  are  termed  ores  ;  and  the  metal  is 
said  to  be  mineralized  by  the  substance  with  which  it  is  united. 

The  processes  followed  in  the  extraction  of  the  metals  must  be,  of 
course,  regulated  by  the  composition  of  the  ores  in  which  it  is  con- 
tained ;  and  as  it  will  save  the  necessity  of  frequent  repetition  here- 
after, I,  shall -describe  the  general  manner  of  treating  each  kind  of 
ore,  so  far  as  may  serve  the  purpose  of  an  elementary  work  like  the 
present,  in  which  the  introduction  of  minute  and  technical  details 
would  be  useless  and  improper.  In  cases  where  the  plan  followed 
for  any  particular  metal  deviates  essentially  from  that  now  about 
to  be  described,  I  shall  notice  the  circumstance  in  its  special  history. 

Where  the  metal  exists  in  a  simply  oxidized  condition,  it  is  only 
necessary  to  heat  the  ore  strongly  in  contact  with  the  fuel,  by  which 
carbon  is  supplied  in  abundance  for  its  reduction.  The  carbon  com- 
bines with  the  oxygen,  and  the  metal  is  set  free.  It  is  not  often  that 
the  ores  have  this  simple  constitution,  but  in  many  cases  the  metal 
exists  as  a  carbonate,  and  then  the  carbonic  acid  being  expelled  by 
the  first  application  of  the  heat,  the  oxide  which  remains  is  reduced 
by  the  deoxidizing  action  of  the  ignited  fuel.  Thus  the  native  car- 
bonates of  lead,  of  copper,  of  zinc,  and  especially  of  iron,  are  simply 
reduced  in  this  way:  the  last  mentioned  is  the  ore  which  consti- 
tutes the  great  iron  deposite  of  the  neighbourhood  of  Glasgow. 

If  the  mineralizing  substance,  however,  be  any  other  than  oxygen, 
carbon,  no  matter  how  intensely  heated,  cannot  produce  any  effect 
upon  the  ore.  Thus  the  native  sulphurets  and  arseniurets  are  not 
acted  upon  by  carbon.  Nor  can  the  metals  be  obtained  in  a  pure 
form  from  any  of  their  salts,  except  the  carbonates,  by  means  of  car- 
bon, for  the  oxygen  of  the  acid  and  base  being  simultaneously  re- 
moved by  its  agency,  the  radical  of  the  acid  remains  united  with  the 
metal,  which  is  thus  only  changed  into  a  new  kind  of  ore.  Thus, 
if  sulphate  of  lead  be  heated  with  any  of  the  forms  of  carbon,  it  is 
converted  into  sulphuret  of  lead,  S.Og-l-Pb.O.  and4C.  giving  S.+Pb 
and  4C.0.  And  if  arseniate  of  iron  be  ignited  with  carbon,  all  the 
oxygen  is  removed,  and  the  arsenic  and  iron  remain  in  combination. 
In  such  cases,  it  is  necessary  to  adopt  somewhat  more  circuitous  , 
methods,  suited  to  the  constitution  of  the  individual  ores. 

In  the  case  of  certain  metallic  sulphurets,  the  metal  may  be  very 
simply  separated  by  melting  the  ore  with  a  proportional  quantity  of 
a  metal  having  a  greater  affinity  for  sulphur.  Thus  metallic  anti- 
mony is  very  generally  obtained  by  the  fusion  of  the  native  sulphu- 
ret with  iron  j  SbaSg  and  3Fe.  giving  3Fe.S.  and  Sb^.     On  the  large 


REDUCTION     OF     THE     METALS. 


333 


scale,  however,  this  method  would  not  be  economically  available. 
In  order  to  extract  the  metal  from  its  sulphuret,  as  in  the  generality 
of  the  ores  of  lead,  of  copper,  and  of  zinc,  the  ore,  first  reduced  to 
fine  powder,  is  heated  to  redness  in  a  current  of  air,  by  the  oxygen 
of  which  the  sulphur  is  converted  into  sulphurous  and  sulphuric  acid, 
while  the  metal  is  oxidized.  This  process  is  tQTvaeA  calcination.  A 
great  part  of  the  sulphuric  acid  formed  is  carried  off  with  the  cur- 
rent of  air,  and  the  remaining  product  is  a  sulphate  of  the  metal, 
with  excess  of  base.  When  the  salt  so  formed  is  deoxidized  by 
contact  with  the  ignited  fuel,  the  excess  of  oxide  abandoning  its  ox 
ygen,  yields  an  equivalent  quantity  of  metal,  which,  however,  would 
be  impure  and  of  inferior  quality,  by  having  dissolved  a  portion  of 
the  sulphuret  reproduced  by  the  reduction  of  the  sulphur  from  the 
sulphuric  acid.  It  is  therefore  necessary  to  get  rid  of  that  residual 
portion  of  the  sulphuric  acid  before  the  deoxidizing  process  com- 
mences, and  this  is  effected  by  mixing  up  a  proper  quantity  of  lime 
with  the  calcined  mass.  The  lime  decomposes  the  metallic  sulphate, 
combines  with  the  sulphuric  acid,  and  sets  the  oxide  free  ;  and  when 
the  deoxidizing  flames  of  the  furnace  pass  over  the  calcined  mass, 
the  metallic  oxide  being  reduced,  yields  a  pure  metal,  while  the  sul- 
phate of  lime,  by  losing  its  oxygen,  is  brought  to  the  state  of  sul- 
phuret of  calcium,  and  remains  as  glassy  scoria  upon  the  surface 
without  injury.  This  kind  of  operation  is  generally  carried  on  in  a 
sort  of  furnace  termed  reverberatory,  from  its  office  of  beating  down 
the  flames  from  the  fireplace  upon  the  materials  strewed  upon  itp, 
hearth.  The  adjoining  figures  will 
give  an  idea  of  its  construction.  The 
upper  is  a  vertical,  and  the  lower  a 
horizontal  section,  to  which  the  same 
letters  apply,  a  is  the  fireplace,  and 
b  the  ash-pit ;  at  c  a  low  wall  is  rais- 
ed, termed  the  bridge,  and  the  flames 
and  heated  air  ascending  from  the 
fire  are  reflected  downward  by  the 
low,  vaulted  roof,  and,  impinging  up- 
on the  hearth,  or  sole  of  the  furnace, 
d,  produce  the  greatest  heating  ef- 
fect upon  the  materials  laid  thereon. 
The  openings  i  and  g  serve  for  the 
introduction  of  the  materials,  and  for 

giving  them  the  arrangement,  agitation,and  mixture  most  cond* 
cive  to  the  success  of  the  operation 
regulates  the  draught,  and  hence  the  intensity  of  the  fire. 

In  this  furnace,  the  calcining  or  oxidizing,  and  the  reducing  op 
deoxidizing  effect  is  produced,  according  as  the  supply  of  fuel  and 
of  air  is  regulated  ;  and  thus  the  two  stages  just  described,  in  the 
extraction  of  a  metal  from  its  native  sulphuret,  are  carried  on.  The 
hearth,  d,  is  generally  dished  or  concave  towards  the  centre,  so  that 
the  reduced  metal,  in  its  melted  condition,  may  flow  there,  and  be 
run  out  by  an  aperture  in  the  side  of  the  furnace  when  the  opera- 
tion is  concluded. 

In  the  case  of  sulphuret  of  lead,  a  very  simple  and  beautiful  pro 


The  damper,  p,  in  the  fluw, 


334  GENERAL     PRINCIPLES     OF     THE 

cess  of  reduction  consists  in  roasting  the  ore  at  a  moderate  temper- 
ature, so  that  about  one  half  of  it  shall  be  converted  into  sulphate 
of  lead  by  oxidizement,  without  any  of  the  sulphuric  acid  being  driv- 
en offj  and  then,  having  mixed  this  up  well  with  the  unaltered  por- 
tion of  the  ore,  increasing  the  temperature  very  rapidly,  so  that  the 
two  shall  be  fluxed  together.  The  result  is  the  complete  conversion 
of  the  mixture  into  sulphurous  acid  gas,  which  passes  off,  and  pure 
metallic  lead,  which  remains,  the  sulphur  of  the  unaltered  ore  com- 
bining with  the  sulphur  and  oxygen  of  that  portion  which  had  been 
oxidized.  Thus  S.Oa+Pb.O.  and  S.+Pb.  produce  exactly  2S.O2  and 
2Pb. 

One  of  the  most  interesting  processes  of  reduction  is  that  by  which 
iron  is  obtained  from  its  most  abundant  ore,  the  clay  iron  stone. 
This  substance  consists  of  oxide  of  iron  of  greater  or  less  purity, 
combined  with  alumina  and  silica.  Now,  as  carbon  cannot  deprive 
silica  of  oxygen  except  under  very  peculiar  circumstances,  such  as 
those  described  in  page  323,  so  the  metal  cannot  be  obtained  by 
mere  deoxidation ;  and  even  if  the  oxygen  were  removed,  the  result 
would  not  be  pure  iron,  but  a  compound  of  silicon  and  iron,  which, 
indeed,  is  formed  in  small  quantity,  and  is  found  generally  in  cast 
iron.  It  is  necesifeary,  therefore,  to  decompose  the  silicate  of  iron 
of  which  the  ore  is  constituted,  and  this  is  effected  by  means  of  lime. 
The  coal  or  coke  and  the  ore  are  introduced  into  the  furnace,  mixed 
with  a  proportion  of  limestone,  which,  being  calcined  by  the  heat, 
yields  lime,  which  seizes  upon  the  silicic  acid,  and  the  oxide  of  iron 
being  set  free,  is  immediately  reduced  by  the  carbon  of  the  fuel  with 
which  it  is  in  contact,  and  produces  metallic  iron.  The  lime,  the 
silica,  and  the  alumina  being  melted  together,  form  a  substance  of 
a  nature  somewhat  between  glass  and  porcelain,  which  floats  upon 
the  mass  of  melted  metal,  and  constitutes  the  slags  or  scorise  of  the 
iron  furnaces. 

In  the  case  of  ores  containing  arsenic,  of  which  only  the  arseniu- 
rets  of  cobalt  and  nickel  are  of  technical  importance,  the  method 
followed  is  to  roast  the  ore  in  a  furnace  so  constructed  that  a  pow- 
erful oxidizing  action  shall  be  produced  by  a  current  of  air  stream- 
ing over  the  ignited  ore  5  both  metals  being  thus  oxidized,  arsenious 
acid,  and  oxide  of  cobalt  or  of  nickel  are  produced ;  the  greater 
part  of  the  former  is  expelled  by  the  heat,  and,  being  carried  off  by 
the  draught,  is  conducted  into  large  chambers,  where  it  is  gradually 
deposited  under  the  form  of  a  fine  white  powder  upon  the  walls  and 
floor.  The  metal  with  which  the  arsenic  had  been  combined  re- 
mains in  the  state  of  oxide  united  with  a  little  arsenious  acid,  and 
is  subsequently  extracted  or  employed  in  other  processes. 

The  reduction  of  a  metal  from  the  state  of  sulphuret  is  frequently 
effected  upon  the  small  scale  by  fusion  with  a  mixture  of  lime  and 
charcoal,  or  of  carbonate  of  potash  and  charcoal,  which  last  is  fa- 
miliarly  termed  black  flux.  The  theory  of  this  process  is  very  sim* 
pie.  Thus,  if  sulphuret  of  antimony,  lime,  and  charcoal  be  melted 
together,  the  sulphur  combines  with  the  calcium  of  the  lime,  the 
oxygen  of  which  unites  with  the  antimony,  Sb2S3  and  3Ca.O.  giving 
SCa.S.  and  SbjOs.  This  last  is  then  decomposed  by  the  charcoal, 
the  oxygen  combining  with  the  carbon,  and  the  metallic  antimony 
separates. 


REDUCTION     OF    THE     METALS.  335 

The  black  flux  used  in  such  operations  is  prepared  by  deflagrating 
together  equal  parts  of  nitre  and  cream  of  tartar ;  the  nitrogen  and 
oxygen  of  the  former  unite  with  the  carbon  and  hydrogen  of  the 
latter,  forming  carbonic  acid,  nitrogen,  and  water:  the  potash  of 
both  remains  behind  as  carbonate,  mixed  with  the  excess  of  carbon 
which  had  escaped  combustion.  If  two  parts  of  nitre  be  used  with 
one  of  cream  of  tartar,  there  remains  after  deflagration  a  white 
mass  of  carbonate  of  potash,  which  is  known  as  white  flux,  and  used  in 
processes  where  the  deoxidizing  effect  of  the  carbon  is  not  required. 
Thus,  for  the  reduction  of  chloride  of  silver,  it  is  sufficient  to  fuse 
it  with  half  its  weight  of  white  flux  ;  the  chlorine  combines  with  the 
potassium,  and  the  silver,  which  at  a  lower  temperature  would  have 
united  with  the  oxygen  and  carbonic  acid,  is  separated,  those  two 
bodies  escaping  in  the  gaseous  form  j  the  formula  of  the  reaction 
being  that  K.O.  .  C.O^  and  Gl.Ag.  give  K.Ch  and  free  Ag.,  while  O. 
and  C.O2  are  driven  off. 

Hydrogen,  although  inapplicable  to  the  reduction  of  the  metals 
upon  the  large  scale,  and  for  the  purposes  of  the  arts,  is  yet  to  the 
chemist  a  most  valuable  agent  for  this  office,  as  it  acts  upon  all  va- 
rieties of  metallic  combinations,  whether  oxides,  chlorides,  or  sul- 
phurets ;  and  that  the  results  it  gives  are  so  accurate  as  to  serve  as 
bases  for  some  of  the  most  fundamental  propositions  of  the  science. 
Thus  we  have  already  seen  that  the  composition  of  water  is  best 
determined  by  the  action  of  hydrogen  gas  upon  oxide  of  copper, 
and  in  analytical  investigations,  the  isolation  of  a  metal,  by  decom- 
posing its  chloride  or  sulphuret  in  a  stream  of  hydrogen  gas,  is 
frequently  employed.  The  deoxidizing  action  of  hydrogen  is  oc- 
casionally used  in  an  indirect  manner.  Thus  a  very  convenient 
mode  of  obtaining  silver  from  the  chloride  consists  in  fusing  it 
with  some  common  resin :  this  consists  of  carbon,  hydrogen,  and 
oxygen,  of  which  only  the  hydrogen  is  active  ;  it  combining  with 
the  chlorine  carries  it  off  as  muriatic  acid  gas,  while  the  metallic 
silver  is  separated.  If  the  chloride  of  silver  be  diffused  through 
water  rendered  slightly  acid,  and  a  slip  of  zinc  be  introduced,  an 
evolution  of  hydrogen  commences,  and  the  silver  separates  as  a  fine 
metallic  powder  as  the  zinc  dissolves.  But  the  action  is  here  more 
properly  galvanic  ;  an  equivalent  (32'3)  of  zinc  combining  with  the 
chlorine  in  place  of  each  equivalent  (108)  of  silver  which  is  set 
free.  The  precipitation  of.  copper  from  the  water  of  copper  mines, 
which  holds  sulphate  of  copper  dissolved,  by  dipping  therein  pieces 
of  iron,  and,  indeed,  all  cases  of  the  precipitation  of  one  metal  by 
another,  are  referrible  to  the  same  source. 

The  physical  agent,  electricity,  which  has  been  already  found  to 
influence  chemical  action  to  so  remarkable  a  degree,  has  been  em- 
ployed with  considerable  success  in  the  reduction  of  certain  met- 
als. It  was  first  applied  by  Davy,  who  thereby  made  his  wonderful 
discoveries  of  the  composition  of  the  alkalies  and  earths.  It  has 
been  totally  superseded  in  that  point  of  view  by  simpler  processes, 
but  has  recently  been  applied  by  Becquerel,  upon  the  large  scale,  to 
the  extraction  of  the  precious  metals  from  their  ores. 

There  are  many  other  methods  of  reduction,  which,  however, 
being  limited  in  their  application  to  individual  metals,  will  form 
more  properly  a  part  of  their  special  history. 


336  POTASSIUM. 


CHAPTER  XIII. 

OF    THE   INDIVIDITAL   METALS,    AND    OF   THEIR    COMPOUNDS   WITH    OXVGEN, 
SULPHUR,  SELENIUM,  AND  PHOSPHORUS. 

SECTION  I. 
METALS  OF  THE  FIRST  CLASS. 

Of  Potassium. 

Potassium  is  the  metallic  basis  of  the  alkali  potash.  It  was  ongi 
nally  discovered  by  Sir  Humphrey  Davy,  who  obtained  it  by  sub- 
mitting a  piece  of  caustic  potash,  slightly  moistened,  so  as  to  be  a 
conductor  of  electricity,  to  the  action  of  a  powerful  galvanic  bat- 
tery J  the  water  and  the  potash  were  simultaneously  decomposed, 
oxygen  being  evolved  at  the  positive  electrode,  while  hydrogen  and 
potassium  were  separated  at  the  negative  wire.  From  the  heat 
generated  by  the  intense  power  used,  the  metallic  globules  gener- 
ally burned  as  soon  as  they  came  into  contact  with  the  air,  and  it 
was  with  difficulty  that  a  quantity  was  obtained  sufficient  for  the 
important  researches  in  which  it  was  employed  by  its  illustrious 
discoverer.  By  using  mercury  as  the  negative  electrode,  the  de- 
composition can  be  effected  by  a  much  weaker  force,  and  even 
with  a  single  pair  of  plates,  as  in  the  arrangement  of  Dr.  Bird,  de- 
scribed in  p.  199. 

The  decomposition  of  potash  by  truly  chemical  means  is  due  to 
Gay  Lussac,  but  it  is  by  the  process  of  Brunner  that  the  metal  is 
now  universally  obtained.  As  it  is  carried  on  only,  however,  in  the 
most  extensive  and  best-appointed  laboratories,  a  very  short  sketch 
of  it  will' suffice  here. 

Cream  of  tartar,  which  consists  of  tartaric  acid  united  to  potash, 
is  to  be  ignited  in  a  covered  crucible,  until  there  remains  a  mass  of 
carbonate  of  potash  mixed  wdth  carbon  in  a  state  of  very  minute 
division,  and  this  mass  is  to  be  intimately  mixed,  while  still  hot, 
with  a  quantity  of  coarsely-powdered  wood  charcoal,  which  serves 
to  render  the  w^hole  porous,  so  as  to  allow  of  the  escape  of  the 
gases  generated  in  its  interior  without  its  swelling  up.  The  mate- 
rial so  prepared  is  introduced  into  an  iron  bottle,  such  as  those  in 
which  quicksilver  is  imported  ;  to  the  mouth  of  the  bottle,  which  is 
laid  horizontally  in  a  wind  furnace,  is  adapted  a  short  iron  tube, 
passing  to  a  copper  condenser  partly  filled  with  rectified  naptha, 
and  so  constructed  with  partitions  as  to  exclude  the  air,  while  there 
passes  through  it  a  stout  iron  wire,  terminated  by  a  screw,  with 
which  the  iron  tube  can  be  cleared  of  any  solid  material  that  might 
be  deposited  in  it.  The  apparatus  being  so  arranged,  and  the  re- 
ceiver surrounded  by  ice,  a  fire  is  lighted  in  the  furnace,  and  when 
the  iron  bottle  has  become  white  hot,  the  decomposition  of  the 
potash  begins,  the  metal  distils  over,  and  condenses  in  the  receiver 


PREPARATION    AND    PROPERTIES    OF    POTASSIUM.    337 

in  globules,  which  are  protected  by  the  naptha,  in  which  they  sink, 
while  the  oxygen  of  the  potash  and  of  the  carbonic  acid  combines 
with  carbon,  forming  carbonic  acid,  which,  escaping  under  the  par- 
titions in  the  receiver,  passes  away  j  K.O.-I-C.O2  and  2C.  producing 
K.  and  3C.0.  The  great  difficulty  and  loss  in  this  process  arise, 
however,  from  a  cause  which  is  not  at  first  apparent ;  it  is,  that 
carbonic  oxide  and  potassium  unite  to  form  a  dark  gray  mass, 
which  sublimes,  and,  condensing  in  the  short  iron  tube,  renders  the 
screw  necessary  to  keep  the  passage  clear,  and  frequently  causes 
the  failure  of  the  process.  Even  in  the  most  successful  results, 
one  half  of  the  metal  actually  reduced  is  lost  by  combining  with 
the  carbonic  oxide. 

The  potassium  thus  obtained  is  very  impure,  containing  much 
carbon,  and  a  quantity  of  that  compound  of  carbonic  oxide  which 
passes  over  into  the  receiver.  To  purify  it,  it  is  redistilled  in  cast 
iron  retorts,  from  which  the  air  has  been  previously  excluded  by 
vapour  of  naptha,  and  it  is  thus  obtained  in  globules  like  peas,  in 
which  state  it  may  be  preserved  under  naptha  perfectly  free  from 
oxygen. 

At  common  temperatures,  potassium  is  soft,  and  may  be  moulded 
in  the  fingers  like  wax.  At  32°  it  is  quite  brittle,  and  crystallizes 
in  cubes  J  at  70^  it  is  pasty,  and  at  150^  perfectly  liquid.  At  a  dull 
red  heat  it  boils,  forming  a  green  vapour,  and  may,  as  described 
above,  be  easily  distilled.  It  is  specifically  lighter  than  water,  its 
specific  gravity  being  0-865. 

The  colour  of  potassium  is  of  a  bluish  white,  but  its  surface  in 
stantly  becomes  gray  when  exposed  to  the  air,  owing  to  the  absorp- 
tion of  oxygen  and  the  formation  of  a  crust  of  potash.  If  it  be 
heated,  it  burns  with  a  vivid  violet  flame.  So  great  is  its  affinity 
for  oxygen  that  it  decomposes  water,  and  even  ice,  with  great  vio- 
lence, so  much  heat  being  evolved  that,  if  the  experiment  be  made 
in  the  air,  the  hydrogen  gas  evolved  and  the  metal  both  inflame 
and  burn  with  a  fine  violet  colour.  When  the  metal  has  been  all 
consumed,  a  globule  of  fused  dry  potash  remains,  which,  when  it 
has  cooled  to  a  certain  degree,  combines  with  water  with  a  loud  re- 
port, and  instantly  then  dissolves. 

Potassium  is  remarkably  characterized  by  its  great  affinity  for  ox- 
ygen, which  it  abstracts  from  almost  all  bodies  ;  thus  its  use  in  the 
preparation  of  boron  and  silicon  has  been  already  noticed  ;  and  al- 
though, at  very  high  temperatures,  iron  and  carbon  take  oxygen  from 
potassium,  yet  at  a  lower  degree  of  heat,  oxide  of  iron  and  carbonic 
acid  are  both  decomposed  by  potassium,  carbon  being  deposited 
^rom  the  one,  and  metallic  iron  separated  from  the  other. 

The  symbol  of  potassium  is  K.,  the  initial  of  the  word  Kalium, 
6y  which  the  metal  is  designated  by  most  of  the  Continental  chem- 
ists; the  old  name  kali  being  still  retained  in  preference  to  the  word 
notash,  which  has  been  adopted  only  in  Great  Britain  and  in  France. 
the  equivalent  is  490  or  39-3,  according  to  the  scale. 

Oxides  of  Potassium. — Potassium  combines  with  oxyo-en  in  two 
proportions,  forming  a  protoxide  K.O.,  and  a  peroxide  K  O3. 

The  protoxide  of  potassium  constitutes  the  important  alkali  pou 
ash  ;  A\  can  only  be  obtained  free  from  water  by  exposing  potassium 

U  u 


338    PREPARATION     AND     PROPERTIES     OF     POTASH. 

to  the  action  of  dry  air,  when  it  is  converted  into  a  white  powder, 
which  is  fusible  at  a  red,  and  volatile  at  a  white  heat ;  if  this  sub- 
stance be  once  united  with  water,  it  cannot  be  separated  from  it 
except  by  combination  with  an  acid.  The  potash  of  commerce, 
and  that  used  in  the  laboratory,  is,  therefore,  always  hydrate  ot 
potash;  the  dry  potash,  in  uniting  with  water,  becomes  ignited. 
Before  the  discovery  of  carbonic  acid,  the  alkalies  and  their  carbon- 
ates were  distinguished  from  each  other  by  the  epithets  of  mild 
and  caustic,  and  hence  for  medicinal  purposes,  and  in  some  phar 
macoposias,  the  hydrate  of  potash  is  still  termed  caustic  potash. 

To  prepare  a  solution  of  potash,  the  carbonate  of  potash  of  com- 
merce, derived  from  the  sources  to  be  detailed  in  its  description,  is 
to  be  dissolved  in.  ten  parts  of  water,  and  the  solution  being  made 
to  boil  smartly,  is  to  be  decomposed  by  one  part  of  slacked  lime  in 
fine  powder,  which  is  to  be  gradually  added,  the  boiling  being  briskly 
kept  up ;  the  lime  abstracts  the  carbonic  acid  from  the  potash,  and 
carbonate  of  lime  is  formed,  which  at  that  temperature,  constituting 
minute  crystals  of  arragonite,  is  rapidly  and  completely  deposited. 
The  clear  liquor  is  to  be  tested  occasionally  by  adding  to  a  small 
quantity  of  it  an  excess  of  muriatic  acid ;  as  soon  as  the  absence  of 
effervescence  shows  that  all  the  alkaline  carbonate  has  been  decom- 
posed, the  pan  is  to  be  removed,  and  being  laid  aside,  carefully  cov- 
ered, until  the  carbonate  of  lime  has  been  well  settled,  the  clear  li- 
quor may  be  siphoned  off.  The  decomposition  of  the  carbonate  of 
potash  by  the  lime  would  take  place  also  at  ordinary  temperatures, 
but  the  precipitate  would  be  in  the  rhombohedral  form,  and  being 
specifically  lighter  and  more  finely  divided,  would  occupy  much 
more  room,  and  would  not  separate  so  well.  Jf  the  carbonate  of 
potash  be  dissolved  in  less  than  six  parts  of  water,  it  is  not  decom- 
posed by  lime  ;  on  the  contrary,  when  a  strong  solution  of  caustic 
potash  is  boiled  with  carbonate  of  lime,  carbonate  of  potash  is  pro- 
duced, and  lime  set  free. 

When  the  solution  of  caustic  potash  is  evaporated  in  a  basin  of 
iron,  or  silver,  or  platina,  there  remains  a  liquid  which  solidifies  on 
cooling  into  the  hydrate  of  potash^  K.O.  .  H.O.  This  liquid  is  gener- 
ally run  into  cylindrical  moulds,  in  which  form  the  caustic  potash 
or  fused  potash  of  the  shops  is  generally  found.  In  this  state  it  is, 
however,  impure,  and  it  requires  to  be  freed  from  the  admixed  sul- 
phate and  carbonate  of  potash,  chloride  and  peroxide  of  potassium, 
and  oxide  of  iron,  which  it  generally  contains,  by  being  dissolved 
in  absolute  alcohol,  the  solution  evaporated  to  dryness,  and  the  re- 
maining potash  fused  a  second  time. 

Hydrate  of  potash  is  a  pure  white  solid,  of  a  crystalline  fracture ; 
it  fuses  below  redness.  In  the  fingers  it  has  a  peculiar  soapy  feel, 
owing  to  its  dissolving  the  cuticle,  with  which  it  forms  a  kind  of 
soap ;  it  acts  powerfully  on  all  organic  tissues,  dissolving  and  decom- 
posing them,  and  hence  its  use  in  surgery,  and  its  name  of  caustic 
potash.  It  dissolves  in  water,  with  the  evolution  of  considerable 
heat  J  a  concentrated  solution  of  it  crystallizes  when  exposed  to 
cold,  in  rhombic  octohedrons,  whose  composition  is  K.0.4-5H.O. 

The  solution  of  potash  is  pre-eminently  alkaline  ;  it  neutralizes  the 
strongest  acids,  browns  turmeric  paper,  and  restores  the  blue  coloui 


SULPHURETS     OP     POTASSIUM.  339 

of  litmus  paper  reddened  by  an  acid.  It  absorbs  carbonic  acid  rap- 
idly from  the  air,  and  must  hence  be  preserved  in  close  vessels.  It 
acts  rapidly  on  glass  containing  much  alkali  or  lead,  and  hence  should 
be  preserved  in  bottles  of  common  green  glass. 

The  uses  of  potash  in  chemistry  are  too  numerous  to  mention  ;  it 
being  the  strongest  base,  is  employed  in  almost  all  cases  of  saline 
decomposition,  and  its  various  compounds  are  of  great  importance 
in  the  chemical  arts,  of  which  many  will  be  noticed  hereafter  in  de- 
tail. 

Potash  is  distinguished,  when  free,  first,  by  its  general  alkaline 
characters,  and  by  its  not  being  precipitated  by  carbonate  of  soda, 
which  separates  it  from  everything  but  soda  and  ammonia.  From 
the  latter  it  is  known  by  the  brown  stain  produced  on  turmeric  paper 
being  permanent,  whereas  the  brown  colour  produced  by  ammonia 
disappears  when  the  paper  is  warmed;  and  from  soda  it  is  known 
by  giving  with  an  excess  of  the  perchloric,  tartaric,  and  hydrofluo- 
silicic  acids,  sparingly  soluble  salts,  whereas  the  soda  salts  of  these 
acids  are  all  easily  soluble.  A  solution  of  potash,  if  neutralized  by 
muriatic  acid,  gives,  on  the  addition  of  chloride  of  platinum,  a  fine 
yellow  precipitate,  whereas,  with  a  solution  of  soda,  no  precipitation 
occurs. 

The  salts  of  potash  act  in  all  respects  similarly,  except  that,  as 
there  is  no  alkali  in  excess,  the  action  on  vegetable  colours  is  not 
that  of  an  alkali.  The  salts  of  ammonia  resemble  precisely  the  salts 
of  potash  in  their  action  on  those  precipitants  described  above,  but 
they  are  at  once  distinguished  by  the  application  of  heat.  The  salts 
of  ammonia  are  all  volatilized,  either  with  or  without  decomposition, 
by  a  red  heat,  while  those  of  potash  are  fixed,  and  give  to  the  flame 
of  the  blowpipe  a  distinct  and  characteristic  violet  tinge. 

Potash  consisting  of  an  equivalent  of  each  element,  its  formula  is 
K.O.,  and  its  composition, 

Potassium,  83-05  One  equivalent  =490  or  39-3 

Oxygen,       16-95  One  equivalent  =100  or    8-0 

100^  590       47^ 

Peroxide  of  Potassium.  K.O3. — This  substance,  which  is  of  very  little  importance, 
is  formed  by  burning  potassium  in  an  excess  of  oxygen  gas  ;  it  is  a  yellow  powder, 
decomposed  by  water,  potash  dissolving,  and  oxygen  being  given  off".  When  hy- 
drate of  potash  is  heated  to  redness  in  air,  some  peroxide  is  always  formed,  and 
hence  the  fused  potash  of  the  shops  generally  gives  off  minute  bubbles  of  oxygen 
gas  when  dissolved  in  water. 

Siilphureis  of  Potassium. — When  potassium  is  gently  heated  in 
contact  with  sulphur,  they  unite  with  brilliant  combustion,  and,  ac- 
cording to  the  proportions  in  which  they  are  employed,  form  the 
sulphurets  of  potassium,  of  which  there  are  altogether  four.  These 
bodies  are,  however,  always  prepared  in  practice  by  more  econom- 
ical processes. 

If  sulphate  of  potash  be  ignited  in  a  glass  tube,  and  a  current  of  dry  hydrogen  gas 
be  passed  over  it,  all  the  oxygen,  both  of  acid  and  base,  is  removed  in  the  state  of 
water,  and  protosulphuret  of  potassium  remains.  Thus  K.O.  .  S.O3  and  411.  produce 
4H.0.  and  K.S.  The  same  result  follows  from  igniting  strongly,  in  a  crucible,  a 
mixture  of  charcoal  and  sulphate  of  potash ;  all  the  oxygen  is  removed  as  carbonic 
oxide,  and  the  sulphur  and  the  potassium  remain  in  combination,  K.O. .  S.O3  and  4C, 
giving  4C.().  and  K.S. 


340        SULPHURETS     OP     POTASSIUM.  SODIuAl. 

This  protosulphuret  is  of  a  brown  colour,  fusible  below  a  red  heat,  easily  solu- 
ble, and  its  solution  is  yellow,  and  reacts  higlily  alkaline  and  caustic.  When  ex- 
posed to  the  air,  it  absorbs  oxygen  rapidly  ;  and  in  preparing  it  from  sulphate  of  pot- 
ash, by  carbon,  if  lampblack  be  used,  so  that  the  product  shall  be  in  a  state  r-f  very 
minute  division,  it  takes  fire  spontaneously  on  coming  into  contact  with  the  air, 
constituting  a  pyrophorus.  If  the  protosulphuret  of  potassium  be  acted  upon  by 
acids,  water  is  decomposed,  K.S.  and  H.O.  giving  K.O.  and  H.S. ;  the  potash  re- 
mains united  with  the  acid,  and  the  sulphuret  of  hydrogen  is  given  off.  No  solid 
sulphur  is  deposited,  and  the  liquor  remains  clear. 

A  solution  of  the  protosulphuret  dissolves  sulphur  in  large  quantity,  the  higher 
aulphurets  being  formed.  It  absorbs  sulphuretted  hydrogen  in  such  proportion  that 
a  compound  is  produced,  K.S.-j-H.S.,  exactly  similar  to  the  hydrate  of  potash, 
K.O.+H.O. 

The  tersulphuret  o/;?ofa55mm  corresponds  to  the  peroxide,  its  formula  being  K.S3. 
It  constitutes  the  mass  of  the  hcpar  sulphuris,  liver  of  sulphur,  of  the  pharmaco- 
poeias. It  may  be  prepared  by  fusing,  at  a  low  red  heat,  one  part  of  sulphur  and 
two  of  carbonate  of  potash,  the  mass  being  kept  liquid  as  long  as  it  effervesces,  from 
carbonic  acid  gas  being  evolved.  In  this  reaction,  a  quantity  of  oxygen  from  the 
potash  combines  with  one  portion  of  the  sulphur,  forming  hyposulphurous  or  sul- 
phuric acid,  according  to  the  temperature,  while  the  remainder  of  the  sulphur  com- 
bines with  the  potassium,  producing  a  sulphuret,  the  composition  of  which  is  de- 
termined by  the  quantity  of  sulphur  present.  With  the  above  proportions  the  reac- 
tion may  be  considered  thus  :  4(K  O.-fCOa)  and  lOS.  give  3K.S3  and  K.O.  .  S.O3, 
which  constitute  the  fused  mass,  while  40. O2  is  driven  off  with  effervescence.  If, 
however,  equal  weights  of  carbonate  of  potash  and  of  sulphur  be  employed,  the 
sulphuret  formed  contains  five  equivalents  of  sulphur :  it  is  the  pentasulphuret. 

These  sulphurets  resemble  each  other  completely  in  external  appearance ;  they 
are  liver-brown ;  they  deliquesce  in  the  air,  and  absorb  oxygen  rapidly.  Their  solu- 
tions, which  are  at  first  deep  yellow,  become  colourless  by  uniting  with  oxygen, 
hyposulphite  of  potash  being  formed,  and  sulphur  precipitated.  If  a  solution  of  the 
tersulphuret  or  pentasulphuret  be  treated  with  an  acid,  water  is  decomposed,  and 
potash  being  formed,  sulphuret  of  hydrogen  is  produced ;  the  remaining  sulphur 
then  separates  in  a  state  of  very  minute  division,  and  of  a  milk-vi^hite  colour,  con- 
stituting the  lac  sulphuris,  or  the  sulphur  precipitatum  of  jiharmacy.  If  the  acid  em- 
ployed be  strong  and  in  great  excess,  a  quantity  of  bisulphuret  of  hydrogen  is  form- 
ed, as  explained  in  page  293. 

Rose  is  of  opinion  that  the  whiteness  of  precipitated  sulphur  depends  not  merely 
upon  its  minute  division,  but  that  it  is  owing  to  the  presence  of  a  trace  of  bisul- 
phuret of  hydrogen.  When  the  hepar  sulphuris  is  decomposed  by  an  acid,  it  is  not 
merely  that  the  excess  of  sulphur  is  set  free,  but  in  addition,  as  there  is  always  hy- 
posulphurous acid  present ;  this,  when  evolved,  acts  on  the  sulphuretted  hydrogen, 
and  the  sulphur  of  both  is  precipitated,  water  being  formed ;  S.O2  and  2PI.S.  giving 
3H.0.  and  2S. 

The  Pentasulphuret  of  Potassium  is  prepared  perfectly  pure  by  decomposing  sul- 
.phate  of  potash  by  sulphuret  of  hydrogen,  at  a  red  heat.  Thus  K.O.  .  S.O3  and 
4H.S.  give  K.S3  and  4H.0.  This  reaction  supports  very  much  the  view  that  this 
pentasulphuret  is  really  sulphate  of  potash,  in  which  the  oxygen,  both  of  acid  and 
base,  is  replaced  by  sulphur,  for  K.S5  may  be  constituted  of  K.S.  and  S.S3. 

The  seleniurets  of  potassium  are  similar  in  constitution  to  the  sulphurets.  They 
evolve  seleniuret  of  hydrogen  when  treated  Jy  acids,  with  precipitation  of  seleni- 
um when  it  is  present  in  greater  proportion  than  one  equivalent. 

Of  Sodium. 
Sodium  exists  in  great  quantities  in  the  mineral  kingdom,  es- 
pecially combined  with  chlorine,  as  common  salt,  of  which  enor- 
mous deposites  are  found  in  England,  Poland,  and  elsewhere,  besides 
forming  the  leading  saline  ingredient  of  the  waters  of  salt  lakes  and 
of  the  ocean.  It  is  found  in  many  minerals,  and  is  remarkably 
prevalent  in  the  animal  fluids,  all  of  which  contain  common  salt. 
Tt  is,  indeed,  from  the  chloride  of  sodium  that  we  derive,  whether 
directly  or  indirectly,  all  the  supplies  of  the  various  compounds  o( 
this  metal. 


SODIUM     AND     SODA.  341 

The  discovery  of  sodium  was  made  in  the  same  manner,  and  im 
mediately  subsequent  to  that  of  potassium,  by  Humphrey  Davy, 
and  it  is  now  prepared  in  exactly  the  same  manner  as  that  metal. 
It  is,  however,  much  more  easily  prepared ;  its  reduction  does  not 
require  so  high  a  temperature,  and  it  does  not  unite  with  carbonic 
oxide,  so  that  the  formation  of  the  black  sublimate,  which  is  the 
principal  source  of  loss  and  failure  in  preparing  potassium,  does  not 
occur. 

Sodium  is  lighter  than  water,  its  sp.  gr.  being  0*972 ;  it  conse- 
quently floats  upon  that  liquid  ;  and  when  a  globule  of  the  metal  is 
thrown  into  a  basin  of  water,  this  is  decomposed  with  great  rapidity, 
hydrogen  being  evolved  ;  but  the  action  is  not  so  energetic  as  with 
potassium  ;  the  gas  does  not  take  fire  spontaneously.  But  if  the 
globule  be  prevented  from  moving  about,  the  water  becomes  heat- 
ed, and  the  action  increases  so  much  as  to  set  fire  to  the  gas ;  this 
occurs  when  there  is  so  little  water  that  the  globule  does  not  swim, 
or  when  it  is  fastened  to  the  edge  of  the  vessel,  or  if  the  water  be 
thickened  by  gum  or  starch.  If  some  oil  of  vitriol  be  added  to  the 
water,  the  action  is  so  much  more  active,  that  combustion  occurs 
even  when  the  metallic  globule  moves  rapidly  about. 

The  symbol  of  sodium  is  Na.,  derived  from  the  word  Natrium,  as 
soda  still  retains  in  many  countries  the  name  Natron.  Its  equiva- 
lent numbers  are  291  or  23-3. 

Sodium  unites  with  oxygen  in  two  proportions,  forming  the  pro- 
toxide, or  soda,  Na.O.,  and  the  peroxide,  of  which  the  constitution 
is  not  exactly  known.  This  last  is  prepared  just  as  the  peroxide  of 
potassium,  which  it  resembles  completely  in  its  properties.  The 
former  only  requires  detailed  notice. 

The  preparation  of  dry  soda  is  effected  like  that  of  potash,  by 
heating  the  metal  in  dry  air  or  oxygen.  It  is  grayish  white,  and 
absorbs  water  with  excessive  power.  From  the  hydrate  of  soda 
the  water  can  be  expelled  only  by  an  acid.  The  caustic  soda  is, 
therefore,  always  like  caustic  potash,  a  hydrate  of  the  alkali.  For 
the  preparation  of  caustic  soda,  the  same  process  is  to  be  followed 
as  for  that  of  potash.  The  carbonate  of  soda  of  commerce,  dissolv- 
ed in  boiling  water,  is  decomposed  by  slacked  lime,  it  being  neces- 
sary, however,  to  use  one  third  more  lime,  from  the  smaller  equiv- 
alent number  of  soda.  The  solution  of  caustic  soda  resembles  that 
of  caustic  potash  in  all  its  alkaline  characters,  but  its  action  is  not 
so  intense.  It  is  a  weaker  alkali,  its  salts  being  decomposed  in 
all  cases  by  potash. 

The  soda  consists  of  an  equivalent  of  each  element  j  its  formula 
is  Na.O.,  and  its  composition, 

Sodium,  74-42         One  equivalent  =291  or  23-3 

Oxygen,  25-58         One  equivalent  =100  or    8.0 

100-00  391       SFS 

The  detection  of  soda  is  very  simple.  On  adding  to  a  solution  of 
the  substance  to  be  examined  a  solution  of  carbonate  of  soda,  if  there 
be  no  precipitate  produced,  the  base  of  the  salt  present  must  be  an 
alkali.  On  then  applying  the  various  tests  for  potash  and  for  am- 
monia detailed  in  the  last  section,  if  no  evidence  of  their  presence 


342  L  I  T  H  I  U  M. B  A  R  I  U  M. 

be  obtained,  the  alkali  must  be  soda ;  and  even  where  potash  also 
is  present,  a  small  quantity  of  soda  may  be  recognised,  by  its  tin- 
ging the  flame  of  the  blowpipe  of  a  fine  yellow  colour. 

The  compounds  of  soda  are  very  numerous  and  important,  and 
will  be  described  in  their  proper  place,  among  the  salts. 

The  sulphurets  of  sodium  resemble  so  completely  the  sulphurets  of  potassium  a^ 
not  to  require  more  than  a  reference  to  their  description.  To  the  seleniurets  of 
sodium  the  same  remark  applies. 

Lithium, 

This  metal  is  found  only  in  a  few  minerals,  of  which  one  of  the 
most  common,  spodumene,  occurs  at  Killiney,  near  Dublin.  Thia 
mineral  is  a  double  silicate  of  the  alkali  lithia  (oxide  of  lithium)  and 
alumina.  The  metal  has  been  obtained  by  voltaic  decomposition, 
but  only  in  very  small  quantity.  It  is  white,  like  sodium,  and  be- 
comes oxidized  immediately  on  exposure  to  the  air.  Its  symbol  is 
L.,  and  its  equivalent  number  80*3  or  6'4i. 

To  obtain  lithia,  the  simplest  process  is  to  mix  the  mineral  containing  it  (gener- 
ally lepidolite  or  spodumene),  previously  reduced  to  very  fine  powder,  with  fluor 
spar,  and  digest  the  mass  with  oil  of  vitriol,  until  it  is  completely  decomposed ;  the 
silica  is  carried  off  by  the  hydrofluoric  acid  (see  page  324),  and  the  hme,  the  alumina, 
and  the  lithia  remain  combined  with  the  sulphuric  acid.  By  the  action  of  a  small 
quantity  of  water,  the  sulphates  of  lithia  and  alumina  are  dissolved  out,  and  the  last 
then  precipitated  by  ammonia.  The  sulphates  of  lithia  and  ammonia  being  then  ig- 
nited, the  sulphate  of  ammonia  is  decomposed,  and  the  sulphate  of  lithia  obtained 
pure.  This  is  but  a  general  outline  of  the  process,  which  requires  many  additional 
operations  for  a  fully  successful  result. 

Lithia  is  distinguished  from  the  other  alkalies  by  the  sparing  sol- 
ubility of  its  carbonate,  in  which  character  it  approximates  to  the 
property  of  the  earths,  thus  connecting  the  two  classes  of  metals. 
Being  so  rarely  found,  and  of  no  application  in  the  arts,  its  history 
is  not  of  much  importance. 

Lithia  is  recognised  by  the  sparing  solubility  of  its  carbonate,  and 
by  tinging  the  flame  of  the  blowpipe  of  a  brilliant  red  colour.  This 
last  character  easily  distinguishes  it  from  soda.  Lithia  is  a  protox- 
ide, its  formula  being  L.O.  ;  its  equivalents  180*3  or  144. 

The  sulphurets  and  seleniurets  of  lithium  do  not  possess  any  in- 
terest. 

The  alkali  ammonia  might,  on  one  hypothesis  of  its  nature,  be  described  here. 
When  combined  with  hydrogen,  it  is  considered  by  BerzeUus  and  many  other  chem- 
ists to  form  a  remarkable  compound  metal,  ammonium,  N.H4,  whose  relations  to 
potassium  are  of  an  exceedingly  intimate  kind ;  and  the  salts  of  ammonia,  which 
contain  ammonia  and  water,  N.H3-4-H.O.,  are  looked  upon  as  consisting  of  an  oxide 
of  that  metal,  N.H4 .  O.  in  combination  with  an  acid.  I  prefer,  however,  to  study  the 
history  of  ammonia,  and  all  the  classes  of  compounds  into  which  it  enters,  among 
the  bodies  of  organic  origin. 

Bariuvu 

Barium  is  found  exclusively  in  the  mineral  kingdom,  where  its 
oxide,  barytes,  is  the  basis  of  several  minerals,  as  the  sulphate  and 
carbonate,  which  are  the  usual  sources  from  which  it  is  obtained 
for  use. 

The  metal  barium  was  discovered  by  Sir  Humphrey  Davy  imme- 
diately after  the  discovery  of  the  basis  of  the  alkalies.  It  may  be 
prepared  by  voltaic  action,  as  described  under  the  head  of  potassium, 


PREPARATION      OF     BARYTES.  343 

or  much  better  by  passing  the  vapour  of  potassium  over  barytes 
heated  to  redness ;  the  potassium  takes  the  oxygen  of  the  barytes, 
and  the  barium  is  set  free.  By  washing  the  residue  with  mercury, 
the  metallic  barium  is  dissolved  out,  and  the  mercury  being  then 
distilled  off  in  a  retort  of  hard  glass,  the  barium  remains  behind  ;  it 
is  a  white  metal  like  silver  ;  it  fuses  below  a  red  heat ',  it  is  denser 
than  oil  of  vitriol :  it  decomposes  water  with  great  rapidity,  evolv- 
ing hydrogen  gas  and  forming  barytes  (oxide  of  barium). 

The  name  barium  is  derived  from  jSapv^j  heavy  ;  the  native  sul- 
phate of  barytes  having  been  called  formerly  terra  ponderosa,  or  heavy 
spar.     Its  symbol  is  Ba. ;  its  equivalent  numbers  856*9  or  68*7. 

Barium  combines  with  oxygen  in  two  proportions,  forming  a  pro- 
toxide, which  is  the  earth  barytes,  Ba.O.,  and  a  deutoxide,  Ba.Oo. 
The  preparation  of  this  last  has  been  described  so  fully  when  ex- 
plaining its  only  important  use,  the  formation  of  deutoxide  of  hy- 
drogen (p.  258),  that  it  need  not  be  farther  noticed  here.  The 
protoxide,  barytes,  is,  however,  one  of  the  most  important  earths. 

To  procure  pure  barytes,  the  nitrate  of  barytes  is  to  be  gently 
heated  to  redness  in  a  porcelain  crucible.  It  fuses  at  a  dull  red, 
and  boils  briskly  from  the  rapid  escape  of  oxygen ;  when  this  has 
terminated,  there  remains  a  gray  loosely  coherent  powder,  which 
is  barytes.  The  melted  salt  is  in  this  process  very  apt  to  froth  up, 
so  much  as  to  overflow,  unless  the  vessel  be  of  considerable  size  ; 
this  is  very  simply  avoided  by  mixing  the  nitrate  of  barytes,  before- 
hand, with  twice  its  weight  of  sulphate  of  barytes  in  fine  powder. 
When  the  nitrate  melts,  the  sulphate  gives  the  mass  a  degree  of 
consistence  which  prevents  its  frothing  up,  and  on  boiling  the  re- 
sidual mass  with  water,  all  the  pure  barytes  dissolves,  the  sulphate 
remaining  totally  unacted  on. 

If  the  native  carbonate  of  barytes,  Ba.O, .  C.O2,  be  strongly  heated  with  carbon,  the 
carbonic  acid  is  converted  into  carbonic  oxide,  which  passes  off,  and  pure  barytes 
remains  behind,  Ba.O. .  C.O2  and  C.  giving  Ba.O.  and  2C.0.  ;  the  former  process  is, 
however,  so  much  easier,  that  it  alone  is  now  usually  employed.  Graham  has  sug- 
gested the  employment  of  iodate  of  barytes  as  a  substitute  for  the  nitrate :  other 
processes  will  be  described  under  the  head  of  sulphuret  of  barium. 

Pure  barytes  is  a  heavy  gray  powder  ;  when  exposed  to  the  air, 
it  absorbs  water  rapidly,  giving  out  much  heat,  and  falling  into  a  fine 
white  powder,  hydrate  of  barytes^  Ba.O.+H.O.  Another  hydrate  may 
be  obtained  crystallized,  by  dissolving  barytes  in  three  parts  of  boil- 
ing water,  and  allowing  the  solution  to  cool  slowly;  it  contains  nine 
equivalents  of  water.  The  solution  of  barytes  is  very  caustic  and 
alkaline ;  exposed  to  the  air,  it  absorbs  carbonic  acid,  and  a  white 
precipitate  of  carbonate  of  barytes  is  formed ;  it  is  hence  used  to 
determine  the  quantity  of  carbonic  acid  present  in  the  air  (p.  263), 
and  in  some  other  cases. 

The  detection  of  barytes  is  very  simple ;  its  soluble  compounds 
give  white  precipitates  with  carbonate  of  soda,  with  sulphuric  acid, 
and  with  hydrofluosilicic  acid,  and  none  of  these  are  affected  by  a 
solution  of  sulphuretted  hydrogen  gas  in  water.  The  sulphate  of 
barytes  is  not  merely  insoluble  in  water,  but  also  in  nitric  and  mu- 
riatic acids,  which  is  a  farther  characteristic  of  this  earth. 

The  formula  of  barytes  is  Ba.O.,  and  its  composition, 


344  SULPHUR  ET     OP     BARIUM. STRONTIUM. 

Barium,    89-55         One  equivalent  =856-9  or  68-7 

Oxygen,   10-45         One  equivalent  =100-0  or    8-0 

100^  95T9       7^7 

The  soluble  compounds  of  barytes  are  all  poisonous,  and  the  car- 
bonate, although  insoluble  in  water,  is  yet  dissolved  by  the  free 
acids  of  the  stomach,  and  becomes  poisonous.  The  antidote  to  all 
barytic  preparations  is  sulphate  of  soda,  or  sulphate  of  magnesia, 
administered  in  excess  j  the  sulphate  of  barytes  then  produced  is 
absolutely  inert. 

Sulphuret  of  Barium.  Ba.S. — This  body  is  of  considerable  inter- 
est, as  the  source  of  barytes  and  of  most  of  its  ordinary  compounds  j 
to  prepare  it,  sulphate  of  barytes  in  fine  powder  is  to  be  mixed  with 
one  fourth  of  its  weight  of  lampblack,  and  exposed  to  a  very  strong 
heat  for  two  hours ;  the  carbon  removes  all  the  oxygen  from  the 
salt;  carbonic  oxide  is  evolved,  and  sulphuret  of  barium  remains; 
Ba.O.  .  S.O3  and  4C.  giving  4C.0.  and  Ba.S.  The  mass  thus  ob- 
tained is  to  be  boiled  in  water  j  a  deep  yellow  solution  is  then  pro- 
duced, from  which  the  sulphuret  of  barium  crystallizes  on  cooling ; 
it  is  then  a  hydrate,  but  its  water  of  crystallization  may  be  removed 
by  a  moderate  heat.  The  sulphuret  of  barium  is  decomposed  by 
acids,  sulphuret  of  hydrogen  being  evolved,  and  a  salt  of  barytes 
formed :  it  is  thus  that  the  salts  of  barytes  are  obtained  for  labora- 
tory use. 

A  simple  mode  of  obtaining  caustic  barytes  directly  from  the  sul- 
phuret of  barium  has  been  recently  given  by  Mohr.  It  consists  in 
adding  to  a  boiling  solution  of  the  sulphuret,  black  oxide  of  copper, 
until  the  whole  of  the  sulphuret  of  barium  is  decomposed,  as  is  easily 
ascertained,  by  adding  a  drop  of  the  solution  to  a  solution  of  acetate 
of  lead  ;  the  copper  combines  with  the  sulphur,  while  the  barium 
and  the  oxygen  unite,  Ba.S.  and  Cu.O.  producing  Ba.O.  and  Cu.S. 
This  is  probably  the  simplest  and  cheapest  means  of  obtaining  pure 
barytes. 

Of  Strontium, 

This  metal  is  the  basis  of  the  earth  strontia,  protoxide  of  stron- 
tium, which  exists  native  combined  with  sulphuric  and  carbonic 
acids.  The  native  carbonate  of  strontia  was  first  found  at  Strontian 
in  Scotland,  and  proved  to  contain  an  earth  different  from  barytes 
by  Dr.  Hope.  The  similarity  of  these  two  earths  is  very  great,  so 
that  the  general  outline  of  the  history  of  strontia  is  the  same  as  that 
of  barytes. 

The  metal  strontium  is  obtained  precisely  as  barium,  with  which 
it  perfectly  agrees  in  character  so  far  as  its  properties  have  been 
ascertained.  Its  symbol  is  Sr.,  and  its  equivalent  number  547-3  or 
43-8.  To  obtain  strontia^  the  same  processes  may  be  employed  which 
were  described  for  the  preparation  of  barytes,  substituting  the  native 
carbonate  or  sulphate  of  strontia  for  the  compounds  of  barytes.  The 
strontia  is  gray,  slacks  on  exposure  to  the  air,  forming  a  hydrate, 
Sr.O. .  H.O.,  and  by  crystallization  from  its  watery  solution,  another 
hydrate,  Sr.O.  -\-  9H.0.  Strontia  is  less  soluble  than  barytes,  its  tast^ 
is  not  so  caustic,  nor  is  it  so  poisonous 


COMPOUNDS     OF     CALCIUM.  345 

Strontia  is  distinguished  from  barytes  by  tinging  the  flame  of  the 
blowpipe  a  rich  crimson.  The  red  lights  used  in  fireworks  owe 
their  colour  to  nitrate  of  strontia,  which  is  used  in  the  preparation. 
Like  barytes,  the  soluble  salts  of  strontia  are  precipitated  by  sul- 
phuric acid,  but  the  sulphate  of  strontia  is  not  so  very  insoluble  as 
sulphate  of  barytes  j  a  solution  of  strontia  is  also  precipitated  by 
carbonate  of  soda.  The  hydrofluosilicic  and  the  hyposulphurous 
acids,  which  precipitate  barytes,  do  not  precipitate  strontia,  and  thus 
these  earths  may  be  distinguished  and  separated  from  each  other  3 
the  chromic  acid  acts  in  a  similar  manner. 

The  sulphuret  and  seleniuret  of  strontium  resemble  perfectly  thos» 
of  barium,  and  are  prepared  in  the  same  way. 

Of  Calcium. 

The  existence  of  this  metal  was  first  recognised  by  Sir  Humphrey 
Davy,  it  being  obtained  from  lime  by  the  same  method  as  that  de- 
scribed under  the  head  of  barium;  it  is  white  like  silver;  it  sinks  in 
water,  which  it  decomposes  rapidly,  evolving  hydrogen, and  uniting 
with  oxygen,  forms  lime  (protoxide  of  calcium).  The  symbol  of 
calcium  is  Ca.,  and  its  equivalent  number  256  or  20'5. 

Calcium  combines  with  oxygen  only  in  one  proportion,  forming 
lime,  the  most  important  of  the  earths.  It  is  found  very  extensively 
distributed  in  the  mineral  kingdom,  principally  combined  with  sul- 
phuric and  carbonic  acids,  forming  sulphate  of  lime  (gypsum,  plas- 
ter of  Paris)  and  carbonate  of  lime  (marble,  limestone,  chalk).  These 
substances  exist  as  rocks  or  crystallized,  the  last  constituting  the 
mineral  species,  arragonite  and  calc  spar,  often  referred  to  under 
the  heads  of  crystalline  systems,  isomorphism,  and  dimorphism. 
Lime  is  found  also  combined  with  phosphoric  and  arsenic  acids  in 
several  minerals,  and  the  native  fluoride  of  calcium  is  the  fluor  spar, 
used  for  the  preparation  of  the  hydrofluoric  acid  and  other  com- 
pounds of  fluorine.  ^^ 

Notwithstanding  the  immense  quantities  of  carbonate  of  lime 
which  are  found  constituting  a  great  portion  of  the  surface  of  the 
globe,  as,  for  instance,  the  whole  centre  of  Ireland  is  one  vast  plain 
of  limestone,  and  in  that  as  well  as  other  forms,  chalk,  marble,  &c., 
it  is  equally  extensive  in  most  other  countries,  it  is  questionable 
whether  lime  should  not  be  looked  upon  as  rather  a  characteristic 
of  the  animal  than  of  the  mineral  kingdom  of  nature.  The  bony  or 
testaceous  skeleton,  by  which  the  softer  portions  of  the  animal  frame 
are  attached,  is  always  found  to  consist  of  lime  united  either  with 
carbonic  or  phosphoric  acids,  and  the  diversity  of  chemical  compo- 
sition in  this  respect  is  found  to  coincide  in  a  remarkable  degree 
with  the  most  natural  physiological  classification.  The  skeletons  of 
the  vertebrated  animals  consist  principally  of  phosphate  of  lime, 
while  in  the  shells  of  the  invertebrate  animals,  the  carbonate  of  lime 
is  the  prevalent  component.  The  teeth  also  consist  of  phosphate 
of  lime  ;  in  all  these  cases,  the  phosphate  of  lime  is  associated  with 
fluoride  of  calcium,  just  as  occurs  in  the  native  phosphate,  the  min- 
eral apatite. 

Now  it  is  remarkable  that  all  the  great  geological  formations 
which  contain  carbonate  of  lime  are  found  to  consist  of  the  aggre- 

X  X 


346  PROPERTIES     OP     LIME. 

gated  skeletons  (shells)  of  myriads  of  the  tribes  of  invertebrated  an- 
imals, which  had  existed  in  some  former  period  of  the  world's  his- 
tory. From  the  densest  and  hardest  limestone  to  the  softest  chalk, 
the  entire  mass  resolves  itself  ultimately  into  a  congeries  of  animal 
remains,  and  hence  the  great  supply  of  lime  in  the  mineral  state 
arises  from  the  destruction  of  its  animal  sources.  Even  those  crys- 
talline marbles  in  which  no  organic  remains  can  be  traced,  appear 
destitute  of  them  only  from  having  been  subjected,  by  volcanic  heat 
or  otherwise,  to  the  influence  of  causes  which  have  gradually  render- 
ed the  texture  of  the  mass  completely  uniform.  The  lime  which 
exists  in  nature  must  therefore  be  looked  upon  as  being  continually 
in  a  state  of  passage  between  the  organized  and  the  inorganic  king- 
doms. The  plants  which  grow  upon  the  soil  take  up,  by  dissolution 
in  their  juices,  salts  of  lime,  which  pass  into  the  substance  of  the 
animal  which  feeds  upon  them,  and,  accumulating  in  its  system,  af- 
ford materials  for  the  proper  development  of  the  skeleton.  When 
the  animal  dies,  the  materials  of  its  tissues  either  serve  for  the  nu- 
trition of  some  other  animal,  or,  being  totally  decomposed,  its  ele- 
ments return  to  the  mineral  kingdom,  to  be,  in  after  ages,  the  sub- 
ject of  similar  alternations. 

Lime  is  always  obtained,  for  the  purposes  of  chemistry  and  of 
the  arts,  by  the  decomposition  of  the  native  carbonate.  To  obtain 
lime  perfectly  pure,  crystals  of  calc  spar  or  pieces  of  Carrara  mar- 
ble should  be  strongly  heated  in  a  crucible  loosely  covered,  so  that 
the  carbonic  acid  can  readily  escape.  In  the  presence  of  carbonic 
acid,  carbonate  of  lime  is  not  decomposed  by  heat,  as  was  explained 
already  in  p.  170.  On  the  large  scale,  lime  is  obtained  by  burning 
the  ordinary  limestone  in  kilns.  At  the  bottom  is  a  grate  on  which 
fuel  is  laid,  and  the  kiln  then  filled  with  limestone  and  fuel  (culm  or 
small  coal),  mixed  in  sui|able  proportions  j  when  the  fire  is  lighted 
on  the  grate,  the  combustion  extends  throughout  the  mass,  and  as 
the  perfectly  burned  lime  is  extracted  at  the  bottom  by  the  orifice 
of  the  grate,  new  quantities  of  fuel  and  limestone  are  introduced 
above,  so  that  the  combustion  is  continuous ;  the  carbonic  acid 
evolved  is  completely  removed  by  the  rapid  draught  through  the 
fire. 

Lime  is  a  pure  white  earth.  When  exposed  to  the  air,  it  rapidly 
absorbs  water,  and  falls  into  a  white  powder  (slacked  lime),  which 
is  a  hydrate, Ca.O. .  H.O.  If  a  little  water  be  poured  on  a  piece  of 
well-burned  lime,  it  is  absorbed  instantly,  and  the  lime  appears  quite 
dry,  but  after  a  few  moments  cracks,  and  falls  into  the  powder  of 
hydrate,  evolving  so  much  heat  as  to  char  wood  and  inflame  gun- 
powder when  in  large  quantities.  It  is  thus  that  vessels  laden  with 
lime  have  been  burned  at  sea,  by  water  penetrating  to  the  hold. 
Lime  is  soluble  in  water,  though  but  sparingly,  and  still  less  soluble 
in  boiling  than  in  cold  water  j  one  part  of  lime  requiring  778  of  wa- 
ter at«60^,  and  1270  at  212^  for  its  solution  ;  hence,  when  lime-water 
is  boiled,  it  becomes  turbid.  The  solution  of  lime  has  an  acrid,  slight- 
ly caustic  taste  ;  it  reacts  alkaline ;  exposed  to  the  air,  it  absorbs 
carbonic  acid,  becoming  covered  with  a  crystalline  pellicle  of  car- 
bonate of  lime.  On  breathing  into  lime-water  through  a  glass  tube, 
it  is  immediately  rendered  turbid  by  the  carbonate  of  lime  produced 


SULPHURETS     OF     CALCIUM.  ^  347 

by  respiration  5  an  excess  of  the  carbonic  acid,  however,  dissolves 
the  precipitate.  It  is  in  this  way  that  carbonate  of  lime  is  held  dis- 
solved in  almost  all  ordinary  spring  and  river  waters.  If  lime  be 
perfectly  dry,  it  has  little  or  no  tendency  to  absorb  carbonic  acid ; 
it  requires  to  be  first  slacked,  and  then  the  hydrate  is  decomposed, 
the  water  being  expelled  by  the  carbonic  acid;  the  absorption  is 
very  rapid  until  the  lime  becomes  one  half  saturated,  a  compound 
of  Ca.O. .  C.02+Ca.O. .  H.O.  being  probably  formed,  but  after  that 
point  it  advances  very  slowly. 

Lime  being  a  protoxide,  its  formula  is  Ca.O.,  and  its  composition 
and  equivalent  numbers  are  as  follows ; 

Calcium,  71'91  One  equivalent  =256-0  or  20-5 

Oxygen,   28-09  One  equivalent  =^1Q0-Q  or    8-0 

lOO^OO  356-0       28-5 

Lime  is  easily  distinguished  by  its  dilute  solutions  not  being  pre- 
cipitated by  sulphuric  acid  or  sulphate  of  soda,  but  giving  a  white 
precipitate  of  oxalate  of  lime  on  the  addition  of  a  solution  of  oxalic 
acid  j  an  excess  of  oxalic  acid  does  not  redissolve  this  precipitate. 
The  nitrate  of  lime  is  deliquescent  and  soluble  in  alcohol,  in  which 
it  also  differs  from  the  preceding  earths.  The  compounds  of  lime, 
when  ignited  before  the  blowpipe,  tinge  the  flame  of  a  brick-red 
colour. 

Lime  is  of  great  importance  in  the  arts,  from  its  use  in  making 
mortar,  and  in  agriculture  from  its  application  as  a  manure.  The 
lime  in  mortar  is  not  as  carbonate,  and  its  coherent  property  ap- 
pears to  depend  only  on  the  gradual  drying  of  the  hydrate  by  which 
the  stones  are  retained  together,  as  boards  are  by  the  drying  of  the 
glue  between  their  surfaces.  The  use  of  lime  as  a  manure  arises 
from  its  decomposing  the  insoluble  organic  matters  of  the  soil, 
woody  fibres,  ulmine,  &c.,  and  producing  other  products  more  read- 
ily taken  up  by  the  radicles  of  the  growing  plants.  It  is  hence  on 
such  soils  as  possess  a  large  quantity  of  organic  matter,  but  are 
still  barren  from  its  not  being  in  the  suitable  condition,  that  the  ben- 
eficial effects  of  lime  are  peculiarly  marked. 

There  is  a  deutoxide  of  calcium,  Ca.02,  prepared  by  adding  a  solution  of  deutoxids 
of  hydrogen  to  lime-water  ;  it  resembles  deutoxide  of  barium,  but  is  of  no  impor 
tance. 

There  are  three  compounds  of  sulphur  and  calcium  known ;  the  first,  or  proto- 
sulphuret  of  calcium,  Ca.S.,  may  be  prepared  by  heating  sulphate  of  lime  to  redness 
in  a  stream  of  hydrogen  gas,  or,  more  simply,  by  igniting  sulphate  of  lime  with  one 
third  of  its  weight  of  lampblack ;  all  the  oxygen  of  the  salt  is  carried  off  as  watei 
m  the  one,  or  as  carbonic  oxide  in  the  other  case,  and  the  suljihur  and  calcium  re- 
main united.  It  is  a  white  powder,  but  very  sparingly  soluble  in  water.  It  plays 
an  important  part  in  the  manufacture  of  carbonate  of  soda,  as  will  be  hereafter  ex- 
plained. When  flowers  of  sulphur  and  slacked  lime  are  boiled  together  in  water,  a 
deep  yellow  solution  is  obtained,  which  is  said  to  be  a  sulphuret  of  lime,  but  which 
really  consists  of  a  mixture  of  hyposulphite  of  lime  and  bisulphuret  of  calcium,  6S. 
and  3Ca.O.  producing  S202+Ca.O.  and  2Ca.S2.  If  the  solution  be  concentrated,  thia 
last  separates  in  yellow  prisms  with  water  of  crystallization.  It  is  from  this  yellow 
liquor  that  the  precipitated  sulphur  is  prepared  ;  for,  on  adding  to  it  an  acid,  sulphu- 
ret  of  hydrogen  is  evolved  from  the  sulphuret  of  calcium  in  such  proportion  as  to 
decompose  the  hydros ulphurous  acid,  and  all  the  sulphur  is  precipitated,  while  the 
lime  remains  in  combination  with  the  acid  which  is  employed.  If  the  sulphur  be 
in  great  excess  in  proportion  to  the  lime,  a  pentasulphuret  of  calcium  may  be  formed. 

The  seleniuret  of  calcium  is  not  important.     If  phosphorus  in  vapour  be  passed 


348  PREPARATION     OF     MAGNESIUM. 

through  a  red-hot  tube  loosely  filled  with  lime,  a  brown  substance  is  produced,  pop- 
ularly termed  phosphuret  of  lime,  but  which  is  a  mixture  of  phosphate  of  lime  and 
phosphuret  of  calcium ;  the  temperature  must  not  be  raised  too  high,  or  else  the 
phosphorus  may  be  expelled  again.  When  this  phosphuret  of  calcium  is  brought 
into  contact  with  water,  it  is  decomposed,  phosphite  of  lime  and  phosphuretted  hy- 
drogen being  produced ;  this  last  being  evolved  in  its  spontaneously  inflammable 
condition,  it  is  an  interesting  experiment  to  throw  a  fragment  of  the  brown  sub- 
stance into  a  glass  of  water  ;  numerous  gas  bubbles  are  immediately  formed,  which 
explode  when  they  reach  the  air,  as  described  in  p.  300. 

Of  Magnesium. 

This  metal,  like  the  bases  of  the  other  earths,  was  first  recog- 
nised by  Humphrey  Davy,  but  the  process  by  which  it  is  best  pre- 
pared is  that  given  by  Bussy.  A  few  pieces  of  potassium  are  to  be 
placed  at  the  bottom  of  a  tube  of  hard  glass,  and  then  a  quantity  of 
anhydrous  chloride  of  magnesium  in  small  fragments  to  be  laid  upon 
them  i  the  part  of  the  tube  containing  the  earthy  chloride  is  to  be 
heated  to  near  its  point  of  fusion,  and  the  metal  converted  into  va- 
pour by  the  application  of  the  lamp,  as  in  the  figure,  p.  321 ;  as 
soon  as  the  vapour  of  the  potassium  comes  into  contact  with  the 
heated  salt,  vivid  ignition  ensues,  and  chloride  of  potassium  being 
formed,  the  magnesium  is  liberated  in  the  metallic  state,  Mg.Cl. 
and  K.  giving  K.Cl.  and  Mg.  When  the  action  has  ceased  and  the 
tube  is  completely  cool,  the  mass  is  to  be  washed  with  warm  wa- 
ter; the  chloride  of  potassium  dissolves,  and  leaves  the  magnesium, 
with  perfect  metallic  properties,  behind.  It  is  Avhite  like  silver,  mal- 
leable and  fusible  at  a  red  heat ;  it  is  not  changed  by  dry  air,  and 
but  slowly  oxidized  by  damp  air  ;  it  may  be  boiled  in  water  without 
this  being  decomposed.  If  magnesium  be  heated  to  redness  in  air 
or  oxygen,  it  burns  with  brilliancy,  forming  magnesia,  and  it  in- 
flames spontaneously  in  chlorine  ;  it  dissolves  in  dilute  acids  with 
the  evolution  of  hydrogen  gas,  and  the  formation  of  a  salt  of  mag- 
nesia. The  symbol  of  magnesium  is  Mg.,  and  its  equivalent  number 
is  158*3  or  12*7  according  to  the  standard. 

Magnesia,  the  only  known  compound  of  magnesium  and  oxygen, 
is  a  protoxide.  It  exists  in  considerable  quantity  in  nature,  being 
a  constituent  of  a  great  variety  of  minerals ;  it  is  found  as  hydrate, 
as  carbonate,  sulphate,  and  silicate,  but  its  most  abundant  source  is 
the  magnesian  limestone,  common  both  in  Ireland  and  in  England, 
which  consists  of  an  equivalent  of  each  carbonate,  its  formula  being 
Ca.O. .  C.Oa  +  Mg.O. .  C.O2.  The  pure  magnesia  is  always  prepared 
by  exposing  the  carbonate  of  magnesia  of  commerce,  the  preparation 
of  which  will  be  described  among  the  salts,  to  a  full  red  heat ;  the 
carbonic  acid  is  expelled,  and  the  earth  remains  pure.  Magnesia  is 
a  very  light  white  powder,  without  taste  or  smell ;  it  is  almost  per- 
fectly infusible ;  but  it  and  lime  are  remarkable  for  becoming  beau- 
tifully phosphorescent  when  strongly  heated,  and  it  is  hence  that 
lime  is  used  as  a  source  of  the  most  brilliant  light  when  it  is  heated 
in  the  jet  of  the  oxyhydrogen  blowpipe.  It  is  very  sparingly  solu- 
ble in  water,  and  still  less  so  in  hot  than  in  cold  water ;  its  solution 
browns  turmeric  paper  very  slightly.  It  is  remarkably  inferior  to 
lime  in  basic  power,  but  still  neutralizes  the  strongest  acids  perfect- 
ly, forming  excellently  characterized  classes  of  salts. 

The  formula  of  magnesia  is  Mg.O.,  and  its  composition  and  equiv- 
alent numbers  are, 


PREPARATION     OF      ALUMINUM.  849 

Magnesium,  61-29         One  equivalent  rr  158-3  or  12-7 

Oxygen,         38-81         One  equivalent  =^0^  or    8-0 

lOOOO'  258-3        20-7 

Magnesia  is  recognised  by  its  sulphate  being  very  soluble  in  wa- 
ter, and  a  solution  containing  it  being  precipitated  by  the  alkalies 
and  their  carbonates.  The  precipitate  so  obtained  is  redissolved 
on  adding  to  the  liquor  a  strong  solution  of  sal  ammoniac.  The 
most  delicate  test  for  magnesia  consists  in  rendering  the  liquor  sus- 
pected to  contain  it  alkaline  by  ammonia,  and  then  adding  a  solution 
of  phosphate  of  soda ;  after  a  short  time  the  phosphate  of  ammonia 
and  magnesia  crystallizes  on  the  side  of  the  glass,  particularly  if  it 
be  scratched  by  a  glass  rod :  this  double  salt  is  almost  completely 
insoluble  in  an  alkaline  liquor.  A  solid  substance  containing  mag- 
nesia possesses  the  property,  that,  if  it  be  moistened  by  a  very  small 
quantity  of  nitrate  of  cobalt,  and  ignited  strongly  by  the  blowpipe, 
it  becomes  a  fine  pink  or  rose  colour :  the  presence  of  other  bodies 
may,  however,  interfere  with  this  result. 

The  sulphurets  and  seleniurets  of  magnesium  are  of  no  impor- 
tance ;  they  resemble,  almost  perfectly,  those  of  calcium  already 
noticed. 

SECTION  II. 

METALS  OF  THE  SECOND  CLASS. 

Of  Aluminum. 

This  metal  is  prepared  by  the  action  of  potassium  upon  its  chlo- 
ride, exactly  as  described  for  magnesium  in  the  last  division,  but  the 
operation  must  be  performed  in  vessels  of  platinum  or  porcelain, 
as  the  heat  spontaneously  evolved  during  the  reaction  is  so  intense 
as  to  fuse  the  most  refractory  glass ;  the  quantity  operated  on 
should  likewise  be  small.  A  gray  melted  mass  of  chloride  of  potas- 
sium and  metallic  aluminum  remains,  which  is  to  be  washed  with 
cold  water,  and  the  metal  is  thus  obtained  in  minute  but  brilliant 
scales. 

Aluminum  does  not  decompose  water  at  ordinary  temperatures, 
and  only  slowly  even  at  a  boiling  heat,  but  it  dissolves  rapidly  in 
dilute  acids,  and  also  in  solutions  of  the  caustic  alkalies,  with  the 
evolution  of  hydrogen  gas,  from  the  water  being  decomposed.  The 
synrbol  of  aluminum  is  Al.,  and  its  equivalent  numbers  are  171*2  or 
13-7,  according  to  the  scale. 

There  is  but  one  compound  known  of  aluminum  and  oxygen :  it 
is  alumina.  This  earth  exists  in  very  large  quantity  in  nature,  being 
even  still  more  abundant  than  lime ;  it  is  a  principal  ingredient  of 
almost  all  rocks,  except  the  purest  kinds  of  limestone  ;  it  constitutes 
the  great  mass  of  the  ordinary  clays  and  soils,  these  deposites  bemg 
produced  by  the  gradual  decomposition  and  detrition  of  various  kinds 
of  rocks.  In  all  these  forms  the  alumina  is  generally  combined  with 
silica,  and  sometimes  with  sulphuric  or  phosphoric  acids;  it  is  also 
met  with  pure,  or  at  least  contaminated  by  the  presence  of  only  a 
trace  of  foreign  matter;  thus  the  ruby  and  the  sapphire,  two  of  the 
most  highly  prized  precious  stones,  are  alumina,  combined  with  small 


350      PREPARATION     AND     PROPERTIES     OP     ALUMINA. 

quantities  of  colouring  matter.  The  importance  of  alumina  in  the 
arts  is  very  great ;  it  is  a  necessary  ingredient  in  the  formation  of  all 
kinds  of  earthenware,  from  tiles  or  bricks  to  the  finest  kinds  of  por- 
celain,  and  is  extensively  used  as  the  basis  or  mordant  for  some  of 
the  most  brilliant  and  durable  colours  that  can  be  fixed  upon  cotton 
or  woollen  cloth.  The  alumina  derives  its  name  from  the  salt  which 
it  forms  with  potash  and  sulphuric  acid,  the  alum  of  commerce,  from 
which  it  is  always  prepared  for  the  purposes  of  the  chemist. 

To  prepare  pure  alumina,  a  solution  of  alum  is  to  be  decom- 
posed by  carbonate  of  potash,  and  the  precipitate  separated  by  the 
filter.  This  precipitate  is  alumina,  the  sulphuric  acid  being  taken 
by  the  potash,  and  the  carbonic  acid,  which  cannot  combine  with 
the  alumina,  being  evolved  as  gas.  The  alumina  thus  produced  is, 
however,  not  quite  pure  \  it  always  carries  down  with  it  a  little  sul- 
phate of  potash,  from  which  it  must  be  separated  by  being  dissolved 
in  dilute  muriatic  acid,  and  again  precipitated  by  carbonate  of  am- 
monia ;  being  then  well  washed,  until  the  water  passes  from  the  fil- 
ter completely  free  from  sal  ammoniac,  it  may  be  looked  upon  as 
pure.  The  alumina  so  obtained,  when  dried  at  common  tempera- 
tures, constitutes  a  bulky  gummy  mass,  which  is  a  hydrate,  the  earth 
and  the  water  containing  equal  quantities  of  oxygen.  To  expel  this 
water  completely,  it  must  be  exposed  to  a  white  heat ;  in  drying  it 
contracts  very  much.  It  was  on  the  measurement  of  this  contrac- 
tion that  Wedgewood  founded  his  pyrometer,  now  gone  out  of  use, 
and  to  allow  for  it,  all  vessels  of  earthenware  and  china  are  made 
much  larger  than  they  are  intended  to  be  when  completely  baked. 

In  consequence  of  the  great  power  with  which  alumina  absorbs 
and  retains  moisture,  it  adheres  strongly  to  the  tongue,  producing  a 
very  peculiar  sensation  when  applied  to  it.  The  more  or  less  reten- 
tive quality  of  soils  results  from  the  same  property,  and  is  generally 
proportional  to  the  quantity  of  pure  clay  which  they  contain. 

Alumina  is  white  ;  if  dried  at  moderate  temperatures,  it  dissolves 
freely  in  acids  and  in  solutions  of  the  fixed  caustic  alkalies,  but  if 
it  be  very  strongly  heated,  particularly  if  fused  by  the  oxy hydrogen 
blowpipe,  it  dissolves  much  more  slowly.  It  is  particularly  remark- 
able for  its  tendency  to  unite  with  organic  matters.  If  a  cotton  cloth 
be  immersed  in  a  solution  of  acetate  of  alumina,  the  earth  will  de- 
posite  itself  completely  on  the  fibres  of  the  cotton,  and  leave  the  acetic 
acid  free.  The  most  important  proces^s  in  calico  printing  repose 
upon  this  principle. 

Although  alumina  is  the  only  compound  of  aluminum  and  oxygen, 
it  is  yet  not  to  be  considered  as  a  protoxide.  I  have  already  de- 
scribed, pages  213  and  223,  the  isomorphous  and  other  relations  which 
establish  its  constitution  to  be  similar  to  that  of  peroxide  of  iron. 
It  is  hence  a  sesquioxide,  and  its  formula  is  AI2O3.  Its  composition 
and  equivalent  numbers  are, 

Alumina,  53-3  Two  equivalents,     =342-4  or  27-4 

Oxygen,  46-7  Three  equivalents,  =300-0  or  24-0 

1000  "6424        51-4 

Alumina  is  easily  recognised.  Its  solution  is  precipitated  by  the 
alkalinb  carbonates,  and  the  precipitate  is  dissolved  by  the  caustic 


GLUCINUM,     YTTRIUM,     THORIUM,     ETC.  351 

fixed  alkalies,  but  not  by  ammonia.  It  is  also  precipitated  white  by 
hydrosulphuret  of  ammonia.  If  a  solid  substance  containing  alumina 
be  moistened  with  a  trace  of  nitrate  of  cobalt,  and  ignited  by  the 
blowpipe,  it  becomes  of  a  beautiful  blue  colour. 

If  aluminum  be  heated  in  the  vapour  of  sulphur,  it  takes  fire,  and  forms  a  gray 
mass  of  sulphur et  of  aluminum.  This  is  decomposed  by  water,  producing  alumina 
and  sulphuretted  hydrogen,  showing  that  its  formula  was  AI2S3,  which  with  3H.0. 
give  AI2O3  and  3H.S.  This  sulphuret,  therefore,  cannot  be  formed  in  solution ;  and 
when  a  solution  of  alumina  is  precipitated  by  hydrosulphuret  of  ammonia,  as  already 
noticed,  the  precipitate  is  pure  alumina,  and  the  liquor  contains  sulphuret  of  hy- 
drogen. 

The  seleniuret  and  phosphuret  of  aluminum  are  known,  but  are  of  no  importance. 

Of  Glucinum, 

The  earth  of  which  this  metal  is  the  basis  has  been  found  but  in  a  few  rare  min- 
erals, and  as  it  exercises  no  influence  on  science  from  the  nature  of  its  compounds, 
and  is  of  no  application  in  medicine  or  in  the  arts,  a  very  brief  notice  of  it  will  suf- 
fice. It  exists  in  the  emerald,  beryl,  and  euclase.  To  obtain  it  from  beryl,  the 
mineral  is  fused  with  carbonate  of  potash,  the  mass  treated  with  dilute  muriatic 
acid,  and  evaporated  to  dryness  to  separate  the  silica.  The  portion  which  dissolves 
then  in  water  is  to  be  decomposed  by  ammonia,  which  precipitates  the  alumina  and 
glucina  together,  and  the  moist  precipitate  digested  in  a  strong  cold  solution  of  car- 
bonate of  ammonia,  in  which  the  glucina  dissolves.  On  boiling  the  filtered  liqdor 
so  obtained,  the  glucina  separates  in  combination  with  carbonic  acid,  from  which  it 
is  freed  by  ignition,  and  so  obtained  pure. 

This  earth  is  tasteless  and  inodorous ;  it  is  insoluble  in  water,  and  has  no  action 
on  vegetable  colours.  Its  salts  taste  remarkably  sweet,  whence  its  name  {yTiVKvg). 
It  is  easily  recognised  by  its  relation  to  pure  and  carbonated  ammonia,  described  in 
the  details  of  its  preparation.  The  metal  glucinum  is  prepared  from  its  chloride 
precisely  as  aluminum  and  magnesium,  which  it  resembles  very  closely  in  all  its 
properties.     Its  symbol  is  G.,  and  its  equivalent  numbers  are  .3314  or  265. 

Glucina  is  considered  to  be,  like  alumina,  a  sesquioxide,  and  its  formula  being 
G2O3,  its  composition  and  equivalents  may  easily  be  calculated. 

Of  Yttrium^  Thorium,  and  Zirconium. 

These  metals  are  the  bases  of  earths,  concerning  which,  from  the  rarity  of  the 
sources  from  which  they  have  hitherto  been  derived,  but  little  is  known,  and  from 
their  being  destitute  of  scientific  importance  as  well  as  of  practical  application,  short 
notice  of  their  characters  only  need  be  given. 

Yttrium. — The  earth  yttria,  oxide  of  yttrium,  exists  in  some  rare  Swedish  min- 
erals, which  were  its  only  sources  until  the  very  remarkable  discovery,  by  Apjohn, 
of  its  presence  in  the  ordinary  Bohemian  garnet  or  pyrope.  The  method  of  its  ex- 
traction is  too  complicated  for  description  here.  It  is  insoluble  in  the  fixed  caustic 
alkalies,  and  is  precipitated  by  the  yellow  prussiate  of  potash,  by  which  it  is  com- 
pletely distinguished  from  the^other  earths.  It  is  a  protoxide.  Its  formula  is 
hence  Y.O. 

Thorium. — The  earth  thoria,  oxide  of  thorium,  Th.O.,  has  been  found  but  in  two 
very  rare  minerals.  It  is  the  heaviest  of  all  the  earths,  its  sp.  gr.  being  9  4,  It  re- 
sennbles  yttria  closely  in  its  properties. 

Zirconium. — The  earth  zirconia,  sesquioxide  of  zirconium,  Zr203,  is  found  in  two 
rare  minerals,  the  hyacinth  and  zircon.  It  resembles  alumina  very  closely  in  all  its 
properties,  and  in  some  respects  assimilates  itself  to  silica,  and  appears  to  form  the 
link  by  which  the  metallic  and  non-metallic  bodies  are  connected  in  this  direction. 
Thus  the  double  fluoride  of  zirconium  and  potassium  is  a  sparingly  soluble  salt,  like 
the  fluoride  of  silicon  and  potassium,  and  it  is  from  this  double  fluoride  that  zirco- 
nium is  obtained,  by  a  process  identical  with  that  which  is  described  in  page  321, 
for  the  preparation  of  silicon. 

Cerium.     Lanthanum. 

These  metals  are  found  in  a  few  rather  rare  minerals,  and  have  been  but  very 
recently  distinguished  from  one  another.    They  are  always  associated  together  in 


352  MANGANESE,    ITS     PREPARATION,    ETC. 

nafure.  Their  history  does  not  possess  any  particular  interest,  and  need  hence  be 
noticed  but  very  briefly. 

Tlie  metallic  cerium  is  obtained  by  igniting  the  protochloride  of  cerium  with  po- 
tassium, as  has  been  already  described  'for  other  metals.  It  is  a  shghtly  coherent 
brown  powder,  which  decomposes  water  slowly,  evolving  hydrogen,  particularly  if 
the  water  be  hot,  and  forming  oxide  of  cerium.  It  combines  with  oxygen  in  two 
proportions,  forming  a  protoxide  and  a  sesquioxide,  Ce.O.  and  Ce203.  But  all  the 
results  obtained  with  it  now  require  revision,  as  the  discovery  of  lanthanum  has 
thrown  much  doubt  on  the  purity  of  the  substances  that  have  been  hitherto  analyzed 
as  compounds  of  cerium,  and  on  its  received  atomic  weight.  The  protoxide  of 
cerium  is  of  a  pale  fawn  colour.  If  it  be  heated  in  the  open  air,  it  absorbs  oxygen, 
and  changes  into  the  dark  brown  peroxide ;  and  if  this  be  reduced  by  hydrogen 
gas,  at  a  red  heat,  it  forms  a  yellow  complex  oxide,  probably  Ce304. 

Lanthanum. — It  was  found  by  Mosander,  that  by  calcining  protoxide  of  cerium 
so  as  to  convert  it  into  peroxide,  only  a  portion  of  it  became  insoluble  in  dilute  ni- 
tric acid,  and  that  which  dissolved  was  found,  on  accurate  examination,  to  be  really 
an  oxide  of  a  new  metal,  which,  not  forming  an  insoluble  peroxide,  may  be  thus 
separated  from  oxide  of  cerium.  From  its  having  been  so  long  hidden  in  the  oxide 
of  cerium  usually  made,  he  named  it  lanthanum  {XavOavu),  but  its  detailed  his- 
tory remains  yet  undeveloped. 

Of  Manganese. 
This  metal  exists  very  extensively  diffused  through  nature,  al- 
though not  in  very  great  quantity.  Traces  of  it  are  found  in  the  an- 
imal and  vegetable  kingdoms,  but  its  great  sources  are  the  numerous 
combinations  which  it  forms  with  oxygen,  and  which  are  employed 
for  the  purposes  of  the  arts  and  of  research.  Its  name  is  a  modifi- 
cation of  magnesia,  for  the  native  peroxide  was  once  termed  magne' 
sia  nigra  ;  but  when  the  peculiar  metal  which  it  contained  was  recog- 
nised, the  present  appellation  was  given  to  it. 

Manganese  is  one  of  the  metals  most  difficult  to  reduce,  from  its 
great  affinity  for  oxygen,  and  the  liigh  temperature  necessary  for 
its  fusion.  To  obtain  it,  the  oxide  must  be  taken  in  a  state  of  very 
fine  division,  and  for  that  object  it  is  best  to  use  an  oxide  artificially 
prepared,  as  described  farther  on.  This  is  to  be  mixed  with  an 
equal  weight  of  lampblack,  and  made  into  a  dough  with  oil,  and  this 
mass  fixed  into  a  crucible,  previously  coated  with  a  mixture  of  clay 
and  charcoal  powder.  The  crucible,  so  filled,  being  covered,  is  to 
be  exposed  to  the  most  violent  heat  of  a  smith's  forge  for  a  couple 
of  hours.  On  then  examining  it,  a  button  of  metallic  manganese 
will  be  foimd  occupying  its  lowest  portion. 

The  metallic  manganese  is  grayish  white,  granular,  and  brittle  ; 
its  sp.  gr.  8*013.  It  is  exceedingly  infusihJe.  It  very  soon  tarnishes 
in  the  air,  absorbing  oxygen,  and  falling  into  a  black  powder  after 
some  time.  It  decomposes  pure  water,  but  very  slowly;  but  rapidly 
dissolves  in  dilute  sulphuric  acid,  with  the  evolution  of  hydrogen 
gas,  sulphate  of  the  protoxide  of  manganese  being  formed. 

The  symbol  of  manganese  is  Mn.,  and  its  atomic  weight  is  346  or 
27*7,  according  to  the  standard. 

It  is  remarkable  for  the  number  of  compounds  which  it  forms  with 
oxygen,  which  are  as  follows  : 

Protoxide  of  manganese      ....     Mn.O. 

Sesquioxide  of  manganese       .     .     .     MngOg. 

Peroxide  of  manganese       ....     Mn.Oa. 

Manganic  acid Mn.Og. 

Permanganic  acid MnzOy. 


OXIDES     OF     MANGANESE.  353 

In  addition,  there  are  two  complex  oxides : 

The  red  oxide     ....    MnaO,,  or  Mn-O.+Mn^Og. 
Varvicite Mn40„  or  Mn203+2Mn.02. 

The  metallic  manganese  being  of  such  difficult  preparation,  the 
various  compounds  of  it  are  usually  obtained  from  its  most  abundant 
source,  the  native  peroxide,  which  is  sent  into  commerce  in  large 
quantities,  to  be  employed  in  the  arts  for  the  fabrication  of  chlorine, 
and  in  chemistry  to  prepare  oxygen,  and  many  other  purposes. 
The  simplest  way  of  preparing  the  salts  of  manganese  from  this  na- 
tive peroxide,  which  is  usually  associated  with  a  large  quantity  of 
oxide  of  iron,  consists  in  dissolving  it  in  an  excess  of  muriatic  acid, 
and  evaporating  the  liquor  so  obtained  to  dryness.  The  resulting 
mass  consists  of  chloride  of  manganese  mixed  with  perchloride  of 
iron.  When  this  mass  is  heated  to  redness,  the  perchloride  of  iron 
is  partly  decomposed  and  partly  volatilized,  and  on  digesting  the 
residual  mass  in  water,  oxide  of  iron  remains  undissolved,  and  a 
colourless  or  faintly  amethystine  solution  of  protochloride  of  man- 
ganese is  obtained.  From  this  the  various  other  preparations  may 
be  easily  formed. 

Protoxide  of  Manganese — ^]\In.O. ;  equivalent  446  or  35*7 — may 
be  prepared  in  many  ways.  If  to  a  solution  of  protochloride  of 
manganese  an  excess  of  a  caustic  alkali  be  added,  a  bulky  white 
precipitate  is  produced,  which  is  hydrated  protoxide  of  manganese. 
In  this  state  it  rapidly  absorbs  oxygen  from  the  air,  becoming  reddish 
brown,  being  converted  into  red  oxide,  which  is  the  most  permanent 
of  the  oxygen  compounds  of  manganese.  If  any  of  the  higher  ox- 
ides of  manganese,  in  a  state  of  fine  division,  such  as  the  red  oxide 
or  peroxide  artificially  prepared,  be  heated  to  redness  in  a  tube  of 
hard  glass,  in  a  stream  of  hydrogen  gas,  oxygen  is  removed  in  such 
proportion  as  to  leave  protoxide  of  manganese  behind.  The  oxide 
so  obtained  is  of  a  greenish  gray  colour ;  it  does  not  absorb  oxygen 
at  all  so  rapidly  as  the  hydrated  oxide  j  but  if  it  be  exposed  to  the 
air  while  hot,  it  rapidly  becomes  brown,  or  even  burns.  But  it  is 
best  obtained  by  mixing  together  chloride  of  manganese,  carbonate 
of  soda,  and  sal  ammoniac,  and  exposing  them  in  a  kind  of  platinum 
crucible  to  a  full  red  heat.  The  chloride  of  manganese  is  decom- 
posed by  the  carbonate  of  soda,  chloride  of  sodium  and  carbonate 
of  manganese  being  formed  j  Mn.Cl.  and  Na.O. .  C.Og  giving  Na. 
CI.  and  Mn.O. .  COg.  The  carbonic  acid  is,  however,  driven  off  by 
the  high  temperature,  and  the  protoxide  of  manganese  set  free,  being 
evolved  in  presence  of  the  sal  ammoniac,  which  readily  yields  hy- 
drogen, is  prevented  from  passing  to  a  higher  degree  of  oxidation. 
The  oxide  obtained  at  this  high  temperature  has  no  tendency  to 
combine  farther  with  oxygen  under  ordinary  circumstances,  and 
may  hence  be  easily  preserved.  • 

The  oxide  is  of  various  shades  of  grayish  green,  according  to  the 
method  of  preparation.  It  is  without  action  on  vegetable  colours, 
but  it  combines  with  all  the  acids,  evolving  in  some  cases,  as  with 
oil  of  vitriol,  intense  heat,  and  forms  salts  remarkable  for  their  def- 
initeness  and  neutrality.  These  salts  are  generally  colourless,  but 
often  of  a  peculiar  rose  colour,  which  is  not  due  to  the  presence  of 

Yy 


d-J-\      SESQUIOXIDE     AND    PEROXIDE     OF     MANGANESfi. 

any  higher  degree  of  oxidation,  but  to  a  peculiar  (isomeric)  con- 
dition of  the  salt  itself. 

Sesquioxide  of  Manganese. — MuaOg.  Equivalent  992  or  79'4.  This 
oxide  is  found  in  nature  in  considerable  quantity,  either  pure,  as  in 
the  mineral  braunite^  or  combined  with  water,  as  in  the  mineral  man- 
ganite.  It  may  be  prepared  artificially  by  exposing  the  peroxide  for 
a  short  time  to  a  dull  red  heat,  but  it  is  difficult  to  manage  the  de- 
composition of  that  substance  so  that  it  shall  not  proceed  too  far. 
The  sesquioxide  is  of  a  dark  brown  colour  j  exposed  to  a  strong 
heat  it  is  partly  decomposed,  evolving  oxygen,  and  being  reduced 
to  the  state  of  red  oxide.  It  combines  with  acids,  forming  salts 
which  are  of  a  deep  red  colour,  and  which  are  isomorphous  with 
those  of  alumina.  Its  salts  are  immediately  decolorized  by  sulphur- 
ous acid  and  by  sulphuretted  hydrogen.  This  oxide  possesses  the 
property  of  staining  glass  purple  or  violet,  and  by  this  character  an 
exceedingly  small  trace  of  manganese  can  be  detected  by  fusing  the 
substance  with  borax  in  the  oxidating  flame  of  the  blowpipe. 

Peroxide  of  Manganese^  or  Black  Oxide. — Mn.Og.  Equivalent  546 
or  43.7.  This  substance,  which  is  the  most  abundant  source  of 
manganese,  and  that  from  which  all  its  technical  applications  are 
derived,  exists  in  nature  in  a  variety  of  forms.  Crystallized  and  pure, 
it  forms  the  m.mQX^\  pyrolusite  ;  combined  with  water,  2Mn.02  +  H. 
O.,  it  constitutes  the  mineral  Wadd^  which, in  an  impure  form,  con- 
taminated with  variable  quantities  of  peroxide  of  iron,  carbonate  of 
lime,  and  carbonate  of  barytes,  forms  the  earthy  varieties,  which  are 
those  usually  found  in  commerce.  This  oxide  may  be  prepared  ar- 
tificially by  decomposing  the  protochloride  of  manganese, by  a  solu- 
tion of  chloride  of  lime,  Mn.Cl.  and  2Ca.0.  +  Cl.  producing  2Ca.Cl. 
and  Mn.Oa.  It  is  also  produced  when  permanganate  of  potash  is  de- 
composed by  any  organic  substance.  In  these  cases  it  is  precipita- 
ted in  combination  with  one  equivalent  of  water,  Mn.024-H.O.,  from 
which  it  may  be  freed  by  a  temperature  below  redness. 

This  peroxide  of  manganese  is  black  ;  exposed  to  heat,  it  abandons 
oxygen,  being  reduced  first  to  the  state  of  sesquioxide,  and  finally 
to  that  of  red  oxide.  It  does  not  unite  with  either  acids  or  alkalies  j 
but,  when  heated  with  strong  sulphuric  acid,  it  is  decomposed  in  the 
manner  fully  described  under  the  head  of  oxygen,  in  page  244.  Its 
use  in  the  preparation  of  chlorine  has  been  also  noticed,  page  301. 
An  important  object  to  which  it  is  applied  is  to  peroxidize  the  iron 
contained  in  the  ordinary  materials  used  in  the  manufacture  of  glass. 
If  the  iron  were  as  protoxide,  it  would  colour  the  glass  green  ;  but  the 
red  oxide  produces  only  a  very  faint  yellowish  tinge  ;  and  as  the 
protoxide  of  manganese  is  itself  destitute  of  colouring  power,  by  the 
action  of  Mn.Oa  on  2Fe.O.  there  are  formed  Mn.O.  and  Fe203,  two 
substances  which  have  no  injurious  effect  upon  the  glass ;  if,  how- 
ever, the  peroxide  of  manganese  be  added  in  excess,  a  purple  colour 
is  produced. 

Of  the  complex  oxides,  the  red  oxide  is  alone  of  interest.  It  is 
the  most  stable  of  the  compounds  of  manganese  ;  and  whenever  the 
quantity  of  this  metal  present  in  a  substance  is  to  be  determined  by 
analysis,  it  is  always  as  the  red  oxide  that  it  is  obtained.  A  solution 
of  any  salt  of  manganese,  being  precipitated  by  an  excess  of  a  caus- 


ANALYSIS     OF     PEROXIDE     OF     MANGANESE.       355 

tic  alkali,  the  precipitate,  cautiously  washed  and  ignited  in  an  open 
crucible,  gives  the  quantity  of  red  oxide  corresponding  to  the  quan- 
tity of  manganese  present.  The  varvacite,  the  other  complex  oxide, 
is  a  mineral  of  rare  occurrence,  and  only  of  interest  as  it  may  be 
mistaken  for  the  peroxide,  to  which  it  is  inferior  in  technical  value- 

The  peroxide  of  manganese  found  in  commerce  is  never  quite  pure  ;  and  as  its 
use  in  the  arts,  and,  consequently,  its  price,  are,  generally  speaking,  due  exclusively 
to  the  quantity  of  oxygen  it  is  capable  of  yielding,  a  ready  mode  of  effecting  its  anal- 
ysis becomes  of  great  importance.  There  are  two  modes  in  which  this  may  be  ac- 
complished upon  very  simple  principles,  and  in  a  short  time,  with  sufficient  accu- 
racy for  all  practical  purposes.  The  first  consists  in  converting  oxalic  acid  into 
carbonic  acid,  by  means  of  the  second  atom  of  oxygen  which  the  peroxide  of  man- 
ganese contains  ;  for  Mn.02  and  C2O3  produce  Mn.O.  and  2C.O2.  For  this  purpose 
100  grains  of  the  manganese  are  to  be  introduced  into  a  weighed  flask,  and  150 
grains  of  oxalic  acid,  dissolved  in  500  grains  of  water,  are  to  be  then  poured  upon 
it ;  to  this  350  grains  of  oil  of  vitriol  are  to  be  added,  and  the  orifice  of  the  flask 
closed  by  a  cork,  through  which  passes  a  tube  containing  fragments  of  recently-fused 
chloride  of  calcium.  The  weight  of  this  cork  and  tube  are  to  be  included  in  the  tare 
of  the  flask.  On  the  addition  of  the  oil  of  vitriol,  a  brisk  effervescence  takes  place, 
owing  to  the  escape  of  carbonic  acid  gas,  which,  passing  over  the  fragments  of 
chloride  of  calcium  in  the  tube,  are  dried,  so  that  the  gas  alone  passes  off.  When 
the  action  slackens,  a  gentle  heat  may  be  applied  until  all  the  oxide  of  manganese 
has  dissolved ;  a  small  quantity  of  a  light  brownish  sediment,  w^hich  generally  forms, 
is  easily  distinguished  from  the  particles  of  black  oxide :  as  soon  as  the  action  is 
quite  over,  the  flask  is  suffered  to  cool,  and  as  it  contains  still  a  quantity  of  carbonic 
acid  gas,  this  is  removed  by  taking  out  the  cork,  and  blowing  air  into  the  flask 
gently  by  a  glass  tube  ;  the  cork  is  then  to  be  replaced,  and  the  flask,  with  its  con- 
tents, weighed.  It  is  found  to  be  lighter  than  it  and  the  materials  together  had 
been,  and  the  loss  is  the  carbonic  acid.  The  quantity  of  carbonic  acid  formed  is 
thus  found,  and  the  quantity  of  oxygen  it  contained  calculated ;  one  fourth  of 
this  had  been  derived  from  the  peroxide  of  manganese  by  its  conversion  into  pro- 
toxide, which  remains  combined  with  sulphuric  acid  in  the  liquor,  and  the  quantity 
of  peroxide  in  the  100  grains  of  the  ore  is  thus  directly  found.  Thus,  taking  as 
an  example  an  actual  determination,  the  flask  and  materials  weighed  altogether 
1876  grains;  after  the  action  had  terminated  it  weighed  18165  grains;  the  loss 
was,  therefore,  59  5.  This  consisted  of  16  3  of  carbon  and  432  of  oxygen.  The 
oxygen  derived  from  the  mineral  was,  therefore,  ^=10-8,  which  represent  59 
grains  of  pure  peroxide  of  manganese  in  the  100  of  the  substance  used. 

The  second  mode  of  analysis  consists  in  treating  a  certain  quantity  of  the  native 
oxide  with  an  excess  of  muriatic  acid,  and  passing  the  chlorine  so  evolved  through 
water  in  which  lime  is  difTused  ;  chloride  of  lime  is  formed.  A  certain  quantity  of 
protosulphate  of  iron  (green  copperas)  is  to  be  dissolved  in  water,  and  the  solution 
of  chloride  of  lime  added  thereto,  until  the  iron  liquor  ceases  to  strike  a  blue  colour 
with  a  drop  of  solution  of  red  prussiate  of  potash  ;  then  comparing  the  quantity  of 
the  solution  of  chloride  of  lime  required  with  the  quantity  that  was  produced,  the 
total  quantity  of  chlorine  generated,  and,  hence,  the  total  quantity  of  oxygen  availa- 
ble in  the  mineral,  are  known.  The  theory  of  the  process  may  be  still  more  simply 
expressed  by  the  formulae  of  the  bodies  engaged,  as  follows  :  Mn.Oj  and  2H.C1., 
acting  together,  produce  Mn.Cl.  and  2H.0.,  while  CI.  is  given  ofFas  gas ;  this  combines 
with  Ca.O.  When  the  compound  Ca.O.Cl.  is  brought  in  contact  with  2(Fe.O. .  S.O3), 
the  oxygen  passing  from  the  hme  to  the  iron,  we  have  Ca.Cl.  and  FcaOg .  2S.O3  pro- 
duced. As  long  as  any  protosulphate  of  iron  exists,  the  solution  gives  Prussian 
blue  with  the  red  prussiate  of  potash  ;  but  when  all  the  iron  is  changed  to  peroxide, 
the  blue  colour  is  no  longer  produced.  The  following  example  of  an  actual  opera- 
tion will  complete  this  explanation.  100  grains  of  commercial  oxide  of  manganese 
were  placed  in  a  flask  with  about  one  ounce  of  strong  spirits  of  salt,  and  the  chlo- 
rine evolved  was  conducted  by  a  bent  tube  to  the  bottom  of  a  deep  jar  containing 
1600  grains  of  water  with  100  grains  of  slacked  lime ;  when  the  oxide  of  manga- 
nese had  been  completely  decomposed  by  the  muriatic  acid,  and  all  evolution  of 
chlorine  had  ceased,  a  quantity  of  the  solution  of  chloride  of  lime  was  filtered  for 
use  ;  this  being  very  strong,  500  grains  of  it  were  diluted  with  1000  of  water.  On 
the  other  hand,  100  of  crystallized  protosulphate  of  iron  were  dissolved  in  1000 
grains  of  water,  and  the  dilute  solution  of  chloride  of  lime  added  thereto  by  droj*9 


356  MANGANIC     AND     PERMANGANIC     ACIDS. 

from  an  accurately  graduated  tube,  until,  by  the  test  of  red  prussiate  of  potash,  am 
the  iron  was  peroxidized.  It  required  1300  grains  of  the  dilute  solution,  and  henco 
433  of  the  strong  solution.  Now,  as  100  grains  of  the  mineral  had  given  1600 
grains  of  this  strong  solution,  the  433  grains  corresponded  to  27  grains  ;  the  avail- 
able oxygen  of  which  was  exactly  equivalent  to  transfer  the  iron  of  the  protosul- 
phate  to  the  state  of  peroxide.  Now  the  100  grains  contain  456  of  water,  289  of 
acid,  and  255  of  protoxide  of  iron,  consisting  of  19-7  of  iron  and  58  of  oxygen,  and 
it  requires  one  half  more,  that  is,  2  9,  to  form  peroxide.  The  result  is,  that  in  the 
27  grains  of  commercial  oxide  of  manganese,  the  available  oxygen  is  29,  and  the 
quantity  of  pure  peroxide  consequently  158  grains,  or  58*7  per  cent.  This  whole 
process,  although,  when  thus  described  in  detail,  it  may  appear  complex,  is  exceed- 
ingly simple  in  execution,  and  does  not  occupy  much  time.  In  accuracy,  the  two 
metliods  are  about  equal,  giving  results  which  may  be  depended  on  to  one  per  cent. 

A  mode  has  been  recommended,  which  consists  in  simply  adding  the  green  sul- 
phate of  iron  directly  to  the  muriatic  acid  and  oxide  of  manganese  in  the  flask,  until 
the  salt  is  found  to  be  slightly  in  excess  by  the  filtered  liquor  giving  Prussian  blue 
with  red  prussiate  of  potash  ;  the  quantity  of  green  copperas  added  is  known  by 
having  previously  weighed  out  a  quantity,  and  then  weighing  what  may  remain 
after  the  process  has  been  completed.  If  no  chlorine  could  escape  the  action  of  the 
iron  salt,  this  method  would  be  much  the  shortest  and  simplest  that  could  be  em- 
ployed ;  but  it  is  exceedingly  difficult  so  to  manage  the  decomposition  as  to  avoid 
its  partial  loss.  On  this  account,  I  look  upon  this  method  as  inferior  in  accuracy, 
and  really  not  much  simpler  of  execution,  than  those  previously  described. 

The  composition  of  the  commercial  oxide  is  very  variable,  but  the  general  hmits 
may  be  considered  as  being  between  60  and  70  per  cent,  of  pure  peroxide  in  100. 
Frequently,  the  commercial  substance  contains  sesquioxide,  or  one  of  the  complex 
oxides ;  but  in  all  these  cases,  the  methods  given,  as  they  determine  the  quantity  of 
available  oxygen,  show  the  true  value  of  the  specimen,  no  matter  what  the  state  oJ 
combination  of  the  metal  may  be. 

Manganic  Acid. — Mn.Og.  Equivalent  646  or  51-7.  If  peroxide 
of  manganese  be  mixed  with  caustic  potash,  or  carbonate  or  nitrate 
of  potash,  in  a  crucibk,  and  ignited  strongly,  a  green  fused  mass  is 
obtained,  which  dissolves  in  a  small  quantity  of  water  with  a  fine 
grass-green  colour.  After  some  time,  particularly'-  if  the  solution 
be  dilated,  it  gradually  changes  colour,  a  brown  precipitate  separ- 
ates, and  the  liquor  becomes  of  a  splendid  red  colour.  This  sub- 
stance first  got  the  name  of  mineral  chameleon  from  these  changes, 
but  their  production  is  now  known  to  depend  on  the  formation  of 
two  distinct  acids  of  manganese.  The  peroxide  of  manganese  in 
these  cases  combines  with  another  atom  of  oxygen  to  form  man- 
ganic acid,  which  unites  with  the  potash.  If  potash,  caustic  or  car- 
bonated, be  used,  the  oxygen  is  derived  from  the  air  ;  if  nitre,  it  sup- 
plies oxygen  ;  but  the  best  source  consists  in  mixing  four  parts  of 
peroxide  of  manganese  in  fine  powder  with  3|  parts  of  chlorate  of 
potash,  and  adding  thereto  five  parts  of  caustic  potash  dissolved  in 
a  small  quantity  of  water.  This  mixture  is  to  be  evaporated  to  dry- 
ness, powdered,  and  afterward  ignited  in  a  platinum  crucible,  at  a 
low  red  heat  insufficient  for  fusion.  By  digestion  of  this  mass  in 
cold  water,  a  deep  green  solution  is  obtained,  from  which,  by  evap- 
oration in  vacuo,  the  manganate  of  potash  is  obtained  in  crystals. 
The  salts  of  this  acid  are  isomorphous  with  those  of  the  sulphuric 
and  chromic  acids.  They  are  decomposed  very  easily,  particularly 
if  organic  matter  be  present,  and  the  acid  itself  is  hence  incapable 
of  being  exhibited  in  an  isolated  form. 

Permanganic  Acid, — MnaO^.  Equivalent  1392  or  111-4.  When  a 
/olution  of  manganate  of  potash  is  diluted  with  boiling  water,  a  co- 
pious precipitate  of  hydrated  peroxide  of  manganese  forms,  and  a 


DETECTION     OF     MANGANES  E. 1  RON.  357 

tine  crimson  solution  of  permanganate  of  potash  is  obtained. 
SMn.Og  produces  Mn.Og  and  MnaO^.  By  rapidly  evaporating  this 
solution  until  a  pellicle  forms,  an  abundant  crop  of  crystals  of  per- 
manganate of  potash  is  obtained  on  cooling:  these  are  isomorphous 
with  the  perchlorate  of  potash,  and  are  almost  completely  black, 
but  with  a  very  peculiar  bronze  lustre.  The  salts  of  this  acid  are 
very  stable,  and  by  treating  the  permanganate  of  barytes  with  a 
proper  quantity  of  dilute  sulphuric  acid,  a  deep  crimson  solution  of 
permanganic  acid  is  obtained.  This  acid  cannot  be  had  solid,  ac- 
cording to  Mitscherlich,  its  solution  when  heated  to  100°  F.  being 
decomposed  into  peroxide  of  manganese  and  oxygen  gas.  It  is 
very  probable  that  the  solid  substance  described  as  dry  perman- 
ganic acid  by  some  chemists  contained  some  other  matter  combined 
with  it. 

The  formation  of  these  acids  by  the  action  of  sulphuric  acid  on 
peroxide  of  manganese  has  been  already  noticed,  and  the  most 
delicate  test  of  the  presence  of  manganese  in  minerals  consists  in 
fusing  a  fragment  of  the  substance  with  a  little  carbonate  of  soda 
on  a  slip  of  platina  foil,  by  means  of  the  oxidizing  flame  of  the  blow- 
pipe. The  mass,  on  cooling,  becomes  apple-green,  from  the  forma- 
tion of  manganate  of  soda,  if  there  be  the  smallest  trace  of  manga- 
nese in  the  substance  used. 

There  is  but  one  sulphuret  of  manganese.  It  is  found  as  a  min- 
eral, and  formed  also  by  heating  oxide  of  manganese  and  sulphur 
(page  285).  It  is  precipitated  in  a  hydrated  state,  when  a  solution 
of  manganese  is  decomposed  by  hydrosulphuret  of  ammonia.  Its 
colour  is  then  flesh  red.     Its  formula  is  Mn.S. 

The  detection  of  manganese  is  very  simple.  When  in  a  solid 
form,  its  compounds  are  recognised  by  giving  before  the  blowpipe  a 
purple  glass  with  borax,  and  a  green  bead  with  carbonate  of  soda. 
In  solution,  if  the  manganese  be  as  protoxide,  the  solution  is  col- 
ourless, and  yields  with  the  caustic  alkalies  a  white  precipitate  (Mn. 
O.),  rapidly  becoming  brown  QilnsO^)  :  with  the  alkaline  carbonates, 
a  white  precipitate,  Mn.O.  .  C.O2 ;  and  with  hydrosulphuret  of  am- 
monia, a  flesh  red  hydrated  sulphuret.  The  yellow  prussiate  of  pot- 
ash precipitates  the  salts  of  manganese  pure  white,  if  there  be  no 
trace  of  iron  present.  When  the  manganese  is  not  in  the  state  of 
protoxide,  the  solution  is  always  coloured  red  or  green.  These  so- 
lutions are  decolorized  by  sulphurous  acid  and  by  sulphuretted  hy- 
drogen, which  absorbs  oxygen  from  all  the  higher  degrees  of  oxida- 
tion, and  a  colourless  solution  of  protoxide  is  then  obtained,  which 
gives  the  reactions  already  described. 

SECTION  III. 

METALS   OF    THE    THIRD    CLASS. 

Of  Iron. 

This  is  the  most  extensively  distributed,  and  also  the  most  im- 
portant of  the  metals  ;  it  may,  indeed,  be  considered  as  being,  after 
those  elements  necessary  to  the  functions  of  animal  existence,  that 
■«vhich  is  most  indispensable  to  man  for  the  wants  of  ordinary  life. 
•)n  its  employment  and  applications  is  founded  every  important 


358  STATE     OP     IRON     IN     NATURE. 

Step  which  marks  the  gradual  progress  of  the  human  race  from  har 
barism  to  civilization.  The  difficulties  which  its  reduction  from  the 
state  of  ore  present,  the  variety  of  conditions  necessary  for  its  being 
successfully  wrought  into  useful  forms,  and. the  pre-eminent  advan- 
tage it  possesses  over  every  other  metal  for  the  construction  equally 
of  the  simplest  tool  and  the  most  complex  machine,  for  the  imple- 
ments of  war  as  well  as  peace,  all  combine  to  excite  the  energies 
of  a  people  to  its  acquisition,  whether  by  their  own  labour  or  by 
commerce  ',  and  thus  impel  them  to  mental  activity  and  civilization, 
either  of  native  and  independent  growth,  or  borrowed  from  more 
advanced  neighbours.  As  gold  and  jewels  hence  become  the  type 
of  ignorant  and  barbaric  pomp,  so  iron  may  be  regarded  as  the  great- 
est material  source  of  national  intelligence  and  industry. 

Iron  exists  in  nature  under  a  variety  of  forms  ;  it  is  found  native  ; 
for,  in  addition  to  loose  blocks  of  metallic  iron  found  on  the  surface 
in  various  countries,  and  to  which  a  different  nature  may  be  assigned, 
it  is  found  in  veins,  in  mines,  in  Russia  and  America.  Its  most 
abundant  form  is  that  of  oxide,  either  pure,  forming  the  various 
black  and  magnetic  oxides,  the  haematite,  or  red  oxide,  &c.,  or  com- 
bined with  carbonic  acid,  constituting  the  clay  iron  stone  from  which 
the  iron  of  commerce  is  principally  extracted.  Its  sulphurets  are 
also  found  in  abundance,  and  native  arseniates,  phosphates,  sulphates, 
and  other  salts  have  been  found. 

A  most  remarkable  source  of  iron  is  one  not  truly  terrestrial,  but 
that,  occasionally,  masses  appear  in  our  atmosphere  at  great  heights 
above  the  surface,  and  presenting  all  the  appearances  of  vivid  igni- 
tion and  combustion  j  they  move  generally  with  great  velocity  ob- 
liquely towards  the  ground,  and  generally,  before  touching,  or  at  the 
moment  of  contact  with  the  surface,  burst  with  an  explosion,  scat- 
tering their  fragments  to  considerable  distances.  These  masses  are 
termed  cerohthes ;  they  consist,  in  general,  of  an  alloy  of  iron,  with 
some  nickel  and  chrome,  with  traces  of  other  metals,  and  are  generally 
invested  with  a  vitreous  glaze  of  earthy  matter,  which  is  constituted 
of  minerals  (olivine  and  pyroxene)  found  native  in  volcanic  rocks. 
The  only  theory  which  can  explain  the  origin  of  these  meteors  is, 
that  they  are  expelled  violently  from  the  active  volcanoes  which 
telescopic  research  has  proved  to  exist  in  great  numbers  on  the  sur- 
face of  the  moon,  and  that,  passing  beyond  the  limits  of  the  attrac- 
tion of  our  satellite,  they  come  under  the  influence  of  this  earth,  and 
fall  towards  its  surface.  No  such  substances  are  ever  found  pro- 
jected from  terrestrial  volcanoes. 

The  general  principles  of  the  smelting  of  the  clay  iron  stone 
have  been  already  noticed  (p.  334),  both  considering  it  as  a  mere  car- 
bonate of  iron,  and  where  it  contains  clay,  silica,  and  alumina,  so 
as  to  render  lime  necessary  as  a  flux.  It  is,  however,  a  remarkable 
property  of  iron — one  on  which  rests,  perhaps,  its  most  useful  appli- 
cations— that  the  metal  so  obtained  is  not  pure.  The  iron,  when 
reduced,  combines  with  a  quantity  of  carbon,  generally  about  five 
per  cent.,  approximating  to  the  formula  C.4-4Fe.,  and  forming  cast 
iron,  which  is  easily  fusible,  while  the  pure  metal  is  almost  quite 
infusible.  The  cast  iron  is,  however,  not  by  any  means  a  pure  car- 
buret of  iron  j  it  contains  small  quantities  of  silicon  and  phosphorus, 


PREPARATION     OF     MALLEABLE     IRON.  359 

according  to  the  proportions  of  which  it  varies  in  properties,  so  as 
to  constitute  a  number  of  varieties,  known  in  the  arts  by  their  col- 
our and  texture,  but  of  which  it  would  be  superfluous  to  speak  here. 
When  cast  iron  remains  under  water  for  a  considerable  time,  it  be- 
comes gradually  oxidized,  magnetic  oxide  of  iron  being  formed, 
and  the  carbon  remaining  under  the  form  of  a  spongy  mass,  pre- 
serving, even  in  minute  details,  the  figure  of  the  original  mass. 

Cast  iron  has  a  great  tendency  to  crystallize  in  becoming  solid, 
and  then  expands  powerfully  ;  hence  its  property  of  filling  up  the 
most  minute  crevices  of  moulds  into  which  it  is  poured  in  the  li- 
quid state,  and  its  multifarious  uses  for  making  castings,  from 
whence  it  derives  its  name. 

Pure  or  malleable  iron  is  made  from  cast  iron  by  taking  advantage 
of  the  fact  that,  though  iron  and  carbon  are  both  combustible,  yet 
carbon  is  the  more  so  of  the  two.  Hence,  if  cast  iron  be  melted  in 
a  reverberatory  furnace  (see  p.  333),  and  exposed  to  a  current  of 
air,  the  carbon  is  gradually  burned  out,  the  metal  becomes  less  and 
less  fusible,  and  ultimately  breaks  up  into  an  incoherent  granular 
mass  like  sand ;  by  then  increasing  the  heat,  these  grains  aggluti- 
nate, and  are  worked  up  into  a  ball  about  the  size  of  a  large  loaf, 
which  is  taken  out  of  the  furnace  on  a  shovel,  and  subjected  to 
great  pressure  by  machinery.  The  soft,  pasty  particles  of  malleable  > 
iron  are  thus  welded  to  each  other,  and  any  portions  of  liquid,  un- 
altered cast  iron  that  might  remain  are  squirted  out,  as  water 
would  be  by  pressure  from  the  pores  of  a  sponge ;  this  lump  of 
malleable  iron  is  then  passed  through  a  succession  of  rollers,  driven 
by  powerful  steam  engines  ;  each  pair  of  rollers  having  a  smaller  in- 
terval than  the  preceding,  the  mass  is  gradually  elongated  into  a 
bar,  and  finally  is  delivered,  at  the  end  farthest  from  the  furnace,  in 
the  form  of  the  soft  bar  iron  of  commerce.  The  heat  evolved  by 
the  enormous  pressure  to  which  the  metal  is  subjected  in  this  pro- 
cess is  so  great,  that  the  bar  remains  soft  enough  to  be  moulded 
by  the  rollers  all  through  its  passage. 

This  process  by  the  reverberatory  furnace  is  termed  pudling^  and 
has  been  very  much  improved  lately  by  burning  out  the  carbon  by 
means  of  a  certain  quantity  of  oxide  of  iron  or  oxide  of  manganese. 
Thus,  by  heating  together  two  parts  of  cast  iron  and  one  of  scales 
of  black  oxide  of  iron  from  a  forge,  all  the  carbon  and  oxygen  pass 
off  as  carbonic  acid,  and  the  iron  of  both  remains  pure.  Fe304  and 
Fe^C^  produce  Fe,,  and  C2O4. 

The  bar  iron  thus  obtained  differs  remarkably  from  the  cast  iron 
in  all  characters :  it  is  soft,  flexible,  ductile,  and  malleable,  none  of 
which  properties  cast  iron  possesses.  It  fuses  only  at  the  very 
highest  temperatures,  and  then  becomes  only  semifluid.  It  is,  con- 
sequently, quite  impossible  to  run  it  into  moulds.  It  possesses, 
however,  the  important  character  of  welding  at  a  white  heat ;  that 
is  to  say,  it  assumes  a  doughy  consistence,  so  that  several  pieces 
of  it,  laid  together,  may  be  kneaded  into  one  by  blows  of  a  hammer 
or  by  pressure  between  rollers,  so  as  to  form  a  single  mass,  the 
points  of  junction  being  totally  undistinguishable.  It  is  thus  that 
soft  iron  is  always  worked  at  a  white  heat.  Its  strength  is  much 
increased  by  several  pieces  being  thus  welded  together,  and  hence 


360  MANUFACTURE     OF     STEEL. 

all  parts  which  require  to  possess  peculiar  tenacity,  such  as  anchors, 
&c.,  are  always  made,  not  in  a  single  piece,  but  by  thus  welding  to 
gether  a  bundle  of  small  bars. 

A  third  and  equally  important  form  in  which  iron  exists  in  the 
arts,  is  that  of  steel.  Steel  is  intermediate  to  cast  iron  and  bar  iron 
in  constitution,  containing  generally  about  1-5  per  cent,  of  carbon. 
Steel  may  be  formed  directly  from  the  ore  or  from  cast  iron  by  pro- 
portioning the  action  of  the  fuel  and  of  the  air  in  the  furnaces  so  as 
to  leave  combined  with  the  iron  as  much  carbon  as  constitutes  steel. 
But  the  most  important  and  curious  mode  of  making  steel  is  by  what 
is  termed  cementation.  Bars  of  iron  are  laid  in  boxes,  imbedded  in 
powdered  charcoal,  and  exposed  for  some  hours  to  a  full  red  heat ; 
the  carbon  gradually  penetrates  through  the  whole  substance  of  the 
iron,  changing  it  into  a  bar  of  steel  of  pretty  uniform  structure. 
The  bar  becomes  frequently  blistered  from  gas  bubbles  forming  in 
its  substance.  This  process  can  be  effected  even  though  the  car- 
bon may  not  directly  touch  the  iron,  provided  oxygen  be  present; 
carbonic  oxide  being  formed,  which  is  decomposed  by  the  iron,  half 
the  carbon  being  absorbed,  and  carbonic  acid  given  off.  It  is  the  es- 
cape of  this  last  gas  under  the  form  of  bubbles  that  produces  the 
blistering  of  steel.  The  decomposition  of  the  carbonic  oxide  takes 
place  at  the  surface  of  the  bar  in  great  part,  but  the  carbon  is  trans- 
ferred from  particle  to  particle  of  the  iron  until  the  entire  mass  as- 
sumes the  same  constitution.  Steel  is  harder  and  more  fusible  than 
pure  iron,  but  its  peculiar  hardness  is  given  to  it  only  when  it  has 
been  heated  to  redness  and  suddenly  cooled  j  it  is  then  exceedingly 
brittle,  hard,  and  elastic,  and  is  thus  fitted  for  its  extensive  use  in 
cutting  instruments,  pivots,  files,  &;c.  The  steel,  when  it  has  cooled 
slowly,  is  so  soft  that  it  is  easily  engraved  upon,  cut,  and  may  be 
welded  with  soft  iron ;  the  instrument  being  so  constructed,  it  is 
heated  to  redness  and  suddenly  cooled ;  it  is  thus  hardened,  but  is 
still  unfit  for  being  employed  until  it  is  tempered  to  the  particular 
use  for  which  it  is  destined  by  being  heated  in  oil  to  a  certain  de- 
gree, and  then  allowed  to  cool  slowly.  By  this  means  the  excess 
of  hardness  is  got  rid  of,  and  the  steel  remains  of  the  quality  re- 
quired. 

The  peculiar  property  of  iron  and  steel  of  becoming  magnetic, 
has  been  described  in  page  143.  Not  only  is  iron  in  the  pure 
state,  and  when  combined  with  carbon,  attracted  by  the  magnet, 
but  several  of  its  oxides  and  sulphurets  possess  the  same  charac- 
ter ;  of  these,  one  constitutes,  indeed,  the  natural  magnet,  the  native 
loadstone. 

Pure  iron  is  bluish  white,  exceedingly  brilliant,  very  malleable 
and  ductile  ;  it  is  the  strongest  of  all  the  metals.  Its  specific  grav- 
ity is  7-8.  It  becomes  pasty  when  intensely  heated,  whence  its  re- 
markable power  of  welding,  which  belongs,  besides,  to  platinum  and 
sodium. 

When  iron  in  mass  is  exposed  to  dry  air,  it  does  not  become  ox. 
idized ;  but  when  in  a  state  of  very  minute  division,  it  takes  fire 
when  gently  warmed,  and  burns,  forming  peroxide  of  iron ;  when 
strongly  heated  in  oxygen  gas,  as  by  attaching  a  little  sulphur  or  a 
bit  of  taper  wick  to  a  wire,  and  plunging  it  into  a  vessel  of  oxygen. 


PASSIVE     CONDITION     OF     IRON.  361 

it  burns  with  exceeding  brilliancy,  and  forms  globules  of  black  ox- 
ide of  iron,  Fe304.  The  true  product  of  the  combustion  is  peroxide, 
FcaOa,  but  this  loses  one  ninth  of  its  oxygen  by  the  intense  tempera- 
ture, and  forms  the  black  magnetic  oxide.  It  is  hence  that,  when 
iron  is  burned  in  oxygen  gas,  the  oxide,  which  is  thrown  off  in  mi- 
nute grains,  collects  on  the  inside  of  the  jar  as  peroxide,  but  the  lar- 
ger globules,  which  are  intensely  heated  for  some  time  before  they 
melt  off  the  wire,  are  reduced  to  the  state  of  black  oxide.  It  is  not 
quite  certain  whether  iron  decomposes  water  in  the  absence  of  an 
acid,  but  the  presence  of  a  small  quantity  even  of  carbonic  acid  pro- 
duces decided  action,  and  hence  the  rapid  corrosion  of  iron  in  damp 
air,  forming  carbonate  of  iron  (rust).  In  dilute  sulphuric  acid  iron 
dissolves  with  great  rapidity,  evolving  hydrogen,  which,  however, 
is  very  impure,  for  even  the  softest  iron  contains  traces  of  carbon, 
which  combines  with  some  of  the  hydrogen,  forming  compounds, 
which  give  the  gas  a  peculiar  odour,  and  colour  its  flame  yellow. 
At  a  red  heat  water  is  decomposed  rapidly  by  iron,  as  fully  descri- 
bed in  p.  "246.  If  iron  be  immersed  in  water  holding  potash,  lime, 
or  soda  in  solution,  or  if  the  iron  be  covered  up  in  quicklime,  all 
rusting  is  prevented,  probably  from  any  carbonic  acid  present  being 
totally  taken  up  by  the  base. 

A  remarkable  property  of  iron,  though  not  absolutely  peculiar  to 
it  alone,  is,  that  when  placed  in  contact  with  the  hydrated  nitric  acid, 
sp.  gr.  1-35,  it  may  remain  unacted  on,  hecom'mg  passive ;  although, 
under  ordinary  circumstances,  it  is  rapidly  dissolved  by  that  acid 
with  evolution  of  nitric  oxide.  This  passive  condition  may  be  pro- 
duced in  many  ways.  1st.  If  one  end  of  a  long  iron  wire  be  igni- 
ted, and  then,  when  cool,  the  wire  be  immersed  in  the  acid,  the  ig- 
nited end  being  dipped  first,  it  remains  unaltered.  2d.  If  a  piece 
of  platina  wire  be  fastened  to  a  piece  of  iron  wire,  and  then  immer- 
sed in  the  acid,  the  platina  first.  3d.  By  placing  a  platina  wire  in 
the  acid,  then  immersing  an  iron  wire  in  contact  with  it,  the  platina 
wire  maybe  withdrawn,  and  the  iron  wire  remain  passive.  4th.  By 
making  the  iron  wire  the  positive  pole  of  a  galvanic  battery.  5th. 
By  contact  with  a  wire  already  passive ;  thus,  an  iron  wire  being 
immersed  in  the  acid,  as  in  No.  3,  another  wire  may  be  put  in  con- 
tact with  it,  and  the  first  then  withdrawn,  and  so  on  for  an  unlimited 
succession  of  wires.  These  are  not  the  only  methods,  but  merely 
the  most  remarkable. 

The  properties  of  iron  thus  rendered  passive  are  curious.  It  ap- 
pears to  have  lost  all  tendency  to  unite  with  oxygen ;  it  does  not 
dissolve  in  acids;  it  does  not  precipitate  copper  from  its  solutions; 
and  when  used  as  a  positive  electrode  for  a  voltaic  battery,  oxygen 
is  evolved  from  it  precisely  as  if  the  electrode  had  been  platinum. 
We  do  not  as  yet  know  the  true  theory  of  these  effects.  The  most 
available  explanation  is,  that  the  iron,  by  an  alteration  of  molecular 
structure,  assumes  a  condition  by  which  it  becomes  similar  in  its 
electrical  relations  to  the  noble  metals.  It  is  possible  that  this 
property  may  be  connected  with  the  equivalency  of  two  equivalents 
of  the  iron  and  manganese  group  of  metals  to  one  of  chlorine,  and 
that  when,  by  a  change  of  molecular  arranoement,  like  isomerism^ 

Zz 


362  VARIOUS     OXIDES     OF     IRON. 

the  particle  becomes  Fca  in  place  of  Fe.,  it  is  incapable  of  acting  as 
the  positive  element  in  galvanic  ot  chemical  combinations. 

The  equivalent  of  iron  is  not  so  accurately  known  as  those  of 
metals  much  less  important  and  less  common.  The  best  determi- 
nations make  it  about  339  upon  the  oxygen,  and  27*2  upon  the  hy- 
drogen scale.     Its  symbol  is  Fe.,  from  its  Latin  name. 

Oxides  of  Iron. — Iron  combines  with  oxygen  in  two  proportions, 
forming  a  protoxide  and  a  sesquioxide,  and  these,  again,  unite  to  form 
complex  oxides,  the  black  or  magnetic  oxides  of  iron. 

Protoxide  of  Iron. — Fe.O.  Equivalent  439  or  35"2.  This  oxide 
cannot  be  obtained  pure  in  a  dry  state,  from  the  rapidity  with  which 
it  absorbs  oxygen.  It  exists  as  the  basis  of  a  very  extensive  class 
of  salts,  the  green  or  protosalts  of  iron.  From  their  solutions,  it  is 
precipitated  by  an  alkali  as  a  white  hydrate,  which  rapidly  becomes 
green,  and  finally  brown-red,  from  absorption  of  oxygen.  If  we  at- 
tempt to  form  the  protoxide  by  processes  similar  to  those  described 
for  obtaining  protoxide  of  manganese,  the  iron  is  reduced  either  to 
black  oxide  or  to  the  metallic  state.  This  oxide  exists  native,  com- 
bined with  carbonic  acid,  in  the  common  carbonate  of  iron,  and  is  the 
form  in  which  the  metal  exists,  dissolved  in  all  chalybeate  springs. 

Peroxide  of  Iron. — Ye^O^.  Equivalent  978  or  78*4.  This  substance 
exists  in  very  great  abundance  in  nature,  crystallized  in  rhombohe- 
drons,  being  isomorphous  with  the  crystallized  alumina,  corundum. 
This,  the  ologist  iron,  constitutes  the  celebrated  Elba  iron  ore.  It 
forms,  in  a  more  or  less  hydrated  condition,  the  hematite,  of  various 
shades  of  red  and  brown,  from  which  a  great  deal  of  the  best  iron 
and  steel  is  made.  It  exists  in  a  variety  of  minerals,  and  forms  the 
red  or  yellow  colouring  matter  of  clay  and  of  the  different  kinds  of 
ochres.  I  have  noticed  that  when  iron  is  burned  in  a  full  supply  of 
oxygen,  this  red  oxide  is  formed,  and  it  is  produced  also  when  iron 
rusts,  for  the  protocarbonate  which  first  forms  is  gradually  decom- 
posed, abandoning  its  acid,  and  absorbing  oxygen.  It  is  thus  that 
the  margins  of  chalybeate  springs  become  coated  with  an  ochrey 
deposite  j  the  carbonate  of  iron  originally  dissolved  being  gradually 
converted  into  red  oxide,  while, the  carbonic  acid  passes  off. 

The  peroxide  of  iron  may  be  artificially  prepared  by  precipitating 
a  solution  of  any  of  its  salts  with  an  alkali  caustic  or  carbonated. 
In  the  latter  case,  the  carbonic  acid  is  given  off,  as  the  peroxide  of 
iron  does  not  combine  with  it.  The  hydrated  peroxide  which  is 
precipitated  is  of  a  light  reddish-brown  colour,  but  when  dried  it 
becomes  dark  brown.  Strongly  ignited,  it  becomes  nearly  black  j 
and,  indeed,  by  an  intense  heat  it  loses  some  of  its  oxygen,  3(Fe203) 
giving  2(Fe304),  and  O.  escaping,  being  decomposed  just  as  the  ses- 
quioxide of  manganese,  but  requiring  much  greater  heat.  The  per- 
oxide of  iron  combines  with  acids  to  form  salts,  which  are  all  acid, 
and  easily  decomposed.  They  will  be  described  hereafter.  Its 
chemical  combinations  resemble  those  of  alumina  and  sesquioxide 
of  manganese,  with  which  they  are  isomorphous. 

When  a  solution  of  a  protosalt  of  iron  is  exposed  to  the  air,  it 
gradually  absorbs  oxygen  until  two  thirds  of  the  iron  become  per- 
oxidized,  and  then  the  decomposition  ceases.  The  liquor  then  con- 
tains a  compound  oxide,  Fe.O.  -j-FeaOg,  and  on  the  addition  of  a  caus- 


SULPHURETS     OF     IRON.  363 

tic  alkali  this  is  precipitated  as  a  black  powder,  which,  when  dry,  is 
powerfully  attracted  by  the  magnet.  This  is  the  artificial  magnetic 
oxide  of  iron.  It  may  be  prepared  at  will  by  taking  three  equal 
portions  of  protosulphate  of  iron,  and  peroxidizing  two  of  them  by 
means  of  a  little  boiling  nitric  acid,  then  mixing  the  solutions,  and 
precipitating  the  whole  by  water  of  caustic  ammonia.  The  precip- 
itate is  a  hydrate,  but  may  be  deprived  of  the  water  without  altera- 
tion. 

This  magnetic  oxide  of  iron  exists  native  in  great  abundance ;  it 
constitutes  the  common  loadstone,  and  is  that  produced  when  iron 
is  oxidized  at  high  temperatures.  It  thus  constitutes  the  scales  of 
iron  which  form  in  smithies  and  forges  during  the  successive  heat- 
ings and  hammerings  to  which  the  metal  is  subjected.  These  scales 
of  iron  are,  however,  not  uniform  in  constitution,  and  are  hence  in- 
ferior as  a  steady  medicinal"  agent  to  the  oxide  artificially  prepared 
by  precipitation. 

Sulphurets  of  Iron. — Sulphur  combines  with  iron  in  three  propor- 
tions, forming  the  protosulphuret,  the  sesquisulphuret,  and  the  bi- 
sulphuret.  These  again  combine,  so  as  to  produce  complex  (mag- 
netic) sulphurets.     Other  degrees  (subsulphurets)  are  problematical. 

Protosulphuret  of  Iron. — Fe.S.  Equivalent  540*4  or  43*3.  The  af- 
finity of  iron  for  sulphur  is  very  remarkable.  If  a  rod  of  iron  be 
heated  to  whiteness,  and  then  touched  to  a  stick  of  sulphur,  they 
combine  with  energy,  and  the  sulphuret  of  iron  flows  down  in  copi- 
ous drops.  If  vapour  of  sulphur  be  made  to  gush  from  a  jet,  and 
an  iron  wire  heated  to  bright  redness  be  placed  in  it,  it  takes  fire, 
and  burns  with  scintillations  as  brilliantly  as  if  it  had  been  immersed 
in  oxygen  gas.  In  these  cases,  where  the  iron  is  in  excess,  the  pro- 
tosulphuret is  formed.  It  is  most  conveniently  prepared  by  heating 
together  to  bright  redness,  in  a  crucible,  three  parts  of  iron  filings 
or  turnings,  and  two  of  sulphur  j  at  a  high  temperature  the  resulting 
mass  may  be  fused.  This  compound  is  black,  its  fracture  yellowish. 
It  dissolves  in  dilute  acids,  evolving  sulphuret  of  hydrogen,  and  form- 
ing a  salt  of  protoxide  of  iron.  This  is  almost  its  only  use  in  the. 
laboratory.  The  manner  of  obtaining  sulphuret  of  hydrogen  from 
it  has  been  described  in  page  292.  This  protosulphuret  of  iron  ex- 
ists sometimes,  though  rarely,  in  nature,  and  is  dangerous,  particu- 
larly in  coal  mines,  from  the  avidity  with  which,  when  moist,  it  ab- 
sorbs oxygen,  forming  protosulphate  of  iron,  Fe.S.  and  40.  giving 
Fe.O.  .  S.O3 ;  during  which  process  it  occasionally  becomes  so  heat- 
ed as  to  set  fire  to  the  beds  of  coal  near  it,  and  thus  cause  consid- 
erable loss. 

This  sulphuret  may  be  prepared  in  the  moist  way  by  adding  hy- 
drosulphuret  of  ammonia  to  a  protosalt  of  iron.  Thus  Fe.Cl.  and 
S.H.+N.H3  produce  Fe.S.  and  CI.H.+N.H3.  It  is  a  jet  black  pow- 
der, which  dissolves  readily  in  acids,  and  when  exposed  moist  to 
the  air,  rapidly  absorbs  oxygen,  forming  green  copperas. 

Sesquisulphuret  of  Iron. — FcgSg.  Equivalent  1282  or  102-7.  This 
compound,  which  corresponds  to  the  peroxide,  is  very  instable  in 
constitution.  It  may  be  prepared  in  the  moist  way  by  adding  to  a 
persalt  of  iron  in  solution,  hydrosulphuret  of  ammonia.  A  black 
precipitate  forms,  which  may  be  dried  in  vacuo.     It  may  be  also 


364  SULPHURETS     OF     IRON. 

produced  by  heating  peroxide  of  iron  in  a  current  of  sulphuretted 
hydrogen  gas,  water  being  formed.  It  is  not  attracted  by  the  mag- 
net. It  dissolves  in  acids,  but  one  third  of  the  sulphur  is  precipita- 
ted, two  thirds  only  combining  with  hydrogen,  and  the  iron  existing 
in  solution  as  a  protosalt.  Thus  FcaSs^and  2H.C1.  give  2(Fe.Cl.) 
and  2H.S.  with  deposition  of  S.  This  arises  from  the  circumstance 
that  peroxide  of  iron  is  reduced  by  sulphuretted  hydrogen  to  pro- 
toxide, water  being  formed,  and  sulphur  set  free. 

Bisulphuret  of  Iron.  —  Fe-Sg.  Equivalent  741-5  or  SQ-^.  This 
substance  is  met  with  in  very  large  quantity  in  nature,  constituting 
the  iron  pyrites  used  in  the  manufacture  of  sulphuric  acid  and  of 
copperas.  It  is  dimorphous  (pages  229-232),  and  in  its  two  forms 
possesses  very  different  properties.  It  may  be  prepared  artificially 
by  heating  together  the  protosulphuret  in  a  state  of  minute  division, 
with  half  its  weight  of  sulphur.  When  the  excess  of  sulphur  has 
been  distilled  off,  there  remains  a  voluminous  yellow  powder,  noi 
acted  on  by  the  magnet,  and  insoluble  in  acids,  which  is  the  bisul- 
phuret of  iron.  This  bisulphuret  of  iron  is  found  in  a  variety  of 
forms,  which  belong  properly  to  the  different  kinds  of  native  oxides 
of  iron,  which  being  probably  acted  on  by  vapour  of  sulphur  from 
volcanic  sources,  have  lost  their  oxygen,  and,  without  being  melted, 
have  changed  into  bisulphuret.  It  is  also  found  simulating  the  fig- 
ures of  a  variety  of  organic  remains,  as  nautili,  &c.,  where,  proba- 
bly, the  animal  having  perished  in  water  holding  traces  of  sulphate 
of  iron  in  solution,  the  hydrogen  compounds  evolved  by  its  decom- 
position have  reacted  on  the  sulphate  of  iron,  abstracting  its  oxygen 
and  producing  a  deposite  of  pyrites. 

Magnetic  Sulphurets  of  Iron. — Of  these  the  most  remarkable  is  that 
which  corresponds  to  the  magnetic  oxide,  having  the  formula  Fcg 
04=Fe.S.-|-Fe2S3.  It  is  found  native  at  Barege,  and  may  be  formed 
by  exposing  to  a  red  heat,  in  close  vessels,  the  bisulphuret  or  sesqui- 
sulphuret :  the  pyrites  3(Fe.S2)  producing  Ye^i  and  S2,  precisely 
as  peroxide  of  manganese  3(Mn  O^)  produces  O2  and  MngO^.  If, 
however,  the  heat  be  raised  too  high,  more  sulphur  is  expelled,  and 
another  kind  of  magnetic  sulphuret,  Fe7S8=5Fe.S.+Fe2S3,  formed, 
which  is  also  found  native,  and  which  corresponds  to  the  black 
scales  of  oxide  of  iron,  which  are  5Fe.O.+Fe203.  This  compound 
is  always  formed  in  making  the  protosulphuret,  if  there  be  an  excess 
of  sulphur  above  the  proper  proportion  used. 

The  seleniuret  and  phosphurets  of  iron  resemble  very  closely  the 
sulphurets.  Phosphuret  of  iron  exists  generally  in  cast  iron  in  small 
quantity. 

The  detection  of  iron  is  very  simple.  It  may  exist  in  solution  in 
the  state  either  of  protoxide,  black  oxiclip,  or  peroxide ;  and  as  the 
application  of  reagents  becomes  much  simpler  in  the  last  case,  it  is 
best,  when  the  object  is  only  to  ascertain  the  presence  or  absence 
of  iron,  to  boil  the  solution  with  a  few  drops  of  nitric  acid,  by  which 
any  iron  that  may  be  present  is  peroxidized. 

A  solution  containing  peroxide  of  iron  produces  with  water  of 
ammonia  a  reddish-brown  precipitate  of  hydrated  peroxide  ,*  with 
yellow  prussiate  of  potash,  a  fine  Prussian  blue  5  with  sulphocyan- 
ide  of  potassium,  a  deep  blood-red  colour,  but  no  precipitate  j  with 


r  REPARATION     OF     NICKEL.  365 

a  solution  of  tannin  or  tincture  of  galls,  a  deep  violet  or  black. 
With  sulphuret  of  hydrogen  there  is  no  effect  except  the  separation 
of  a  deposite  of  pure  sulphur,  but  with  hydrosulphuret  of  ammonia 
a  black  precipitate  of  sesquisulphuret  of  iron. 

If  the  solution  contain  the  iron  only  as  protoxide,  ammonia  pro^ 
duces  a  precipitate,  at  first  whitish,  but  rapidly  becoming  bluish- 
green.  The  yellow  prussiate  of  potash,  a  precipitate,  at  first  white, 
but  rapidly  becoming  blue.  The  sulphocyanide  of  potassium,  thfe 
tannin,  and  the  sulphuret  of  hydrogen  are  without  effect,  but  the  hy- 
drosulphuret of  ammonia  forms  the  black  protosulphuret.  The  char- 
acteristic reagent  for  protoxide  of  iron  is  the  red  prussiate  of  pot- 
ash, which  gives  Prussian  blue,  but  does  not  act  upon  the  solution 
of  peroxide. 

If  the  solution  contain  at  the  same  time  both  oxides,  the  precipi- 
tate by  ammonia  is,  from  the  commencement,  green  or  black,  and 
all  the  other  reagents  concur  in  the  demonstration  of  the  presence 
of  the  two  states  of  oxidation  of  the  metal. 

Of  MckeL 

An  ore  which,  from  its  external  characters,  was  supposed  by  the 
German  miners  to  contain  copper,  but  resisted  all  endeavours  to 
extract  that  metal  from  it,  received  the  name  of  kupfer-nickely  or  de- 
ceitful copper.  Subsequently  it  was  found  to  consist  of  a  peculiar 
metal  united  to  arsenic,  and  this  metal  retained  the  name  nickel,  its 
meanincr  being  forgotten  or  lost  sight  of.  A  substance  found  in 
commerce,  termed  speiss,  a  residue  from  the  manufacture  of  smalts, 
is  also  an  arseniuret  of  nickel,  and  from  either  of  these  sources  the 
metal  is  generally  extracted. 

The  mass  containing  nickel  and  arsenic  is  dissolved  by  a  mixture  of  nitric  acid 
and  sulphuric  acid,  diluted  with  water.  By  this  means  the  nickel  is  converted  into 
sulphate  of  its  oxide,  and  the  arsenic  into  arsenious  acid.  On  concentrating  the  li- 
quor, most  of  the  latter  is  got  rid  of  by  crystallization.  Carbonate  of  potash  is  then 
to  be  added  to  the  liquor,  until  the  green  precipitate  which  first  forms  ceases  to  be 
redissolved .  On  then  evaporating  and  cooling,  a  double  sulphate  of  nickel  and  pot- 
ash is  obtained,  which,  by  two  or  three  recrystallizations,  is  freed  from  all  traces 
of  arsenic.  This  double  salt  may,  however,  be  contaminated  by  iron  and  copper ; 
from  the  first  it  is  separated  by  sulphuretted  hydrogen,  and  from  the  last  by  the 
solubility  of  the  oxide  of  nickel  in  water  of  ammonia.  From  the  ammoniacal  so- 
lution, the  oxide  of  nickel  may  be  precipitated  by  oxalic  acid,  as  an  insoluble  ox- 
alate, which,  when  dried  and  heated,  gives  off  carbonic  acid,  and  leaves  metallic 
nickel,  Ni.O.-f  C2O3,  producing  2O.O2  and  Ni.  The  metallic  nickel  is  then  in  the 
form  of  a  very  light  sponge. 

It  is  somewhat  more  fusible  than  cast  iron ;  of  a  silvery  white 
colour.  It  does  not  rust  when  exposed  even  to  damp  air.  Its  sp. 
gr.  is  about  85.  It  is  nearly  as  magnetic  as  iron,  and  retains  its  mag- 
netism, resembling  in  that  respect  steel  rather  than  pure  iron.  In 
its  permanency  of  lustre,  nickel  resembles  the  precious  metals,  and 
its  alloys  are  of  singular  brilliancy  and  whiteness.  It  is  hence  that, 
added  to  brass  in  the  proportion  of  one  to  five,  it  is  employed  as  a 
substitute  for  silver,  constituting  the  German  silver,  nickel  silver, 
argentine,  and  British  plate  of  commerce,  as  well  as  the  packfong 
long  used  in  China. 

The  symbol  of  nickel  is  Ni. ;  its  equivalent  369-7  or  29-6. 

Oxides  of  JVickel. — This  metal  combines  with  oxygen  in  two  pro- 
portions, forming  a  protoxide  and  a  sesq;::ioxide. 


366  COBALT     AND    ITS    OXIDE  3. 

The  protoxide,  Ni.O.,  is  prepared  by  precipitating  a  salt  of  nickel  by  caustic  potas^i ; 
a  grass-green  hydrated  oxide  of  nickel  separates,  Ni.O.-|-H.O.,  which,  wlien  dry,  gives 
the  pure  ash-gray  oxide.  This  is  the  only  oxide  of  nickel  which  forms  salts.  It  is 
not,  by  itself,  soluble  in  water  of  ammonia ;  but  if  a  salt  of  nickel  be  decomposed 
by  ammonia,  the  precipitate  which  first  forms  is  dissolved  on  adding  an  excess  of 
the  alkali,  forming  a  blue  solution,  in  a  great  degree  characteristic  of  this  metal. 

The  Peroxide  of  Nickel,  NiaOg,  is  a  black  powder,  prepared  by  boiling  the  pro- 
toxide in  a  solution  of  chloride  of  lime ;  the  oxygen  of  the  lime  changes  the  pro- 
toxide into  peroxide,  2Ni.O.  and  Ca.O.Cl.  producing  Niz .  O3  and  Oa.Cl.  When  igni- 
ted, this  oxide  gives  oxygen  and  protoxide ;  with  muriatic  acid  it  forms  protochloride 
and  chlorine.     It  does  not  form  any  true  salts. 

Nickel  is  easily  recognised  by  its  solutions  giving  with  ammonia 
a  green  precipitate,  which  dissolves  in  an  excess,  forming  a  blue 
solution,  and  by  giving  with  yellow  prussiate  of  potash  a  white 
precipitate.  The  solutions  of  nickel  are  not  precipitated  by  sul- 
phuretted hydrogen,  but  give  a  black  sulphuret  of  nickel  with  hy- 
drosulphuret  of  ammonia. 

The  sulphuret,  seleniuret,  and  phosphuret  of  nickel  do  not  present 
any  point  of  interest. 

Of  Cobalt. 

The  name  of  this  metal  has  its  origin  in  a  still  more  singular  cir- 
cumstance than  that  of  the  preceding ;  from  the  bright  metallic  ap- 
pearance of  its  ores,  the  miners  of  the  Middle  Ages  were  led  to  ex- 
pect an  abundant  produce,  but  the  modes  of  reduction  then  in  use 
were  employed  without  avail ;  it  was  hence  imagined  that  these 
ores  were  especially  protected  by  the  guardian  spirits  of  the  mines, 
or  Kobolds,  and  these  minerals  were  termed  Die  Kobold's  erze^  the 
Kohold's  ores.  At  a  later  period  a  peculiar  metal  was  extracted  from 
them,  and  as  the  older  name  had  been  corrupted  into  kobalt  ore,  the 
metal  was  called  cobalt. 

Cobalt  exists  in  nature,  combined  with  arsenic  and  with  sulphur  ; 
it  is  universally  associated  with  nickel,  which  it  resembles  so  closely 
in  its  properties  that  the  perfect  separation  of  these  two  metals  is 
one  of  the  most  difficult  operations  in  analysis. 

To  obtain  the  cobalt,  the  native  arseniuret  is  roasted  in  a  current  of  air,  so  as  to 
oxidize  both  metals,  as  described,  p.  334.  The  residual  impure  oxide  of  cobalt  is 
sold  in  commerce  under  the  name  of  Zaffre.  This  zaflre  is  dissolved  in  muriatic 
acid,  and  treated  with  sulphuretted  hydrogen,  by  which  the  copper  and  arsenic  are 
separated.  From  the  filtered  liquor,  the  cobalt  is  thrown  down  by  carbonate  of 
potash,  and  then,  to  free  it  from  oxide  of  iron,  it  is  digested  with  oxalic  acid,  which 
dissolves  the  peroxide  of  iron,  and  leaves  an  insoluble  oxalate  of  cobalt ;  this  may 
still  be  contaminated  with  nickel,  but  for  the  details  of  the  separation  of  these  met- 
als, I  must  refer  to  more  extended  works. 

The  oxalate  of  cobalt,  when  ignited,  yields  carbonic  acid  and 
metallic  cobalt  in  a  spongy  form.  Cobalt  melts  into  a  button  more 
easily  than  cast  iron  ;  it  is  reddish-gray  ;  specific  gravity  8-5  j  when 
perfectly  pure,  it  is  not  susceptible  of  becoming  magnetic.  It  acts 
upon  water  and  acids  more  rapidly  than  nickel,  but  much  less  ac 
tively  than  iron  or  zinc.  The  symbol  of  cobalt  is  Co.,  and  its  equiv 
alent  369  or  29-6. 

Oxides  of  Cobalt. — Cobalt  combines  with  oxygen  to  form  two  well 
defined  oxides,  a  protoxide  and  sesquioxide;  there  are  also  a  com- 
plex oxide,  and  a  compound  of  which  the  constitution  is  not  well 
known,  but  which  is  probably  a  deutoxide. 

Protoxide  of  Cobalt,  Co.O.,  is  prepared  by  adding  caustic  potash  to  a  solution  of  a 


USES     OF     COBALT    IN     THE     ARTS. ZINC.  367 

salt  of  cobalt ;  a  fine  blue  powder  falls,  which  is  a  hydrate,  Co.O.  .  H.O. ;  when  de- 
prived of  its  water,  it  becomes  ash-gray  :  it  is  the  only  oxide  of  cobalt  which  forma 
salts  with  acids. 

Sesquioxide  of  Cobalt,  C02O3,  is  prepared  as  the  sesquioxide  of  nickel ;  it  is  a  black 
powder,  which,  with  hydrochloric  acid,  gives  chlorine  and  protochioride :  it  does 
not  form  salts. 

The  complex  oxide  is  Co304=:::Co.O.-|-Co203,  similar  to  the  magnetic  oxide  of 
iron  and  red  oxide  of  manganese. 

Cobalt  is  recognised  in  solution  by  producing  with  water  of  am- 
monia a  blue  precipitate,  which  redissolves  in  an  excess  of  the  al- 
kali, forming  a  liquor  which  is  of  a  fine  rose  colour  if  the  cobalt 
be  pure,  but  brownish  red  if  nickel  be  present ;  it  is  not  precipitated 
by  sulphuretted  hydrogen,  but  is  thrown  down  black  by  hydrosul- 
phuret  of  ammonia.  The  most  remarkable  test  for  cobalt  is  its 
power  of  colouring  glass  blue.  The  most  minute  trace  of  this  metaJ 
may  be  thus  recognised  before  the  blowpipe.  It  is,  indeed,  on  this 
character  that  is  founded  the  most  important  uses  of  cobalt  in  the 
arts ;  glass  coloured  deep  blue  by  cobalt,  and  ground  to  an  impal- 
pable powder,  constitutes  the  smalts  used  to  give  to  writing  paper 
and  to  linen  a  delicate  shade  of  blue.  The  blue  colours  upon  por- 
celain and  delft  are  also  produced  by  cobalt  j  when  speaking  of 
magnesia  (p.  349)  ai^  alumina  (p.  351),  I  have  noticed  the  assistance 
given  by  cobalt  in  the  detection  of  these  earths  before  the  blowpipe  ; 
alumina,  coloured  strongly  blue  by  cobalt,  is  used  in  commerce  as 
a  pigment,  cobalt  blue,  in  place  of  ultramarine. 

The  blue  colours  of  cobalt  are  spoiled  if  brought  into  contact  with  chlorine  or  ox- 
ygen, the  black  sesquioxide  of  cobalt  being  formed.  If  paper  be  blued  by  smalts 
without  the  bleaching  liquor  having  been  well  washed  out  of  the  pulp,  it  is  injured 
by  acquirmg  a  brown  tinge  ;  and  by  melting  together  cobalt-glass  and  hlack  oxide 
of  manganese,  a  deep  black  glass  is  formed,  2(Co.O.)  and  Mn.02  giving  C02O3  and 
Mn.O. 

The  sulphuret  and  seleniuret  of  cobalt  consist  of  an  equivalent  of  each  element^ 
bat  do  not  require  notice. 

Of  Zinc. 

This  metal  is  found  in  nature  in  considerable  quantity,  combined 
with  sulphur,  forming  sulphuret  of  zinc,  zinc  blende;  also  as  oxide 
of  zinc,  which,  united  with- carbonic  acid  or  with  silicic  acid,  forms 
the  two  varieties  of  calamine.  The  reduction  of  the  metal  is  effected 
from  these  ores  respectively  on  the  principles  already  described  in 
Chapter  XII.,  but,  from  the  volatility  of  the  metallic  zinc,  the  process 
is  carried  on  in  crucibles  or  large  earthen  retorts  in  place  of  the 
open  reverberatory  furnace.  In  England  the  crucibles  are  closed 
above,  but  perforated  at  the  bottom,  so  as  to  admit  an  iron  tube  to 
be  fitted  in,  the  top  of  which  rises  a  little  above  the  surface  of  the 
materials,  and  the  bottom  of  which,  passing  through  the  floor  of  the 
furnace,  opens  just  over  the  surface  of  a  reservoir  of  water.  The 
zinc,  when  reduced,  is  converted  into  vapour,  which  escapes  through 
the  tube,  condensing  when  it  gets  below  the  fire  into  a  liquid  metal, 
which,  dropping  into  the  water,  solidifies.  In  Silesia  very  large 
earthen  retorts  are  employed,  not  unlike  those  figured  in  page  289 
for  the  preparation  of  German  oil  of  vitriol. 

The  zinc  of  commei^ce,  as  thus  obtained,  is  impure ;  it  contains 
traces  of  carbon,  iron,  cadmium,  and  often  arsenic.  It  may  be  freed 
from  the  fixed  impurities  by  redistillation  in  an  iron  retort ;  and  by 


368  OXIDE     OF     ZINC. 

rejecting  the  portions  which  distil  over  first,  and  which  contain  the 
cadmium  and  arsenic,  it  may  be  obtained  quite  pure.  It  is  owing 
to  the  presence  of  these  foreign  bodies  that  ordinary  zinc  dissolves 
so  rapidly  in  dilute  sulphuric  acid,  as  explained  in  page  135.  It  is 
a  brilliant  bluish-white  metal,  of  a  very  crystalline  texture ;  its  sin- 
gular variations  of  tenacity  are  described  in  page  328.  At  773^  it 
melts,  and  at  a  full  red  heat  is  volatilized,  its  vapour  burning  in  air 
with  a  splendid  white  flame,  and  forming  clouds  of  oxide  of  zinc,  so 
light  as  to  have  been  called  by  the  older  chemists  lana  philosophica 
and  nihil  album.  When  exposed  to  the  air,  even  in  presence  of  wa- 
ter, zinc  is  not  continuously  oxidized.  It  becomes  covered  with  a 
varnish  of  a  gray  substance,  probably  a  definite  suboxide,  which  is 
not  farther  altered  by  exposure,  and  hence  this  metal  is  admirably 
fitted  for  the  various  purposes  of  domestic  and  technical  use  to 
which  it  has  recently  been  applied.  In  a  galvanic  circuit  of  two 
metals,  zinc  is  almost  always  positive,  and  hence  it  preserves  the 
other  metal,  even  if  it  be  iron,  from  oxidation.  The  actual  corro- 
sion is,  however,  in  this  case,  not  diminished,  but  rather  augmented 
in  amount  j  but,  being  concentrated  solely  upon  the  zinc,  it  is  easy 
to  arrange  it  so  as  to  prevent  injury.  If  zinc  be  quite  pure,  it  is 
little  acted  upon  by  acids  ;  all  that  is  known#f  its  relations  in  this 
respect  has  been  already  described  in  pages  198  and  248. 

The  symbol  for  zinc  is  Zn.     Its  equivalent  number  403*2  or  32-3. 

Oxide  of  Zinc.  —  Zn.O.  Equivalent  503-2  or  40*3.  Although 
there  is  some  reason  to  suppose  the  existence  of  other  oxides  of 
zinc,  yet  at  present  w^e  possess  accurate  knowledge  only  of  the 
protoxide.  This  is  formed  when  the  metal  is  burned  in  air  or  oxy- 
gen. It  is  produced,  also,  when  the  zinc  is  oxidized  by  the  decom- 
position of  water,  either  at  a  red  heat  or  assisted  by  an  acid.  To 
form  the  oxide  by  combustion,  it  is  sufficient  to  proj'ect  a  small  frag- 
ment of  zinc  into  a  crucible  heated  to  bright  redness,  and  slightly 
inclined,  so  that  a  current  of  air  may  pass  through  it.  When  the 
metal  takes  fire,  another  crucible  is  to  be  placed  inverted  over  the 
first,  but  still  allowing  a  certain  access  of  air.  The  oxide  of  zinc 
being  not  really  volatile,  but  only  mechanically  carried  up  by  the 
current  of  air,  is  deposited  on  the  inside  of  the  upper  crucible  as 
a  loose  cottony  mass,  which,  while  very  hot,  is  of  a  fine  canary  col- 
our, but  becomes  pure  white  when  completely  cold. 

Such  is  the  tendency  of  oxide  of  zinc  to  enter  into  combination, 
that  the  precipitates  given  by  the  caustic  alkalies  in  a  solution  of 
a  salt  of  zinc  are  basic  salts,  and  not  the  mere  oxide.  To  prepare 
the  oxide,  a  solution  of  sulphate  of  zinc  is  to  be  decomposed  by 
carbonate  of  soda  ;  the  precipitate  is  carbonate  of  zinc  ;  and  by 
heating  this  to  redness  in  a  crucible,  the  carbonic  acid  passes  off, 
and  the  oxide  of  zinc  remains  pure.  This  oxide  is  a  powerful  base  ; 
it  neutralizes  the  strongest  acids,  and  its  salts  are  some  of  the  most 
definite  and  characteristic  that  exist :  they  are  easily  recognised. 
In  their  solutions,  the  caustic  alkalies  all  produce  voluminous  white 
precipitates,  which  are  redissolved  by  an  excess  of  the  alkali.  An 
alkaline  carbonate  gives  a  similar  precipitate,  which,  however,  is 
not  redissolved  by  an  excess,  except  it  be  carbonate  of  ammonia. 
Hydrosulphuret  of  ammonia  produces  a  white  precipitate  of  hydra 


C  A  D  M  I  U  M. T  I  N.  369 

ted  sulphuret  of  zinc,  if  the  solution  be  not  very  acid.  Sulphuret- 
ted hydrogen  does  so  only  if  the  solution  be  completely  neutral 
A  solution  of  zinc  with  much  free  acid  is  not  affected  by  sulphuret- 
ted hydrogen,  either  free  or  combined. 

The  native  Sulphuret  of  Zinc^  Zn.S.,  is  found  in  crystals  of  a  va- 
riety  of  colours ;   it  is  a  protosulphuret,  and   may  be  artificially 
formed  by  melting  zinc  and  sulphur  together.     It  is  decomposed  by 
acids,  sulphuretted  hydrogen  being  given  off,  and  a  salt  of  zinc  pro 
duced. 

Of  Cadmium* 

This  metal  exists  but  in  small  quantities  in  nature  ;  the  only  ore 
of  it  is  its  sulphuret,  a  mineral  but  lately  found,  and  still  very  rare  j 
it  accompanies  almost  universally,  though  in  small  quantities  only, 
the  ores  of  zinc,  and  is  obtained  in  the  working  of  zinc  ores  by  ta 
king  advantage  of  its  greater  volatility.  The  details  of  its  purifi- 
cation need  not  be  inserted.  It  is  white  like  tin  j  it  is  more  fusible 
and  more  volatile  than  zinc  ;  its  specific  gravity  is  869  j  it  dissolves 
very  slowly  in  dilute  sulphuric  acid,  but  rapidly  in  dilute  nitric  acid  j 
it  combines  with  oxygen  only  in  one  proportion.  Its  symbol  is  Cd., 
and  its  equivalent  696'8  or  55'8. 

The  Oxide  of  Cadmium,  Cd.O.,  equivalent  796  8  or  63  8,  is  obtained  by  processes 
exactly  such  as  described  for  oxide  of  zinc.  When  anhydrous,  it  is  an  orange  pow 
der ;  its  salts,  which  are  very  stable,  resemble  closely  those  of  zinc,  from  which 
they  are  distinguished  by  giving  with  sulphuretted  hydrogen  a  fine  yellow  precipi- 
tate, and  with  carbonate  of  ammonia  a  white  precipitate,  insoluble  in  an  excess : 
its  salts,  like  those  of  zinc,  are  all  colourless. 

Sulphuret  of  Cadmium,  Cd.O.,  is  found  native  near  Greenock;  it  is  yellow  like 
orpiment,  but  is  not  volatile  ;  it  does  not  dissolve  in  water  of  ammonia  nor  of  pot- 
ash. 

Of  Tin. 

This  metal,  from  the  ease  with  which  it  is  extracted  from  its  ores, 
has  been  known  from  the  earliest  ages,  and  in  all  countries,  both  of 
the  East  and  West.  Before  the  working  of  iron  was  discovered, 
cutting  instruments  of  all  kinds  were  made  of  an  alloy  of  tin  and 
copper  (bronze),  which  in  hardness  was  little  inferior  to  steel ;  but, 
from  its  incapability  of  being  tempered  with  the  same  exactness, 
was  only  an  imperfect  substitute  for  it.  It  was  from  the  tin  mines 
of  Cornwall  that  England  first  became  known  to  the  then  more  civ- 
ilized nation  of  Phoenicia.  A  great  quantity  of  the  tin  of  commerce 
is  still  obtained  from  that  county  j  but,  in  addition,  it  is  imported 
from  Mexico  and  the  East  Indies.  The  tin  ore  has  been  found  in 
Ireland  (county  Wicklow),  but  not  as  yet  sought  for  with  a  view 
of  extracting  the  metal  from  it. 

The  usual  ore  of  tin  is  the  native  peroxide,  which  is  found  in 
veins,  and  also  in  fragments  in  the  soil  formed  by  the  disintegration 
of  the  rocks.  The  process  of  reduction  is  the  simplest  possible, 
the  ore  being  smelted  with  the  fuel,  as  described  p.  332.  The  met- 
al thus  obtained  is  still  farther  purified  from  any  admixture  of  for- 
eign metals  by  the  process  of  liquation^  which  is  founded  on  the 
easy  fusibility  of  pure  tin.  The  ingots,  or  pigs  of  tin,  are  gently 
heated  until  they  begin  to  melt,  and  then  the  heat  being  prevented 

A  A  A 


370  OXIDES     OF     TIN. 

from  rising  higher,  the  pure  metal  melts  completely  out,  leaving 
behind  the  impurities  combined  with  a  proportion  of  tin,  forming  a 
mass  of  less  commercial  value.  The  tin  thus  purified  is  termed 
grain  tin  ;  the  residual  mass  is  called  block  tin.  The  former  is 
known  by  presenting  the  appearance  of  a  mass  of  irregular  col- 
umns, like  those  formed  by  starch,  or  by  basalt,  as  in  the  Giant's 
Causeway,  and  emitting,  when  bent,  a  peculiar  creaking  sound. 
The  block  tin  possesses  these  characters  in  a  very  small  degree,  or 
not  at  all. 

Tin,  when  pure,  is  white  like  silver,  brilliant,  and  after  gold,  sil- 
ver, and  copper,  the  most  malleable  of  the  metals.  It  is  very  soft, 
may  be  bent  easily,  and  has  but  little  tenacity.  Its  specific  gravity 
is  7*3.  It  is  one  of  the  most  fusible  of  the  metals,  melting  at  442" 
Fah.  Tin  oxidizes  but  very  slowly  in  contact  with  air  and  water, 
and  is  hence  used  to  protect  the  surface  of  the  more  easily  oxida- 
ble  metals,  particularly  copper,  in  household  use.  It  dissolves  but 
slowly  in  dilute  muriatic  acid,  but  rapidly  if  the  acid  be  strong  and 
boiling.  Nitric  acid  acts  with  great  energy  on  it  when  concentra- 
ted, forming  the  peroxide. 

The  symbol  of  tin  is  Sn.,  derived  from  its  Latin  name  siannum. 
Its  equivalent  numbers  are  735-3  or  58-9. 

There  are  three  oxides  of  tin,  of  which  the  first  acts  as  a  base, 
the  second  appears  indifferent,  and  the  third  possesses  acid  proper- 
ties. 

Protoxide  of  Tin. — Sn.O.  Equivalent  835-3  or  66-9.  On  adding 
water  of  ammonia  to  a  solution  of  protochloride  of  tin,  a  copious 
vi^hite  precipitate  is  obtained,  which  does  not  contain  ammonia,  but 
is  the  hydrated  oxide,  Sn.O.  .  H.O.  The  same  precipitate  is  pro- 
duced by  an  alkaline  carbonate,  the  carbonic  acid  becoming  free. 
When  this  white  hydrate  is  heated  in  a  retort  filled  with  carbonic 
acid  gas,  it  gives  off  its  water,  and  the  true  protoxide  of  tin  re- 
mains as  a  dense  black  powder. 

If  the  hydrate  be  heated  in  the  open  air,  it  absorbs  oxygen,  and  becomes  perox- 
ide ;  and  if  the  black  protoxide  be  touched  when  cold  with  a  red-hot  coal  or  wire, 
it  inflames  and  burns  like  tinder,  forming  peroxide.  The  salts  of  tin  may  be  formed 
by  digesting  the  hydrated  oxide  in  acids.  It  also  dissolves  in  solutions  of  the  caus- 
tic fixed  alkalies,  but  after  some  time  metallic  tin  is  deposited,  and  a  compound  of 
the  alkali  with  peroxide  of  tin  remains  dissolved,  2Sn.O.  producing  Sn.  and  Sn.Oz. 
This  protoxide  of  tin  is  remarkable  for  its  tendency  to  unite  with  more  oxygen. 
Hence,  by  a  solution  of  a  protosalt  of  tin,  the  less  oxidable  metals  are  reduced  from 
their  solutions.  In  this  way  mercury,  silver,  gold,  platina,  may  be  thrown  down  in 
the  metallic  state,  and  iron  and  copper  reduced  from  the  higher  to  the  lower  degrees 
of  oxidation. 

The  Sesquioxide  of  Tin,  Sn^Og,  is  prepared  by  boiling  peroxide  of 
iron  in  a  neutral  solution  of  protochloride  of  tin.  The  sesquioxide 
of  tin  precipitates,  and  protochloride  of  iron  dissolves,  2Sn  CI.  and 
FcjOa  producing  SuiOg  and  2Fe.Cl.  It  is  a  gray  powder  ;  it  absorbs 
oxygen  readily,  and  appears  to  form  salts,  which  have  been,  as  yet, 
little  examined. 

Peroxide  of  Tin.  Stannic  jlcid.—Sn.O^.  Equivalent  935-3  or  74-9. 
This  substance  is  produced  in  all  cases  w^here  tin  is  allowed  to 
combine  with  oxygen  freely.  It  exists  in  nature,  constituting  the 
common  ore  of  tin  (tin  stone).  It  is  most  readily  prepared  artificial- 
ly by  pouring  the  liquid  nitric  acid,  sp.  gr.  1-42,  on  metallic  tin>  in 


SULPflURETS     0  1=^     TIN. CHROME.  371 

foil  or  powder  j  the  action  is  very  violent,  and  the  metal  is  totally- 
converted  into  a  white  powder,  which  is  the  hydrated  peroxide. 
By  ignition  the  water  is  given  off,  and  the  anhydrous  oxide  remains 
of  a  pale  yellow  colour. 

If  the  perchloride  of  tin  be  decomposed  by  an  alkali,  a  white  precipitate  of  hy- 
drated oxide  is  obtained,  in  appearance  identical  with  that  prepared  by  nitric  acid, 
but  so  different  in  properties  that  Berzelius,  and  after  him  many  chemists,  look 
npon  them  as  isomeric  bodies.  He  calls  that  by  nitric  acid,  a  peroxide,  and  that 
from  the  perchloride,  j3  peroxide,  and  their  properties  may  be  contrasted  as  follows 

The  a  modification  is  totally  insoluble  in  nitric  acid  and  in  sulphuric  acid,  wheth 
er  strong  or  dilute.  It  is  insoluble  in  muriatic  acid,  but  is  changed  by  it  into  an  in 
soluble  basic  salt. 

The  /3  modification  dissolves  while  yet  moist  in  dilute  nitric  and  sulphuric  acids 
very  copiously,  and  the  solution  is  permanent  if  some  salt  of  ammonia  be  added  to 
it.     In  muriatic  acid  it  dissolves  rapidly  and  copiously. 

The  two  modifications  of  oxide  of  tin  dissolve  in  solution  of  caustic  potash,  and, 
when  again  precipitated  from  it  by  an  acid,  retain  their  original  properties.  These 
modifications  are  also  capable  of  being  transformed  into  each  other;  the  a  into  /? 
by  distillation  with  strong  muriatic  acid,  and  the  /?  into  a  by  boiling  with  nitric  acid. 

The  hydrated  peroxide  of  tin  reddens  litmus,  and  combines  with  alkalies  to  form 
salts,  but  not  with  acids,  except  in  the  /3  form.  It  is  used  in  the  arts  as  a  polishing 
material  under  the  name  of  pulty,  and  in  glass  and  enamelling,  in  order  to  give  the 
milk  whiteness  used  for  dials  of  watches  and  other  purposes. 

There  are  three  sulphurets  of  tin  corresponding  to  the  oxides 

The  Protosulphurct,  Sn.S,  is  precipitated  as  a  brown  powder  from  a  solution  of 
protochloride  of  tin  on  the  addition  of  sulphuret  of  hydrogen.  It  thus  serves  for 
the  detection  of  tin  in  that  condition.  The  Sesquisidphuret,  SngSg,  is  of  no  impor- 
tance. 

The  Bisulphuret  of  Tin,  Sn.S«,  equivalent  1137-6  or  91-1,  may  be  prepared  by 
decomposing  a  solution  of  perchloride  of  tin  by  sulphuretted  hydrogen,  which  it 
precipitates  of  a  golden  yellow  colour.  This  is  a  strong  sulphur  acid.  It  dissolves 
readily  in  solutions  of  the  sulphurets  of  the  alkaline  metals,  forming  sulphur  salts. 
If  it  be'strongly  heated,  it  abandons  an  atom  of  sulphur,  and  is  converted  into  the 
protosulphurct.  It  may  be  also  prepared  in  the  dry  way,  and  then  possesses  con- 
siderable interest  as  being  one  of  those  substances  which,  being  obtained  from  the 
common  metals,  and  simulating  the  appearance  and  some  of  the  properties  of  gold, 
led  the  ancient  alchemists  to  the  belief  of  probable  success  in  their  attempts  at 
transmutation.  The  bisulphuret  of  tin  may  be  prepared  in  the  dry  way  according 
to  several  processes,  but  to  give  it  the  peculiar  lustre  which  obtained  for  it  its  name 
of  mosaic  gold,  the  following  is  the  best  though  not  the  most  simple  :  twelve  parts 
of  pure  tin  are  to  be  melted  with  six  parts  of  mercury,  and  rubbed  up  in  a  glass 
mortar  with  seven  of  flowers  of  sulphur  and  six  of  sal  ammoniac.  This  mixture  is 
to  be  placed  in  a  glass  flask,  and  heated  in  a  sand-bath  until  no  more  fetid  white 
vapours  are  given  off.  The  heat  is  to  be  then  raised  to  dull  redness,  sulphuret  of 
mercury  and  chloride  of  tin  sublime,  and  the  mosaic  gold  remains  in  the  bottom  of 
the  vessel  in  metallic-looking  scales  of  a  brilliant  gold  colour.  The  use  of  the  mer- 
cury in  this  process  is  to  facilitate  the  combination  of  the  tin  and  sulphur,  and  the 
sal  ammoniac  seems  by  its  evaporation  to  prevent  the  temperature  becoming  so 
high  as  to  decompose  the  bisulphuret. 

The  seleniurets  and  phosphurets  of  tin  are  not  known. 

Tin  is  easily  recognised  in  solution  by  the  action  of  hydrosulphu- 
ret  of  ammonia,  which  produces  with  solutions  of  the  peroxide  a 
golden  yellow,  and  in  solutions  of  the  protoxide  a  brown  precipitate. 
These  both  dissolve  in  an  excess  of  the  precipitant.  The  protoxide 
of  tin  is  also  known  by  its  power  of  reducing  the  salts  of  gold,  silver, 
and  mercury  to  the  metallic  state. 

*  Of  Chromium,  or  Chrome. 

This  metal  derives  its  name  from  the  variety  and  brilliancy  of  the 
colours  of  its  compounds  (Xpw/ioc).  It  exists  as  chromic  acid  com- 
bined with  lead  or  with  copper  in  some  rare  minerals,  but  abundant- 


372  OXIDE     AND     ACID     OF      CHROME. 

ly  as  chromic  oxide  in  the  chrome-iron  ore  (Fe-O.+CraOg).  It 
is  from  this  source  that  all  the  preparations  of  chrome  are  obtained 
indirectly,  but  that  ore  being  treated  upon  the  large  scale  for  the 
manufacture  of  chromate  of  potash,  it  is  this  salt,  as  found  in  com- 
merce, that  may  be  looked  upon  as  the  source  of  chrome  for  all 
other  purposes.  The  metal  is  obtained  by  mixing  the  oxide  with 
lampblack  and  oil,  and  exposing  it  to  an  intense  heat  in  a  crucible 
lined  with  charcoal.  It  is  a  grayish-white  metal,  very  infusible, 
brittle,  not  magnetic,  and  sp.  gr.  5-9  or  6*0.  It  is  not  attacked  by 
dilute  sulphuric  or  muriatic  acids,  but  dissolves  in  hydrofluoric  acid 
with  evolution  of  hydrogen  gas. 

Chrome  combines  with  oxygen  in  two  proportions,  forming  an  ox 
ide  and  an  acid.  Its  symbol  is  Cr.,  and  its  equivalent  numbers  are 
351-8  or  28-19. 

Oxide  of  Chrome,  CraOg,  equivalent  1003-6  or  80-4,  may  be  ob- 
tained by  a  great  variety  of  processes.  Thus,  if  chromate  of  mer- 
cury be  heated  to  redness,  the  oxide  of  mercury  and  half  the  oxy- 
gen of  the  chromic  acid  are  expelled,  and  the  chromic  oxide  remains 
of  a  beautiful  green  colour. 

If  bichromate  of  potash  be  mixed  with  sal  ammoniac  and  heated  to  redness,  chlo- 
ride of  potassium,  water,  nitrogen,  and  oxide  of  chrome  result,  and  the  latter  is 
obtained  pure  by  washing  the  residual  mass  with  boiling  water.  In  this  process, 
SCr.Og+K.O.  and  CI.N.H4  produce  K.Cl.,  N.,  4H.0.,  and  Ct^O^.  The  oxide  so 
obtained  is  pulverulent,  but  it  may  be  obtained  crystallized  as  follows :  the  vapour 
of  a  compound  which  will  be  hereafter  described,  chlovochromic  acid,  is  to  be  pass- 
ed through  a  tube  of  hard  glass,  kept  at  a  full  red  heat,  oxygen  and  chlorine  gases 
are  given  off,  and  oxide  of  chrome  is  deposited  on  the  inside  of  the  tube  in  rhombic 
octohedrons,  isomorphous  with  those  found  native  of  alumina  (corundum)  and  per- 
oxide of  iron  ;  the  chlorochromic  acid,  2(Cr.0£Cl.)  giving  off  2C1.  and  0.,  and 
CraOg  remaining. 

This  oxide  of  chrome  is  the  basis  of  an  extensive  class  of  salts, 
and  it  may  also  be  obtained  by  precipitation  from  any  solution  con- 
taining it.  Its  salts  are  generally  made  from  the  bichromate  of  pot- 
ash of  commerce,  by  the  addition  of  some  deoxidating  agent  and  the 
necessary  acid.  Thus,  to  form  sulphate  of  chrome,  a  solution  of 
bichromate  of  potash  is  warmed,  and  treated  successively  with  sul- 
phuric acid  and  alcohol,  until  its  orange  colour  is  changed  into  deep 
green.  The  liquor  then  contains  the  double  sulphate  of  chrome  and 
potash  (chrome  alum),  and  from  it  the  oxide  may  be  precipitated  on 
the  addition  of  an  alkali,  as  a  pale  green  hydrate.  In  this  condition, 
the  oxide  of  chrome  dissolves  readily  in  acids,  and  also  in  solutions 
of  the  fixed  caustic  alkalies,  but  scarcely  in  ammonia,  resembling 
very  closely,  in  all  these  characters,  alumina.  Its  solutions  are 
either  green  or  purple,  and  it  is  probable  that  this  difference  is  due 
to  more  than  a  mere  difference  in  the  degree  of  concentration. 
When  the  hydrated  oxide  is  heated  nearly  to  redness,  it  suddenly 
begins  to  glow  like  tinder,  giving  off  its  water,  and  losing  its  solu- 
bility in  acids,  except  they  be  hot  and  concentrated.  It  is  remark- 
able that  sulphate  of  chrome,  made  from  the  ignited  oxide,  will  not 
combine  with  sulphate  of  potash  to  form  a  chrome  alum. 

Chromic  Acid.  —  Qr.O^.  Equivalent  651-8  or  52-2.  To  prepare 
'his  acid,  a  solution  of  bichromate  of  potash  is  to  be  treated  by  hy- 
drofluosilicic  acid  gas,  until  the  potash  has  been  precipitated  com- 
pletely.    The  resulting  liquor  is  to  be  cautiously  evaporated  to  dry- 


V  A  N  A  D  I  U  M. T  U  N  G  S  T  E  N.  373 

* 

ness,  and  then  redissolved  in  a  small  quantity  of  water.  The  solu- 
tion is  of  a  dark  brownish-red,  and  when  evaporated  again  gives  the 
dry  chromic  acid.  It  may  be  obtained  in  a  beautiful  form,  though 
not  in  quantity,  by  decomposing  the  vapour  of  the  perfluoride  of 
chrome  by  a  moistened  slip  of  paper.  Cr.Fg  and  3H.0.  produce  3 
H.F.  and  Cr.Oa,  which  last  is  deposited  on  the  surface  of  the  paper 
in  crimson  scales  and  needles  of  great  brilliancy.  This  acid,  when 
heated  strongly,  gives  up  half  its  oxygen,  being  reduced  to  the  state 
of  oxide.  It  combines  with  bases,  forming  several  important  classes 
of  salts,  in  which  it  is  isomorphous  with  the  sulphuric  and  manganic 
acids.  Its  salts  are  all  coloured,  generally  yellow,  orange,  or  red. 
They  will  be  described  in  another  chapter. 

Chromium  is  characterized  by  the  remarkable  colours  of  its  com 
pounds  when  dissolved,  and  by  giving,  when  in  the  state  of  oxide, 
a  green  precipitate  with  the  alkalies.  In  the  state  of  acid,  it  is  known 
by  producing,  with  the  salts  of  lead,  a  yellow,  and  with  the  salts  of 
the  black  oxide  of  mercury,  an  orange  precipitate.  It  is  at  once 
recognised  by  the  beautiful  green  colour  which  it  communicates  to 
glass.  It  is,  on  this  account,  extensively  used  in  staining  glass  and 
painting  on  porcelain,  and  a  number  of  its  salts  are  employed  as  pig- 
ments and  as  dyes. 

By  the  action  of  deoxidizing  agents,  or  sulphurous  acid  or  sugar,  upon  bichromate 
of  potash,  a  brown  substance  is  generated,  concerning  the  nature  of  which  opinion 
is  very  much  unsettled.  There  is  reason  to  suspect  the  existence  of  a  peroxide 
of  chrome,  Cr.Oa,  which  this  matter  may  possibly  be.  When  it  is  washed  with 
much  water,  or  digested  in  alkaline  liquors,  chromic  acid  is  dissolved  out  and  oxide 
of  chrome  remains,  CraOa-f-Cr.Og^aCr.Oz. 

The  sulphurets,  seleniurets,  and  phosphurets  of  chrome  are  not  important. 

Of  Vanadium, 

This  metal,  of  recent  discovery,  derives  its  name  from  Vanadis,  a  deity  of  Scan- 
dinavian mythology.  It  is  found  native  as  vanadic  acid,  in  a  very  rare  mineral, 
vanadiate  of  lead,  but  is  of  so  little  importance  that  a  slight  notice  of  it  will  suf- 
fice, although  it  forms  a  great  variety  of  combinations,  which  resemble  very  remark- 
ably those  of  manganese  and  chrome.  The  metal  itself  has  been  obtained,  but  of 
its  properties  nothing  positive  is  known.  Its  symbol  is  V. ;  its  equivalent  numbers 
are  856  9  or  68  7. 

The  Protoxide  of  Vanadium,  V.O.,  is  a  black  powder,  formed  by  acting  on  vanadic 
acid  at  a  red  heat  with  hydrogen  gas.  It  combines  with  acids,  forming  salts  which 
resemble  probably  those  of  the  protoxide  of  manganese.  When  heated  in  the  air, 
it  absorbs  oxygen  and  becomes  vanadic  oxide,  V.O2,  which  is  a  base  combining  with 
acids  and  forming  salts  which  are  generally  blue.  It  acts  also  as  an  acid,  forming 
frystallizable  salts  with  the  fixed  alkalies. 

The  Vanadic  Acid,  V.O3,  resembles  very  much  the  chromic  and  manganic  acids. 
It  is  a  red  powder,  which  may  be  melted  at  a  red  heat  without  losing  oxygen.  It 
is  very  slightly  soluble  in  water.  It  forms  various  classes  of  salts,  of  which  some 
are  while,  some  yellow,  and  others  orange  red.  In  these  characters  it  resembles 
the  chromic  acid,  but  it  is  distinguished  from  chrome  by  producing,  when  deoxidized, 
a  blue  solution,  while  that  from  chrome  is  green. 

SECTION  IV. 

METALS    OF    THE    FOURTH    CLASS. 

Tungsten  and  Molybdenum. 
Tungsten. — This  metal  exists,  combined  with  oxygen,  as  tungstic  acid,  in  the 
native  tungstates  of  lime  and  iron  ;  by  boiling  the  tungstate  of  lime  in  strong  mu- 
riatic acid,  the  lime  is  dissolved  out,  and  tungstic  acid  remains  as  a  yellow  powder, 
which  may  be  farther  purified  by  solution  in  water  of  ammonia,  and  igniting  the 


I-J74  T  U  N  G  S  T  E  N. M  OLYBDENU  M. O  S  M  I  U  M. 

tungstate  of  ammonia.  It  is  a  deep  yellow  powder,  which  forms  well-defined  crys- 
taliizable  salts  with  the  alkalies.  The  symbol  of  tungsten  is  W.,  from  its  German 
name  Wolfram,  and  its  equivalents  1183  or  94-8.  The  tungstic  acid  resembles  the 
chromic  acid,  being  W.O3.  When  this  acid  is  exposed  to  a  current  of  hydrogen 
gas  at  a  temperature  about  dull  redness,  it  loses  one  third  of  its  oxygen,  and  forms 
tu/ngstic  oxide,  W.O2,  of  a  copper-red  colour.  This  may  be  also  formed  by  diflusing 
tungstic  acid  through  dilute  muriatic  acid  in  which  a  slip  of  zinc  is  immersed ;  the 
nascent  hydrogen  then  effects  the  deoxidation.  At  a  full  red  heat,  hydrogen  reduces 
tungsten  to  the  metallic  state,  removing  all  the  oxygen.  The  metal  is  like  iron  in 
appearance,  and  very  heavy,  its  sp.  gr.  being  about  175. 

The  most  curious  fact  in  the  history  of  tungsten  is  its  producing  a  substance  hav- 
ing an  extraordinary  similarity  to  gold.  It  is  prepared  by  adding  to  fused  tungstate 
of  soda  as  much  tungstic  iacid  as  it  will  dissolve,  and  exposing  the  product  at  a  full 
red  heat  to  a  current  of  hydrogen  gas ;  the  residual  tungstate  of  soda  is  then  to  be 
dissolved  out.  The  new  compound,  which  consists  of  tungstic  oxide  united  to  soda, 
Na.O.-|-2W.02,  remains  in  scales  and  cubes  of  a  splendid  gold  colour.  It  resists  the 
action  of  acids  and  alkalies,  even  of  aqua  regia,  in  which  gold  dissolves,  and  only 
yields  to  strong  hydrofluoric  acid.  Had  it  been  discovered  at  an  earlier  period  in 
science,  it  might  have  lent  exceedingly  plausible  support  to  the  belief  in  transmuta- 
tion. It  is  the  more  curious,  as  it  cannot  be  formed  by  directly  combining  soda  with 
tungstic  oxide,  which,  indeed,  appears  unable  to  unite  either  with  alkalies  or  acids. 

There  exist  two  sulphurets  of  tungsten,  W.S2  and  W.Sa,  of  which  the  latter  is  the 
most  interesting.  It  is  formed  by  dissolving  tungstic  acid  in  hydrosulphuret  of  am- 
monia, and  precipitating  by  an  acid.  It  is  a  blackish-brown  powder,  and  one  of  the 
strongest  sulphur  acids.  Many  of  its  compounds  with  the  sulphurets  of  the  alka- 
line metals  may  be  crystallized. 

Molybdenum. — This  metal  exists  combined  with  sulphur,  and  also  with  oxygen,  as 
molybdic  acid,  in  some  minerals.  It  is  not  of  any  considerable  interest.  When  ob- 
tained in  the  metallic  state  it  is  white,  sp.  gr.  8-6,  acted  on  only  by  concentrated  ni- 
tric and  sulphuric  acids,  and  by  aqua  regia.  Its  symbol  is  Mo.  Its  equivalent 
598-5  or  47-9.     It  combines  with  oxygen  in  three  proportions. 

Molybdic  Acid,  M0.O3,  is  easily  prepared  by  roasting  the  native  sulphuret  of 
molybdenum ;  the  sulphur  burns  out  as  sulphurous  acid  gas,  and  the  molybdenum, 
absorbing  oxygen,  remains  as  molybdic  acid.  This  may  be  purified  as  described  for 
tungstic  acid.  Molybdic  acid  prepared  at  a  low  temperature  is  white,  but  becomes 
yellow  when  fused  at  a  red  heat.  It  is  sparingly  soluble  in  water.  It  dissolves  in 
alkaline  liquors,  forming  salts  which  are  neutral  and  crystallizable. 

Molybdic  Oxide,  M0.O2,  is  best  prepared  by  mixing  together  molybdate  of  soda 
and  sal  ammoniac  in  a  crucible,  and  igniting  the  mass  rapidly.  When  the  product 
is  washed  with  water,  a  dark  brown  powder  is  obtained,  which  is  molybdic  oxide. 
This  oxide  appears  to  form  salts  with  both  acids  or  alkalies,  of  which  some  may  be 
crystallized.  A  molybdate  of  molybdenum,  or,  rather,  a  complex  oxide,  also  exists, 
Mo.O2-i-2Mo.O3— -M03O8.    It  is  a  blue  powder. 

When  a  solution  of  molybdate  is  decomposed  by  as  much  muriatic  acid  as  redis- 
solves  the  molybdic  acid,  which  is  at  first  thrown  down,  and  a  slip  of  zinc  is  immer 
sed  in  the  liquor,  the  hydrogen  evolved  deoxidizes  the  molybdic  acid,  and  a  precipi 
tate  is  formed  upon  the  zinc,  at  first  blue,  then  brown,  and  finally  black ;  thus  passing 
through  all  the  intermediate  degrees  to  the  last,  the  Molybdoiis  Oxide,  Mo.O.  This 
is  a  very  feeble  base,  forming  with  acids  salts  which  do  not  crystallize. 

Sulphur  combines  with  molybdenum  in  three  proportions,  forming  M0.S2,  M0.S3, 
and  M0.S4.  Of  these  the  bisulphuret,  M0.S2,  is  important,  as  being  the  native  ore 
from  which  the  metal  and  its  compounds  are  generally  prepared.  It  is  a  soft  gray 
substance,  so  like  black  lead  as  to  have  been  mistaken  for  it  until  its  nature  was 
pointed  out  by  Scheele.    All  these  sulphurets  are  sulphur  acids,  and  form  salts. 

Of  Osmium. 

This  metal  exists  in  nature  alloyed  with  iridium,  and  accompanies  the  ores  of 
platinum.  The  methods  of  its  extraction  from  these  ores  are  so  complex  and  circui- 
tous that  I  shall  not  introduce  them  here.  In  the  systematic  works,  a  complete  ac- 
count of  the  processes  pursued  will  be  found. 

The  most  interesting  property  of  osmium  is  its  forming  a  highly  x^olatile  oxide  of 
an  exceedingly  penetrating  odour,  whence  the  name  {oaix-n).  When  this  is  dissolved 
in  muriatic  acid,  and  placed  in  contact  with  mercury,  the  osmium  is  reduced,  and  by 
distilling  off  the  mercury  it  is  obtained  as  a  black  powder;  but  by  heat  and  compres- 
sion it  may  be  rendered  coherent,  and  of  a  brilliant  white  colour.  In  the  state  of 
powder,  osmium  bums  when  heated  to  redness  in  the  air,  and  is  oxidized  by  nitric 


COLUMBIUM    AND    TITANIUM.  375 

acid,  but  loses  both  these  characters  when  ignited.  The  symbol  of  osmium  is  Os. 
Its  equivralent  is  1244-5  or  99-7.    It  combines  with  oxygen  in  three  proportions. 

The  Osniic  Add,  or  Peroxide  of  Osmium,  OS.O4,  is  always  formed  when  osmi- 
um is  burned  in  air  or  in  oxygen  gas.  It  condenses  in  long  white  needles.  _  Us 
odour  is  remarkably  acid  and  pungent.  It  melts  at  212°,  and  boils  at  a  heat  little 
higher.  It  is  soluble  in  water.  The  solution  has  no  action  on  vegetable  colours, 
but  it  combines  with  the  alkalies,  forming  osvdates. 

The  Osmic  Oxide,  Deutoxide  of  Osmium-,  OS.O2,  is  produced  by  the  decomposi- 
tion of  a  solution  of  osmiate  of  ammonia,  by  a  temperature  of  150° ;  nitrogen  gas  is 
given  off,  and  a  brown  powder  is  deposited. 

The  Protoxide  of  Osmium  is  produced  by  decomposing  a  solution  of  protochloride 
of  osmium  by  potash;  a  deep  green,  almost  black,  powder  is  thrown  down,  in  which 
the  oxide  is  combined  with  water  and  traces  of  the  alkali. 

The  sulphurets  of  osmium  are  not  known. 

Columbium,  or  Tantalum, 

This  metal  was  discovered  first  in  an  American  mineral,  from  whence  its  name, 
it  was  subsequently,  but  independently,  discovered  in  some  very  rare  Swedish  min- 
erals, and  from  the  difficulty  of  its  extraction,  the  name  tantalum  was  given  to  it, 
which  it  still  bears  upon  the  Continent,  and  from  whence  its  symbol  is  Ta.  The 
process  required  to  prepare  it  need  not  be  described,  as  it  is  similar  to  that  for  ob- 
taining silicon. 

Metallic  Columbium,  or  Tantalum,  is  a  black  powder,  which,  when  burnished, 
appears  iron  gray.  No  acid  but  the  hydrofluoric  appears  to  have  any  action  on  it. 
It  takes  fire  when  heated  in  the  air,  and  burns  vividly.  Its  equivalent  nimibers  are 
230-7  or  185.     It  combines  with  oxygen  in  two  proportions. 

Tayitalic,  or  Columbic  Acid,  Ta.Os,  exists  native  in  all  the  minerals  containing 
the  metal.  To  procure  it,  the  mineral  is  fused  with  carbonate  of  potash,  and  the 
tantalate  of  potash,  which  is  soluble,  is  to  be  decomposed  by  muriatic  acid.  The 
tantalic  acid  precipitates  as  a  white  powder,  which  contains  water,  and  reddens  lit- 
mus paper.  When  tantalic  acid  is  heated  strongly  in  a  crucible  with  charcoal,  but 
a  slight  film  of  it  is  reduced  to  the  metallic  state,  the  great  mass  being  brought  only 
to  the  state  of  tantalic  oxide,  Ta.02.  This  substance  is  gray.  It  is  insoluble  in  all 
acids. 

The  similarity  of  tantalum  to  silicon  is  very  great;  it  resembles  it  in  forming,  with 
fluorine  and  potassium,  a  double  fluoride,  from  which  the  metal  is  obtained. 

Titanium. 

This  metal,  although  not  met  with  in  large  quantities,  is  yet  found  in  a  great  va- 
riety of  minerals.  It  is  not  found  native  in  a  metallic  state,  but  combined  with  ox- 
ygen, forming  titantic  acid.  To  obtain  metallic  titanium,  the  volatile  perchloride 
is  employed.  This  body  absorbs  ammonia,  forming  a  white  substance,  Ti.Cl2+2 
N.H3,  which,  when  heated  to  redness,  gives  metallic  titanium,  with  sal  ammoniac 
and  nitrogen,  the  hydrogen  carrying  off  the  chlorine.  It  is  of  a  bright  copper  colour, 
almost  perfectly  infusible.  Titanium  exists  in  most  of  the  clay  iron  stone,  and 
hence,  being  reduced  during  the  smelting  of  the  iron,  is  found  in  the  slags,  crystal- 
lized in  cubes  of  excessive  hardness  and  brilliancy,  sp.  gr.  5-3.  This  metal  is  not 
acted  upon  by  any  acid  except  a  mixture  of  nitric  acid  with  hydrofluoric  acid,  and 
is  oxidized,  but  very  slowly,  by  melted  nitre.  It  is  perfectly  unalterable  by  air  or 
water.  Its  symbol  is  Ti.  Its  equivalent  numbers  are  303*7  or  24-3,  and  it  com- 
bines with  oxygen  in  two  proportions. 

Titanic  Acid,  Ti.02,  exists  native,  constituting  the  mineral  rutile,  isomorphous 
with  tin  stone  (Sn.02),  and  also  in  the  mineral  anatase.  More  abundantly  it  is  found 
in  the  titanic  iron,  ilmenite,  the  formula  of  which  is  Fe.O.  .  Ti.02,  and,  which  is 
very  remarkable,  from  having  the  same  crystalline  form  as  peroxide  of  iron,  Fe203, 
sf:;  that  the  titanium  would  appear  to  replace  the  second  atom  of  iron,  and  the  formu- 
la to  be  Fe.Ti.+Oa.  This  is  merely  speculative,  however,  as  iron  is  never  iso- 
morphous with  tin,  and  in  no  other  case  with  titanium,  and  I  hence  consider  this 
histance  as  one  of  the  coincidences  of  form  described  in  pages  221  and  236. 

Titanic  acid  is  artificially  prepared  from  the  titanate  of  iron  by  igniting  it  with 
sulphur.  The  oxide  of  iron  and  sulphur  form  sulphurous  acid  and  sulphuret  of  iron, 
and  when  this  last  is  dissolved  out  by  muriatic  acid,  the  titanic  acid  remains  be- 
hind. It  requires  other  processes  to  render  it  absolutely  pure, which  need  not  be  de- 
scribed here.  It  is  a  pure  white  powder,  resembling  silica  very  remarkably  in  its 
propel  ties,  and,  like  it,  having  a  soluble  and  an  insoluble  modification.    It  is  remark- 


376  ARSENIC,    ITS     PREPARATION,     ETC. 

aJt)ly  characterized  by  its  solution  in  muriatic  acid,  giving  with  tincture  of  gall^ 
an  orange  precipitate,  and  by  the  immersion  of  a  slip  of  zinc  a  fine  purple  powder, 
which  is  Oxide  of  Titanium,  Ti.O. ;  the  second  atom  of  oxygen  being  removed  from 
the  acid  by  the  nascent  hydrogen.  This  oxide  of  titanium  may  also  be  procured  by 
igniting  titanic  acid  with  charcoal ;  it  is  then  a  black  powdej,  insoluble  in  all  acide. 
The  Bisulphuret  of  Titanium,  Ti.S2,  is  a  strong  sulphur  acid,  but  not  otherwise 
important. 

Of  Arsenic. 

This  metal  exists  in  nature  in  a  great  variety  of  forms,  and  m 
considerable  quantity.  It  is  found  native,  but  more  generally  com- 
bined with  other  metals,  as  nickel,  cobalt,  iron  j  being  considered, 
like  oxygen  and  sulphur,  as  a  mineralizer  of  other  metals.  Combined 
with  sulphur,  it  constitutes  the  native  orpiment  and  realgar  ,•  and 
with  oxygen,  as  arsenic  acid,  it  is  united  with  metallic  oxides  in  the 
native  arseniates  of  lime,  of  iron,  of  lead,  &c.  The  great  proportion 
of  the  arsenic  of  commerce  is  obtained  in  the  roasting  of  the  cobalt 
and  nickel  ores,  as  described  in  p.  334.  The  current  of  hot  air 
which  has  passed  over  the  ignited  ore  carries  with  it,  into  a  series 
of  large  chambers,  the  volatile  arsenious  acid,  which  is  deposited 
under  the  form  of  a  fine  grayish  powder  on  the  walls  and  floor. 
This  is  discoloured  by  some  of  the  oxide  of  the  fixed  metals,  which 
is  carried  over  mechanically  by  the  draught,  and  it  is,  therefore, 
resublimed  in  iron  vessels,  the  covers  of  which  are  allowed  to  be- 
come so  hot  that  the  arsenious  acid,  in  condensing,  shall  aggregate 
itself  into  a  vitreous  mass,  in  which  state  it  is  sent  into  commerce. 

The  metallic  arsenic  may  be  prepared  from  the  arsenious  acid  in 
many  ways,  but  best  by  mixture  with  three  times  its  weight  of  black 
flux  (p.  334)  in  a  crucible  or  earthenware  retort,  which  is  then  to 
be  heated  to  redness.  If  a  crucible  be  used,  another  cold  crucible, 
somewhat  larger,  must  be  inverted  over  it,  on  the  inside  of  which 
the  metal  condenses,  but  with  a  retort  it  is  deposited  in  the  neck  as 
an  irregular  mass  of  rhombohedrons,  variously  modified.  It  is  very 
brittle  j  its  sp.  gr.  5*96.  It  sublimes  at  356"^  F.  without  previously 
melting.  The  sp.  gr.  of  its  vapour  is  10362.  Its  vapour,  if  in  con- 
tact with  the  air,  has  a  very  characteristic  garlic  odour  j  which, 
however,  belongs  not  to  the  pure  metal,  but  to  an  oxide  produced 
by  a  low  degree  of  combustion  which  occurs.  In  the  air  it  gradu- 
ally absorbs  oxygen,  and  falls  into  gray  powder  {suboxide^  fly  powder). 
By  nitric  acid  it  is  rapidly  oxidized,  and  deflagrates  violently  in 
melted  nitre.  In  fine  powder  it  burns  spontaneously  in  chlorine 
gas,  with  a  brilliant  -^vhite  flame,  and  burns  similarly  when  heated 
in  oxygen  gas.  The  symbol  of  arsenic  is  As.,  and  its  equivalent 
numbers  are  940*1  or  75-34. 

Arsenic  combines  with  oxygen  in  three  proportions,  forming  a 
suboxide^  of  which  the  composition  is  not  known.  Many  chemists 
look  upon  it  as  a  mere  mixture  of  metal  and  arsenious  acid,  for 
when  it  is  heated  it  separates  into  these  bodies.  The  other  degrees 
of  oxidation,  the  arsenious  acid  and  arsenic  acid,  are  of  great  im- 
portance. 

Arsenious  Acid.  White  Arsenic.  Oxide  of  Arsenic — As.Og,  equiv- 
alent 1240"  1  or  99*34 — is  found  in  commerce  in  masses,  which,  if 
recently  sublimed,  are  perfectly  colourless  and  transparent,  but 


r 


A  R  S  E  N  I  O  UVS     A  OI  D. A  RSENIC      ACID.  377 

gradually  become  milk-white  and  opaque.  In  general,  the  outer 
portions  of  the  commercial  masses  have  thus  changed,  while  the  in- 
terior retains  its  original  transparency.  This  alteration  is  probably 
connected  with  the  dimorphism  of  arsenious  acid  (p.  228),  for  the 
acid  in  these  conditions  differs  in  density  and  in  solubility.  The 
transparent  is  sp.  gr.  3-74i,  and  100  parts  of  boiling  water  dissolve. 
9-68  parts  of  it ;  but  the  opaque  acid  is  of  sp.  gr.  3-69,  and  11-47  of 
it  are  soluble  in  100  parts  of  boiling  water.  A  solution  of  the  vit- 
reous acid  reddens  litmus  paper,  but  that  of  the  opaque  acid  restores, 
though  feebly,  the  blue  colour  of  litmus  paper  already  reddened  by 
an  acid.  The  taste  of  arsenious  acid  is  not  marked,  but  rather 
slightly  sweet :  it  leaves  upon  the  palate,  however,  an  acrid  sensa 
tion. 

The  arsenious  acid  sublimes  at  380^  F.  without  previously  melt- 
ing.    Its  vapour  is  of  sp.  gr.  13670,  being  produced  by 

One  volume  of  vapour  of  arsenic    =10362-0 

Three  volumes  of  oxygen      .    .    =  3307  8 

the  four  volumes  forming  one     .     .    =13669-8 

If  it  be  very  slowly  sublimed,  it  condenses  in  regular  octohedrons 
of  exceeding  brilliancy.  It  is,  however,  sometimes  found,  in  the 
roasting  of  its  ores,  in  crystals  belonging  to  a  different  system  (the 
rhombohedral).  Arsenious  acid  is  dissolved  by  liquid  muriatic  acid 
in  large  quantity,  but  crystallizes  from  that  solution  in  octohedrons. 
If  the  opaque  acid  had  been  employed,  the  crystallization  is  not  pe- 
culiar ;  but  if  it  had  been  the  transparent  variety,  the  deposition  of 
every  crystal  is  accompanied  by  a  sudden  flash  of  light,  very  brill- 
iant in  the  dark.  The  crystals  so  produced  belong  to  the  opaque 
kind,  so  that  it  would  appear  as  if,  at  the  moment  of  deposition,  the 
particles  changed  their  mode  of  arrangement,  so  as  to  pass  from 
the  transparent  to  the  opaque  dimorphous  form,  and  that  the  alter- 
ation in  molecular  constitution  occasioned  the  evolution  of  light, 
and  probably  of  heat  and  electricity. 

The  arsenious  acid  combines  with  bases  to  form  salts,  which  are, 
however,  of  such  unstable  constitution  that  they  are  but  little 
known.  It  is  particularly  of  importance  from  its  highly  poisonous 
properties,  and  from  its  being,  more  frequently  than  any  other  sub- 
stance, administered  to  produce  death.  Its  recognition  is,  there- 
fore, to  the  medical  chemist,  one  of  the  most  important  problems 
in  analysis,  and  will  be  fully  discussed  when  the  other  combinations 
of  arsenic  have  been  described. 

Jlrsenic  Acid. — As.O^.  Equivalent  1440*1  or  115*34.  To  obtain 
this  acid,  eight  parts  of  arsenious  acid  are  to  be  placed  in  a  retort 
with  two  parts  of  strong  muriatic  acid,  and  boiled,  while  twenty- 
four  parts  of  dilute  nitric  acid,  of  sp.  gr.  1*25,  are  to  be  added  in 
small  quantities  at  a  time.  The  mixture  is  to  be  distilled  in  a  re- 
tort to  the  consistence  of  a  sirup,  and  then  transferred  to  a  platina 
dish,  in  which  it  is  to  be  evaporated  to  perfect  dryness,  and  heated 
until  all  traces  of  nitric  acid  are  expelled.  The  residual  mass  is 
milk-white,  but  anhydrous  arsenic  acid.  The  heat  should  not  be 
raised  to  near  redness,  for  then  the  arsenic  acid  is  decomposed  into 
arsenious  acid  and  free  oxygen.     The  mass  thus  obtained  dissolves 

Bbb 


378  ARSENIUREr     OF     HYDROGEN. 

but  slowly  in  water,  but  ultimately  the  solution  is  complete  ;  the 
arsenic  acid  has  even  so  much  affinity  for  water  as  to  deliquesce 
rapidly  in  vessels  which  are  not  kept  carefully  closed. 

The  arsenic  acid  reddens  litmus  paper  strongly,  and  forms  with 
the  alkalies  perfectly  neutral  salts.  At  a  high  temperature  it  is  ca- 
pable of  expelling  all  the  volatile  acids,  even  the  sulphuric  acid, 
from  their  combinations.  In  its  compounds  it  resembles  very  close- 
ly the  phosphoric  acid  j  but  it  appears  capable  of  forming  only  one 
of  the  three  classes  of  salts  which  phosphoric  acid  produces.  The 
arseniates  are  all  tribasic,  but  as  the  quantity  of  fixed  base  varies, 
there  are  some  neutral  and  others  acid  arseniates  j  the  latter  were 
formerly  called  binarseniates.     Thus  there  are, 

3Na.0.-f  As.Oj-f-24  aq.  called  subarseniate  of  soda, 

2Na.O. .  H.O.+As.O^-j-M  aq.     "      neutral  arseniate  of  soda, 

Na.O.  .  2H.O.-I-AS.O5  +  2  aq.       "      binarseniate  of  soda  j 
but  the  quantity  of  base  is  really  constant,  being  in  each  three  atoms, 
made  up  partly  of  water  and  partly  of  soda. 

The  arsenic  acid  is  recognised  by  being  precipitated  golden  yel- 
low by  sulphuretted  hydrogen.  The  precipitate  dissolves  instantly 
in  ammonia,  and  even  in  an  excess  of  sulphuret  of  hydrogen ;  so 
that  it  may  not  be  visibly  produced,  if  the  quantity  of  arsenic  be 
small,  until  the  liquid  shall  have  been  well  boiled.  A  solution  of 
any  arseniate  gives  with  nitrate  of  silver  a  brick-red  powder,  arse- 
niate of  silver,  3Ag.O.+As.05,  the  formation  of  which  is  easily  ex- 
plained. An  insoluble  arseniate  heated  in  a  glass  tube  with  char- 
coal powder  gives  a  sublimate  of  metallic  arsenic. 

Arseniuret  of  Hydrogen. — It  has  been  supposed,  that  when  metal- 
lic arsenic  is  used  as  the  negative  electrode  of  a  voltaic  battery, 
the  hydrogen  evolved  combines  with  it,  ajid  forms  a  brown  powder, 
hydruret  of  arsenic.  The  same  body  was  supposed  to  be  generated 
in  other  ways  j  but  it  is  now  known  that  this  substance  is  only  me- 
tallic arsenic  finely  divided,  and  that  there  is  but  one  compound  of 
arsenic  and  hydrogen,  the  gaseous  arseniuret  of  hydrogen.  As.Hg. 

This  compound  is  easily  obtained  whenever  nascent  hydrogen 
comes  into  contact  with  naetallic  arsenic  :  thus,  when  an  alloy  of 
equal  parts  of  zinc  and  arsenic  is  dissolved  in  dilute  sulphuric  acid, 
the  hydrogen  evolved  combines  with  the  arsenic,  3(S.03-[-H.O.) 
and  ZuaAs.  producing  3(S.03+Zn.O.)  and  H  As.  It  is  still  more 
easily  prepared  by  adding  muriatic  acid  to  a  solution  of  arsenious 
acid  in  water,  and  immersing  therein  a  piece  of  zinc  ;  the  hydrogen 
first  evolved  reduces  the  arsenious  acid,  and  the  metal  is  then  sep- 
arated as  a  fine  brown  powder,  with  which  the  hydrogen  next 
evolved  combines.  This  gas  is  generally  stated  to  have  a  very  dis- 
agreeable odour,  which,  however,  I  have  not  found  it  to  possess. 
It  is  excessively 'poisonous;  it  burns  with  a  brilliant  white  flame, 
water  being  formed,  and  arsenious  acid  or  metallic  arsenic  being 
deposited  according  to  the  supply  of  oxygen  to  the  gas  j  it  is  not 
absorbed  by  water ;  its  specific  gravity  is  2694,  formed  by 

One  volume  of  arsenic  vapour  .  .  =10362  0 
Six  volumes  of  hydrogen  68  8  X  6  .  =  4128 
The  seven  being  condensed  to  four  .  107748 
Of  which  one  weighs 26937 


SUL  PHUKETS  OF  ARSENIC.  379 

Arseniuret  of  hydrogen  decomposes  most  metallic  solutions,  pre- 
cipitating metallic  arseniurets  of  corresponding  constitution  (RoAs.). 
If  a  current  of  it  be  passed  over  chloride  of  copper,  heated  to  about 
400-,  it  is  decomposed,  HgAs.  and  3Cu.Cl.  giving  CugAs.  and  3H.C1. 
This  gas  is  absorbed  by  dry  sulphate  of  copper,  which  it  decompo- 
ses, water  being  evolved,  and  a  blackish  compound  of  sulphuric 
acid  and  arseniuret  of  copper  being  produced.  This  property  is 
made  available  in  the  medico-legal  examination  of  substances  con- 
taining arsenic.  If  a  fragment  of  chloride  of  mercury  be  heated 
in  this  gas,  it  is  rapidly  decomposed,  muriatic  acid  gas  and  arse- 
niuret of  mercury  being  formed.  At  a  full  red  heat  the  gas  is  de- 
composed completely  by  itself,  so  that  if  a  single  point  of  a  tube, 
through  which  it  streams,  be  ignited,  all  the  arsenic  is  deposited  a 
little  beyond  that  point,  in  the  metallic  state,  and  only  pure  hydro- 
gen passes  on. 

Sulphur  and  arsenic  combine  in  several  proportions :  the  Bisulphu- 
ret  of  Arsenic^  AS.S2,  exists  native,  forming  the  mineral  rea/g-ar.  It  is 
prepared  by  fusing  the  following  sulphuret  with  metallic  arsenic, 
and  subliming  the  product.  It  is  a  ruby-red  crystalline  mass  ;  when 
it  is  digested  in  solution  of  caustic  potash,  a  blackish  powder  re- 
mains, which  may  be  looked  upon  as  a  subsulphuret ;  its  definite 
nature  is  problematical.  The  Tersulphuret  of  Arsenic^  As. S3,  yellow 
arsenic,  orpiment,  is  found  native,  and  may  be  easily  prepared  by  de- 
composing a  solution  of  arsenious  acid  with  sulphuret  of  hydrogen, 
AS.O3  and  3H.S.  giving  As. S3  and  3H.0.  It  is  a  rich  yellow  powder  j 
when  heated,  it  melts ;  and  in  close  vessels  sublimes  unaltered,  but 
otherwise  it  burns,  partly  forming  arsenious  and  sulphurous  acids ; 
it  is  not  quite  insoluble  in  water.  It  is  insoluble  in  acids,  and  best 
precipitated  from  an  acid  liquor.  It  is  a  strong  sulphur  acid,  com- 
bining with  the  sulphur  bases  to  form  salts,  sulpho-arsenites.  It 
hence  dissolves  readily  in  hydrosulphuret  of  ammonia,  and  also  in 
the.  caustic  alkalies.  In  the  last  case  there  exists  in  solution  an 
ordinary  arsenite  besides  the  sulphur  salt ;  for,  using  potash,  2As. 
S3  and  6K.0.  produce  (AS.S3+3K.S.)  and  (AS.O3  +  3K.O.).  When 
sulphuret  of  arsenic  is  ignited  with  black  flux,  metallic  arsenic  sub- 
limes ;  and  the  separation  of  the  metal  is  still  more  elegantly  efl^ect- 
ed  by  heating  the  sulphuret,  mixed  with  carbonate  of  potash,  in  a 
current  of  dry  hydrogen  gas. 

The  Persulphuret  of  Arsenic,  As.Sj,  corresponds  to  the  arsenic  acid, 
and  is  prepared  by  decomposing  a  solution  of  it,  or  of  any  of  its  salts, 
by  sulphuretted  hydrogen.  It  is  yellow,  paler  than  orpiment  5  sub- 
limes without  alteration  in  close  vessels  j  is  a  strong  sulphuric  acid, 
and  hence  dissolves  in  solutions  of  the  alkaline  hydrosulphurets, 
forming  sulpho-arseniates  ;  the  metal  may  be  eliminated  from  it  by 
the  same  means  as  those  described  for  orpiment. 

A  substance  sold  in  this  country  for  killing  flies,  under  the  name 
of  king^s  yellow,  is,  or  ought  to  be,  orpiment.  The  best  sort  is  made 
by  boiling  together  lime,  sulphur,  and  white  arsenic  j  but  much  of 
it  consists  merely  of  white  arsenic  coloured  by  some  sulphur  mixed 
with  it.  From  the  facility  with  which  it  may  be  obtained,  and  the 
manner  in  which  it  is  left  exposed,  it  is  very  frequently  the  source 
of  fatal  accidents. 


380  DETECTION     OF     ARSENIC. 

Notwithstanding  the  scientific  importance  which  arsenic  possesses 
from  the  number  and  variety  of  its  compounds,  it  is  of  much  higher 
interest  in  consequence  of  the  frequent  necessity  for  the  detection 
of  excessively  minute  traces  of  it  in  cases  of  suspected  poisoning, 
where  a  responsibility,  involving  the  life  of  a  fellow-creature,  rests 
on  the  skill  and  accuracy  of  the  medical  chemist.  The  detection 
of  arsenic  under  all  possible  circumstances  is  an  object,  therefore, 
to  which  all  the  powers  of  analysis  should  be  brought  to  bear,  and 
the  methods  at  our  disposal  appear,  if  properly  applied,  to  be  satis- 
factory and  complete.  In  a  question  so  grave  as  this,  no  colours 
of  precipitates,  however  so  marked — no  arrangement  of  mere  results 
by  test,  no  matter  how  corroborative,  should  be  considered  as  by 
themselves  decisive  ;  the  object  of  the  chemist  should  be,  the  iso- 
lation and  production  of  the  metallic  arsenic  ;  and  where  this  has  not 
been  done,  it  is  certain  that  either  there  is  no  arsenic  present,  or 
that  the  skill  of  the  operator  cannot  be  absolutely  relied  on. 

In  poisoning  by  arsenic,  the  substance  used  is  almost  universally 
arsenious  acid.  To  this,  therefore,  I  shall  confine  my  remarks  at 
present  j  I  shall  afterward  notice  the  peculiarities  of  its  other  prep- 
arations. 

The  arsenious  acid  being  a  very  heavy  powder,  and  but  sparingly 
soluble,  it  is  very  rapidly  deposited  from  any  liquid  through  which 
it  might  have  been  diffused,  and  hence  the  vessels  in  which  food 
had  been  contained  should  be  carefully  examined  for  any  traces  of 
it  which  might  remain.  This  should  not  be  omitted,  even  though 
they  might  appear  to  have  been  subsequently  rinsed.  Any  substan- 
ces vomited  by  the  person  suspected  to  be  poisoned  should  be  care- 
fully examined  for  the  same  object  j  and  in  case  of  death,  the  mate- 
rials in  the  stomach  and  its  mucous  surface  must  be  similarly  search- 
ed. The  little  grains  of  arsenious  acid  adherent  to  the  surface  of 
the  stomach  are  frequently  tinged  yellow  at  the  surface  by  sulphu- 
retted hydrogen,  if  the  examination  be  deferred  until  some  time  af- 
ter death. 

In  case  of  such  traces  of  white  powder  being  found,  the  examina 
tion  is  very  simple.     Their  porperties  are : 

1st.  Heated  alone  in  a  glass  tube,  the  powder  sublimes  and  con- 
denses in  minute  brilliant  octohedrons. 

2d.  Mixed,  in  a  tube  closed  at  one  end,  with  a  little  black  flux, 
and  ignited,  metallic  arsenic  sublimes,  forming  a  steel-gray  crust, 
brilliant  on  the  side  next  the  tube,  but  dull  and  crystalline  on  the 
inside.  On  applying  the  nose  to  the  open  end  of  the  tube  and  in- 
spiring, a  garlic  odour  is  perceived. 

3d.  On  cutting  off  the  sealed  end  of  the  tube,  and  then  heating 
the  part  containing  the  metallic  crust,  the  tube  being  slightly  incli- 
ned, the  metal  disappears,  and  a  crust  of  white  arsenic  condenses  a 
little  higher  up.  A  current  of  air  passes  through  the  tube,  with  the 
oxygen  of  which  the  metal  combines.  In  this  process  the  garlic 
smell  becomes  more  marked  than  in  No.  2. 

4th.  The  white  powder  dissolves  in  water.  It  yields  precipitates 
with  the  following  reagents : 

A.  Sulphuretted  Hydrogen. — A  rich  yellow :  soluble  in  ammonia, 
and  precipitated  on  the  addition  of  an  acid.     This  precipitate  is  or- 


LIQUID     TESTS     FOR     ARSENIC.  381 

B.  Ammonia-nitrate  of  Silver. — A  canary  yellow ;  arsenite  of  silver. 
This  reagent  is  very  delicate,  but  the  precipitate  is  soluble  both  in 
acids  and  ammonia,  so  that  an  excess  of  either  must  be  avoided. 

C.  Ammonia-sulphate  of  Copper. — A  fine  apple-green.  This  is  re- 
dissolved  also  by  an  excess  of  acid  or  of  ammonia. 

Each  of  these  liquid  reagents  is  liable  to  fallacy,  which  must  be 
guarded  against. 

A.  Sulphuretted  Hydrogen  gives  precipitates  more  or  less  resem- 
bling that  from  arsenic  with  the  following  metals : 

Cadmium.  Antimony. 

Tin  (persaltsj.  Iron  (persalts). 

The  precipitate  from  cadmium  is  not  soluble  in  water  of  ammonia. 

The  precipitate  from  tin,  when  dried  and  ignited  with  black  flux, 
gives  no  sublimate  of  metal. 

The  precipitate  of  antimony  acts  in  the  same  way  as  tin,  but  also 
it  dissolves  in  strong  muriatic  acid,  and  the  solution,  diluted  with 
much  water,  gives  a  white  precipitate.  The  sulphuret  of  antimony 
is  much  more  orange-coloured  than  that  of  arsenic. 

The  precipitate  from  a  persalt  of  iron  is  pure  sulphur ;  heated,  it 
melts  and^burns  completely  away,  without  forming  any  solid  pro- 
duct. 

B.  Ammonia-nitrate  of  Silver. — Phosphate  of  soda  produces  a  yel- 
low precipitate  of  tribasic  phosphate  of  silver,  exactly  resembling 
the  arsenite.  It  is,  however,  much  more  soluble  in  ammonia.  They 
are  at  once  distinguished  by  being  collected  and  ignited.  The  ar- 
senite gives  off  oxygen  and  arsenious  acid,  while  metallic  silver  re- 
mains ;  but  the  phosphate  gives  no  volatile  product. 

C.  The  Ammonia-sulphate  of  Copper  is  uncertain,  unless  it  be  dried 
and  reduced ;  for  there  are  numerous  basic  compounds  of  copper, 
which  resemble  it  very  much  in  colour. 

None  of  these  liquid  reagents  are,  therefore,  in  themselves  posi- 
tive, unless  by  extraction  of  the  metal  j  and  this  is  the  more  impor- 
tant when  the  operator  has  to  work,  not  with  the  clear  solutions 
prepared  intentionally  for  illustration,  but  with  the  complex  and 
discoloured  liquids  obtained  from  the  stomach  and  intestines. 

The  process  to  be  then  followed  may  be  either  of  two  kinds ;  the 
first  consists  in  converting  the  arsenic  into  sulphuret,  the  second 
into  arseniuret  of  hydrogen.     I  will  describe  each  in  their  turn. 

The  contents  of  the  stomach  and  small  intestines,  or  the  matter 
ejected  by  vomiting  during  life,  are  to  be  boiled  in  distilled  water 
for  half  an  hour,  and  then  the  liquor  strained  through  a  linen  cloth. 
If  it  be  too  thick  or  coloured  to  allow  of  a  small<quantity  of  precip- 
itate being  observed  and  separated,  a  current  of  chlorine  gas  is  to 
be  passed  through  it,  by  which  most  of  the  animal  matter  dissolved 
is  coagulated,  and  a  more  convenient  solution  obtained.  This  be- 
ing strained  or  filtered,  is  to  be  well  boiled  to  expel  the  excess  of 
chlorine,  and  then  submitted  to  the  action  of  a  current  of  sulphuret- 
ted hydrogen  gas.  The  animal  matters  may  also  be  removed  from 
the  solution  by  rendering  it  acid  by  nitric  acid,  and  then  adding  an 
excess  of  nitrate  of  silver.  When  the  precipitate  which  forms  has 
been  separated,  the  excess  of  silver  is  to  be  thrown  down  by  some 


382       marsh's  test  for  arsenic. 

common  salt,  and  the  liquor  being  then  filtered,  is  fit  for  the  action 
of  the  sulphuretted  hydrogen. 

When  the  liquor  smells  strongly  of  this  gas,  there  has  been 
enough  passed  through,  and  it  is  then  to  be  boiled  briskly  for  a  few 
minutes  to  expel  the  excess,  and  favour  the  deposition  of  the  pre- 
cipitate produced.  This  is  to  be  then  collected  on  a  filter,  washed 
carefully  with  water  acidulated  by  muriatic  acid,  and  dried  at  a 
moderate  heat. 

When  completely  dry,  it  is  to  be  mixed  with  about  twice  its  bulk 
of  black  flux,  and  ignited  in  a  small  tube  of  hard  glass  closed  at  one 
end.  In  introducing  the  materials,  care  must  be  taken  not  to  soil 
the  sides  of  the  tube  ;  metallic  arsenic  sublimes,  which  is  recog- 
nised by  the  characters  given  already  in  pages  376,  380. 

The  process  by  arseniuretted  hydrogen  was  first  proposed  by  Mr 
Marsh,  and  has  been  found  of  surprising  delicacy  and  exactness; 
the  liquid  having  been  freed  from  animal  matters,  and  obtained  as 
thin  a  fluid  as  possible  by  either  of  the  processes,  by  chlorine  or 
nitrate  of  silver,  already  described,  it  is  rendered  moderately  acid 
by  muriatic  or  sulphuric  acid,  and  introduced  into  a  flask  or  bottle, 
to  the  neck  of  which  is  adapted  a  narrow  tube  of  hard  glass,  which, 
after  passing  horizontally  for  a  few  inches,  turns  up  and  forms  a 
jet  J  a  piece  of  zinc  being  introduced  into  the  acid  liquor,  hydrogen 
is  evolved,  which  combines  with  any  arsenic  that  may  be  present, 
and,  forming  the  gaseous  arseniuret  of  hydrogen,  passes  ofi'.  When 
the  gas  issuing  from  the  jet  is  set  on  fire,  if  the  hydrogen  be  pure, 
no  other  product  is  generated  but  water ;  but  if  a  slight  trace  of 
arsenic  be  present,  the  flame  is  whitish,  and  on  holding  over  the  jet 
a  fragment  of  glass  or  porcelain,  or  a  film  of  mica,  a  deposite  is  pro- 
duced, which  may  be  white  from  arsenious  acid,  or  brown  from  me- 
tallic arsenic,  according  to  the  height  at  which  the  plate  is  held, 
and  the  consequent  completeness  of  the  combustion,  or  the  reverse. 
If  the  quantity  of  arsenic  be  too  small  to  produce  this  eftect  in  a  cer- 
tain time,  it  may  be  better  detected  by  igniting  a  portion  of  the  hori 
zontal  arm  of  the  tube.  All  the  arseniuretted  hydrogen,  in  passing 
that  point,  deposites  its  arsenic,  which  is  carried  a  little  beyond  the 
heated  portion  by  the  current,  and  condenses  there  as  a  distinct 
metallic  film  ;  as  the  tube  may  be  kept  thus  red-hot  for  some  hours, 
the  smallest  trace  of  arsenic  may  be  thus  concentrated  on  a  single 
point,  and  its  properties  accurately  verified. 

Where  the  liquor  is  still  thickish  from  dissolved  organic  matter, 
the  gas  bubbles  would  not  break  rapidly,  but  form  a  froth,  which, 
passing  into  the  tube,  would  prevent  altogether  the  successful  em- 
ployment of  the  methods  just  described.  In  this  case  the  liquid 
should  be  made  so  feebly  acid  as  that  the  gas  shall  be  generated  but 
very  slowly,  and  that  there  shall  be  but  little  hydrogen  in  excess. 
The  tube,  in  place  of  terminating  in  a  jet,  is  to  be  bent  down  so 
that  it  shall  pass  under  the  edge  of  a  jar  in  the  pneumatic  trough, 
and,  the  apparatus  being  so  left  for  any  length  of  time,  the  gas 
evolved  may  be  collected  and  subsequently  examined.  Or,  what  is 
perhaps  still  better,  the  tube  may  dip  under  the  surface  of  a  dilute 
solution  of  nitrate  of  silver  or  of  sulphate  of  copper,  and  all  the  ar- 
seniuretted hydrogen  being  then  absorbed  and  decomposed,  metallic 


SOURCES     OF     ERROR.  383 

arsemurets  are  produced,  which  easily  yield,  by  the  application  of 
heat,  the  arsenic  in  the  metallic  form. 

In  this  mode  of  detecting  the  presence  of  arsenic,  it  is  necessary 
to  avoid  some  sources  of  error,  into  which,  without  previous  knowl- 
edge of  their  existence,  an  operator  might  easily  fall.  If  the  effer- 
vescence be  rapid,  it  frequently  happens  that  very  minute  portions 
of  zinc,  or  of  the  salt  of  zinc  generated,  may  be  carried  up  by  the 
stream  of  gas,  and,  being  deposited  upon  the  plate,  form  a  crust, 
which  might  lead  to  suspicion,  or  perhaps  wrong  conclusions.  This 
may  be  avoided  by  either  moderating  the  effervescence,  or  by  pass- 
ing the  gas,  before  using  it,  through  a  tube  filled  loosely  with  cotton, 
by  which  it  is  filtered,  as  it  were,  and  all  mechanically  diffused 
particles  separated.  Much  more  important  sources  of  error  arise, 
however,  from  the  existence  of  arsenic  in  most  of  the  zinc  and  some 
of  the  sulphuric  acid  of  commerce.  The  ores  of  zinc  occasionally 
contain  orpiment,  which  being  reduced  along  with  the  other  sul- 
phuret,  it  is  necessary  to  distil  the  zinc  in  order  to  have  it  pure, 
and  to  reject  it  as  long  as  it  contains  arsenic.  The  iron  pyrites 
also  occasionally  contains  traces  of  orpiment,  and  this  passes  into 
the  oil  of  vitriol.  In  employing  this  method,  it  is  necessary,  there- 
fore, to  test  the  purity  of  the  zinc  and  sulphuric  acid  by  the  method 
itself.  A  jet  of  the  hydrogen,  evolved  from  the  zinc  and  dilute 
sulphuric  acid  simply,  should  be  burned,  or  the  gas  passed  through 
a  solution  of  ammonia-nitrate  of  silver  for  a  quarter  of  an  hour.  If 
no  trace  of  deposition  of  arsenic  occur,  the  materials  may  be  con- 
sidered as  pure,  and  the  suspected  liquor  may  then  be  employed 
with  confidence  in  the  result. 

A  more  remarkable  source  of  error  arises  from  the  fact  that  the 
compounds  of  antimony  yield,  under  similar  circumstances,  a  pre- 
cisely similar  gas,  antimoniuret  of  hydrogen.  It  would  anticipate  too 
much  the  history  of  that  metal  to  enter  into  the  details  of  the  means 
of  distinguishing  that  gas  from  the  arseniuretted  hydrogen,  but  they 
will  be  fully  described  in  their  proper  place. 

Arsenious  acid  possesses  the  power  of  preventing  the  putrefac- 
tion of  animal  substances,  and  hence  the  bodies  of  persons  that  have 
been  poisoned  by  it  do  not  readily  putrefy.  The  arsenious  acid 
combines  with  the  fatty  and  albuminous  tissues  to  form  solid  com- 
pounds, which  are  not  susceptible  of  alteration  under  ordinary  cir- 
cumstances. It  hence  has  frequently  occurred,  that  the  bodies  of 
persons  poisoned  by  arsenic  have  been  found,  long  after  death, 
scarcely  at  all  decomposed,  and  even  where  the  general  mass  of  the 
body  had  completely  disappeared,  the  stomach  and  intestines  had 
remained  preserved  by  the  arsenious  acid  which  had  combined  with 
them,  and  by  its  detection  the  crimes  committed  many  years  before 
were  brought  to  light  and  punished.  In  the  cases  where  the  whole 
body  has  been  found  fresh,  it  resulted  from  the  person  having  survi- 
ved for  a  length  of  time  sufficient  for  the  complete  permeation  of  the 
tissues  by  the  absorption  of  the  poison  ;  in  the  others,  death  had 
occurred  while  it  was  yet  only  in  the  intestinal  tube.  The  absorp- 
tion of  the  arsenious  acid  in  cases  where  death  has  not  been  rapid, 
renders  its  detection  possible  in  all  the  various  organs,  particularly 
where  the  poisoning  has  been  produced,  not  by  the  administration 


384    ANTIDOTE     TO     ARSENIOUS     ACI  D. A  N  T  I  M  O  N  Y. 

of  a  single  dose,  but  by  frequently  repeated  doses,  each  insufficient 
to  produce  rapid  poisoning.  The  decision  in  such  cases  is  rendered, 
however,  extremely  difficult  by  the  fact,  recently  established,  that 
the  resemblance  of  function,  so  often  alluded  to,  between  arsenic 
and  phosphorus,  is  such,  that  the  latter  element,  which  character 
izes  the  animal  tissues  by  its  almost  constant  presence,  may  be 
replaced  as  a  constituent  of  our  organs  by  arsenic.  Thus,  the 
bones  may  contain  arseniate  of  lime  as  a  substitute  for  some  of 
their  proper  phosphate  of  lime,  and  in  the  phosphoric  salts,  which 
are  found  in  the  blood,  a  similar  replacement  may  occur.  It  is 
certain  that  the  quantity  of  arsenic  thus  found  naturally  replacing 
phosphorus  in  the  body  is  very  small,  but  there  is  no  necessary 
limit  to  its  extent  ^  and  although,  in  cases  of  suspected  chronic  poi- 
soning, the  analysis  of  the  organs  might  lead  to  useful  evidence, 
ret  the  discovery  of  arsenic  out  of  the  alimentary  canal  should,  as 
conceive,  not  without  great  caution,  be  considered  as  necessarily 
involving  its  having  been  administered. 

The  sulphuret  of  arsenic  of  commerce,  king's  yellow^  when  taken 
as  a  poison,  is  recognised  by  its  solubility  in  ammonia,  from  which 
It  is  again  thrown  down  by  an  excess  of  any  acid.  Its  reduction  to 
the  metallic  state  has  been  already  fully  described. 

An  antidote  has  been  recently  discovered  to  the  poisonous  effects 
of  arsenious  acid,  which  is  founded  on  a  very  remarkable  reaction. 
When  hydrated  peroxide  of  iron  is  made  into  a  thin  paste  with  so- 
lution of  arsenious  acid,  this  disappears,  being  changed  into  arsenic 
acid,  and  the  iron  into  protoxide,  2Fe203  and  As.Og  producing  4Fe.O. 
~f- As.Og.  This  arseniate  of  iron  has  no  action  on  the  system ,  and 
hence,  in  cases  of  poisoning  by  arsenic,  this  hydrated  peroxide 
should  be  administered  as  largely  and  as  rapidly  as  possible.  It 
may  be  made  in  a  few  moments  by  adding  carbonate  of  soda  to  any 
salt  of  red  oxide  of  iron  (permuriate,  muriate,  or  acetate  tincture). 
It  need  not  be  washed,  as  the  liquor  contains  only  a  salt  of  soda, 
which  would  be,  if  not  beneficial,  certainly  not  injurious. 

The  preparations  of  arsenic  are  of  very  extensive  use  in  the  arts. 
The  metal  is  used  to  alloy  the  lead  of  which  shot  is  made.  White 
arsenic  is  employed  in  glass-making,  to  prevent  the  deoxidation  of 
the  oxide  of  lead,  and  the  orpiment  is  employed  to  render  indigo 
soluble  in  some  processes  of  dyeing.  It  has  many  other  less  exten- 
sive uses. 

Of  Antimony. 

This  metal  was  first  discovered,  and  its  preparations  introduced 
into  medicine  by  Basil  Valentine,  from  the  unpleasant  results  of 
whose  experiments  upon  his  fellow  monks  it  got  the  name  of  anti' 
moine  ;  its  proper  Latin  name  is  stibium^  and  hence  its  symbol,  Sb. 
Antimony  exists  in  nature,  principally  as  sulphuret,  sometimes  as 
oxide,  and  also  these  two  combined,  forming  the  oxysulphuret,  red 
antimonial  ore.  It  is  from  the  native  sulphuret  that  the  metal  is 
prepared.  The  process  for  obtaining  it  by  means  of  iron  is  no- 
ticed p.  332,  but  it  is  had  purer  by  fusing  the  sulphuret  at  a  bright 
red  heat  with  black  flux.  Sulphuret  of  potassium  and  oxide  of  an- 
timony are  first  formed,  and  this  last  being  decomposed  by  the  car- 


OXIDES     OF     ANTIMONY.  385 

bon,  carbonic  oxide  is  evolved,  and  metallic  antimony  separates; 
this  process  is  farther  detailed  in  p.  334. 

The  antimony  thus  obtained  is  a  brilliant  white  metal,  of  a  highly 
crystalline  fracture,  and  may  be  obtained  crystallized  in  rhombohe- 
drons,  like  those  of  arsenic,  by  fusion,  as  described  in  p.  23  ;  its 
specific  gravity  is  6*8 ;  it  melts  at  about  800^,  just  below  redness, 
and  may  be  volatilized  by  a  white  heat.  If  heated  violently  in  con- 
tact with  air,  it  takes  fire,  burning  with  a  brilliant  white  flame,  and 
forming  antimonious  acid,  which,  though  not  volatile,  is  carried  up 
by  the  current  of  air,  and  is  deposited  on  the  neighbouring  bodies 
as  a  white  ipowder,  flowers  of  antimony.  Antimony  in  powder  takes 
fire  spontaneously  in  chlorine,  burning  with  a  yellowish  flame  ;  the 
antimony  is  not  oxidized  by  exposure  to  the  air  nor  by  water ;  it 
is  not  acted  on  by  sulphuric  nor  muriatic  acids,  but  is  rapidly  oxi- 
dized by  nitric  acid.  The  symbol  of  antimony  is  Sb. ;  its  equiva- 
lent numbers  are  1613  or  129*2 ;  it  combines  with  oxygen  in  three 
proportions. 

Oxide  of  jlntimony — Sb.Og ;  equivalent  1913  or  153'2 — may  be 
prepared  by  adding  to  an  acid  and  boiling  solution  of  chloride  of 
antimony  in  water,  carbonate  of  soda  in  excess.  The  carbonic  acid 
does  not  combine  with  oxide  of  antimony,  which  therefore  precip- 
itates pure ;  it  is  a  white  powder,  not  quite  insoluble  in  water,  and 
becomes  yellowish  when  heated.  If  metallic  antimony  be  burned 
in  a  limited  supply  of  air,  this  oxide  forms,  and  has  been  obtained 
crystallized  both  in  the  prismatic  and  octohedral  forms  of  arsenious 
acid,  with  which  it  is,  therefore,  isodimorphous  ;  both  the  metal  and 
this  oxide,  when  ignited  in  a  full  supply  of  air,  produce  antimonious 
acid. 

This  oxide  of  antimony  combines  with  acids  to  form  salts  of  very 
little  stability,  but  it  produces  with  the  acid  potash  salts  of  the  veg- 
etable acids,  double  salts  of  remarkable  constitution ;  of  these  the 
potash  tartrate  of  antimony  (tartar  emetic)  is  the  most  important ;  it 
also  acts  as  a  feeble  acid ;  thus,  if  in  its  preparation  caustic  potash 
be  used  to  decompose  the  chloride,  a  granular  white  powder  is  ob- 
tained, in  which  the  oxide  of  antimony  is  combined  with  potash ; 
it  is  on  this  account  called  hypo-antimonious  acid  by  many  chemists. 

0 xy sulphur et  of  Antimony. — Sb.O3H-2Sb.Ss.  This  substance  con- 
stitutes the  red  ore  of  antimony,  and  may  be  artificially  produced 
by  roasting  the  native  sulphuret  in  contact  with  the  air;  the  sulphur 
burns  out  as  sulphurous  acid,  and  the  antimony  becomes  oxidized  ; 
the  product  generally  contains  an  excess  of  oxide,  which  may  be  dis- 
solved out  by  tartaric  acid,  and  it  is  thus  that  the  basis  for  tartar 
emetic  is  sometimes  prepared  ;  by  continued  roasting,  the  whole  of 
the  sulphur  may  be  expelled,  and  an  impure  oxide  of  antimony  pro- 
duced ;  this,  when  melted,  constitutes  the  glass  of  antimony,  and 
the  oxysulphuret  is  the  crocus  of  antimony  of  the  older  pharmaco- 
poeias. 

Antimonious  Acid.  Peroxide  of  Antimony. — Sb.04.  Equivalent 
2013  or  161-2.  This  is  the  most  stable  compound  of  oxygen  and  an- 
timony ;  it  is  formed  when  antimony  is  oxidized  freely,  either  by 
combustion  or  by  the  action  of  nitric  acid,  and  igniting  the  resulting 
powder.     It  is  a  white  powder,  insoluble  in  water  ;  it  is  not  volatile  ; 

Ccc 


386  SU  LP  BURETS     OF     ANTIMONY. 

it  combines  with  alkalies,  forming  salts  insoluble  in  water,  and  from 
which,  by  a  stronger  acid,  it  is  separated  as  a  hydrate,  Sb.04+H.O. 
This  hydrate  dissolves  in  strong  muriatic  acid. 

Antimonic  j^cid.—Sh.O^.  Equivalent  2113  or  169-2.  This  sub- 
stance is  first  formed  when  metallic  antimony  is  oxidized  by  an  ex- 
cess of  nitric  acid,  and  remains  as  a  pale  yellow  powder,  which, 
when  exposed  to  a  dull  red  heat,  abandons  one  atom  of  oxygen, 
leaving  antimonious  acid,  as  just  described  j  it  is,  however,  more 
stable  in  combination,  and  may  hence  be  prepared  by  deflagrating 
antimony  with  nitre  j  when  the  resulting  mass  is  digested  in  cold 
water,  nitrate  and  nitrite  of  potash  dissolve  out,  and  leave  the  anti- 
moniate  of  potash  as  a  white  powder  j  this  is  decomposed  by  boiling 
water,  which  dissolves  a  basic  salt,  and  leaves  one  with  an  excess  of 
acid  behind.  In  its  hydrated  condition,  this  acid  dissolves  in  hy- 
drochloric acid. 

Antimony  and  sulphur  combine  in  three  proportions,  forming  sul- 
phurets,  which  resemble  completely,  in  constitution,  the  oxygen 
compounds ;  they  are  sulphur  acids,  dissolving  in  a  solution  of  the 
alkaline  sulphurets,  and  forming  sulphur  salts. 

Sulphuret  of  Antimony. — Sb.Sg.  Equivalent  2216-6  or  177*5.  This 
substance  constitutes  the  common  gray  ore  of  antimony,  and  crys- 
tallizes in  the  same  form  as  orpiment,  with  which  it  is  frequently 
contaminated  ;  in  its  native  state  it  is  dark  gray,  with  highly  metallic 
lustre,  crystalline  in  structure,  and  very  easily  reduced  to  powder; 
it  may  be  prepared  also  by  precipitation  from  a  solution  of  any  salt 
of  oxide  of  antimony,  as  the  chloride,  or  tartar  emetic,  by  sulphu- 
retted hydrogen  ;  it  is  then  an  orange  powder,  Avhich  becomes  darker 
on  being  dried,  and  has  the  same  composition  as  the  native  sulphu- 
ret,  with  which  it  becomes  identical  in  appearance  by  fusion.  This 
sulphuret  dissolves  in  alkaline  solutions,  on  which  circumstance  are 
founded  the  various  pharmacopoeial  processes  for  its  formation.  It 
has  been  used  in  medicine  ever  since  the  first  discovery  of  antimony, 
and  in  all  countries ;  the  methods  of  preparation,  and  the  purity  of 
the  products  obtainable,  are,  therefore,  exceedingly  variable. 

When  finely  powdered  sulphuret  of  antimony  is  boiled  in  a  strong 
solution  of  caustic  potash,  it  dissolves,  and  the  liquor  contains  two 
salts  perfectly  similar  to  one  another,  but  containing,  the  one  sul 
phur  and  the  other  oxygen,  united  to  antimony  and  potassium.  For 
one  half  of  each  substance  is  decomposed,  the  oxygen  passing  to 
the  antimony,  and  the  sulphur  to  the  potassium,  so  that  oxide  of  an 
timony  and  sulphuret  of  potassium  result,  and  these  respectively 
combine  with  the  quantities  of  potash  and  sulphuret  of  antimony 
that  had  not  been  altered ;  in  this  way, 

C  Sb.Sa      3K.0.  )  C    Sb.Sg-f  3K.S.  ) 

<  and  V  produce  <  and  > 

(  Sb.Sa      3K.0.  )  I  Sb.03+3K.O.  ) 

When  the  solution  cools,  both  compounds  are  partly  decomposed, 
so  that  a  quantity  of  sulphuret  and  of  oxide  of  antimony  precipitate 
mixed  together  j  and  hence  an  opinion  has  generally  prevailed,  and, 
indeed,  been  supported  by  the  high  authorities  of  Leibig  and  Gay 
Lussac,  that  these  bodies  are  chemically  united  in  the  precipitate 


PREPARATION     OF     KERMES     MINERAL.  387 

SO  obtained,  and  that  it  is  an  oxysulphuret,  identical  in  constitution 
with  that  already  described.  It  is,  however,  quite  established,  par- 
ticularly by  the  experiments  of  Berzelius  and  H.  Rose,  that  the  ox- 
ide and  the  sulphuret  are  but  mechanically  mixed  ;  under  the  mi- 
croscope, the  former  is  seen  as  brilliant  white  crystals,  mixed  with 
the  fine  amorphous  brown  powder  of  the  latter}  and,  besides,  the 
quantity  of  oxide  is  completely  variable,  and  in  no  case  so  great  as 
the  composition  of  the  true  oxysulphuret  should  require. 

The  precipitate  thus  obtained  by  cooling  is  generally  of  a  fine 
orange -brown  colour,  the  exact  shade  of  which  varies  very  much 
with  the  temperature,  and  the  degree  of  concentration  of  the  liquor. 
It  is  termed  in  pharmacy  kermes  mineral^  from  a  very  remote  analogy 
of  its  colour  to  that  afforded  by  the  insect  kermes  {coccus  ilicis)^ 
which  is  used  as  a  cheap  substitute  for  cochineal. 

After  the  separation  of  the  kermes,  the  liquor,  containing  still  the 
sulphur  and  oxygen  salts  above  described,  but  with  a  greater  pro- 
portion of  base,  is  precipitated  by  adding  an  acid  in  excess.  The 
sulphuret  of  potassium  is  decomposed,  and  the  sulphuret  of  anti- 
mony, with  which  it  had  been  combined,  separates ;  at  the  same 
time,  the  sulphuretted  hydrogen,  evolved  from  the  sulphuret  of  po- 
tassium, reacts  on  the  oxide  of  antimony,  converting  it  into  sul- 
phuret. This  precipitate  is  much  lighter-coloured  generally  than 
the  kermes,  and  is  sometimes  called  the  golden  sulphuret  of  anti- 
mony^ although  that  name  properly  belongs  to  a  different  substance, 
to  be  described  farther  on.  In  many  cases,  in  place  of  collectinof 
the  kermes  and  the  portion  precipitated  by  the  acid  separately  as 
now  described,  the  hot  filtered  liquor  is  added  to  the  acid  before 
the  kermes  has  had  time  to  separate,  and  the  whole  being  then 
mixed,  assumes  an  intermediate  shade  of  colour,  and  constitutes  the 
brown  sulphuret^  or  orange  sulphuret  of  antimony  of  the  British  phar- 
macopoeias. 

In  place  of  caustic  potash,  the  native  sulphuret  of  antimony  is 
frequently  boiled  with  carbonate  of  soda.  In  this  case  the  whole 
of  the  carbonic  acid  unites  with  one  half  of  the  soda,  forming  bicar- 
bonate, and  the  other  half  of  the  soda  acts  with  the  sulphuret  of 
antimony  precisely  as  if  it  had  been  used  in  the  caustic  state. 

An  important  mode  of  preparing  these  pharmaceutical  substances 
consists  in  fusing  the  materials  together  instead  of  boiling  their  solu- 
tions. Thus  an  excellent  kermes  is  prepared  by  fusing  together 
three  parts  of  native  sulphuret  and  one  of  carbonate  of  potash.  The 
general  reaction  is  the  same  as  described  when  the  materials  were 
dissolved ;  the  melted  mass  is  boiled  in  water,  and  the  solution  so 
obtained  treated  as  already  noticed.  Rose  has,  however,  directed 
attention  to  a  circumstance  which,  though  occurring  in  all  cases,  is 
more  marked  in  this  process  than  the  others.  It  is,  that  some  anti- 
mony separates  in  the  metallic  state,  while  another  portion  is 
changed  into  persulphuret  j  thus  SSb.Sg  produces  SSb.Sg,  and  2Sb.  is 
set  free.  The  solution  contains,  therefore,  not  only  the  ordinary 
sulphuret,  but  some  persulphuret  of  antimony,  the  colour  of  which 
is  much  brighter  than  that  of  the  other,  and  it  hence  modifies  the 
tint  of  the  preparation  in  a  variable  manner.  The  persulphuret  car- 
ries down  with  it  also  some  sulphuret  of  potassium,  and  hence  the 


388  ANTIMONIURET     OF     HYDROGEN. 

ordinary  kermes  mineral  appears  always  to  contain  traces  of  potash. 
The  quantity  of  persulphuret  of  antimony  present  seldom  exceeds 
two  or  three  per  cent. 

Sulpho-antimonious  Acid. — Sb.S4.  This  substance  is  produced  as 
a  yellow  powder  when  the  solution  of  antimonious  acid  is  decom- 
posed by  sulphuretted  hydrogen. 

Sulpho-antimonic  Acid — Persulphuret  of  Antimony^  Sb.S^ — is  obtain- 
ed when  a  solution  of  antimonic  acid  in  muriatic  acid  is  treated 
with  sulphuretted  hydrogen.  It  is  of  a  fine  golden  orange  colour. 
Its  formation  in  the  process  for  kermes  mineral  has  been  already 
explained.  This  is  the  true  golden  sulphuret.  To  obtain  it  in  large 
quantity,  as  is  given  in  many  pharmacopoeias,  three  parts  of  sul- 
phuret of  antimony  and  one  of  carbonate  of  potash  are  to  be  fused 
with  one  half  part  of  sulphur  ;  this  last  converts  the  antimony  into 
the  persulphuret.  The  fused  mass  is  to  be  dissolved  in  water,  and 
decomposed  by  muriatic  acid. 

Antimoniuret  of  Hydrogen. — Sb.Hg.  When  hydrogen  is  evolved 
in  contact  with  antimony  in  a  nascent  or  finely  divided  state,  th^y 
combine  and  form  a  gas,  which,  in  properties  and  constitution,  has 
a  remarkable  similarity  to  arseniurct  of  hydrogen.  The. easiest  mode 
of  effecting  this  is  to  dissolve  zinc  in  dilute  sulphuric  acid  to  which 
tartar  emetic  has  been  added.  The  gas  so  evolved  is  colourless,  in- 
soluble in  water,  has  neither  acid  nor  alkaline  reaction.  It  precip- 
itates the  salts  of  mercury  and  most  metals,  but  not  copper,  by 
which  it  is  distinguished  from  the  arseniuret  of  hydrogen.  Its 
specific  gravity  has  not  been  experimentally  determined  ;  but  if  it  be 
composed,  like  arseniuretted  hydrogen,  of  one  volume  of  metallic 
vapour  and  six  of  hydrogen  condensed  to  four,  it  should  be  4504*7. 
When  this  gas  burns,  water,  is  formed,  and  antimony  deposited, 
either  as  metal  or  as  oxide,  according  to  the  supply  of  oxygen.  It 
hence  superficially  resembles  in  its  combustion  the  gas  containing 
arsenic,  but  it  is  distinguished  readily  by  the  following  characters. 

1st.  The  antimoniuret  of  hydrogen,  when  it  is  decomposed  by 
heating  a  point  of  the  tube  through  which  it  passes  to  redness, 
deposites  the  metal  at  the  heated  part,  while  arsenic  settles  at  a 
certain  distance  beyond,  where  the  tube  is  colder. 

2d.  The  metallic  crust  is  not  volatilized  at  any  temperature  which 
can  be  applied  to  glass. 

3d.  If  the  metallic  scale  be  deposited  on  a  porcelain  plate,  and  ox- 
idized by  the  outer  flame  of  the  blowpipe,  it  forms  a  powder  yel- 
low while  hot,  but  white  when  cold,  which  is  not  volatilized  by 
any  farther  application  of  the  flame.  Arsenic,  on  the  contrary,  be- 
comes oxidized  only  in  the  act  of  being  vaporized. 

In  certain  cases  of  compound  poisoning,  and  where  tartar  emetic 
has  been  given  as  an  emetic  in  cases  of  poisoning  by  arsenic,  it  is 
possible  that  the  two  metals  may  coexist  in  solution.  In  theie 
cases  they  may  be  separated  by  converting  both  into  the  hydrogen 
compounds,  and  decomposing  the  mixed  gases  by  igniting  the  tube 
through  which  they  pass.  The  antimony  is  deposited  close  to  the 
heated  part,  and  the  arsenic  at  a  little  distance. 

The  detection  of  antimony  is  generally  simple ;  in  all  its  combi- 
nations it  is  immediately  recognised  by  the  formation  of  its  com- 


TELLURIUM     AND     ITS     COMPOUNDS.  889 

pound  with  hydrogen  just  described.  In  solution,  in  the  state  of 
oxide,  it  gives  with  sulphuretted  hydrogen  the  orange  precipitate 
of  sulphuret.  In  the  other  states  of  oxidation  the  precipitates  by 
sulphuret  of  hydrogen  are  more  yellow,  but  are  all  easily  distinguish- 
ed from  orpiment  by  not  being  volatile,  and  from  the  bisulphuret 
of  tin  by  yielding  the  antimoniuret  of  hydrogen.  From  the  sul- 
phuret of  cadmium  they  are  known  by  their  solubility  in  hydrosul- 
phuret  of  ammonia. 

Of  Tellurium, 

This  is  one  of  the  rarest  of  the  metals,  and,  although  classified  with  them,  from  its 
lustre  and  power  of  conducting  electricity  and  heat,  in  which  it  is,  however,  far  in- 
ferior to  the  others,  it  ranks  naturally  with  sulphur  and  selenium,  to  which  last  it 
assimilates  completely  in  its  properties.  It  exists  in  nature,  native,  and  combined 
with  a  variety  of  metals,  gold,  silver,  antimony,  lead,  &c.,  forming  ores  of  very  in- 
definite constitution.  Its  extraction,  which  is  still  farther  complicated  by  the  pres- 
ence of  sulphur  and  selenium,  would  require  too  detailed  description,  and  is  too  sel- 
dom an  object  with  chemists  to  require  description  here.  Its  properties  and  princi- 
pal compounds  alone  deserve  attention. 

Pure  tellurium  is  silver  white  and  very  brilliant.  It  crystallizes  easily  in  rhom- 
bohedrons.  It  is  brittle  and  easily  powdered.  Its  sp.  gr.  is  6-14:.  It  is  about  as  fu- 
sible as  antimony,  and  at  a  very  high  temperature  may  be  volatilized.  Its  vapour 
smells  like  selenium ;  when  heated  in  the  air  it  burns  with  a  bluish  flame,  forming 
tellurous  acid.     It  is  rapidly  oxidized  by  nitric  acid. 

The  analogy  of  tellurium  to  sulphur  is  very  close.  When  tellurium  is  boiled  in 
a  strong  solution  of  potash,  there  is  formed  tellurite  of  potash  and  telluret  of  potas- 
sium; but  if  this  solution  be  diluted,  the  potassium  reduces  the  tellurous  acid,  and 
the  metal  is  precipitated,  potash  being  regenerated.  The  symbol  of  tellurium  is  Te. 
Its  equivalent  numbers  are  801-8  and  64-2. 

Tellurium  combines  with  oxygen  in  two  proportions,  forming  tellurous  and  tel- 
luric acids.  The  former,  telltirous  acid,  Te.O^,  is  prepared  by  decomposing  the  bi- 
chloride of  tellurium  by  water,  Te.Clz  and  2H.O.  producing  2H.C1.  and  Te.02. 
This  last  precipitates  as  a  bulky  white  powder  containing  combined  water.  In  this 
state  it  is  sensibly  soluble  in  water,  and  reddens  litmus.  It  dissolves  readily  both 
in  acid  and  alkaline  solutions,  forming  compounds  of  a  very  instable  character. 
When  its  solution  in  water  is  heated  to  about  110=',  it  deposites  the  tellurous  acid  in 
an  anhydrous  form.  The  water  is  also  expelled  by  a  moderate  heat  from  the  hy- 
drated  acid  in  powder.  The  anhydrous  acid  thus  obtained  differs  essentially  from 
the  hydrated  form.  It  is  insoluble  in  water,  in  acids,  and  in  alkalies,  and  has  no 
acid  reaction  whatsoever.  No  salts  of  it  can  be  formed  in  the  humid  way;  but  if  it 
be  fused  at  a  red  heat  with  carbonate  of  potash,  the  carbonic  acid  is  expelled,  and 
tellurite  of  potash  formed,  which  dissolves  in  water ;  from  this  solution  the  hydra- 
ted tellurous  acid  is  thrown  down  on  the  addition  of  an  acid. 

Berzelius  considers  these  remarkable  differences  of  properties  as  indicating  an 
isomeric  distinction  between  the  two  acids.  In  a  subsequent  chapter  I  shall  point 
out  the  manner  in  which  I  believe  such  compounds  should  be  viewed. 

Tdluric  Acid,  Te.Oa,  is  prepared  by  deflagrating  tellurous  acid  with  nitre;  a  sol- 
uble tellurate  of  potash  is  thus  obtained,  which,  when  mixed  with  nitrate  of  ba- 
rytes,  gives  an  insoluble  tellurate  of  barytes,  and  this,  acted  on  by  sulphuric  acid, 
yields  sulphate  of  barytes,  and  in  solution  telluric  acid,  which  crystallizes  in  large 
prisms  containing  three  atoms  of  water.  Of  these,  two  are  given  ofl'  at  212°  F. 
It  does  not  taste  acid,  but  reddens  litmus  slightly.  It  combines  readily  with  bases, 
forming  classes  of  salts  containing  one,  two,  and  four  equivalents  of  acid.  When 
the  crystallized  telluric  acid  is  heated  to  redness,  all  its  water  passes  ofl',  it  becomes 
orange,  and  undergoes  a  change  of  properties  like  stannic  acid.  It  becomes  insolu- 
ble in  water,  in  acids,  and  alkaline  solutions;  when  very  strongly  heated,  it  gives 
off  oxygen,  and  tellurous  acid  remains ;  but  if  this  anhydrous  acid  be  fused  with 
potash,  tlie  tellurate  of  potash  which  dissolves  contains  the  acid  in  its  hydrated 
state.  These  forms  are  considered  as  being  isomeric,  and  not  identical  bodies ; 
their  real  nature  will  be  noticed  hereafter. 

Tellurium  and  hydrogen  combine  to  form  a  gas,  telluret  of  hydrogen,  H.Te,,  which 
resembles  in  its  characters  sulphuret  of  hydrogen,  particularly  in  its  odour;  it  red- 


890      URANIUM     AND     ITS     COMPOUND  S. C  O  P  P  E  R. 

dsns  litmus,  is  soluble  in  water,  decomposes  the  alkalies  and  earths,  forming  soluble 
tellurets,  and  precipitates  insoluble  tellurets  from  solutions  of  the  other  metals. 

Tellurium  combines  with  sulphur  in  two  proportions,  forming  sulphurets,  which 
do  not  require  detailed  notice.  Its  compounds  with  the  metals  resemble  so  com- 
pletely the  metallic  sulphurets  as  to  render  a  separate  account  unnecessary.  Thus, 
in  every  case  where  a  metallic  sulphuret  evolves  sulphuretted  hydrogen  gas  with  an 
acid,  the  telluret  of  the  metal  produces  telluretted  hydrogen,  and  the  metallic  tellu- 
rets are  soluble  or  insoluble  in  water,  precisely  as  the  sulphurets  of  the  same  metals 
are. 

Of  Uranium. 

This  metal  exists  in  some  rather  rare  minerals,  particularly  mpeckblende,  combined 
with  oxygen;  the  processes  for  its  extraction  are  rendered  very  complex  by  the 
presence  of  a  great  number  of  other  metals,  and  I  shall  refer,  therefore,  to  the  sys- 
tematic works  for  the  details  of  its  extraction ;  the  metal  itself  is  easily  obtained 
pure  by  the  action  of  hydrogen  gas  on  either  of  its  oxides  at  a  red  heat.  It  is  of  a 
dark  gray  colour,  difficultly  fusible,  specific  gravity  90.  Its  symbol  is  U.,  its  equiv- 
alents are  2711  or  217-3,  being  the  largest  numbers  for  any  oi  the  simple  bodies;  it 
combines  with  oxygen  in  two  proportions. 

Protoxide  of  Uranium,  U.O.,  is  obtained  by  decomposing  any  salt  of  uranium  by 
a  caustic  alkali ;  it  precipitates  as  a  greenish  hydrate,  which  rapidly  becomes  yel- 
low, forming  the  peroxide  by  absorbing  oxygen :  the  protoxide  of  uranium  is  dis- 
solved by  an  excess  of  ammonia.  Peroxide  of  uranium,  U.O3,  is  formed  when  the 
protoxide  is  heated  in  air ;  it  is  yellow,  and  possesses  some  of  the  characters  of  an 
acid,  uranic  acid ;  it  reddens  litmus ;  it  enters  into  combination  as  well  with  alka- 
lies as  with  acids ;  the  alkaline  and  earthy  uranates  are  insoluble,  yellow  or  orange 
coloured.    This  oxide  is  used  to  colour  glass  of  a  fine  lemon  yellow. 

The  sulphurets,  &c.,  of  uranium  are  unimportant. 

SECTION  V. 
METALS   OF    THE   FIFTH    CLASS. 

Of  Copper. 

Copper  is  one  of  the  most  important  of  the  metals,  and  one,  also, 
of  the  most  extensively  diffused  through  nature.  It  exists  native  in 
veins,  and  frequently  crystallized,  in  forms  belonging-  to  the  regular 
system  ;  in  the  state  of  oxide  it  is  found,  both  uncombined  and  form- 
ing arseniates,  phosphates,  carbonates,  and  other  salts,  but  its  most 
abundant  source  is  the  native  sulphuret.  The  ordinary  copper  ore, 
copper  pyrites^  is  a  double  sulphuret  of  copper  and  iron,  CuaS.+FegSa, 
and  from  this  the  metal  is  extracted  for  the  purposes  of  commerce. 

The  general  processes  for  the  reduction  of  a  metallic  sulphuret 
have  been  already  described  (p.  333),  but,  from  the  composition  of 
the  copper  ore,  some  additional  management  is  required  ;  there  are 
two  metals  present  in  the  ore,  and  as  neither  is  volatile,  the  product 
after  complete  reduction  should  be,  if  the  process  was  simply  man- 
aged as  for  a  simple  sulphuret,  not  pure  copper,  but  an  alloy  of  one 
equivalent  of  copper  and  two  of  iron  ;  this  is  avoided  by  arresting 
the  process  of  reduction  at  a  certain  stage  ;  the  copper,  having  less 
affinity  for  oxygen  than  the  iron,  assumes  the  metallic  state  first, 
and,  if  it  were  possible  to  work  so  accurately,  the  whole  of  the  cop- 
per might  be  reduced  before  any  iron,  and  this  last  metal  left  alto- 
gether in  the  scoriae  as  oxide  or  silicate  ;  but  this  not  being  feasible, 
the  copper  first  obtained  is  rendered  impure  by  the  presence  of  a 
quantity  of  iron,  and  also  of  sulphur  ;  this  impure  copper  is  then 
calcined  ;  the  iron  and  sulphur,  being  the  more  combustible  bodies, 
are  first  oxidized,  and  then  again,  by  other  reductions  and  calcina- 
tions, the  copper  is  ultimately  brought  to  a  state  of  complete  purity 


PROPERTIES     OF     COPPER.  391 

The  separation  of  the  iron  is  facilitated  by  adding  a  small  quantity 
of  sand  to  the  calcined  mass  before  the  process  of  reduction  j  the 
silicic  acid  unites  exclusively  with  the  oxide  of  iron,  and  the  silicate 
of  iron  not  being  reducible  under  ordinary  circumstances,  the  puri- 
fication of  the  copper  is  more  rapidly  effected. 

Though  the  copper  is  thus  rendered  quite  pure  from  iron,  great 
care  is  still  required  in  these  operations,  in  order  to  secure  the 
proper  softness,  ductility,  and  tenacity  necessary  in  the  employ- 
ment of  this  metal  in  the  arts  j  thus,  if  it  has  been  too  long  in  con- 
tact with  the  fuel,  it  combines  with  a  small  quantity  of  carbon  ;  if,  on 
the  other  hand,  the  deoxidizing  action  of  the  fuel  be  not  applied  long 
enough,  some  suboxide  remains  undecomposed,  which  dissolves  in 
the  metallic  copper.  In  both  these  cases  the  metal  is  brittle  and 
of  a  bad  grain,  so  as  to  be  unfit  for  many  of  its  uses. 

Copper  is  obtained  also  in  the  metallic  state  by  precipitation  from 
the  water  which  collects  in  the  galleries  and  shafts  of  copper  mines, 
and  which,  from  the  oxidation  of  the  sulphuret  of  copper,  contains 
sulphate  of  copper  dissolved.  Fragments  of  old  iron  are  thrown 
into  the  reservoirs  in  which  the  drainage  water  of  the  mine  is  col- 
lected, and  by  electro-chemical  action,  as  described  p.  193,  195, 
and  335,  the  iron  is  dissolved  and  the  copper  precipitated  in  irreg- 
ularly crystallized  masses. 

Pure  copper  is  of  a  peculiar  well-known  reddish  colour.  It  is 
very  malleable  and  ductile  ;  after  iron,  it  is  the  strongest  of  the  met- 
als. It  crystallizes  by  fusion  in  a  form  which  is  not  the  same  as 
that  found  native,  or  produced  when  the  metal  is  precipitated  from 
its  solutions.  Its  sp.  gr.  is  8'9.  It  is  fusible  at  1996'-".  It  is  not 
volatile.  In  dry  air  it  is  not  tarnished,  but  in  damp  air  it  gradually 
becomes  covered  with  a  greenish  coating  of  basic  carbonate  of  cop- 
per. When  heated  in  contact  with  air,  copper  combines  rapidly 
with  oxygen,  and  passes  through  a  variety  of  rainbow  colours,  but 
is  at  last  converted  into  black  oxide,  which  forms  as  scales  upon  its 
surface.  The  series  of  colours  arises  first  from  the  action  of  light 
upon  the  thin  coating  of  oxide,  as  also  happens  in  the  oxidation  of 
iron.  The  generality  of  acids  do  not  act  on  copper  at  ordinary 
temperatures,  unless  in  contact  with  air,  for  the  copper  is  incapable 
of  decomposing  water  ;  but  at  the  point  of  contact  with  air,  oxygen 
is  directly  absorbed,  and  the  acid  combines  with  the  oxide  so  gen- 
erated. In  this  way  the  feeblest  acids  may  act  upon  copper,  as  the 
acetic  acid  and  the  acids  contained  in  the  various  fatty  bodies,  and 
the  metal  be  thus  introduced  into  culinary  preparations,  and  so  pro- 
•  duce  poisonous  effects.  The  acids  which  give  off  oxygen  directly 
dissolve  copper,  as  nitric  acid,  with  evolution  of  nitric  oxide.  Strong 
oil  of  vitriol,  also,  when  boiled  on  copper,  gives  sulphate  of  copper 
and  sulphurous  acid  gas. 

The  symbol  of  copper  is  Cu.,  from  its  Latin  name  j  its  equivalent 
395-7  or  31-7. 

Copper  combines  with  oxygen  in  two  proportions,  forming  a  sub- 
oxide and  a  protoxide. 

Protoxide  of  Copper. — Cu.O.  Equivalent  495-7  or  39-7.  This  ox- 
ide is  formed  by  exposing  copper,  at  a  red  heat,  to  a  current  of  air. 
It  may  also  be  obtained  by  igniting  the  nitrate  of  copper.     It  is  a 


392  OXIDESOFCOPPER.  ' 

dull  black  powder,  which,  by  a  very  high  temperature,  m^y  be  melt- 
ed, and  crystallizes  on  cooling.  It  dissolves  but  slowly  in  acids, 
forming  the  ordinary  blue  or  green  salts  of  copper.  When  heated, 
even  below  redness,  in  a  stream  of  hydrogen  gas,  it  is  perfectly  re- 
duced, water  being  formed.  It  is  thus  that,  as  described  in  p.  253, 
the  composition  of  water  is  best  determined.  At  a  dull  red  heat, 
this  oxide  is  reduced  completely  by  carbon  and  all  its  compounds, 
carbonic  acid  being  produced.  For  this  reason  it  is  extensively 
employed  in  the  ultimate  analysis  of  organic  substances,  of  which  it 
converts  the  carbon  into  carbonic  acid,  and  the  hydrogen  into  water. 
The  metallic  copper  thus  obtained  by  the  reduction  from  the  oxide 
is  a  fine  pinkish-red  powder,  which  has  a  remarkable  affinity  for 
oxygen,  and  is  hence  used  in  the  analysis  of  organic  substances  con- 
taining nitrogen,  to  prevent  the  formation  of  nitrous  or  nitric  oxides. 

When  a  solution  of  caustic  potash  is  added  in  excess  to  a  solu- 
tion of  a  salt  of  copper,  the  protoxide  is  thrown  down  as  a  hydrate, 
Cu.O.  .  H.O.  It  is  a  fine  blue  powder,  which  is  decomposed  by  a 
very  gentle  heat,  so  that  even  if  a  liquor  containing  it  be  boiled,  it 
becomes  brown  and  anhydrous,  though  in  the  midst  of  water.  It  is 
hence  that,  if  the  solution  of  copper  be  added  to  a  boiling  solution 
of  potash,  the  precipitate  is  the  dark  brown  anhydrous  oxide,  which, 
however,  obstinately  retains  a  little  potash. 

Suboxide  of  Copper. — CugO.  Equivalent  891*4  or  71-4.  This  body 
exists  native,  constituting  the  ruby  copper  ore,  and  may  be  prepared 
artificially  by  igniting  a  mixture  of  five  parts  of  black  oxide  of  cop- 
per and  four  of  copper  filings  j  half  of  the  oxygen  of  the  former 
passes  to  the  latter,  and  the  whole  becomes  suboxide.  It  is  like- 
wise made  by  fusing  together  three  parts  of  subchloride  of  copper 
and  two  of  dry  carbonate  of  soda ;  chloride  of  sodium  and  suboxide 
of  copper  result,  CU2CI.  and  Na.O.  giving  CugO.  and  Na.Cl.,  while 
the  carbonic  acid  is  given  off.  This  suboxide  of  copper  is  a  red- 
dish-brown powder,  which  is  much  less  acted  on  by  moist  air  than 
pure  copper  ;  and  hence,  under  ordinary  circumstances,  when  cop- 
per becomes  brown  by  being  coated  with  this  oxide,  the  action 
ceases.  Articles  of  copper  are  thus  coated  intentionally,  for  the 
purpose  of  preserving  their  surface,  by  covering  them  with  a  paste 
of  red  oxide  of  iron,  which,  when  heated,  is  thus  reduced  to  the 
state  of  protoxide,  2Cu.  and  Fe203  giving  CU2O.  and  2Fe.O.  j  this 
last  is  then  removed  by  digestion  in  a  boiling  solution  of  acetate 
of  copper. 

The  generality  of  acids  decompose  the  suboxide  of  copper  into 
metallic  copper,  and  the  black  oxide  with  which  the  acid  combines; 
but,  besides  the  subchloride  of  copper,  several  of  its  salts  may  be 
formed  by  the  action  of  deoxidizing  agents  on  the  salts  of  the  black 
oxide  J  thus  sulphurous  acid  converts  the  hydrate  of  the  black  oxide 
into  sulphate  of  the  suboxide,  S.O2  and  2Cu.O.  producing  S.O3  + 
CuaO.  From  the  solution  of  this  salt,  a  fine  orange  hydrate  of  the 
red  oxide  is  thrown  down  by  the  caustic  alkalies.  Protochloride 
of  tin  and  protosulphate  of  iron  also  reduce  the  salts  of  copper  to 
this  state  of  oxidation. 

Sulphur  combines  with  copper  in  two  proportions,  forming  sul- 
phurets  equivalent  to  the  oxides  just  described;  they  are  both  found 


DETECTION     OF     COPPER.  393 

native,  and  constitute,  particularly  the  subsulphuret,  important  ores 
of  copper.  They  may  be  prepared  artificially  by  fusing  together 
sulphur  and  metallic  copper  ;  the  union  takes  place  with  brilliant 
combustion.  If  some  sulphur  be  placed  in  a  flask,  and  heat  be  appli- 
ed so  as  to  fill  the  flask  with  the  vapour  of  sulphur,  a  thin  copper 
wire  dipped  in  it  burns,  as  iron  does  in  oxygen,  forming  the  subsul- 
phuret J  these  bodies  are  not  of  importance,  except  as  the  great 
sources  of  metallic  copper. 

The  sulphurets  of  copper  may  also  be  formed  by  precipitating  the 
salts  of  copper  with  sulphuretted  hydrogen;  a  deep  brown  powder  is 
produced,  which  is  CU2S.  or  Cu.S.,  according  as  the  solution  contain- 
ed the  suboxide  or  the  protoxide  of  the  metal. 

The  detection  of  copper  in  solution  is  very  simple  ;  the  salts  of 
the  black  oxide  are  generally  green  or  blue  ;  on  the  addition  of  am- 
monia, a  precipitate  is  produced,  bluish  or  green,  according  to  the 
acid  with  which  the  oxide  had  been  combined,  but  in  all  cases  pro- 
ducing with  an  excess  of  the  ammonia  a  deep  violet-coloured  solu- 
tion. The  only  metal  which  resembles  copper  in  this  respect  is 
nickel,  and  from  it,  it  is  distinguished  by  all  its  other  properties, 
particularly  by  the  yellow  prussiate  of  potash,  which  produces  a  fine 
chocolate  broAvn  precipitate  of  ferrocyanide  of  copper.  With  sul- 
phuret  of  hydrogen,  the  salts  of  copper  give  a  dark  brown  sulphuret, 
insoluble  in  hydrosulphuret  of  ammonia ;  and  when  a  slip  of  clean 
iron  or  zinc  is  introduced  into  a  liquor  containing  copper,  this  is  re- 
duced, and  deposited  upon  the  surface  of  the  zinc  or  iron  as  a  bright 
coating  of  metallic  copper. 

When  the  copper  exists  as  suboxide,  its  reactions  are  very  differ- 
ent; it  gives,  with  ammonia,  a  white  precipitate,  which  redissolves 
in  an  excess,  forming  a  colourless  liquor ;  if  there  be  no  excess  of 
acid,  chloride  of  sodium  gives  a  white  precipitate  of  subchloride  of 
copper.  But  in  practice  it  is  never  necessary  to  look  for  copper  by 
these  reactions,  the  salts  of  the  suboxide  absorbing  oxygen  with 
such  avidity,  that  by  a  few  minutes'  exposure  to  the  air  their  con- 
stitution changes.  The  colourless  solution  of  suboxide  of  copper  in 
ammonia  becomes  violet  blue  in  the  act  of  pouring  it  from  one  bot- 
tle to  another ;  and  hence,  for  the  mere  detection  of  copper,  the 
properties  of  the  protoxide  alone  need  be  taken  into  account. 

Like  the  oxides  of  cobalt  and  nickel,  the  oxides  of  copper  are  not, 
by  themselves,  soluble  in  water  of  ammonia.  The  solutions  of  these 
metallic  compounds  in  water  of  ammonia  are  basic  salts,  to  the  con- 
stitution of  which  the  acid,  with  which  the  metallic  oxide  had  been 
originally  combined,  is  necessary.  The  detailed  nature  of  these 
bodies  will  be  noticed  among  the  compounds  of  ammonia. 

The  detection  of  copper  by  the  blowpipe  is  very  simple  and  dis- 
tinct. Fused  with  borax,  a  substance  containing  the  most  minute 
trace  of  copper  gives  a  glass,  which,  when  heated  in  the  oxidizing 
flame,  becomes  green,  being  coloured  by  the  protoxide  ;  but  when 
ignited  in  the  reducing  flame  and  suddenly  cooled,  is  deep  ruby 
red,  generally  opaque.  This  change  of  colour  arises  from  the  cop- 
per being  reduced  to  the  state  of  suboxide  The  colour  given  to 
glass  by  this  suboxide  is  a  pure  prismatic  red,  so  homogeneous  that 
red  light  may  be  obtained  for  optical  experiments  by  transmitting 

Ddd 


rsKPUi.  AI.I.OTS  or  copper. — lead. 

m^ke  B^  tkio«gk  tlus  endowed  ^ass^  and  tht  tint  is  so  fine  that 
tkis  raby  gkss  is  tlw  nofit  valaaUe  that  can  be  used  for  ornamental 


TWe  salits  of  cofiptK  geaeiaDy  tinge  tlie  flame  of  tlie  blowpipe 
U«e  tMT  gieea,  acemdia|r  to  tlie  other  bodies  that  Biay  be  present. 

ladepeadcat  of  die  direct  aapkyymeiit  of  copper  in  the  arts,  for 
%Aich  its  pn^erties  eminentlf  qnalify  it,  A  enters  into  the  compo- 
cifagreatnaBberofallojscif^reatiHiportaiice.  Thosbronze, 
r  vaed  as  a  iwbaritnte  fw  sle^  aid  still  employed  in  the 
_  of  stataes  aad  mowuDamtSk  from  the  aocoracy  with  which  it 
adapts  itsetf  to  the  moald,  and  its  dnrabilitj,  consists  of  ninety  pans 
<if  copper  and  ten  of  tia  in  100.  It  is  curkHis,  that  from  the  Tery 
^i^rltffa*  ages,  this,  which  is  stiU  the  best  {m^ortiott,  should  hare  been 
employed  ^  the  bronze  swords  fr«m  ancient  l^ypt,  from  Scandina- 
Tia,  and  those  found  in  Ireland,  haTing  aU  this  constitution.  Gwt 
rngtalf  or  dmt  of  which  cannons  are  cast,  is  an  inferior  kind  of  bronze. 

The  elasticitj  and  sonoronancss  td  these  aDoys  are  very  remark- 
able. That  naed  for  hefk^  Ml  mmmi,  couists  of  80  parts  of  copper 
and  20  of  tin.  The  Indian  gw^i  hare  this  composiiion,  bat  com- 
mon bdk  contain  less  tin,  and,  in  place  of  it,  some  lead  and  zinc. 
In  Ae  pn^mtion  of  two  parts  of  eopfct  to  one  of  tin,  or,  more 
accnratety,  of  four  atoms  of  copper  to  one  of  tin,  127  to  59,  an 
aBoy  is  formed  of  exceeding  hritdaiesB  and  hardness,  and  so  brill- 
iant, when  traly  jioKshrd,  as  to  be  nsed  for  ^e  mirror  surface  in 
Tcflectii^telesi^^ies;  it  is  hence  called  ^pccWnm  wcte/.  The  quality 
of  this  aHoj  is  rwnarkaMy  detcn<»ated  by  a  slight  deriation  to  ei- 
tha  side  erf"  thetrae  atomic  proportions. 

The  alloys  of  zinc  and  copper  are  Tery  numerous  and  important, 
conslitnting  the  diftrent  varieties  of  brmn.  The  best  brass  consists 
of  four  atoms  of  coppn  to  one  of  zinc;  but,  bj  changing  the  pro- 


of Ac  mcials,  a  ranety  of  shades  of  gold  lustre, 
countofeit  jewidrj,  are  obtained,  b  dw  prc^portion  of  equal  parts 
of  copper  and  zine,  imd  MtUkr  is  prodnced|  this  is  used  in  solder- 
ing togeAer  sm&ces  of  bnai  and  copper. 

OfUmL 

This  metal  exists  in  nature,  Tery  extensirely  difinsed,  and  in  a 
Turiety  of  forms.  The  Hulphsff,  phosphate,  arseaiate,  car- 
and  chloride  of  lead  are  found  natiTe  ;  but  it  is  exclosirely 
die  salphuret  of  lead,  g«2ena,  that  the  metal  is  extracted  for 
1^  puiposes  «^  covnmerce.  The  methods  used  in  its  redaction 
huTe  bran  Tery  fully  descrihed  in  die  preceding  chapter,  p.  3^. 
Lead  is  one  of  due  softest  and  least  tenacious  of  the  metals  ;  it  is 
white,  and  Tery  brilliant,  hut  rapidly  tarnishes  in  the  air,  be- 
c<rrered  with  a  gnjidft  coating,  beyond  which  the  action 
does  not  a^ear  to  extend;  its  ^ecific  graTitr  is  11-44  ;  it  melts  at 
613^,  and  in  solidifying  diminiiAes  in  Tolume,  so  that  it  is  unfit  for 
accunte  castings  ;  it  may,  howerer,  be  obtained,  by  fusion,  crystal- 
lized in  octobedrons  ;  it  is  not  Tolatile  ;  it  is  not  sensiblT  acted  on 
by  muriatic  nor  sulphuric  acids,  exc^  at  Tery  high  temperatures, 
Iwt  by  nitric  aeid  it  is  rapidly  oxidized  and  disK^lred. 


OXIBES    OF    LBAH. 


Whes  lead  is  cnoMd  at  dKauwiiaie  to  air  a 
oeceda  witk  gieaf  nfidilj,  ao  as  to  be 
air  ^2^).    The  cxnie  so  fonBed  is 
Ua,  so  that  a^en  pare  mter,  laia,  or  erem 
preaenred  ia  leadea  ctitenis,  aa  iaqaegaalkm  vilk  lead  i 

habitaalij  as  a  ^oA,    Foftvaatelf ,  this  is  ohratfad, 

tile  aaiall  qaaatities  of 

aH 


ofitfioai 
OBtheiateriorortiMs 

it  froBi  ihe  oiidiilag  aetioB  af  the  air ;  ao  daager  is  tMtnJmm.  to 
he  ^ipicheBded  froat  the  sapplf  of  vater  to  a  otj 

lefas;for 
tke%cnoriociB 

for  its  iirotcctiom. 

ThesyabolofleadisFbsftoaiitaLatiaaaaie;  ite 
t3t94r9  or  103^.    It  r  iwdiiai  ■  vi&  ozjgcB  ia  two 


af  Lm£— Fh.0.    Eqairdeaft  139^  or  111-7.    TUa 
■Mjbe  prepared  hf  riposiag  ■tlillii  lead  at  a  red  heat  to  a  car- 

ao  prodaeed  laaea.    It  foraM,  oa  coalii^  crjatailBe  aaaaes  of  a 

arhich  is  gemeaStf  obtnaed  ia  the  capdbtioo  of  lead  for  tke  par- 
pose  of  extiattia^  feat  it  the  sBaU  qotitjr  of  alver  vhicb  its  ana 
gcBerallj  eoataiB.    Wkea  the  fitharge  is  kept  lor  ssbk  tiaM.  Ae 

heat.    This 

of  thecryalaBiaeforaiofthelilharge.    TW  tcIIow  lbr» 
to  be  wne  aeraaaeat  if  the  r 


bepndaeedoffhe 
ofleadata 
the  fasiaa  of  the  oxide. 

Tins  oxide  any  also  be  prepared  by 
of  lead  by  eaaade  potash  ;  a  vhke 

akydrateof  theo9ade,2FbL-fH.O.;  byagicatexceasof< 
ashthepncip^ateaiajbeiediaMdved.    The  oxide  of 
to  ha^e  the  power  af  aaitiaff  wi^  oMMt  of  tke 
to  forai  coBipoaai 

ed  by  bofliap  Ine  aad  filbuge  toveiher,  is  capable  af  • 
and  is  aaed  to  dye  the  hair  blade    The 
a  Uaek  aalpharet  of  lea 

<Aaage.    The  protoxide  of  lead  icqaiies  12,000  parts  of 
dissolve  k  ;  the  solatioa  reads  fc^lr  daliae ;  it  is  a 
aad  the  oaiy  oxide  of  kwd  which  co^Ums  with 
adeari^lVOU»«bl»a.db, 


396  OXIDES    AND     SULPHURET     OF     LEAD. 

in  chlorine  water,  or  in  a  solution  of  chloride  of  lirrie.  In  the  first 
case,  2Pb.O.  and  CI.  produce  Pb.Oa  and  Pb.Cl.  In  the  second  case, 
Pb.O.  and  Ca.O.Cl.  produce  Pb.O^  and  Ca.Cl.  ;  another  simple  plan 
consists  in  heating  red  lead,  which  is  a  compound  of  the  protoxide 
and  the  peroxide,  with  dilute  nitric  acid,  until  all  the  protoxide  is 
dissolved  out,  washing  the  residue  well,  and  drying  it  at  a  moderate 
heat.  The  peroxide  so  obtained  is  of  a  dull  dark  brown  colour  j 
when  heated  it  gives  off  half  its  oxygen,  leaving  litharge.  With 
muriatic  acid  it  produces  chlorine  and  protochloride  of  lead,  and 
with  sulphurous  acid,  which  it  rapidly  absorbs,  neutral  white  sul- 
phate of  lead,  Pb.Oa  and  S.O^  producing  Pb.O.  +  S.Og.  This  oxide 
of  lead  does  not  form  salts. 

The  Red  Lead,  or  Minium,  Pb304=2Pb.O.  +  Pb.02,  is  produced 
when  lead  is  oxidized,  so  that  the  oxide  formed  shall  not  be  fused, 
and  when  the  metal  is  all  converted  into  the  yellow  powder,  increas- 
ing the  heat  to  incipient  redness.  Oxygen  continues  to  be  absorbed 
until  one  third  of  the  metal  is  converted  into  peroxide,  giving  the 
constitution  above  expressed.  This  is  the  pure  red  lead,  the  colour 
of  which  is  exceedingly  brilliant ;  but  the  generality  of  red  lead 
found  in  commerce  contains  an  excess  of  protoxide,  which  may  be 
removed  by  boiling  in  a  solution  of  neutral  acetate  of  lead. 

When  red  lead  is  ignited,  it  gives  off  oxygen  and  becomes  pro- 
toxide ;  with  muriatic  acid  it  forms  protochloride  and  chlorine.  It 
does  not  form  any  proper  salts,  but  it  dissolves  in  acetic  acid  com- 
pletely, giving  a  colourless  liquor,  from  which,  after  a  little  time, 
peroxide  of  lead  separates. 

It  is  probable  that  there  exist  other  oxides  of  lead  ;  thus  the  gray 
coating  which  forms  on  lead  exposed  to  the  air  is  looked  upon  by 
many  chemists  as  a  suboxide  ;  and  on  heating  oxalate  of  lead  to  low 
redness,  a  gray  powder  is  obtained  of  a  similar  nature,  and  yields, 
on  analysis,  the  formula  PbaO.  In  general,  these  bodies  have  been 
considered  as  mixtures  of  the  metal  in  powder  with  the  real  pro- 
toxide J  but  I  think  the  evidence  of  their  definite  constitution  very 
strong. 

From  the  similarity  of  the  formula  of  red  lead,  Pb304,  to  those  of 
the  black  oxide  of  iron,  FcgO^,  and  of  the  red  oxide  of  manganese, 
Mn304,  it  has  been  suggested  that  it  may  contain  sesquioxide  of  lead, 
PbaOg,  similar  to  FcaOa  and  MnjOg.  The  formula  of  red  lead  should 
then  become  Pb.O.+PbiOa ;  but  this  idea,  though  interesting,  is  only 
hypothetical. 

Sulphuret  of  Lead. — There  is  but  one  compound  of  sulphur  and 
lead,  the  protosulphuret,  Pb.S.  It  constitutes  the  abundant  lead 
ore,  galena,  and  may  be  formed  artificially,  either  by  fusing  together 
lead  and  sulphur,  or  by  decomposing  a  solution  of  a  salt  of  lead  by 
sulphuretted  hydrogen  gas  or  hydrosulphuret  of  ammonia.  It  is 
then  a  black  powder,  insoluble  in  water,  and  in  alkalies,  and  dilute 
acids.  It  is  rapidly  oxidized  by  nitric  acid,  being  converted  into 
sulphate  of  lead.  From  the  perfect  insolubility  and  marked  colour 
of  this  sulphuret,  a  salt  of  lead  and  sulphuretted  hydrogen  are  re- 
spectively the  most  delicate  reagents  for  each  other. 

There  are  some  indications  of  the  existence  of  other  sulphuret* 
of  lead,  which,  however,  do  not  require  special  notice.     If  a  salt  o[ 


DETECTION     AND     USES     OF     LEA  D. B  I  S  M  U  T  H.  397 

lead  be  decomposed  by  bisulphuret  of  calcium,  a  red  precipitate  ap- 
pears, possibly  a  bisulphuret  of  lead^  analogous  to  the  deutoxide,  and 
galena  may  be  fused  with  metallic  lead,  forming  a  homogeneous 
mass,  in  which,  probably,  subsulphurets  are  contained. 

The  detection  of  lead  is  simplified  very  much  by  its  forming  but 
one  series  of  salts,  those  of  the  protoxide.  Its  solutions  are  recog- 
nised by  giving,  with  caustic  potash,  a  white  precipitate,  soluble  in 
excess  ;  with  carbonate  of  potash,  one  also  white,  but  insoluble  in 
excess;  with  sulphuretted  hydrogen,  one  dark  brown  or  black, 
whose  characters  are  described  above ;  Mdth  a  solution  of  bichro- 
mate of  potash,  the  salts  of  lead  produce  a  fine  yellow  precipitate, 
chrome  yellow  ;  and  with  iodide  of  potassium,  the  iodide  of  lead,  in 
brilliant  yellow  scales,  like  fragments  of  gold  leaf.  Yellow  prussiate 
of  potash  gives  a  white  precipitate,  and  sulphate  of  soda  a  white 
sulphate  of  lead,  insoluble  in  water,  but  not  insoluble  in  acids.  If 
the  solution  contain  much  lead,  any  soluble  chloride  throws  down 
sparingly  soluble  chloride  of  lead,  which,  however,  remains  dissolv- 
ed, if  the  solution  be  dilute. 

Lead  and  its  preparations  are  of  the  most  extensive  use  in  the  arts. 
In  making  pipes  and  cisterns,  sulphuric  acid  chambers,  bullets,  and 
a  variety  of  other  purposes,  the  metal  is  employed  unaltered ;  and 
its  alloys  are  also  of  important  application.  Thus  the  metal  of  which 
printing  types  are  made  consists  of  three  parts  of  lead  to  one  of 
antimony.  The  inferior  sorts  of  pewter  are  alloys  of  lead  and  tin, 
but  the  fine  kinds  should  be  tin  with  very  little  lead,  and  some  anti- 
mony and  bismuth.  The  solder  used  for  soldering  surfaces  of  lead, 
or  of  tinned  iron,  to  each  other,  consists  of  lead  and  tin,  the  propor- 
tions of  which  vary  from  two  parts  of  tin  and  one  of  lead,  to  three 
parts  of  lead  and  one  of  tin,  according  to  the  object.  The  more  tin 
the  alloy  contains,  the  more  fusible  it  is.  Fine  solder  fuses  at  360°, 
coarse  solder  at  500°. 

Of  Bismuth. 

Bismuth  is  not  a  common  metal.  It  is  found  but  in  a  few  places, 
and  only  in  the  metallic  state  in  quantity,  for  the  sulphuret  of  bis- 
muth is  too  rare  to  be  of  technical  interest.  '  It  is  extracted  from 
the  rocks  through  which  it  is  disseminated  by  reducing  them  to 
coarse  powder,  and  igniting  this  in  a  kind  of  kiln  ;  the  bismuth,  being 
very  fusible,  melts  out,  and  collects  at  the  bottom  in  a  trough  pla- 
ced to  receive  it. 

It  is  a  white  metal,  with  a  peculiar  reddish  shade,  and  remarkably 
crystalline  structure.  It  may  be  obtained  in  separate  crystals  of 
considerable  size,  which  are  cubes,  generally  hollow  at  the  sides. 
To  obtain  good  crystals,  the  metal  should  be  perfectly  pure  ;  this 
is  effected  by  deflagrating  some  nitre  on  the  surface  of  the  melted 
metal ;  the  impurities  are  more  easily  oxidized  than  the  bismuth,  and 
hence  pass  into  the  scoriae  which  form  on  the  surface.  The  crys- 
tals so  obtained  have  frequently  beautiful  rainbow  tints  on  their  sur- 
face, from  an  exceedingly  thin  layer  of  oxide  of  bismuth  by  which 
they  become  coated. 

Bismuth  is  very  brittle  and  easily  oxidized.  It  is  scarcely  acted 
on  by  sulphuric  or  muriatic  acid,  but  it  decomposes  nitric  acid  vio- 


398  BISMUTH     AND     ITS     COMPOUNDS. 

lently,  evolving  nitric  oxide,  and  forming  oxide  of  bismuth,  with 
which  the  nitric  acid  combines.  It  fuses  at  497^^,  is  volatile  at  a  white 
heat,  and  then  burns  with  a  bluish-white  flame.     Its  sp.  gr.  is  9-9. 

The  symbol  of  bismuth  is  Bi.  Concerning  its  equivalent,  there  is 
some  doubt  at  present  as  to  whether  it  should  be  886*9,  or  three 
times  so  much,  2660*7,  on  the  oxygen  scale,  and  hence  71*1,  or 
213*3,  on  the  hydrogen  scale. 

The  first  number  assumed  would  make  the  oxide  of  bismuth  a  protoxide,  Bi.O,, 
the  last  a  teroxide,  Bi.Oa.  The  ground  upon  which  the  former  view  stands  is  the 
supposed  similarity  of  some  salts  of  bismuth  to  those  of  magnesia  and  the  protoxide 
of  copper,  but  recent  examination  has  gone  to  show  that  this  analogy  is  not  at  all 
so  strong  as  had  been  supposed,  and  that  their  diiierence  is  more  remarkable  than 
their  resemblance.  On  the  other  hand,  the  sulphuret  of  bismuth  is  isomorphous 
with  the  sulphurets  of  antimony  and  arsenic,  and  the  equivalent  deduced  from  the 
specific  heat  of  bismuth  agrees  with  those  for  arsenic  and  antimony,  and  assigns 
the  same  constitution  to  the  compounds  of  the  three.  The  salts  of  the  oxide  of  bis- 
muth are  exceedingly  instable,  and,  like  those  of  antimony,  are  decomposed  by  wa- 
ter, so  that,  while  it  allies  itself  to  that  metal  in  every  important  point  of  physical 
and  chemical  characters,  it  recedes  in  all  the  important  facts  of  its  history  from  cop- 
per, iron,  zinc,  and  the  other  metals  of  the  magnesian  class,  I  therefore  think 
these  are  suflicient  grounds  for  abandoning  the  numbers  8869  and 71-1,  given  in  the 
table,  p.  205,  and  to  assume  2660-7  and  213-3,  as  the  equivalents  of  bismuth  on  the 
oxygen  and  hydrogen  scales  respectively. 

Oxide  of  Bismuth — Bi.Og ;  equivalent  2960*7  or  237*3 — may  be 
prepared  by  the  combustion  of  bismuth  at  a  high  temperature,  or  by 
the  ignition  of  the  subnitrate  of  bismuth.  It  is  a  bufl*-coloured  pow- 
der, which  may  be  melted.  It  combines  with  acids  to  form  well- 
characterized  salts. 

The  Superoxide  of  Bismuth,  Bi.Og,  is  prepared  by  boiling  finely- 
levigated  oxide  of  bismuth  in  a  solution  of  chloride  of  soda.  A  fine 
brown  powder  is  produced,  which  is  freed  with  great  difficulty  from 
admixed  unaltered  oxide.  When  heated  to  dull  redness  it  is  decom- 
posed into  oxygen  and  oxide  of  bismuth  ;  with  muriatic  acid  it  gives 
chlorine  and  ordinary  chloride  of  bismuth.  Its  composition  was 
supposed  to  corroborate  the  idea  that  the  yellow  oxide  was  a  pro- 
toxide, for  on  that  idea  this  would  be  a  sesquioxide,  Bi203,  like  the 
sesquioxides  of  cobalt  and  nickel,  which  it  resembles  so  much  in 
properties ;  but  the  formula,  Bi.Oa,  agrees  as  well  with  the  analyti- 
cal results,  and  I  look  upon  it  as  corresponding  to  antimonic  acid. 

Sulphuret  of  Bismuth,  Bi.Sg,  exists  native,  in  crystals  isomorphous 
with  the  sulphurets  of  antimony  and  arsenic.  It  may  be  prepared 
by  fusing  bismuth  and  sulphur  together,  or  by  adding  sulphuretted 
hydrogen  to  a  solution  of  a  salt  of  bismuth :  it  then  precipitates  as 
a  brown  powder.  It  is  insoluble  in  water  and  in  hydrosulphuret 
of  ammonia. 

Bismuth  is  easily  known  by  its  solutions  being  precipitated  brown 
by  sulphuretted  hydrogen  and  by  iodide  of  potassium,  and  yellow 
by  chromate  of  potash.  The  caustic  and  carbonated  alkalies  pro- 
duce a  white  precipitate  of  hydrated  oxide  of  bismuth,  which  is  in- 
soluble in  excess.  A  strong  solution  of  a  salt  of  bismuth  is  decom- 
posed by  the  addition  of  water,  whereby  a  white  basic  salt  is  pre- 
cipitated, and  the  liquor  contains  free  acid. 

Bismuth  is  extensively  employed  for  some  purposes  in  the  arts. 
The  alloy  used  for  casting  stereotype  plates  consists  of  tin,  lead, 
and  bismuth  j  and  by  increasing  the  quantity  of  bismuth,  the  fusibil- 


EXTRACTION     OF      SILVER    FROM     ITS     ORE.        399 

ity  of  this  alloy  becomes  so  great,  that  a  compound  of  two  parts  of 
bismuth,  one  of  tin,  and  one  of  lead,  fuses  at  201°.  This  is  the  fu- 
sible metal  used  for  the  bath  in  taking  the  specific  gravities  of  va- 
pours, as  described  p.  14,  and  for  supplying  a  steady  source  of 
heat  for  other  purposes. 

SECTION  VI. 

METALS    OF    THE    SIXTH    CLASS. 

Of  Silver. 

This  metal  exists  native,  and  in  the  state  of  sulphuret,  in  a  great 
variety  of  places  j  and  from  the  facility  with  which  it  may  be  ex- 
tracted, and  the  permanence  of  its  lustre,  it  became  known  at  a  very 
early  period.  The  principal  sources  of  silver  are  the  mines  of 
South  America ;  in  Europe,  those  of  Saxony  are  the  most  remark- 
able. A  great  deal  of  silver  is  also  obtained  from  the  ores  of  lead, 
the  sulphuret  of  lead  being  generally  accompanied  by  the  sulphuret 
of  silver  in  small  quantity. 

The  native  silver  of  America  exists,  generally  speaking,  too  fine- 
ly disseminated  to  be  simply  melted  out.  It  is  washed  out  by  mer- 
cury, this  fluid  metal  dissolving  the  silver,  and  being  then  distilled 
off,  leaves  the  precious  metal  behind.  A  very  remarkable  process 
is  used  to  extract  the  silver  from  the  sulphuret.  This  ore  is  roast- 
ed in  a  reverberatory  furnace  with  chloride  of  sodium,  by  which 
chloride  of  silver  and  sulphuret  of  sodium  are  formed,  Ag.S.  and 
Na.Cl.  giving  Ag.Cl.  and  Na.S.  This  last  is  washed  out,  and  then 
the  chloride  of  silver  being  put  into  barrels  with  some  water,  pieces 
of  iron,  and  mercury,  the  iron  decomposes  the  chloride  of  silver, 
forming  chloride  of  iron  and  setting  the  silver  free,  and  this  dis- 
solves in  the  mercury,  forming  a  fluid  amalgam  ;  this  is  strained 
through  leather  bags,  by  which  a  great  part  of  the  mercury  passes 
off,  and  a  pulpy  mass  of  amalgam  of  silver  is  obtained,  which  is  then 
submitted  to  distillation,  by  which  the  mercury  is  separated,  and  the 
silver  remains  pure. 

The  method  of  extraction  of  the  silver  which  accompanies  the 
lead,  in  galena,  is  founded  on  the  greater  rapidity  with  which  lead 
combines  with  oxygen.  In  the  smelting  of  the  ore,  the  silver  is  re- 
duced with  the  lead,  and  the  resulting  impure  metal  is  melted  in  a 
shallow  porous  dish  made  of  bone  ashes,  and  when  at  a  full  red  heat 
a  current  of  air  is  urged  across  it  from  powerful  bellows.  The  lead 
becomes  converted  into  litharge,  as  described  in  p.  395,  and  new 
coatings  of  oxide  of  lead  succeed  one  another  upon  the  surface, 
until  the  whole  quantity  of  that  metal  has  been  removed.  When 
the  silver  remains  pure,  the  surface  becomes  suddenly  brilliant,  and 
the  completion  of  the  work  is  known  by  the  metal  thus  flashing  or 
lightening^  as  it  is  technically  termed.  This  is  the  process  of  cupeU 
lation.  The  porous  bone  earth  capsule,  or  cupel^  absorbs  a  great 
deal  of  the  litharge,  and  the  rest  is  blown  away  from  the  surface, 
as  it  forms,  by  the  blast  of  air,  and  is  collected  in  the  front  of  the 
furnace. 

This  process  has  been  remarkably  shortened  by  the  discovery 


400  PROPERTIES     OF     SILVER. 

that  the  quantity  of  silver  may  be  concentrated  in  a  comparatively 
small  quantity  of  lead,  by  crystallization.  The  silver  is  not  diffused 
uniformly  through  all  the  lead,  but  combined  in  atomic  proportions 
with  a  certain  quantity  of  it,  forming  an  alloy,  which  is  then  mixed 
with  the  excess  of  lead.  This  alloy  is  more  fusible  than  lead,  so 
that  when  a  large  basin  of  lead,  containing  a  small  quantity  of  sil- 
ver, is  melted,  and  allowed  to  cool  very  slowly,  so  as  to  crystallize, 
the  portions  which  first  solidify  are  pure  lead,  and  these  being  re- 
moved with  iron  colanders,  all  the  silver  remains  in  the  mother  li- 
quor. The  process  must  be  stopped,  however,  before  this  begins 
to  congeal.  By  a  succession  of  crystallization  of  this  sort  the  great 
excess  of  lead  is  gradually  got  rid  of,  and  the  quantity  to  be  oxi- 
dized at  the  cupel  diminished  in  a  corresponding  degree. 

The  silver  of  commerce  is  never  pure,  and  hence,  for  chemical 
purposes,  must  be  freed  from  the  metals,  generally  copper,  associa- 
ted with  it.  For  this  purpose  it  is  dissolved  in  nitric  acid,  and  its 
solution  precipitated  by  common  salt.  Chloride  of  silver  separates, 
which  is  then  reduced  by  any  of  the  methods  described  in  p.  332, 
333.  The  method  of  assaying  may  also  be  used  to  obtain  pure  sil- 
ver. The  impure  silver  is  melted  with  from  four  to  eight  times  its 
weight  of  lead,  and  this  alloy  cupelled  as, already  detailed  ;  the  lead 
is  not  only  itself  oxidized,  but  the  other  metals  present,  which  would 
not  otherwise  separate,  are  converted  into  oxides,  which  pass  off 
with  the  oxide  of  lead.  It  is  in  this  way  that  the  standard  alloys 
of  silver,  for  coinage  and  plate,  are  verified  at  the  mint  and  other 
offices. 

Silver,  when  completely  pure,  is  very  brilliant ;  it  is  the  whitest 
of  the  metals,  and  takes  a  fine  polish.  It  is  very  ductile  and  malle- 
able. Its  sp.  gr.  is  10  5;  it  fuses  at  1873^.  It  is  not  altered  byair 
or  water,  but  when  kept  melted  for  a  considerable  time,  it  absorbs 
oxygen,  which  it  appears  to  hold  rather  dissolved  than  combined, 
for  on  solidifying  it  discharges  this  oxygen,  by  which  the  surface  is 
thrown  into  irregular  granulations.  The  quantity  of  oxygen  may 
be  so  great  as  twenty  times  the  volume  of  the  metal. 

Silver  is  very  soft.  It  is  hence  necessary,  in  coin,  and  in  articles 
for  domestic  use,  to  add  a  certain  quantity  of  copper,  to  render  it 
less  liable  to  deterioration  from  use  or  in  being  cleaned. 

When  silver  is  exposed  to  the  air,  it  gradually  tarnishes,  which  is 
due,  not  to  the  formation  of  oxide,  laut  of  sulphuret,  the  air  always 
containing  traces  of  sulphuretted  hydrogen,  derived  from  organic 
bodies.  It  is  not  acted  on  by  sulphuric  or  muriatic  acid,  but  is  rap- 
idly dissolved  by  nitric  acid,  with  evolution  of  nitric  oxide  gas. 

Silver  combines  with  oxygen  in  three  proportions,  forming  ox- 
ides, of  which  only  one,  the  protoxide,  is  well  known.  The  equiv- 
alent of  silver  is  1351-6  or  108-3,  and  its  symbol  is'Ag.,  from  the 
Latin  name. 

Protoxide  of  Silver — Ag.O. ;  equivalent  145 1-6  or  116-3 — may 
be  prepared  by  adding  caustic  potash,  or  lime  water,  to  a  solution 
of  nitrate  of  silver.  A  brown  powder  is  thrown  down,  which  may  be 
dried  at  a  gentle  heat  without  alteration.  It  then  becomes  very 
dark.  When  heated  strongly,  it  is  decomposed  into  oxygen  and 
metallic  silver,  and  this  takes  place  even  at  ordinary  temperatures. 


SULPHURET     OF     SILVER.  401 

if  It  be  in  contact  with  organic  matter.  It  neutralizes  the  strongest 
acids,  as  the  sulphuric  and  nitric,  and  forms  well-characterized  salts. 
It  is  not  acted  on  by  the  fixed  alkalies,  but  with  ammonia  it  gives 
fulminating  silver^  one  of  a  series  of  bodies  to  be  hereafter  examined. 
When  citrate  of  silver  is  heated  to  212"^  in  a  current  of  hydrogen 
gas,  the  metal  is  not  reduced,  as  should  have  occurred  with  the  pure 
oxide,  but  one  half  of  the  oxygen  is  removed,  and  the  citric  acid 
remains  combined  with  the  suboxide  of  silver^  AgjO.  This  salt  dis- 
solves in  water,  the  solution  being  brown,  and  giving  a  brown  pre- 
cipitate of  suboxide  with  potash.  When  a  solution  of  this  salt  is 
heated,  it  becomes  colourless,  contains  a  salt  of  the  peroxide,  and 
metallic  silver  separates.  Some  other  silver  salts  of  organic  acids 
give  the  same  result  with  hydrogen  gas.  When  a  solution  of  ni- 
trate of  silver  is  decomposed  by  the  battery,  a  substance  is  deposited 
upon  the  positive  electrode  in  needles,  sometimes  half  an  inch  long. 
These  are  resolved  by  sulphuric  acid  into  protoxide  of  silver  and 
oxygen,  and  give,  with  muriatic  acid,  chloride  of  silver  and  free 
chlorine.  They  are,  therefore,  crystals  oi  peroxide  of  silver^  proba- 
bly Ag.O,. 

Although  silver  does  not  combine  with  oxygen  directly,  yet  when 
it  is  heated  in  contact  with  glass,  it  stains  this  of  a  deep  yellow  or 
orange  colour,  being  converted  into  oxide. 

Sulphuret  of  Silver,  equivalent  1552*8  or  124''4),  exists  native 
pure,  and  also  in  combination  with  other  metallic  sulphurets,  par- 
ticularly those  of  lead,  antimony,  copper,  and  arsenic,  forming  a  va- 
riety of  minerals.  It  is  the  most  common  o*e  of  silver.  It  may 
be  formed  artificially  by  fusing  together  sulphur  and  silver,  the  ex- 
cess of  sulphur  being  expelled  by  the  heat.  Silver  has,  indeed,  a 
remarkable  affinity  for  sulphur,  so  that  it  even  decomposes  sulphu- 
retted hydrogen,  and  hence  arises  the  tarnishing  of  silver  when  ex- 
posed to  the  atmosphere.  An  exceedingly  delicate  test  for  sulphur 
in  a  solid  body  consists  in  igniting  a  minute  fragment  of  it  on  char- 
coal, in  the  reducing  flame  of  the  blowpipe ;  the  fused  globule  is  to 
be  then  laid  on  a  bright  surface  of  silver,  as  on  a  clean  shilling,  and 
moistened;  if  there  be  a  trace  of  sulphur  in  the  substance,  a  black 
or  olive  spot  will  form  on  the  silver  where  it  is  moistened. 

The  sulphuret  of  silver  may  be  formed  also  in  the  wet  way,  by 
adding  sulphuretted  hydrogen  or  hydrosulphuret  of  ammonia  to  a 
solution  of  a  salt  of  silver.  It  forms  as  a  black  powder,  which  is 
not  soluble  in  an  excess  of  the  precipitant.  This  sulphuret  is  a 
powerful  sulphur  base,  and  in  its  native  forms  is  generally  associa- 
ted with  negative  metallic  sulphurets. 

The  detection  of  silver  is  very  easy  ;  from  the  facility  with  which 
its  oxide  is  reduced  to  the  metallic  state,  its  solutions  are  precipi- 
tated by  the  sulphites,  by  protosulphate  of  iron,  and  by  protochlo- 
ride  of  tin,  the  silver  being  reduced.  A  solution  of  common  salt 
or  muriatic  acid  gives  a  white  curdy  precipitate  of  chloride  of  sil- 
ver, which  is  insoluble  in  water  and  in  acids,  but  dissolves  in  water 
of  ammonia  ;  when  exposed  to  light  in  contact  with  organic  matter, 
the  chloride  of  silver  becomes  tinged  violet  or  black,  owing  to  the 
formation  of  a  subchloride;  on  this  is  founded  its  application  in 
photography,  described  p.  173.     The  solutions  of  silver  give,  with 

E  E  E 


402    MERCURY,     ITS    EXTRACTION     FROM     ITS    ORE. 

iodide  of  potassium,  a  canary-yellow  precipitate,  insoluble  in  ammo- 
nia, and  with  sulphuretted  hydrogen  a  deep  brown  sulphuret  of 
silver. 

The  uses  of  silver  are  well  known  j  its  advantages  as  a  medium 
of  exchange  depend  on  the  steadiness  of  the  quantity  of  it  brought 
into  commerce,  which  preveiits  great  changes  in  its  value,  and  on 
its  not  being  corroded  or  worn  down  by  ordinary  agents.  In  'i  pure 
state  it  would,  however,  be  too  soft  to  be  used  as  coin,  and  is  hence 
hardened  by  being  alloyed,  in  the  proportions  of  222  parts  to  18  of 
copper;  this  is  the  standard  silver  of  the  mint ;  the  silver  used  for 
the  purposes  of  luxury  contain  a  greater,  but  a  variable  quantity  o'' 
copper. 

Of  Mercury y  or  Quicksilver. 

From  the  remarkable  properties  of  this  metal,  and  its  occurring  in 
the  metallic  state  in  nature,  it  has  attracted  much  attention  from 
the  earliest  ages,  and  formed  the  object  of  the  most  elaborate  in- 
quiries of  the  older  chemists.  Its  volatility  and  the  variety  of  its 
compounds  made  it  enter  into  the  theories  of  that  period  as  an  im- 
portant element,  and  hence  there  is,  perhaps,  no  metal  concerning 
which  so  much  valuable  knowledge  was  obtained  in  the  infancy  of 
chemistry. 

Mercury  is  found  native,  and  also  combined  with  gold  and  silver, 
but  its  most  abundant  ore  is  the  native  sulphuret,  cinnabar ;  from 
this  it  is  extracted  by  one  or  other  of  two  processes.  The  first  con- 
sists in  distilling  the  ore  with  lime,  or  with  iron  in  small  pieces ;  in 
the  first  case,  Hg.S.  and  Ca.O.  produce  Ca.S.,  while  Hg.  and  0.  pass 
off,  the  temperature  being  too  high  to  allow  of  the  formation  of  ox- 
ide of  mercury ;  in  the  second  case,  Hg.S.  and  Fe.  produce  Fe.S. 
and  Hg.  j  this  process  is  carried  on  in  long  furnaces,  in  which  are 
arranged  numbers  of  earthen  or  iron  retorts,  to  which  are  adapted 
receivers,  in  which  the  mercurial  vapours  condense.  The  other 
plan,  which  is  that  now  adopted  in  the  hest  arranged  works,  con- 
sists of  a  kiln,  like  that  in  which  the  pyrites  is  roasted  for  the  man- 
ufacture of  oil  of  vitriol :  below,  there  is  a  grate  on  which  is  lighted 
a  fire  of  brushwood ;  over  this  is  a  light  arch  of  fire-brick,  with  nu 
merous  perforations,  and  on  this  js  arranged  the  cinnabar,  the  poor- 
est kinds  being  placed  below,  until  the  kiln  is  filled  nearly  to  the 
orifice  of  the  chimney,  which  passes  off  at  the  side ;  the  fire  com- 
municating to  the  ore,  the  sulphur  contained  in  it  burns,  and  the 
mercury  is  set  free,  Hg.S.  and  20.  producing  S.O2  and  Hg.  The 
kiln  is  so  hot  that  the  metal  is  completely  volatilized,  and  the  mixed 
vapour  of  mercury  and  sulphurous  acid  gas  are  carried  by  the 
draught  into  the  chimney,  which  leads  into  a  wide  chamber  of  brick- 
work, the  sides  of  which  are  hung  with  leather ;  on  these  the  mer- 
cury condenses  in  drops,  which  gradually  flow  down  and  collect  on 
the  floor,  while  the  sulphurous  acid  gas  passes  away  by  a  small 
chimney  at  the  farther  end,  by  means  of  which  the  continuous  com 
bustion  of  the  ore  is  sustained;  at  certain  periods,  an  aperture  in 
the  side  of  this  chamber  is  opened,  and  the  mercury  which  had  col- 
lected is  withdrawn. 

The  mercury  is  sent  into  commerce  in  iron  bottles,  but  generally 


OXIDES     OP     MERCURY.  403 

in  a  very  impure  state,  it  being  intentionally  adulterated  with  the 
alloy  of  tin,  lead,  and  bismuth,  already  noticed  p.  398,  of  which  it 
can  dissolve  large  quantities.  It  may  be  purified  by  distillation,  or 
by  being  left  for  some  time  in  contact  with  dilute  nitric  acid.  The 
mercury,  having  less  affinity  for  oxygen  than  any  of  the  other  metals 
present,  is  the  last  to  dissolve,  and  as  soon  as  the  liquor  is  found  to 
contain  mercury,  the  metal  remaining  may  be  looked  upon  as  pure. 

Mercury  is  distinguished  by  being  liquid  at  ordinary  tempera- 
tures j  this,  together  with  its  resemblance  to  silver  in  brilliancy,  is 
the  origin  of  its  various  names,  hydrargyrum  (ydoyp  apyvpeog),  quick- 
silver^ argentum  vivum.  If  pure,  it  is  not  tarnished  by  exposure  to 
the  air,  but  in  damp  air  its  impurities  become  oxidized  very  rapidly, 
in  consequence  of  a  complete  galvanic  circuit  being  formed  with 
the  mercury  and  the  other  metals  present.  At  39^  it  becomes  solid, 
and  crystallizes  in  octohedronsj  it  then  contracts  very  much;  its 
sp.  gr.  being  135  when  liquid,  and  14*0  when  solid.  At  662°  it 
boils,  and  forms  a  colourless  vapour,  the  sp.  gr.  of  which  is  6978. 
At  and  just  below  its  boiling  point  it  absorbs  oxygen  from  the  air, 
forming  oxide,  which  at  a  red  heat  is  again  decomposed. 

Mercurj'^  is  not  acted  on  at  common  temperatures  by  sulphuric  or 
muriatic  acid ;  nitric  acid  oxidizes  it  rapidly,  the  nature  of  the  pro- 
duct varying  with  the  circumstances.  Boiling  oil  of  vitriol  is  de- 
composed by  mercury,  sulphurous  acid  being  evolved,  and  oxide  of 
mercury  produced.  There  are  two  oxides  of  mercury,  a  suboxide 
and  a  protoxide.  The  symbol  of  mercury  is  Hg.,  from  its  Latin 
name,  and  its  equivalent  is  1265'8  or  101*4. 

Suboxide  of  Mercury.— Yig^O.  Equivalent  2631-6  or  210-8.  This 
oxide  is  the  basis  of  many  important  preparations,  and  is  best  pre- 
pared by  decomposing  calomel  (subchloride  of  mercury)  by  a  solu- 
tion of  potash.  The  calomel  being  insoluble,  the  action  must  be 
favoured  by  mixing  the  two  together  well  by  agitation  in  a  mortar  ; 
a  black  powder  is  produced,  which  must  be  dried  in  the  dark,  and 
by  a  very  gentle  heat.  In  this  process,  HgaCl.  and  K.O.  produce 
K.Cl.  and  Hg^O.  Lime  water  may  be  used  in  place  of  potash. 
When  this  suboxide,  or,  as  it  is  often  called,  black  oxide  of  mercury, 
is  heated,  it  is  resolved  into  metallic  mercury  and  the  protoxide, 
and  this  change  occurs  slowly  at  ordinary  temperatures  if  it  be  ex- 
posed to  the  light.  This  oxide  combines  with  acids  and  forms  well 
characterized  salts. 

Protoxide  of  Mercury — Hg.O.  j  equivalent  1365*8  or  109*4 — may 
be  prepared  in  a  variety  of  ways :  1st.  By  exposing  mercury  for  a 
long  time  to  the  action  of  the  air,  at  a  temperature  just  below  its 
boiling  point,  it  is  gradually  converted  into  small  deep  red  crystals 
of  this  oxide ;  in  this  state  it  was  the  red  precipitate  per  se  of  the 
older  chemists.  2d.  By  heating  crystals  of  nitrate  of  mercury  until 
all  the  water  and  nitric  acid  have  been  expelled,  the  oxide  remam- 
ing  is  a  crystalline  powder  of  an  orange-red  colour,  the  red  precipi- 
tate by  nitric  acid.  3d.  When  a  solution  of  chloride  of  mercury  (cor- 
rosive sublimate)  is  decomposed  by  caustic  potash  or  lime  water, 
Hg.Cl.  and  K.O.  produce  K.Cl.  and  Hg.O.  It  is  thus  obtained  as  a 
canary-yellow  hydrate,  which,  however,  when  dried,  becomes  deeper 
coloured.  The  red  precipitate  also,  when  finely  divided,  assumes  the 
same  yellow  tint. 


404  SULPHURETS     OF    MERCURY. 

This  oxide  of  mercury  is  slightly  soluble  in  water.  The  solution 
browns  turmeric  paper  slightly,  and  restores  the  blue  colour  of  red- 
dened litmus.  It  combines  with  acids,  forming  a  numerous  and  im- 
portant class  of  sdlts.  At  a  full  red  heat  it  is  totally  resolved  into 
mercury  and  oxygen,  as  described  fully  in  page  242.  It  changea 
its  colour  remarkably  with  the  temperature,  becoming  nearly  black 
when  very  hot. 

Subsulphuret  of  Mercury^  Hg^S.,  may  be  prepared  by  decomposing 
any  salt  of  the  suboxide  by  hydrosulphuret  of  ammonia.  It  is  a 
black  powder,  which,  on  the  application  of  heat,  is  decomposed 
into  the  protosulphuret  and  metallic  mercury. 

Protosulphuret  of  Mercury — Hg.S.  j  equivalent  1467  or  117*5 — con 
stitutes  the  native  cinnabar,  the  usual  ore  of  quicksilver.  It  may 
be  prepared  artificially  by  fusing  sulphur  in  a  crucible,  and  adding 
thereto  six  times  its  weight  of  mercury;  they  combine  with  the 
evolution  of  considerable  heat.  The  mass  must  be  stirred  frequent- 
ly to  favour  their  union,  and  covered  in  order  to  prevent  the  sul- 
phur from  burning  away.  In  this  state  it  is  black,  but  when  sub- 
limed at  a  red  heat  in  glass  vessels,  it  becomes  deep  red,  constitu- 
ting factitious  cinnabar^  and  this,  when  levigated,  and  exposed  to 
strong  light,  in  flat  dishes  covered  with  a  thin  layer  of  water,  grad- 
ually assumes  a  very  brilliant  colour,  and  forms  the  pigment  vermil- 
ion. This  sulphuret  may  also  be  prepared  by  adding  to  a  solution 
of  corrosive  sublimate  an  excess  of  hydrosulphuret  of  ammonia  or 
sulphuret  of  hydrogen  ]  it  is  then  a  dense  black  powder.  It  may, 
however,  be  obtained  red,  but  not  so  bright  as  vermilion,  in  the  wet 
■way,  by  digesting  white  precipitate  (chloramide  of  mercury)  with 
hydrosulphuret  of  ammonia,  to  which  an  excess  of  sulphur  has  been 
added.  The  sulphuret  of  mercury  forms  at  first  black,  but  after 
some  time  becomes  red,  which  colour  may  be  brightened  by  the 
action  of  a  warm  solution  of  caustic  potash. 

The  phosphurets  and  seleniurets  of  mercury  are  of  no  importance. 
The  presence  of  mercury  in  solution  is  very  easily  ascertained. 
By  the  immersion  of  a  clean  slip  of  copper,  the  mercury  is  precipi- 
tated in  the  metallic  state,  as  a  gray  powder  on  the  surface  of  the 
copper.  With  a  magnifying-glass,  this  is  found  to  consist  of  mi- 
nute but  brilliant  globules,  and  the  surface  becomes  brilliant  when 
rubbed.  Protochloride  of  tin  and  phosphorous  acid  also  precipitate 
the  mercury  in  the  metallic  state,  which,  by  boiling,  aggregates  into 
larger  globules,  easily  collected  and  recognised.  Any  solid  body 
containing  mercury  gives,  when  ignited  in  a  tube  of  hard  glass,  par- 
ticularly on  the  addition  of  a  little  carbonate  of  potash,  a  sublimate 
of  metallic  mercury,  which,  if  in  very  small  quantity,  appears  only 
as  a  ring  of  gray  powder,  but  is  found  to  consist  of  brilliant  glob- 
ules when  inspected  with  a  lens. 

The  two  classes  of  salts  which  quicksilver  forms  are  very  dis- 
tinctly characterized  by  their  behaviour  to  reagents.  The  salts  of 
the  suboxide  give  with  the  caustic  alkalies  black  or  gray  precipi- 
tates. Sulphuretted  hydrogen  produces  the  black  subsulphuret. 
Solution  of  chloride  of  sodium  gives  a  white  precipitate,  which  is 
calomel,  and  the  bichromate  of  potash  produces  an  orange  chromate 
of  the  suboxide. 


EXTRACTION     AND     PROPERTIES     OF     GOLD.      405 

The  salts  of  the  red  oxide  are  precipitated,  yellowish  by  an  excess 
of  caustic  potash,  and  white  by  ammonia  ;  with  sulphuretted  hydro- 
gen in  excess,  a  black  precipitate  of  protosulphuret ;  and  with  iodide 
of  potassium,  a  red  precipitate,  which  is  redissolved  in  an  excess. 

In  many  cases,  the  appearance  of  these  precipitates  varies  with 
the  nature  of  the  acid  with  which  the  oxide  of  mercury  had  been 
combined  j  but  in  all  cases  ammonia  gives  a  black  precipitate  with 
the  salts  of  the  suboxide,  and  a  white  precipitate  with  those  of  the 
red  oxide,  in  the  cold. 

There  is  a  class  of  pharmaceutical  preparations  obtained  by  trit- 
urating mercury  with  other  inactive  substances.  In  these  the  mer 
cury  is  only  reduced  to  a  state  of  very  minute  division  j  it  is  not 
oxidized.  By  triturating  mercury  with  sulphur,  however,  a  certain 
quantity  of  sulphuret  is  formed,  although  the  great  mass  of  the  met- 
al and  of  the  sulphur  remains  uncombined. 

Of  Gold. 

This  valuable  metal  is  found  only  in  the  metallic  state,  either 
pure  or  alloyed  with  other  metals,  particularly  silver,  tellurium,  and 
mercury ;  the  rocks  in  which  it  is  found  distributed  are  generally 
those  of  igneous  origin,  but  the  greater  part  of  the  gold  of  com- 
merce is  obtained  by  washing  the  sands  of  the  rivers  which  have 
their  source  in  such  mountains,  the  particles  of  metal  being  carried 
down  with  the  detritus  of  the  rock,  and,  from  their  greater  density, 
being  deposited  first  when  the  sand  is  washed  ;  any  fragments  large 
enough  to  be  visible  are  separated  by  the  hand,  but  the  remainder 
is  dissolved  out  by  a  process  of  amalgamation,  similar  to  that  de- 
scribed, p.  399,  for  the  extraction  of  native  silver.  When  the  gold 
is  alloyed  with  silver,  they  are  separated  by  means  of  nitric  acid, 
which  dissolves  the  latter  metal ;  but  if  the  quantity  present  be  small, 
the  gold  protects  it  from  the  action  of  the  acid,  and  a  process  term- 
ed quartation  is  employed ;  this  consists  in  alloying  the  gold  with 
three  times  its  weight  of  silver,  and  then  acting  on  the  mass  with 
nitric  acid ;  when  the  solution  of  the  silver  has  once  commenced,  it 
does  not  cease  until  the  entire  quantity  present  has  been  removed. 

Pure  gold  is  yellow,  very  malleable  and  ductile,  and  nearly  as 
soft  as  lead  ;  hence,  for  the  purposes  of  commerce  and  of  the  coin- 
age, it  is  alloyed  with  a  quantity  of  copper,  amounting  to  83  in  1000. 
Instances  of  the  exceeding  degree  of  division  to  which  this  metal 
may  be  reduced,  have  been  given,  p.  15.  Gold  has  no  tendency  to 
combine  with  oxygen  or  sulphur,  and  hence  retains  its  brilliancy  in 
the  open  air  for  any  length  of  time.  It  melts  at  2016^ ;  its  density 
is  19*5  ;  it  is  not  acted  on  by  any  single  acid,  but  is  dissolved  by  ni- 
tromuriatic    acid,  and  by  a  mixture  of  nitric  and  hydrofluoric  acids. 

The  symbol  of  gold  is  Au.,  from  its  Latin  name,  and  its  equiva- 
lent numbers  are  2486  or  199*2. 

There  are  two  oxides  of  gold,  obtained  by  the  decomposition  of 
the  corresponding  chlorides,  which  will  be  hereafter  described. 
The  deutoxide  of  gold,  Au.Oa,  is  a  green  powder,  which  does  not 
combine  with  acids,  but  dissolves  in  solution  of  caustic  potash,  and 
soon  separates  into  the  higher  oxide  and  metallic  gold.  The  perox 
ide  of  gold,  auric  acid,  Au.Og,  is  best  prepared  by  decomposing  per 


:| 


406  PROPERTIES     OF     GOL  D. P  A  L  L  A  D  I  U  M. 

chloride  of  gold  by  an  excess  of  magnesia  ;  chloride  of  magnesium 
dissolves,  and  an  insoluble  aurate  of  magnesia  remains ;  this  is  to 
be  then  digested  in  cold  dilute  nitric  acid,  which  dissolves  out  the 
magnesia  with  a  little  auric  acid,  but  leaves  the  greater  part  of 
this  last  behind  as  a  reddish  hydrate,  which,  when  dried  in  the  air, 
becomes  brown,  and  at  212°  gives  off  water,  and  remains  black. 
This  substance  does  not  combine  with  any  acid  j  by  muriatic  acid 
it  is  decomposed,  perchloride  of  gold  being  formed  j  it  combines 
,  with  alkalies  strongly,  so  that  the  precipitate  given  by  a  solution  of 
gold  with  a  caustic  alkali  is  always  a  compound  of  auric  acid  with 
the  base ;  there  are  soluble  and  insoluble  aurates,  but  their  atomic 
constitution  has  not  been  studied.  Solutions  of  auric  acid,  and  even 
that  body  in  powder,  are  decomposed  rapidly  on  exposure  to  the 
light,  metallic  gold  being  separated. 

Gold  is  deposited  from  its  solutions  by  means  of  any  of  the  de- 
oxidizing agents  noticed  under  silver  and  mercury.  Protosulphate 
of  iron  gives  a  brown  powder,  which,  under  the  burnisher,  assumes 
the  colour  and  brilliancy  of  the  metal  j  protochloride  of  tin  produ- 
ces a  fine  purple  precipitate,  the  purple  of  Cassius^  which  is  not  me- 
tallic gold,  but  it  appears  to  be  a  compound  of  oxide  of  tin  and  a 
suboxide  of  gold,  for  it  is  perfectly  soluble  in  water  of  ammonia, 
and  mercury  digested  on  it  does  not  dissolve  out  any  metallic  gold. 
Various  processes  are  given  for  this  preparation,  which  it  is  not 
easy  to  obtain  of  the  proper  depth  and  purity  of  colour ;  when  ex- 
posed to  a  red  heat,  it  is  changed  into  a  mixture  of  peroxide  of  tin 
and  metallic  gold,  but  its  purple  colour  remains  j  it  is  hence  employ- 
ed for  painting  on  glass  and  porcelain.  When  metallic  gold  is  heat- 
ed on  the  surface  of  glass,  it  appears  to  become  oxidized,  and  in 
that  state  to  combine  with  the  glass,  staining  it  a  rich  purple  col- 
our. 

Sulphur  and  gold  combine  to  form  sulphurets  similar  in  constitu- 
tion to  the  oxides;  they  are  produced  by  decomposing  the  corre- 
sponding chlorides  by  sulphuretted  hydrogen  ;  they  are  brown  pow- 
ders, which  are  strong  sulphur  acids,  and  dissolve  in  hydrosulphu- 
ret  of  ammonia. 

The  uses  of  gold  are  well  known.  The  commercial  value  of  its 
alloys  is  ascertained,  either  by  cupellation,  p.  399,  by  quartation,  p. 
405,  or  by  the  touchstone,  which  is  a  variety  of  flinty  slate  (Lydian 
stone)  or  basalt,  of  a  uniform  black  colour.  A  streak  is  drawn  on 
the  surface  of  the  stone  with  the  piece  of  gold  to  be  tried,  and  this 
is  compared  with  those  given  by  a  series  of  alloys,  the  composition 
of  which  is  known,  until  one  is  found  identical  in  aspect  with  it, 
which  must  result  from  the  two  being  of  the  same  degree  of  purity. 
In  these  trials  it  is  necessary,  however,  to  know  beforehand  wheth- 
er the  alloy  is  silver  or  copper,  or  whether,  as  frequently  occurs, 
both  be  present. 

Of  Palladium. 
This  metal  is  found  associated  with  platinum,  but  seldom  consti- 
tutes more  than  one  per  cent,  of  the  ore.     After  the  platinum  has 
been  precipitated  from  the  solution  in  aqua  regia,  by  means  of  sal 
ammoniac,  cyanide  of  mercury  is  added,  by  which  all  the  palladium 


COMPOUNDS     OF     PALLADIU  M.-»-P  L  A  T  I  N  U  M.       407 

is  thrown  down  as  cyanide;  this,  when  ignited,  is  totally  decom- 
posed, and  metallic  palladium  remains. 

The  general  characters  of  palladium  are  very  similar  to  those  of 
platinum  ;  it  is  white,  almost  infusible,  but  admits  of  being  welded ; 
it  is  malleable  and  ductile  ;  specific  gravity  11-5.  When  heated 
below  ignition,  its  surface  becomes  blue  and  green,  from  the  forma- 
tion of  a  thin  layer  of  suboxide ;  but  by  a  stronger  heat  this  is  re- 
duced, and  the  metal  becomes  bright.  Palladium  is  not  sensibly 
acted  on  by  muriatic  or  sulphuric  acid,  but  it  dissolves  in  nitric 
acid  with  facility.  The  symbol  of  palladium  is  Pd.,  and  its  atomic 
weight  665-9  or  53-4. 

There  are  three  oxides  of  palladium,  of  which  only  one,  the  protoxide — Pd.O. ; 
equivalent  7659  or  61-4 — has  been  as  yet  studied  with  much  care  ;  this  oxide  is  form- 
ed when  palladium  dissolves  in  nitric  acid,  and  is  obtained  as  a  black  powder  when 
the  nitrate  is  decomposed  at  a  temperature  below  redness ;  by  the  addition  of  potash 
to  a  salt  of  palladium,  this  oxide  is  thrown  down,  hydrated,  as  a  brown  powder. 
If  the  protoxide  of  palladium  be  exposed  to  a  dull  .red  heat,  it  parts  with  half  itis 
oxygen,  and  a  suboxide,  PdzO.jis  produced,  which  gives  a  series  of  salts,  resembling 
in  general  characters  those  of  the  suboxide  of  copper. 

By  decomposing  the  bichloride  of  palladium  with  carbonate  of  potash,  the  deuiox- 
ide,  Fd.02,  is  obtained  as  a  yellowish  brown  powder;  it  appears  to  combine  both  with 
acids  and  alkalies,  but  of  its  properties  very  little  is  known. 

There  are  sulphurets  of  Palladimn,  which  correspond  to  the  oxides,  but  farther  than 
that  they  are  brown  powders,  generated  by  the  action  of  sulphuret  of  hydrogen  on 
the  respective  chlorides,  they  have  not  been  much  examined. 

Palladium  in  solution  is  at  once  recognised  by  giving  with  ammonia  a  flesh-red 
precipitate,  which  redissolves  in  an  excess,  giving  a  colourless  solution ;  with  cya- 
nide of  mercury  it  produces  a  whitish  precipitate,  and  with  iodide  of  potassium,  a 
black  powder. 

Of  Platinum, 

Platinum  was  originally  discovered  in  the  sands  of  some  South 
American  rivers,  and  from  its  similarity  to  silver  (plata),  obtained 
the  name  of  platina  (little  silver).  It  has  since  been  found  more 
abundantly  in  the  mountains  of  the  Oural,  which  separate  European 
from  Asiatic  Russia.  The  supply  of  platinum  has  increased  so 
much  lately,  that  a  coinage  of  it,  issued  some  years  ago  by  the 
Russian  government,  was  obliged  to  be  recalled,  from  the  rapid 
diminution  in  value  which  it  underwent. 

The  platinum  exists  native,  but  is  associated  with  a  great  number 
of  metals,  particularly  four,  remarkable  for  not  being  found  except 
along  with  it.  The  grains  of  metal  are  disseminated  in  rocks  of 
igneous  origin  (granite,  syenite),  and  in  the  sands  of  rivers  which 
flow  over  them.  The  processes  for  the  extraction  of  platinum  from 
the  crude  ore  are  very  complex,  and  as  the  working  of  it  has  be- 
come a  branch  of  manufacture,  the  chemist  always  obtains  the  pure 
metal  in  commerce,  and  its  details  need  not  be  inserted. 

Pure  platinum  is  white  like  silver,  but  not  so  brilliant.  It  is  the 
densest  of  all  bodies,  its  sp.  gr.  being  21-5.  It  is  very  malleable 
and  ductile.  It  is  infusible  except  by  the  hydro-oxygen  blow^pipe,  but 
at  a  high  temperature  may  be  welded  like  iron,  and  thus  worked 
into  the  various  forms  in  which  it  is  employed  in  the  chemical  arts. 
Platinum  may  also  exist  in  a  state  of  minute  division,  and  thereby 
becomes  useful  in  many  operations,  particularly  those  of  slow  com- 
bustion, as  noticed  in  p.  180,  250,  287.  The  finely-divided  platinum 
18  of  two  kinds,  spongy  platinum  and  platinum-black.     The  former  is 


408  COMPOUNDS     OF     PLATINUM. 

prepared  by  dissolving  chloride  of  platinum  and  sal  ammoniac  sep- 
arately in  alcohol,  and  mixing  the  solutions;  the  double  chloride  of 
platinum  and  ammonium  is  thus  produced  as  a  fine  yellow  powder, 
which,  while  yet  moist,  is  to  be  made  into  balls  like  peas,  and  heat- 
ed to  full  redness.  The  chlorine  is  all  carried  off  by  the  hydrogen 
of  the  ammonia,  and  the  platinum  remains  as  a  light  gray  sponge, 
in  the  form  of  the  little  balls ;  it  is  this  kind  of  platinum  that  is 
used  in  the  aphlogi&tic  lamp,  in  the  eudiometer,  and  for  other  pur- 
poses already  noticed.  The  platinum-black  may  be  obtained  either 
by  precipitating  a  solution  of  bichloride  of  platinum  with  zinc,  and 
boiling  the  precipitate  in  muriatic  acid  for  a  few  minutes ;  or,  bet- 
ter, by  dissolving  protochloride  of  platinum  in  a  boiling  solution  of 
potash,  and  adding  thereto  alcohol,  in  small  quantities  at  a  time, 
until  all  effervescence  ceases ;  a  jet-black  precipitate  is  produced, 
which  is  to  be  boiled  successively  with  alcohol,  muriatic  acid,  and 
potash,  and,  finally,  four  or  five  times  in  water.  The  substance 
thus  obtained  is  pure  metallic  platinum,  but  it  is  a  dull  black  pow- 
der. It  absorbs  oxygen  in  considerable  quantity,  and  hence,  when 
brought  into  an  atmosphere  of  any  inflammable  vapour,  it  facilitates 
the  combination  of  the  two  with  remarkable  energy.  Dccbereiner 
terms  it  an  oxyphorus  from  this  property.  Many  interesting  reac- 
tions in  organic  chemistry  succeed  only  by  the  aid  of  this  platinum- 
black. 

Platinum  has  no  tendency  to  combine  with  the  oxygen  of  the 
air,  but  it  is  oxidized  slightly  when  nitre  or  even  potash  is  fused  in 
contact  with  it.  It  resists  the  action  of  all  acids  except  the  nitro- 
muriatic  acid  and  the  nitro-hydrofiuoric  acids,  and  in  these  it  dis- 
solves more  slowly  than  gold. 

The  symbol  of  platinum  is  PI.  Its  equivalent  is  1233*5  or  98-8. 
By  the  decomposition  of  the  chlorides  of  platinum,  two  oxides  of  it 
are  obtained. 

Protoxide  of  Platinum— Ft. O. ;  equivalent  1333-5  or  1068 — is  produced  by  digest- 
ing the  protochloride  with  as  much  potash  as  exactly  suffices  for  its  decomposition. 
An  excess  of  potash  dissolves  it,  forming  a  dark  olive  liquor.  When  pure  it  is  a 
black  powder,  easily  decomposed  by  heat  into  platinum  and  oxygen.  It  combines 
with  acids,  fonning  salts,  which  have  been  as  yet  but  little  studied. 

Deutoxide  of  Platinum. — Pt.02.  Equivalent  1433-5  or  114-8.  This  substance  has 
a  remarkable  tendency  to  combine  with  bases,  and  hence  cannot  be  obtained  pure 
by  the  direct  decomposition  of  the  chloride,  as  it  carries  down  with  it,  always,  a 
quantity  of  the  alkali  employed,  if  this  be  in  excess ;  and  if  it  be  not,  then  only  a 
basic  chloride  is  obtained.  The  nitrate  of  platinum,  however,  when  decomposed 
by  soda,  yields  one  half  of  the  oxide  of  platinum,  pure,  but  hydrated,  forming  a 
brown  powder  like  the  peroxide  of  iron;  when  anhydrous,  it  is  black ;  by  heat  it  is 
resolved  into  oxygen  and  platinum.  This  oxide  appears  to  form  two  kinds  of  salts, 
one  with  acids,  in  which  it  is  the  base,  and  the  other  with  alkalies  and  earths,  in 
which  it  is  the  acid.    In  another  place  I  shall  notice  them  farther. 

There  are  two  sulphurets  of  Platinum  corresponding  to  the  two  oxides.  The  first, 
Pt.S.,  is  produced  by  digesting  the  protochloride  with  sulphuret  of  hydrogen.  It  is 
a  deep  brown  powder,  decomposed  by  a  red  heat,  but  not  otherwise  interesting.  The 
bisulphuret,  Pt.Sg,  is  produced  in  a  similar  way  by  adding  sulphuret  of  hydrogen  to 
a  solution  of  bichloride  of  platinum.  It  is  a  brown  powder,  which  absorbs  oxygen 
rapidly  even  in  drying,  and  becomes  acid.  By  nitric  acid  it  is  converted  with  in- 
tense action  into  sulphate  of  platinum. 

Phosphurets  and  seleniurets  of  platinum  have  been  formed,  but  they  are  not  im- 
portant. 

The  detection  of  platinum  is  effected  easily  by  precipitating  its 
solution  by  a  slip  of  zinc,  when  a  black  powder  separates,  soluble 


IRIDIUM     AND     RHODIUM.  409 

only  in  aqua  regia,  and  then  giving  with  reagents  the  following  re- 
sults. A  solution  of  sal  ammoniac  in  alcohol  gives  a  fine  yellow 
crystalline  precipitate  ',  a  solution  of  iodide  of  potassium  a  black 
precipitate,  which  dissolves  in  an  excess,  producing  a  rich  crimson 
solution ;  with  sulphuret  of  hydrogen,  the  brown  bisulphuret  of  pla- 
tinum j  and  with  protochloride  of  tin,  a  chocolate  precipitate  or  a 
deep  reddish  solution,  according  to  the  quantity  present. 

The  action  of  this  last  reagent  is  founded  on  the  reduction  of  the 
bichloride  of  platinum  to  the  state  of  protochloride  by  the  first  por- 
tion of  protochloride  of  tin  employed.  This  test  acts,  therefore, 
also  with  solutions  of  the  protoxide  of  platinum,  and  the  metal  may 
be  also  known  to  be  in  the  state  of  protoxide,  when,  on  the  appli- 
cation of  iodide  of  potassium  in  excess,  the  liquor  is  not  coloured 
red,  but  becomes  so  on  the  addition  of  a  drop  of  nitric  acid  or  chlo- 
rine water. 

The  great  use  of  platinum  is  for  the  manufacture  of  the  large 
boilers  used  in  the  concentration  of  oil  of  vitriol  j  it  is  also  univer- 
sally employed  as  the  material  for  the  crucibles  used  in  the  more 
delicate  operations  of  mineral  analysis.  Indeed,  the  accuracy  now 
attained  in  that  department  of  research  is  in  a  great  part  due  to  the 
introduction  of  platinum  vessels  into  the  laboratory ;  it  is  also  ac- 
casionally  used  in  enamelling  on  glass  and  porcelain. 

Of  Iridium  and  Rhodium. 

These  metals  are,  like  palladium  and  iridium,  found  only  associated  with  plati- 
num, and  are  extracted  from  the  crude  ore  already  noticed;  the  iridium  and  osmium 
are,  however,  united,  forming  an  alloy,  the  crystalline  grains  of  which  are  merely 
mixed  with  the  particles  of  the  platinum  ore  in  which  the  rhodium  and  palladium 
are  contained ;  when  the  platina  ore  is  dissolved  in  aqua  regia,  the  iridium  and  os- 
mium ore  remains  undissolved,  and  requires  to  be  treated  by  fusion  with  caustic 
potash ;  the  iridium  then  becomes  oxidized,  and  combines  with  the  alkali.  The  pro- 
cesses of  puriticalion  need  not  be  inserted. 

Metallic  iridium  resembles  platinum,  but  is  still  more  infusible ;  when  fused  by 
the  voltaic  battery,  it  is  white  and  very  brilliant;  specific  gravity  18-68  ;  after  being 
strongly  heated,  it  is  insoluble  in  acids,  but  when  obtained  in  the  spongy  form  by 
the  reduction  of  its  oxides  by  hydrogen  at  a  red  heat,  it  becomess  lightly  oxidizedf, 
and  is  soluble  in  aqua  regia. 

Iridium  combines  with  oxygen  in  four  proportions ;  its  symbol  is  Ir.,  and  its  equiv- 
alent 1233-5  or  98-8,  the  same  as  that  of  platinum. 

Protoxide  of  Iridium,  Ir.O.,  is  obtained  by  decomposing  the  protochloride  by  car- 
bonate of  potash;  it  appears  as  a  greenish-grav  hydrate ;  this  oxide  combines  with 
acids.  The  scsquioxide,  IriOs,  is  tliat  formed  when  the  metal  is  ignited  with  potash; 
it  is  a  bluish-black  powder,  and  is  the  most  permanent  of  the  oxides ;  it  is  not  decom- 
posed except  at  a  heat  above  the  melting  point  of  silver,  whereas  the  higher  and 
lower  degrees  pass  into  it  on  the  application  of  heat.  This  oxide  unites  with  acids, 
giving  dark  blood-red  coloured  salts.  The  deuloxide  of  Iridium,  Ir.O 2,  exists  com- 
bined with  acids,  but  has  not  been  isolated.  The  peroxide,  Ir.Oa,  is  formed  in  small 
quantity  when  iridium  is  ignited  with  nitre,  but  is  best  prepared  by  the  decomposf 
tion  of  the  perchloride.  Solutions  containing  salts  of  the  protoxide  and  of  the  per- 
oxide together,  present  a  great  variety  of  shades  of  purple  and  blue,  and  hence  gave 
origin  to  the  name  oi  the  metal  (Iris). 

Rhodium.— This  metal  remains  dissolved  in  the  nitromuriatic  solution  of  the  pla- 
tinum ore  after  the  platinum  and  palladium  have  been  separated  from  it ;  for  the 
mode  of  eliminating  it  from  the  many  metals  which  still  remain,  I  refer  to  the  sys- 
tematic works. 

Metallic  rhodium  is  obtained  by  the  decomposition  of  its  chloride  at  a  red  heat  by 
hydrogen  gas ;  when  rendered  coherent  by  pressure,  it  is  white,  but  very  brittle  and 
hard ;  sp.  gr.  about  11-0.  If  completely  pure,  it  is  not  acted  on  even  by  aqua  regia, 
but  it  illustrates  remarkably  the  principle  of  communicated  affinity,  described  p. 

Fff 


410  GENERAL     CHARACTERS     OF     SALTS. 

237;  for,  when  alloyed  with  copper,  lead,  or  platina,  it  dissolves  along  with  the  othei 
metal  in  aqua  regia.  Rhodium  derives  its  name  from  the  beautiful  rose  (podo^)  col- 
our of  its  solutions ;  it  combines  with  oxygen  in  two  proportions ;  its  symbol  is  R., 
and  its  equivalent  661-4  or  52.2. 

Of  the  protoxide  of  Rhodium,  it  is  only  known  that  it  exists  in  certain  salts  that 
have  been  but  little  examined ;  the  sesquioxide,  R^Os,  is  the  basis  of  the  most  impor- 
tant compounds  of  this  metal.  It  is  prepared  by  igniting  metallic  rhodium  with  a 
mixture  of  caustic  potash  and  nitre;  a  brown  mass  is  formed,  Avhich,  when  decom- 
posed by  muriatic  acid,  yields  the  oxide  as  a  gray  hydrate,  insoluble  in  acids.  Ber- 
zelius  is  of  opinion  that  there  are  two  isomeric  forms  of  this  oxide,  the  salts  of  one 
being  yellow  in  solution,  and  those  of  the  other  being  rose-coloured.  There  are  sup- 
posed to  exist,  also,  complex  oxides  of  rhodium,  resembling,  probably,  the  complex 
oxides  of  iron  and  manganese.  The  equivalent  of  rhodium  is  so  nearly  equal  to 
that  of  palladium,  that  some  relations  might  be  expected  in  the  constitution  of  their 
combinations,  which,  as  yet,  does  not  appear  to  have  been  experimentally  investi- 
gated. 


CHAPTER  XIV. 

ON    THE    GENERAL    PROPERTIES    AND  CONSTITUTION    OF    SALTS. 

The  bodies  included  under  the  name  of  salts  may  be  arranged  in 
two  classes,  characterized  by  a  remarkable  difference  of  chemical 
constitution  j  the  first  comprehends  such  as  are  formed  by  the  union 
of  a  simple  body  of  the  chlorine  family  with  a  metal ;  thus  chloride 
of  sodium,  iodide  of  potassium,  bromide  of  iron,  fluoride  of  calcium, 
are  of  this  kind.  The  salts  of  the  second  class,  on  the  contrary, 
are  formed  by  the  union  of  substances  already  compound,  and  pos- 
sessed of  those  opposite  properties  by  which  one  is  determined  to^ 
be  an  acid  and  the  other  a  base.  The  general  characters  of  acids" 
and  bases,  and  of  the  salts  formed  by  their  union,  have  been  suffi- 
ciently described  in  many  places  already  (p.  151,  154,  157),  and 
need  not  be  here  repeated.  In  general,  the  acids  and  bases  so  en- 
gaged contain  oxygen  as  their  electro-negative  ingredient ;  but  there 
are  classes  of  salts  formed  by  the  Union  of  sulphur  acids  and  sul- 
phur bases,  and,  as  noticed  in  p.  238  and  294,  selenium  and  tellurium 
resemble  oxygen  and  sulphur  in  this  respect.  The  history  of  the 
metallic  compounds  in  the  last  chapter  affords  many  cases  of  the 
existence  of  such  salts,  and  in  the  detailed  history  of  the  more  im- 
portant salts  which  will  follow,  others  will  be  described  ;  but  there 
are  some  points  of  more  general  interest,  touching  the  salts  as  a 
class,  the  laws  of  formation  to  which  they  are  subjected,  and  the 
relations  between  their  several  subdivisions,  which  I  shall  now  pro- 
ceed to  notice  as  briefly  as  the  subject  will  admit. 

I  have  frequently  adverted  to  the  circum«tance  that  the  bodies 
termed  hydracids  were  in  reality  not  acids,  but  compounds  of  hy- 
drogen, in  which  that  element  acted  as  a  positive  metallic  constitu- 
ent ;  and  that,  when  they  act  on  a  metallic  oxide,  double  decomposi- 
tion generally  occurs,  precisely  as  when  a  chloride  or  iodide  of 
zinc  or  copper  is  decomposed  by  potash  or  by  soda.  Thus  Cl.H. 
and  K.O.  produce  Cl.K.  and  H.O.,  precisely  as  when  Cl.Cu.  and  K.O. 


GENERAL     CHARACTERS     OF     SALTS.  411 

produce  Cl.K.  and  Cu.O.  The  chlorides  and  iodides  of  hydrogen, 
although  popularly  called  acids  (muriatic  and  hydriodic  acids),  are 
thus  really  salts,  and  in  all  their  reactions  display  that  constitu- 
tion. Also,  when  a  hydracid  is  put  in  contact  with  a  metal,  the 
solution  of  it  is  determined  altogether  by  its  power  of  expelling  the 
hydrogen  and  of  taking  its  place.  From  Cl.H.  and  Zn.  there  are 
produced  Cl.Zn.,  and  H.  becomes  free,  precisely  as  chloride  of  cop- 
per, Cu.CL,  is  decomposed  by  zinc,  copper  being  precipitated.  The 
hydracids,  therefore,  do  not  unite  with  metallic  oxides  to  form  salts, 
but  they  decompose  them,  water  being  evolved. 

The  hydracids  are  capable  of  forming  what  are  termed  acid-salts ; 
thus  the  fluoride  of  potassium  combines  with  hydrofluoric  acid  to 
form  an  acid  compound ;  the  chloride  of  hydrogen  combines  with 
chloride  of  gold :  but  these  bodies  are  really  double  salts.  The 
compounds  of  hydrogen,  in  such  combinations,  resembling  the  cor- 
responding compounds  of  zinc,  copper,  &c.,  which,  under  the  same 
circumstances,  all  form  corresponding  double  salts. 

I  have  already  described  the  functions  of  water  in  the  hydrates 
of  the  ordinary  oxygen  acids:  these  are  salts  of  water,  subject  to 
the  same  rules  of  composition  as  the  ordinary  salts  of  the  same 
acid.  When  such  an  acid,  as,  for  example,  oil  of  vitriol,  S.O3-I-H.O., 
acts  upon  a  metallic  oxide,  the  water  is  displaced,  and  a  salt  of  the 
metallic  oxide  formed.  When  such  a  hydrated  acid  acts  on  a  met- 
al, this  may  be  dissolved  either  by  substitution  for,  and  displacement 
of  the  hydrogen,  as  in  the  ordinary  cases  of  obtaining  that  gas,  01' 
by  the  direct  decomposition  of  a  part  of  the  acid,  as  in  the  process- 
es for  obtaining  sulphurous  acid  and  nitric  oxide  (p.  285,  274). 

Salts  may  be  either  neutral^  acid,  or  basic.  A  salt  is  neutral  which 
does  not  manifest,  in  its  action  on  vegetable  colours,  acid  or  alka- 
line properties,  and  consists  generally  of  one  equivalent  of  acid 
united  to  one  equivalent  of  base,  this  last  containing  one  equivalent 
of  oxygen.  The  true  neutral  salts  have,  therefore,  for  bases,  either 
suboxides  or  protoxides.  The  salts  of  sesquioxides  and  deutoxides 
generally  react  like  acids,  except  where  there  is  an  excess  of  base. 
The  quantity  of  acid  with  which  metallic  oxides  are  disposed  to 
unite  in  their  most  neutral  salts,  is  subject  to  a  remarkable  propor- 
tion, being  one  equivalent  for  each  atom  of  oxygen  which  the  base 
contains.  Thus  a  protoxide  or  suboxide  combines  with  one  equiv- 
alent of  acid.  The  sulphate  of  zinc  is  Zn.O. .  S.O3  j  sulphate  of  cop 
per  Cu.O. .  S.O3  J  the  subnitrate  of  mercury,  Hg^O. .  N.O5.  A  sesqui- 
oxide  unites  with  three  equivalents  of  acid,  as  sulphate  of  alumina, 
AI2O3+3S.O3.  Salts  in  which  this  law  is  observed  to  hold  are  gen- 
erally described  as  neutral,  even  though  their  action  on  vegetable 
colours  may  indicate  a  preponderance  of  acid ;  and  understanding 
by  the  word,  not  the  absence  or  presence  of  the  property  of  chan- 
ging turmeric  or  litmus,  but  the  state  in  which  the  characteristic 
properties  of  acid  and  base  are  most  neutralized,  the  definition  of 
a  neutral  salt  may  best  be  that  in  which  the  number  of  atoms  of 
acid  is  equal  to  the  number  of  atoms  of  oxygen  in  the  base 

There  are  two  kinds  of  acid  salts  :  1st,  those  in  which  the  excess 
of  acid  is  present  in  its  hydrated  form  j  and,  2d,  those  in  which 
the  dry  acid  is  in  excess.     These  differ  remarkably  in  nature,  those 


412  GENERAL     CHARACTERS     OP     SALTS. 

of  the  first  class  being  not  really  acid  salts,  but  double  salts,  of  which 
one  base  is  water.  Thus  the  common  bisulphate  of  potash,  of  which 
the  formula  is  K.O. .  S.O3  +  H.O.  .  S.O3,  is  one  of  a  family  of  double 
salts,  in  which  sulphate  of  potash  is  united  to  a  sulphate  of  a  pro- 
toxide, as  sulphate  of  copper,  of  zinc,  of  iron,  or  of  magnesia.  There 
is  thus  really  no  excess  of  acid.  In  like  manner,  the  bicarbonate 
of  potash  is  a  double  carbonate  of  potash  and  water,  K.O. .  C.O^-j- 
H.O. .  C.O2,  to  which  similar  analogies  exist.  These  salts  resemble 
completely  the  acid  salts  of  the  hydracids,  described  in  the  begin- 
ning of  this  chapter  J  K.O. .  S.Oa-f-H.O. .  S.O3  corresponding  exact- 
ly to  K.F.+H.F. 

It  is  only  the  salts  which  do  not  contain  water  that  can  be  looked 
upon  as  having  a  true  excess  of  acid.  Of  these,  the  chromates  of 
potash  afford  the  best  examples,  in  which  an  atom  of  potash  is  com- 
bined with  one,  two,  or  three  equivalents  of  acid,  forming  K.O.-j- 
Cr.Oa,  K.O.+2Cr.03,  and  K.O.  +  SCr.Oa-  There  exists  a  similar 
compound  of  sulphuric  acid  and  potash,  which  is  easily  decomposed 
by  water,  being  changed  into  the  ordinary  bisulphate. 

Basic  salts  are  those  in  which  there  is  present  more  than  one 
equivalent  of  base  for  each  equivalent  of  acid  ;  thus,  in  turbeth  min- 
eral there  is  3Hg.O.  +  S.03j  in  basic  nitrate  of  copper,  3Cu.O. +  N. 
Og.H.O.;  in  basic  sulphate  of  copper,  4CU.O.-I-S.O3-I-4H.O.  It  has 
been  thought  that  the  proportion  of  base  in  basic  salts  bore  a  sim- 
ple relation  to  the  quantity  of  oxygen  in  the  acid,  being  generally 
equal  to  it.  This  idea  was  founded  on  the  circumstance  that  the 
early  analyses  of  many  basic  sulphates  gave  the  proportion  of  three 
atoms  of  base  to  one  of  acid  5  but  the  basic  sulphate  of  mercury  is 
the  only  example  I  have  found  really  to  exist  of  that  constitution, 
the  other  sulphates  containing  always  a  quantity  of  metallic  oxide, 
amounting  to  two,  or  four,  or  six  equivalents. 

The  first  and  most  remarkable  insight  into  the  constitution  of 
basic  salts  which  we  obtained  was  the  principle  laid  down  by  Gra- 
ham, that  all  salts  are  really  neutral  in  constitution.  The  analogies 
of  hydrogen  to  the  magnesian  family  of  metals,  and  hence  of  water 
to  the  oxides  of  that  class,  suggested  the  idea  that  the  excess  of 
base  should  not  be  considered  as  actually  combined  with  the  acid, 
but  that  it  replaced  the  water  of  crystallization  which  the  neutral 
salt  contains.  This  view  was  remarkably  supported  by  the  evi- 
dence of  the  basic  nitrates  adduced  by  Graham,  and  has  been  ex- 
tended to  the  chlorides  and  sulphates  by  my  own  investigations. 
Thus  nitrate  of  copper,  in  its  crystallized  and  neutral  condition,  is 
Cu.O.  .  N.O5  +  3H.O.,  and  the  basic  nitrate  is  formed  by  H.O. .  N.Oj 
+  3Cu.O.  Comparing  these  two  with  the  hydrated  nitric  acid,  sp. 
gr.  1*42,  the  formulas 

Nitrate  of  water,  =H.O. .  N.O5+3H.O. 

Nitrate  of  copper,  =Cu.O. .  N.O5+3H.O. 

Basic  nitrate  of  copper,  =H.O. .  N.Oa-j-SCu.O. 

evidently  correspond,  the  only  difference  being  that,  in  place  of 
oxide  of  hydrogen,  there  is  oxide  of  copper  substituted,  in  a  pro- 
portion continually  increasing.  From  these  conditions  it  follows, 
that  with  the  same  acid  and  base  there  may  be  formed  a  great  va- 


SALTS     OF      POLYBASIC     ACIDS. 


413 


riety  of  basic  salts ;  for  the  neutral  salt  may  crystallize  with  many 
different  proportions  of  water,  and  from  each  there  may  be  one  or 
more  basic  salts  derived,  by  substitution  of  metallic  oxide.  Thus 
the  sulphate  of  zinc  generally  contains  eight  atoms  of  base  to  one 
o(  acid  j  and  in  its  common  crystallized  form,  these  consist  of  one  of 
oxide  of  zinc  and  seven  of  water;  but  in  becoming  basic,  the  quan- 
tity of  oxide  of  zinc  gradually  increases,  and  a  series  of  basic  salts 
is  formed,  as 


S.03+Zn.O.-{-7H.O., 
S.03  +  4Zn.O.+4H.O., 


S.03+6Zn.O.  +  2H.O., 

S.Oa+SZn.O. 


The  salts,  consisting  of  a  simple  body  of  the  chlorine  family  uni- 
ted with  a  metal,  as  chloride  of  sodium,  iodide  of  potassium,  &c., 
and  which,  from  the  analogy  of  common  sah,  are  termed  haloid  salts 
(dXg  and  eidog),  combine  frequently  with  the  oxide  of  the  metal 
which  they  contain,  and  form  basic  haloid  salts.  Thus  we  have  Cu. 
CI.  +  3Cu.O.,  basic  chloride  of  copper;  Hg.Cl.-{-3Hg.O.,  basic  chlo- 
ride of  mercury  ;  Pb.I.  +  2Pb.O.,  basic  iodide  of  lead.  Such  com- 
pounds are,  however,  generally  termed  oxychlorides,  oxyiodides,  &c. ; 
they  are  subjected  to  precisely  the  same  laws  of  derivation  and  con- 
stitution as  the  basic  sahs  of  the  same  metals  with  ordinary  acids. 

From  what  has  been  said  above,  it  might  be  concluded  that  a 
neutral  salt  consisted  in  all  cases  of  one  equivalent  of  base  united 
to  one  of  acid,  and  that,  wherever  the  base  was  present  in  larger 
quantity,  the  salt  should  necessarily  be  termed  basic  ;  but  an  im- 
portant distinction  requires  to  be  here  laid  down.  There  are  three 
phosphates  of  silver,  which  contain  respectively  one,*two,  and  three 
atoms  of  oxide  of  silver  united  to  one  atom  of  acid ;  but  we  do  not 
consider  the  first  as  being  neutral,  and  the  others  as  containing  an 
excess  of  base,  for  we  find  them  to  arise  from  the  state  of  the  phos- 
phoric acid,  which,  according  as  it  has  been  combined  with  more 
or  less  basic  water,  gives  origin  to  classes  of  salts  containing  one, 
two,  or  three  equivalents  of  oxide.  The  peculiar  relations  of  the 
phosphoric  acid,  and  of  arsenic  acid  also,  to  water,  and  the  effect 
of  it  on  the  composition  of  these  salts,  have  been  noticed  already  in 
p.  297  and  377.  In  addition,  therefore,  to  ordinary  neutral  salts, 
which  are  monobasic,  or  contain  an  equivalent  of  base  and  one  of 
acid,  there  are  bibasic  and  tribasic  salts,  containing  respectively  two 
and  three  equivalents  of  base  to  one  of  acid,  and  yet  being  neutral  j 
by  which  is  meant,  not  that  they  are  without  action  on  test  paper, 
since  one  tribasic  salt  may  redden  litmus,  while  another  may  brown 
turmeric  paper,  but  that  they  are  derived  from  a  definite  combination 
of  the  acid  with  basic  water,  and  not  by  the  replacement  of  the  wa- 
ter of  crystallization  by  metallic  oxide,  as  in  the  case  of  real  basic 
salts. 

A  simple  distinction  between  bibasic  and  tribasic  salts  on  the  one 
hand,  and  ordinary  basic  salts  on  the  other,  is,  that  in  the  former 
the  different  atoms  of  base  may  be  of  different  kinds,  while  in  the 
latter  the  metallic  oxide  replacing  the  water  is  all  of  the  same  sort. 
Thus,  there  is  basic  sulphate  of  zinc  and  basic  sulphate  of  copper, 
but  there  could  not  be  a  basic  sulphate  partly  of  zinc  and  partly  of 
copper,  the  sulphuric  acid  being  monobasic.     But  there  is  a  tribasic 


414  ~     >    i.  DOUBLE      SALTS. 

*    ■ 

phosphate  of  soda,  ammonia,  and  water  j  another  of  magnesia,  am- 
monia, and  water  j  others  of  potash  and  water.  The  presence  ol 
two  or  more  bases  of  different  kinds  thus  distinguishing  completely 
the  salts  of  the  bibasic  and  tribasic  acids  from  the  ordinary  basic 
salts. 

These  principles,  which  are  now  of  the  highest  importance  in 
philosophical  chemistry,  were  first  applied  by  Graham  to  the  salts 
of  the  phosphoric  and  arsenic  acids,  but  they  have  been  found  to 
throw  light  upon  some  of  the  most  difficult  questions  in  the  history 
of  the  organic  acids,  of  which  a  great  number  have  been  shown  by 
Liebig  to  be  similarly  circumstanced. 

Double  salts  are  formed  by  the  union  of  two  simple  salts.  In  gen- 
eral, both  salts  contain  the  same  acid,  but  different  bases,  and  the 
two  bases  belong  to  different  natural  groups  j  as  when  sulphate  of 
potash  combines  with  the  sulphates  of  the  protoxides  of  the  metals 
of  the  second  isomorphous  group,  replacing  therein  the  atom  of 
constitutional  water  which  they  all  contain.  Thus  ordinary  sul* 
phate  of  zinc,  Zn.O.  .  S.O3 .  H.0.-|-6Aq.,  gives  with  K.O.  .  S.O3  the 
double  salt  (Zn.O.  .  S.O3+K.O.  .  S.03)+6Aq.;  and  sulphate  of  cop- 
per, Cu.O.  .  S.O3  .  H.0.-f4Aq., gives  (Cu.O.  .  S.Oa-^K.O.  .  S-OJ^- 
4Aq.  The  sulphate  of  potash  combines  also  with  the  sesquioxides 
of  the  third  isomorphous  group,  such  as  alumina,  and  gives  origin 
to  the  various  kinds  of  alums.  Similar  classes  of  salts  are  formed 
by  the  union  of  the  other  alkaline  sulphates  with  the  sulphates  of 
the  second  and  third  isomorphous  groups.  The  salts  of  isomorphous 
bases  with  the  same  acid  do  not  appear  capable  of  combining  so  as 
to  produce  double  salts,  but  in  crystallizing  are  mechanically  mix- 
ed (p.  31).  This  rule,  however,  is  not  without  exception,  as  the 
constant  composition  of  the  magnesian  limestone,  Ca.O.  .  C.02+Mg. 
O.  .  C.O2,  indicates  that  its  elements  are  chemically  united. 

Salts  of  different  acids  with  the  same  base  may  combine  to  form 
double  salts,  as  the  oxalate  and  nitrate  of  lead  ;  and  there  are  ex- 
amples, though  few,  of  a  double  salt  containing  two  acids  and  two 
bases. 

The  relations  of  salts  to  water  have  been  fully  discussed  under 
the  heads  of  solution  and  crystallization  (p.  22,  et  seq.),  and  of  the 
chemical  properties  of  water  (p.  253),  to  which  it  is  sufficient  to 
refer. 

The  haloid  salts  combine  together  to  form  double  salts,  as  the 
double  chloride  of  gold  and  sodium,  the  double  chloride  of  copper 
and  potassium,  and  conform  therein  to  the  same  general  principles 
that  have  been  just  described  for  the  oxygen  salts. 

It  has  been  always  mentioned,  that  when  muriatic  acid  acts  on  a 
metallic  oxide,  water  is  formed,  and  a  chloride  of  the  metal  produ- 
ced. The  question  of  whether  this  always  occurs  is  not  without 
interest,  and  has  been  often  agitated.  There  is  no  doubt  but  that 
It  is  the  general  rule,  but  I  am  inclined  to  think  it  may  not  be  with- 
out exception.  The  difference  of  properties  of  the  chlorides  of 
magnesium  and  of  aluminum  in  the  anhydrous  state  and  when  crys- 
tallized with  water,  is  so  great  as  to  give  reason  to  suppose  that 
these  chlorides  decompose  water,  and  that  the  crystallized  hydrated 
sails  are  not  AI2CI3-I-3H.O.  and  Mg.Cl.-f  H.O.,  but  AlA-f  3H,C1.  and 


CONSTITUTION    OF     ACIDS    AND    SALTS.  415 

Mg.O.-}-H.Cl.     Hence  it   is  probable  that  magnesia  and  alumina 
combine  with  hydracids  without  decomposition. 

The  sulphur  salts  consist  of  a  sulphur  acid,  which  is  generally  a 
sulphuret  of  an  electro-negative  metal  or  of  carbon,  combined  with 
a  sulphur  base,  which  is  a  sulphuret  of  an  electro-positive  metal. 
In  their  constitution  they  resemble  the  analogous  oxygen  salts. 
Many  of  their  characters  have  been  described  already  (p.  282,  386). 

The  positive  metallic  sulphurets  combine  frequently  with  the  ha- 
loid, or  oxygen  salts  of  the  same  metal,  to  form  basic  salts  \  this  is 
the  case  particularly  with  mercury.  Thus  there  is  Hg.O.  .  S.O3  + 
2Hg.S.,  similar  to  Hg.O.  .  S.03-|-2Hg.O.,  ordinary  turbeth  mineral. 

It  had  been  long  remarked  as  curious,  that  bodies  so  totally  dif- 
ferent in  composition  as  the  compound  of  chlorine  with  a  metal  on 
the  one  hand,  and  of  an  oxygen  acid  with  the  oxide  of  the  metal  on 
the  other,  should  be  so  similar  in  properties,  that  both  must  be 
classed  together  as  salts^  and  should  give  origin  to  series  of  basic 
and  acid  compounds  for  the  most  part  completely  parallel.  This 
difficulty  has  been  so  much  felt  by  the  most  enlightened  chemists, 
that  doubts  have  been  raised  as  to  whether  the  acid  and  base,  which 
are  placed  in  contact  to  form  by  their  union  an  oxygen  salt,  really 
exist  in  it  when  formed;  and  it  has  been  suggested  that  at  the  mo- 
ment of  union  a  new  arrangement  of  elements  takes  place,  by  which 
the  structure  of  the  resulting  salt  is  assimilated  to  that  of  a  com- 
pound of  chlorine  or  of  iodine  with  a  metal.  This  view,  at  first 
sight  so  far  fetched,  which  considers  that  in  Glauber's  salt  there  is 
neither  sulphuric  acid  nor  soda,  but  sulphur,  oxygen,  and  sodium, 
in  some  other  and  simpler  mode  of  combination,  is  now  very  exten- 
sively received  by  chemists;  and  I  shall  proceed,  therefore,  to  de- 
scribe, with  some  detail,  the  form  which  it  has  assumed,  and  the  ev- 
idence by  which  it  is  supported. 

The  greater  number  of  those  bodies  which  are  termed  oxygen 
acids  have  not  been  in  reality  insulated,  and  what  are  popularly  so 
called  are  merely  supposed  to  contain  the  dry  acid  combined  with 
water.  Thus  the  nearest  approach  we  can  make  to  nitric  acid  is 
the  liquid  N.OgH. ;  to  acetic  acid,  the  crystalline  body  C4H4O4 ;  and 
to  oxalic  acid,  the  sublimed  crystals  C2O4H. ;  we  look  upon  these 
bodies  as  being  combinations  of  the  dry  acid  with  water,  and  we 
write  their  formulae  N.O5+H.O.,  and  C4H303-f-H.O.,  and  CA+H.O.  i 
but  that  these  dry  acids  exist  at  all  is  a  mere  assumption.  Hence, 
with  regard  to  these  instances,  and  they  embrace  the  majority  of 
all  known  acids,  the  idea  that  the  acid  and  base  really  exist  in  the 
salt  formed  by  the  action  of  hydrated  acids  on  a  base  is  purely  the- 
oretical. 

When  we  compare  the  constitution  of  a  neutral  salt  with  that  of 
the  hydrated  acid  by  which  it  is  formed,  we  find  the  positive  result 
to  be  the  substitution  of  a  metal  for  the  hydrogen  of  the  latter  ;  thus 
S.Og-f  H.O.  gives  with  zinc  S.Oa+Zn.O. ;  and  where  a  metal  is 
acted  on  by  a  hydrated  acid,  the  hydrogen  is  thus  evolved  either 
directly  as  gas,  or  it  reacts  on  the  elements  of  the  acid,  and  givea 
rise  to  secondary  products  which  are  evolved,  such  as  sulphurous 
acid,  nitric  oxide,  &c.  In  all  cases  we  may  consider  the  action  of 
a  metal  on  a  hydrated  acid  to  be  primarily  the  elimination  of  hy- 


416  THEORY     RESPECTING     THE     INTIMATE 

drogen  and  the  formation  of  a  neutral  salt.  But  in  this  respect  the 
action  becomes  completely  analogous  to  that  of  the  metal  on  a  hy- 
dracid,  except  that  in  the  latter  case  a  haloid  salt  is  formed  ;  and 
hence  we  assimilate  the  two  classes  in  constitution  by  a  very  sim- 
ple arrangement  of  their  formulae. 

There  are,  however,  a  number  of  acids  which  may  be  obtained 
in  a  dry  and  isolated  form,  as  the  sulphuric,  the  silicic,  the  telluric, 
the  stannic,  the  arsenic,  the  phosphoric,  &c. ;  and  when  they  com- 
bine with  bases,  it  is  most  natural  to  consider  the  union  as  beintr 
direct,  and  that  the  salt  contains  acid  and  base  really  as  such.  This 
is,  accordingly,  the  strongest  point  of  the  ordinary  theory.  But 
other  and  important  circumstances  intervene.  These  acids,  al- 
though they  may  be  obtained  free  from  water,  yet  in  that  state  they 
combine  with  bases  but  very  feebly,  and  require  a  high  temperature 
in  order  to  bring  their  affinities  into  play.  On  the  other  hand,  in 
all  cases  where  these  bodies  manifest  their  acid  characters  in  the 
highest  degree,  they  are  combined  with  water,  as  in  oil  of  vitriol 
and  phosphoric  acid,  and  when  expelled  from  combination  with  a 
base,  they  immediately  enter  into  combination  with  water  in  an 
equivalent  proportion.  Thus,  where  phosphate  of  lime  is  decom- 
posed by  oil  of  vitriol,  it  is  not  phosphoric  acid  (P.O5)  which  is 
found  in  the  liquor,  but  its  terhydrate  (P.Os-j-SH.O.),  as  is  shown 
by  its  forming  with  oxide  of  silver  the  yellow  phosphate,  P.Os+ 
3Ag.O.  In  the  case  of  telluric  acid,  its  hydrate  (Te.Os-'rSH.O  )  is 
very  soluble  in  water ;  it  crystallizes  in  large  prisms  ;  by  212^  two 
atoms  of  water  are  given  off,  but  its  nature  is  not  changed ;  the 
body  which  remains  (Te.Og-fH.O.)  is  still  acid  and  soluble  in  wa- 
ter, perfectly  neutralizing  the  alkalies ;  but  by  a  red  heat  this  last 
atom  of  water  is  driven  off,  and  then  the  whole  nature  of  the  body 
changes;  it  is  insoluble  in  water,  and  even  in  the  strongest  alkaline 
solutions,  and  can  only  be  brought  back  to  its  former  state  by  be- 
ing fused  with  potash  at  a  red  heat.  Here  it  is  evident  that  the 
acid  properties  and  the  water  go  together  ;  and  we  may  conclude 
that,  in  order  to  manifest  strong  acid  properties,  the  acid  must  be  in 
its  hydrated  form.  But  in  that  hydrated  form,  if  the  water  acted 
as  a  base  simply,  the  tendency  of  the  acid  to  combine  v/ith  other 
bases  would  be  inferior  to  that  of  the  dry  acid ;  for  if  we  place 
oil  of  vitriol  and  barytes  together,  the  water  must  be  first  expelled 
before  the  barytes  and  sulphuric  acid  can  unite,  and  hence  an  im- 
pediment would  exist  to  their  union  which  would  not  occur  with 
cold  barytes  and  dry  sulphuric  acid  in  vapour,  and  yet  cold  barytes 
and  oil  of  vitriol  will  combine  with  such  intensity  as  to  produce 
ignition,  while  the  barytes  must  be  heated  before  it  begins  to  com- 
bine with  the  dry  sulphuric  acid.  The  water,  therefore,  is  essential 
to  the  manifestation  of  strong  acid  properties,  and  it  does  not  exist 
in  combination  with  the  acid  merely  as  a  base.  What,  then,  is  the 
constitution  of  a  hydrated  oxygen  acid  1 

When  muriatic  acid  (H.Cl.)  acts  on  zinc,  the  metal  is  taken  up, 
forming  Zn.Cl.,  and  hydrogen  is  expelled  ;  and  if,  in  place  of  zinc, 
oxide  of  zinc  be  taken,  the  effect  is  the  same,  except  that  the  hy- 
drogen combining  with  the  oxygen  of  the  oxide  forms  water,  H.Cl. 
and  Zn.O.  giving  Zn.Cl.  and  H.O.     Now  we  have  in  oil  of  vitriol 


CONSTITUTION     OF     ACIDS     AND     SALTS.  417 

the  elements  S.O4H.  combined  together  j  when  put  in  contact  with 
zinc,  H.  is  expelled,  and  S.04Zn.  is  formed ;  and  with  Zn.O.  and 
S.O4H.,  there  are  produced  S.04Zn.,  and  H.O.  is  set  free.  In  both 
cases,  of  which  the  former  may  be  taken  as  the  type  of  all  the  ha- 
loid salts,  and  the  latter  of  all  salts  formed  by  oxygen  acids,  there  is 
H.  as  the  element,  which  is  removable  by  a  metal,  precisely  as  one 
metal  is  replaceable  by  another,  as,  indeed,  from  the  real  metallic 
character  of  hydrogen,  may  be  considered  to  occur  in  this  case. 
Every  acid  may  therefore  be  considered  to  consist  of  hydrogen 
combined  with  an  electro-negative  element  5  which  may  be  simple^ 
as  chlorine,  iodine,  fluorine  5  or  may  be  compound,  as  cyanogen, 
N.C^,  and  yet  capable  of  being  isolated ;  or,  as  occurs  in  the  great 
majority  of  cases,  its  elements  may  be  such  as  can  only  remain  to- 
gether when  in  combination.  Thus  oil  of  vitriol  does  not  contain 
S.Oj  and  H.O.,  but  consists  of  hydrogen  united  to  a  compound  rad- 
ical S.O4.  Liquid  nitric  acid  does  not  contain  N.0,5  and  H.O.,  but 
consists  of  hydrogen  united  to  a  compound  radical  N-Og,  and  the 
acetic  acid  is  written  C4H3O44-H.,  the  oxalic  acid  CiO^-^-H.,  and 
so  on. 

The  elegance  and  simplicity  with  which  the  laws  of  saline  com- 
bination may  be  deduced  from  these  principles  is  really  remarkable. 
Thus  it  has  been  remarked  as  a  fact  substantiated  by  experiment,, 
that  in  neutral  salts  the  number  of  equivalents  of  acid  was  propor- 
tional to  the  number  of  equivalents  of  oxygen  in  the  base,  but  the 
ordinary  theory  gave  no  indication  of  why  this  should  occur.  It 
follows  necessarily  from  the  principles  of  the  newer  theory.  Thus, 
if  a  protoxide  be  acted  on  by  an  acid,  M.  denoting  the  metal  of  the 
oxide,  and  E.  the  radical  of  the  acid,  the  resulting  action  is, 

M.+O.  and  H.  +  R.  produce  H.  +  O.  and  M.-fR. ; 

and  in  the  neutral  salt,  there  is  an  equivalent  of  each.  Now  in  the 
case  of  a  sesquioxide,  in  order  that  water  shall  be  formed,  and  so 
neither  acid  nor  base  in  excess,  the  reaction  is  that 

M2-I-O3  and  3(H.+R.)  produce  3(H.  +  0.)  and  M2-I-R3, 

a  sesqui-compound  being  formed  perfectly  analogous  to  a  sesqui 
oxide,  and  the  number  of  atoms  of  acid,  3(H.4-R.),  is  equal  to  the 
number  of  atoms  of  oxygen  in  the  base  (M2O3),  because  that  number 
of  atoms  of  hydrogen  is  required  for  the  decomposition  of  the  base. 
In  like  manner,  for  a  deutoxide,  there  is 

M.  +  O,  and  2(H.+R.)  producing  2(H.O.)  and  M.  +  R^. 

The  power  of  salts  to  replace  water  in  the  magnesian  sulphates,  so 
as  to  form  double  salts,  becomes  much  more  intelligible  when  we 
compare  H.  +  O.  with  K.  +  S.O4,  than  where  H.O.  was  contrasted 
with  the  complex  formula  K.O.  +  S.O3. 

The  circumstance  that  on  the  new  theory  (or,  as  it  is  now  often 
called,  the  Binarij  theory  of  salts)  it  is  necessary  to  admit  the  ex- 
istence of  a  great  number  of  bodies  (these  salt-radicals)  which  have 
never  been  isolated,  and  in  favour  of  whose  existence  there  is  no 
other  proof  than  their  utility  in  supporting  this  view,  becomes  more 
powerful  as  an  objection  when  we  proceed  to  apply  its  principles 

G  G  G 


418  BINARY     THEORY     OF     SALTS. 

to  the  salts  of  phosphoric  acid.  For  it  has  been  ah-eady  described 
that  this  acid  forms  three  distinct  classes  of  salts,  all  neutral,  and 
which  have  their  origin  in  the  three  hydrated  states  of  the  phos- 
phoric acid.     These  states  are  written  on  the  two  views  as  follows: 

Old  Theory.  New  Theory. 

Monobasic  acid,    P.O,+H.O.     .     .     .  P.Og+H. 
Bibasicacid,  P.O3-I-2H.O.  .     .     .  F.O^+H^. 

Tribasic  acid,        P.O5-I-3H.O.  .     .     .  P.Os+Ha. 

Now  it  appears  very  useless,  where  the  older  view^  accounts  so 
simply  for  the  properties  and  constitution  of  these  salts,  to  adopt 
so  violent  an  idea  as  that  there  are  three  distinct  compounds  of 
phosphorus  and  oxygen,  which  no  chemist  has  ever  been  able  to 
detect.  But  here,  again,  other  circumstances  must  be  studied  ;  first, 
the  difference  of  properties  of  phosphoric  acid,  in  its  three  states, 
is  totally  inexplicable,  on  the  idea  of  their  being  merely  three  de- 
grees of  hydration.  Nitric  acid  forms  three  hydrates,  but  when 
neutralized  by  potash,  it  always  gives  the  same  saltpetre;  sulphuric 
acid  forms  two  perfectly  definite  hydrates,  but  with  soda  forms  al- 
ways the  same  Glauber's  salt ;  while  phosphoric  acid,  when  neutral- 
ized by  soda,  gives  a  different  kind  of  salt  according  to  the  state  it 
may  be  in.  Also,  the  permanence  of  these  conditions  of  phospho- 
ric acid  is  a  powerful  proof  that  they  do  not  consist  in  the  adhesion 
of  mere  water.  The  idea  that  the  phosphoric  acid  is  a  different  hy- 
dracid  in  each  of  its  three  conditions,  on  the  other  hand,  not  mere- 
ly explains  the  fact  of  these  differences  of  properties,  but  it  renders 
the  formation  of  bibasic  and  tribasic  salts,  which  is  such  an  anoma- 
ly on  the  old  theory,  a  necessary  consequence  of  the  new;  for  the 
phosphoric  salt  r'ldicals,  P.Og,  P.O^,  and  P.O.,  differ  not  merely  in 
the  quantity  of  oxygen  they  contain,  but  are  combined  with  differ- 
ent quantities  of  hydrogen,  and  hence,  in  acting  on  metallic  oxides 
(bases),  there  is  a  different  number  of  atoms  required  for  each  to 
replace  the  hydrogen  ?nd  form  water.     Thus, 

P.OgET.  and  Na.O.  give  R  O,  and  P.OgNa.,  monobasic  phosphate  of 

soda ; 
P.O.H^  and  2Na.O.  give  2H.O.  and  P.0,Na2,  bibasic  phosphate  ; 
P.0«H3  and  3Na.O.  give  3H.0.  and  P.O.Na,,  tribasic  phosphate. 

A  circumstance  which  gives  additional  reason  to  infer  that  the  wa 
ter  is  not  merely  as  base  in  the  phosphoric  acid,  is  the  following: 
if  it  were  so,  then  it  should  be  most  completely  expelled  by  the 
strongest  bases,  and  the  bibasic  and  tribssic  phosphates  of  the  alka- 
lies should  be  those  least  likely  to  retain  any  portion  of  the  basic 
water;  but  the  reverse  is  the  fact;  while  oxide  of  silver,  a  very 
weak  base,  is  that  which  most  easily  and  totally  replaces  the  water. 
On  the  idea,  however,  of  hydracids,  this  is  easUy  understood,  for 
the  oxide  of  silver  is  one  most  easily  reduced  by  hydrogen,  and, 
consequently,  one  on  which  the  action  of  a  hydrogen  'icid,  as  P.O, 
-I-H3,  or  P.07-hH2,  would  be  most  completely  exercised. 

A  remarkable  verification  of  this  theory  has  been  recently  found 
in  the  decomposition  of  solutions  of  the  oxysalts  in  water  by  voltair 
electricity.     It  has  been  already  explained  (p.  1S7,  et  seq.)  that  it  re- 


EVIDENCE     IN     FAVOUR     OP     THE     NEW     THEORY.      419 

quires  the  same  quantity  of  electricity  to  decompose  an  equivalent 
of  any  binary  compound,  such  as  iodide  of  lead,  chloride  of  silver, 
muriatic  acid,  or  water.  Now,  if  we  dissolve  sulphate  of  soda  in 
water,  and  pass  a  current  of  voltaic  electricity  through  that  solution, 
we  have  water  decomposed,  and  also  the  Glauber's  salt  j  oxygen 
and  sulphuric  acid  being  evolved  at  one  pole,  and  soda  and  hydro- 
gen at  the  other.  Here,  on  the  old  view,  the  electricity  performs 
two  decomposing  actions  at  the  same  time,  and,  as  it  thus  divides 
itself,  its  action  on  each  must  be  lessened,  and  the  quantity  of  each 
decomposed  be  diminished,  so  that  the  sum  should  represent  the 
proper  energy  of  the  current.  On  measuring  these  quantities,  how- 
ever, the  result  is  totally  different ;  the  quantity  of  sulphate  of  soda 
decomposed  is  found  to  be  equal  to  the  full  duty  of  the  current,  and 
an  equivalent  of  water  appears  to  be  decomposed  in  addition.  It  is 
quite  unphilosophic  to  imagine  that  the  strength  of  a  current  should 
be  thus  suddenly  doubled,  and  a  simple  and  sufficient  explanation  of 
it  is  found  in  the  new  theory  of  salts.  The  sulphate  of  soda  in  so- 
lution having  the  formula  Na.S.04,  is  resolved  by  the  current  into  its 
elements  Na.  and  S.O4,  as  chloride  of  sodium  would  also  be  ;  the 
sodium,  on  emerging  at  the  negative  electrode  from  the  influence 
of  the  current,  instantly  decomposes  water,  and  soda  and  hydrogen, 
of  each  an  equivalent,  are  evolved  ;  at  the  positive  electrode,  the 
compound  radical  S.O4  also  decomposes  water,  and  produces  H.S.O4 
and  0.  The  appearance  of  the  oxygen  and  hydrogen  is  thus  but 
secondary,  and  the  body  really  decomj^osed  by  the  current  is  only 
Na.S.04. 

In  the  case  of  the  salts  of  such  metals  as  do  not  decompose  water, 
the  phenomena  are  much  more  simple.  Thus,  a  solution  of  sulphate 
of  copper,  when  decomposed  by  the  battery,  yields  metallic  copper 
at  the  negative,  and  sulphuric  acid  and  oxygen  at  the  positive  elec- 
trode, and  the  quantity  of  copper  separated  represents  exactly  the 
energy  of  the  current  which  has  passed;  for  the  salt  being  Cu.S.O^, 
is  simply  resolved  into  its  elements,  but  S.O4  reacting  on  the  water, 
produces  H.S.O4,  and  O.  at  the  positive  electrode.  On  the  old  view 
it  was  supposed  that  water  and  sulphate  of  copper  were  both  de- 
composed, oxygen  and  acid  being  evolved  at  one  side,  and  oxide  of 
copper  and  hydrogen  being  separated  at  the  other  j  which  reacting, 
produced  water  and  the  metal.  Such  an  explanation,  however,  is 
directly  opposed  to  the  law  of  the  definite  action  of  electricity,  and 
cannot  be  received. 

In  the  case  of  solutions  of  chlorides  or  iodides,  where  there  can 
be  no  doubt  of  the  relations  of  the  elements,  the  results  of  voltaic 
decomposition  are  precisely  similar.  Chloride  of  copper  gives  sim- 
ply chlorine  and  copper,  no  water  being  decomposed.  Chloride  of 
sodium  or  iodide  of  potassium  give  chlorine  or  iodine  at  the  one 
electrode,  and  alkali  and  hydrogen  at  the  other  ;  the  evolution  of 
these  last  being  caused  by  the  action  of  the  metallic  basis  on  the 
water  of  the  solution. 

Professor  Daniell,  to  whom  these  important  electro-chemical  re- 
searches arc  due,  considers  the  truth  of  the  binary  theory  of  salts 
to  be  fully  established  by  them. 

If  this  theory  be  adopted,  a  profound  change  in  our  nomenclature 
o£  salts  will  become   necessary.     Graham  has  proposed  that  the 


420  VIEWS     RESPECTING     DOUBLE     SALTS. 

name  of  the  salt-radical  should  be  formed  by  prefixing  to  the  wo»d 
oxygen^  the  first  word  of  the  ordinary  name  of  the  class  of  salts,  and 
that  the  salts  be  termed  by  changing  oxygen  into  oxides.  Thus  eJ. 
O4,  suljphatoxygen^  gives  sulphatoxides  ;  the  sulphates,  N.Oe,  nitrat- 
oxygen,  gives  nitratoxides,  the  nitrates,  and  so  on  ;  but  I  consider 
that  the  form  of  nomenclature  proposed  by  Daniell  deserves  the 
preference.  It  has  been  described  (p.  194)  that  Faraday  proposed 
to  term  the  elements  which  pass  to  the  electrodes  of  the  battery, 
ions  ;  acting  on  this,  Daniell  proposes  to  term  the  electro-negative 
element  of  the  sulphates,  oxysuliihion  ;  that  of  the  nitrates,  oxynitri- 
on,  and  so  on,  and  the  salts  may  be  termed  oxysulphion  of  copper, 
oxynitrion  of  sodium,  &c.  It  would  be  desirable,  however,  for  a 
long  time,  to  introduce  these  names  only  where  theoretical  consid- 
erations rendered  their  employment  decidedly  useful,  and  hence,  in 
all  future  description  of  the  salts,  I  shall  make  use  of  the  language 
of  our  ordinary  views,  and  treat  of  their  preparation  and  composi- 
tion without  any  reference  to  the  discussion  in  which  we  have  been 
engaged. 

The  general  adoption  of  the  binary  theory  of  salts  has  deprived 
of  much  of  its  interest  and  importance  a  question  which  some  years 
since  was  very  ingeniously  discussed,  viz.,  whether,  in  the  forma- 
tion of  double  salts,  the  salts  which  unite  had  the  same  relation  to 
each  other  that  the  acid  and  base  were  then  thought  to  have.  Thus 
it  was  supposed  that  the  electro-negative  qualities  of  sulphuric  acid 
being  less  controlled  by  oxide  of  copper  than  by  potash,  the  alka- 
line sulphate  acted  as  a  base  to  the  sulphate  of  copper  when  these 
two  salts  combined  to  form  the  double  sulphate  of  potash  and  cop- 
per, and  so  on  in  other  instances;  but,  in  addition  to  the  circum- 
stance that  all  we  have  said  as  to  the  constitution  of  the  salts  mili- 
tates against  this  view,  we  have  the  positive  evidence  that,  first, 
these  double  salts  are  formed,  not  by  combination  merely,  but  by 
replacement  of  the  constitutional  water  of  the  sulphates  of  the  cop- 
per or  magnesian  class,  which  water  nobody  would  contend  to  act 
in  them  as  a  base  j  and,  second,  that  when  a  solution  of  such  a  dou- 
ble salt  is  decomposed  by  the  battery,  the  two  salts  are  not  separa- 
ted as  if  they  were  acid  and  base,  but  are  decomposed  independent- 
ly in  the  proportions  of  an  equivalent  of  each,  making  together  the 
sum  of  the  chemical  energy  of  the  current. 

A  similar  idea  was  advocated  by  Bonsdorff  regarding  the  double 
chlorides,  iodides,  &c.  He  proposed  to  consider  the  chlorides  of 
gold,  platina,  mercury,  &c.,  as  chlorine  acids,  and  those  of  potassi- 
um, &c.,  as  chlorine  bases,  and  so  with  the  iodides.  This  view, 
however,  although  at  first  very  extensively  adopted,  has  given  way 
to  the  gradual  growth  of  knowledge.  There  is  no  analogy  between 
a  dry  oxygen  acid  and  a  chloride  ;  but  the  chlorides  are  in  perfect 
analogy  with  the  neutral  salts.  Thus  Cu.Cl.  does  not  resemble  S.O3, 
but  Cu.S.O^  and  Cu.Cl.-f  K.Cl.  are  analogous,  not  to  S.O3 .  K.O.,  but 
to  the  double  salt,  C0.S.O44-K.S.O4.  Bonsdorft^'s  idea  was  exactly 
counter  to  the  direction  of  truth  ;  he  sought  to  bring  all  salts  under 
the  one  head,  by  extending  to  all  the  constitution  of  oxygen  acids 
and  oxygen  bases,  while  the  progress  of  science  has  led  us  to  the 
opposite  generalization  of  reducing  all  salts  to  the  simple  haloid 
type. 


SALTS     OF     POTASH.  421 


CHAPTER  XV. 

BPECIAL  HISTORY  OF  THE  MOST  IMPORTANT  SALTS  OF  THE  INCEGANIC  ACIDS 

AND  BASES. 

The  multitude  of  salts  known  to  chemists  is  so  very  great,  that 
it  is  only  possible  to  detail  the  history  of  the  most  important  of 
each  class.  They  are  arranged  according  to  their  bases,  except  in 
some  few  cases,  where  a  metal  is  also  the  radical  of  their  acid  ele- 
ment. In  that  case,  the  salts  of  the  acids  of  the  metal  are  described 
after  those  formed  by  its  oxides  with  other  acids.  This  plan  has 
been  adopted  in  order  to  give  as  much  unity  as  possible  to  the  his- 
tory of  each  metal,  and  influences  only  the  compounds  of  chrome 
Rnd  arsenic  to  any  degree. 

Of  the  Salts  of  Potash. 

Chloride  of  Potassium. — K.Cl.  Eq.  932  6  or  74-7.  This  salt  may 
be  artificially  produced  by  neutralizing  potash  with  hydrochloric 
acid.  It  exists  abundantly  in  the  water  of  many  brine  springs,  and 
in  the  ashes  of  plants.  It  is  very  soluble  in  water,  producing  so 
much  cold  as  to  be  employed  as  a  freezing  mixture  j  it  crystallizes 
in  cubes,  which  are  anhydrous  j  its  principal  use  is  in  the  manufac- 
ture of  alum. 

Iodide  of  Potassium. — K.I.  Eq.  2069*4  or  165*8.  A  variety  of 
processes  may  be  employed  to  prepare  this  salt.  One  of  the  sim- 
plest consists  in  dissolving  iodine  in  solution  of  potash  until  this  is 
completely  neutralized.  The  potash  being  decomposed,  there  is 
formed  from  61.  and  6K.0.,  5K.I.  and  K.O.  .  I.O5.  The  solution  is 
evaporated  to  dryness,  and  the  mass  being  heated  to  redness,  is 
kept  fused  as  long  as  bubbles  of  oxygen  gas  are  given  off:  the  re- 
sidual salt,  which  is  pure  iodide  of  potassium,  is,  when  cold,  to  be 
dissolved  in  its  weight  of  boiling  water,  and  allowed  to  crystallize 
very  slowly.  A  certain  loss  may  occur  in  this  process  if  the  heat 
applied  be  too  high,  and  if  the  temperature  be  not  high  enough,  io- 
date  of  potash  may  remain  undecomposed  ;  this  last  effect  being 
advantageous  to  the  manufacturer  by  increasing  the  quantity  of 
product,  is  more  liable  to  occur,  and  may  be  detected  by  means  of 
tartaric  acid,  as  very  ingeniously  proposed  by  Mr.  Maurice  Scanlan. 
This  acid  is  without  action  on  pure  iodide  of  potassium,  farther 
than  to  liberate  hydriodic  acid,  which  remains  for  a  certain  time 
unaltered  ;  but  if  a  trace  of  iodate  of  potash  be  present,  the  iodic 
acid  which  is  set  free  immediately  reacts  on  the  hydriodic  acid, 
water  being  formed  and  iodine  liberated,  which  may  be  recognised 
by  means  of  starch. 

Another  process,  adopted  by  the  London  and  Edinburgh  Phar- 
macopeias, consists  in  putting  together  iodine,  metallic  iron,  and 
carbonate  of  potash  ;  the  iron  and  iodine  unite  directly  to  form  a 
soluble  iodide  of  iron,  which  is  decomposed  as  rapidly  as  formed 


422     IODIDE,    BROMIDE,    AND     SULPHATE     OF    POTA.SH. 

by  the  carbonate  of  potash.  Iodide  of  potassium  is  produced  with 
oxide  of  iron  and  carbonic  acid  ;  a  quantity  of  the  latter  combines 
with  the  oxide  of  iron,  but  as  this  is  not  pure  protoxide,  most  of 
the  carbonic  acid  is  evolved  as  gas.  The  reaction  consists  in  Fe.I. 
and  K.O.  .  C.O^,  giving  rise  to  K.I.  and  Fe.O. .  C.O2.  The  liquor  be- 
ing filtered  and  evaporated  to  a  pellicle,  the  iodide  of  potassium  is 
obtained  crystallized.  This  salt  crystallizes  in  cubes;  sometimes 
in  square  prisms,  which  are  macles.  It  is  not  deliquescent  when 
pure,  and  is  without  action  on  turmeric  paper ;  by  this  means  it  is 
known  to  be  free  from  carbonate  of  potash.  It  is  sometimes  adul- 
terated by  chloride  of  potassium,  which  may  be  detected  by  decom- 
posing its  solution  by  nitrate  of  silver,  washing  the  precipitate  with 
water,  digesting  it  in  strong  water  of  ammonia,  and  filtering;  if  the 
solution,  when  rendered  slightly  acid  with  nitric  acid,  give  a  white 
precipitate  of  chloride  of  silver,  chloride  of  potassium  was  present, 
and  its  amount  may  be  thus  determined. 

The  iodide  of  potassium  is  extensively  used  in  medicine,  by  the 
chemist  as  a  reagent,  and  for  the  preparation  of  other  metallic  io- 
dides. 

A  solution  of  iodide  of  potassium  dissolves  iodine  in  large  quan- 
tity, forming  a  brown  liquor  used  in  medicine.  It  is  not  certain, 
however,  that  in  this  case  any  definite  compound  (as  a  biniodide) 
is  formed. 

Bromide  of  Potassium. — ^K.Br.  Eq.  14.68-3  or  117-6.  This  salt 
may  be  prepared  exactly  as  the  iodide  of  potassium,  which  it  re- 
sembles in  most  of  its  physical  characters.  It  is  recognised  by 
giving,  with  oil  of  vitriol,  orange-red  fumes  of  bromine.  The  com- 
mercial article  is  frequently  adulterated  with  chloride  of  potassium, 
the  presence  of  which  may  be  detected  as  follows :  dissolve  100 
grains  of  the  salt  in  four  ounces  of  water,  and  decompose  it  by  an 
excess  of  nitrate  of  silver ;  collect  the  precipitate,  wash  it  carefully, 
and  dry  it  in  a  capsule  tillit  ceases  to  lose  weight ;  then  weigh  it. 
If  it  were  perfectly  pure,  the  bromide  of  silver  should  weigh  158*8 
grains;  but  the  presence  of  chloride  of  potassium  would  have  the 
effect  (from  the  smaller  equivalent  of  chlorine)  of  increasing  the 
weight ;  therefore,  if  the  precipitate,  when  quite  dry,  weighs  more 
than  158-8  grains,  the  sample  is  impure,  and  the  quantity  of  chloride 
present  may  be  calculated  from  the  overplus  weight,  for  100  grains 
of  pure  chloride  of  potassium  should  give  192-6^  grains  of  precipi- 
tate. Thus,  if  there  were  10  per  cent,  of  impurity,  the  precipitate 
would  weigh  162  grains ;  if  20  per  cent.,  it  would  weigh  165'4. 
Thus  the  precipitate  increases  in  weight  about  3-3  for  each  10  per 
cent,  of  chloride  of  potassium  present. 

The  properties  of  the  Fluoride  and  of  the  Silico-Jiuoride  of  Potas- 
sium are  not  of  importance  beyond  what  has  been  already  said  in 
p.  321,  323,  and  324. 

Sulphate  of  Potash.— K.O. .  S.O3  Eq.  109 11  or  87-43.  This  salt 
is  produced  upon  the  large  scale  in  the  manufacture  of  the  sulphu- 
ric and  nitric  acids,  where  nitrate  of  potash  is  employed.  It  may  be 
prepared  by  the  direct  union  of  its  constituents,  and,  being  but  spa- 
ringly soluble,  it  precipitates  as  a  fine  crystalline  powder  when  oil 
of  vitriol  is  mixed  with  a  strong  solution  of  potash.    It  is  more  sol- 


SULPHATE     AND     NITRATE     OF     POTASH.  423 

uble  in  boiling  water,  and  crystallizes,  on  cooling,  in  right  rhombic 
prisms,  or  in  six-sided  prisms  terminated  by  pyramids,  which  are 
macles,  being  formed  by  the  union  of  three  simple  crystals,  as  de- 
scribed in  p.  28.  In  the  figures,  A  represents  the  manner  in  which 
the  three  rhombic  prisms  adhere  together,  the  letters  A 
marking  the  corresponding  planes  in  each  original,  and 
B  the  form  which  results  when  all  traces  of  the  junctions 
have  disappeared.  This  salt  does  not  contain  water ;  its 
crystals  decrepitate  violently  when  heated,  but  are  not  decomposed. 
100  parts  of  water  dissolve  8'3  of  the  salt  at  32'',  and 
25  parts  at  212^.  This  salt  combines  with  dry  sul- 
phuric acid  to  form  a  bisulphate  of  potash,  K.O.-h 
2S.O3,  which  may  be  prepared  by  exposing  the  neu- 
tral salt  to  the  vapour  of  dry  sulphuric  acid,  or  by 
dissolving  it  with  1|  equivalents  of  oil  of  vitriol  in 
the  smallest  possible  quantity  of  distilled  water. 
This  bisulphate  of  potash  crystallizes  in  small  prisms,  wliich  are 
gradually  decomposed  by  water,  the  following  salt  being  formed. 

Common  Bisulphate  of  Potash.  Double  Sulphate  of  Water  and  Pot- 
ash.—K.O.  .S.O.fU.O.  .S.O,.  Eq.  1704-7  or  136-6.  This  salt  is 
produced  when  nitrate  of  potash  is  decomposed  by  two  atoms  of 
oil  of  vitriol,  and  is  formed  when  neutral  sulphate  of  potash  is  gen- 
tly heated  with  half  its  weight  of  oil  of  vitriol  to  just  below  red- 
ness. It  may  be  obtained  crystallized  from  a  strong  solution  in 
right  rhombic  prisms.  It  is  decomposed  into  neutral  sulphate  and 
oil  of  vitriol  by  a  large  quantity  of  water.  When  heated  to  full 
redness,  it  fuses,  and  may  be  obtained,  on  cooling,  in  oblique  rhom- 
bic crystals ;  it  is  thus  dimorphous  (see  p.  227j ;  at  a  higher  tem 
perature  it  abandons  its  excess  of  acid,  and  neutral  sulphate  re- 
mains. 

There  exists  also  a  hydrated  sesquisulphate  of  potash^  2(K.O. .  S.O3) 
-}-H.O. .  S.O;,,  which  crystallizes  in  fine  needles.  Similar  com- 
pounds of  sulphate  of  potash  with  hydrated  nitric  and  phosphoric 
acids  have  also  been  described. 

Mtrate  of  Potash.  Saltpetre.  Mlre.—K.O. .  N.O5.  Eq.  1266-9  or 
101-5.  The  general  principles  of  the  formation  of  nitric  acid  by 
the  conjoined  action  of  decomposing  animal  matter  and  of  earthy 
bases  on  atmospheric  air,  have  been  described  already.  By  lixivi- 
ating the  materials  thus  obtained,  whether  naturally  or  from  arti- 
ficial nitre  beds,  with  water,  a  solution  is  obtained,  containing, 
among  other  saline  matters,  a  considerable  quantity  of  nitrate  of 
lime  j  this  is  then  decomposed  by  an  impure  carbonate  of  potash, 
and  carbonate  of  lime  being  precipitated,  a  solution  of  nitrate  of 
potash  is  obtained,  from  which  the  salt  is  procured  by  evaporation 
and  crystallization.  Its  form  is  that  of  a  six-sided  prism  with  dihe- 
dral summits,  derived  from  the  right  rhombic  system.  It  is  anhy- 
drous;  100  parts  of  water  dissolve  13-3  parts  at  32^  and  240  parts 
at  212°  ;  when  heated  to  redness,  it  melts  and  evolves  oxygen,  at 
first  pure,  but  subsequently  mixed  with  nitrogen  gas. 

As  nitrate  of  potash  contains  oxygen  in  large  quantity,  and  gives  it  out  readily  to 
combustible  bodies,  it  is  much  (wnployed  for  the  preparation  of  fireworks,  and  espe- 
cially of  gunpowder.  The  action  of  gunpowder  depends  upon  its  generating,  when 
decomposed,  a  large  quantity  of  gases,  which  occupy  more  than  lOOO  times  its  vol- 


424  MANUFACTURE     OF     GUNPOWDER. 

ume.  If  this  took  place  instantaneously,  all  bodies  near,  which  could  not  resist 
this  force,  would  be  burst  or  broken;  as  takes  place  with  chloride  of  azote,  which,  if 
placed  in  a  gun,  would  burst  it,  but  have  no  power  to  propel  a  ball ;  the  decomposi- 
tion of  gunpowder,  however,  occupying  a  certain  time,  the  disengagement  of  gas  is 
progressive,  and  the  ball  is  forced  through  the  barrel  with  the  velocity  due  to  the  ul- 
timate efiect  of  the  whole  quantity  of  gas  produced.  When  gunpow  der  is  completely 
decomposed,  the  products  are  found  to  be  sulphuret  of  potassium,  nitrogen,  and  car- 
bonic acid  gas,  and  from  these  the  proportions  by  weight  of  its  constituents  mav  be 
calculated,  for  S.,  K.O.  .  N.O5,  and  3C.,  produce  K.S.,  N.,  and  3C.0z.  The  parts  by 
weight  are,  therefore, 

Tlieorv.  French.         English.        Prussian. 

S.=  161  — il-8  12-5  100  11-5 

30.=  18-3  —  13-5  12-5  15  0  135 

K.O. .  N.Q5=101-5  —  74-7  750  75  0  750 

135-9      1000  1000  1000  1000 

The  proportions  employed  in  the  government  factories  of  the  most  important  coun- 
tries are  given  also  above.  The  Prussian  mixture  agrees  best  with  theory.  For  the 
coarse  blasting  powder,  there  are  employed  sixty-five  parts  of  saltpetre,  twenty  of 
sulphur,  and  fifteen  of  charcoal.  The  excess  of  sulphur  renders  the  explosion  more 
intense,  but  would  corrode  firearms  too  much.  A  mixture  of  three  parts  of  salt- 
petre, four  of  carbonate  of  potash,  and  one  of  sulphur,  is  decomposed  instantaneously 
when  fused,  and  with  an  explosion  so  violent,  that,  if  it  be  placed  on  a  thin  iron  plate, 
it  may  be  perforated.  If  three  parts  of  nitre  be  mixed  with  one  of  finely-powdered 
charcoal,  a  mass  is  obtained  which,  when  touched  with  an  ignited  coal,  burns  nearly 
as  fast  as  loose  gunpowder,  but  totally  without  explosion.  It  is  therefore  the  sul- 
phur which  determines  the  violence  and  rapidity  of  the  deflagration  of  gunpowder, 
while  the  charcoal  produces  the  great  volume  of  gas  on  which  iis  mechanical  elfeci 
depends. 

The  preparation  of  the  materials  for  making  gunpowder  requires  great  care. 
Most  of  the  success  depends  on  the  preparation  of  the  charcoal.  This  should  be 
made  from  a  light  wood  containing  little  ashes,  such  as  birch,  and  carbonized  in  cyl- 
inders, very  slowly,  and  at  the  lowest  possible  heat.  When  reduced  to  impalpable 
powder,  this  charcoal  is  so  inflammable  as  sometimes  to  take  fire  at  ordinary  tem- 
peratures. The  purification  of  the  saltpetre  is  performed  by  successive  recrystalli- 
zations,  and  by  washing  the  crystals  with  water  already  saturated  with  saltpetre, 
which  dissolves  out  any  common  salt  that  may  be  present,  but  does  not  act  on  tlte 
crystals  of  saltpetre.  The  description  of  the  mechanical  operations  of  the  manufac- 
ture would  be  out  of  place  here. 

Hypochlarite  nf  Potash. — When  gaseous  chlorine  is  passed  into  a  solution  of  carbon- 
ate of  potash,  it  is  abundantly  absorbed,  but  no  carbonic  acid  is  disengaged  until 
the  liquor  contains  an  atom  ol'  chlorine  for  every  two  atoms  of  alkaline  carbonate. 
On  examination,  it  is  then  found  to  contain  hypochlorite  of  potash,  chloride  of  potas- 
sium, and  bicarbonate  of  potash,  which  are  mixed  in  solution,  and  may  be  partially 
separated  by  crystallization.  The  reaction  has  been  such  that  2C1.  and  4K.0.  .  C. 
02give  K.Cl.,K.O.  .C1.0.,and  2(K.O.-i-C.02-i-H.O.  .C.O2).  If  the  stream  of  chlo- 
rine be  continued,  carbonic  acid  is  copiously  evolved,  and  as  much  more  clijorine  is 
absorbed,  giving  ultimately  a  mixture  of  K.Cl.  and  K.O. .  Cl.O.  The  liquor  becomes 
deep  yellow,  owing  to  the  liberation  of  a  quantity  of  hypochlorous  acid  by  the  free 
carbonic  acid,  and  hence  the  quantity  of  chlorine  absorbed  amounts  to  much  more 
than  the  exact  atomic  proportion. 

Farther  details  of  the  theory  of  these  bleaching  compounds  are  given  under  the 
head  of  chloride  of  lime. 

Chlorate  of  Potash.— K.O.  .  CI.O5.  Eq.  1532-6  or  122-81.  When 
chlorine  gas  is  passed  into  a  strong  solution  of  potash,  it  is  absorbed 
rapidly  until  the  alkali  is  completely  neutralized,  and  chloride  of 
potassium  and  hypochlorite  of  potash  are  formed  ;  2K.0.  and  2C1. 
giving  K.Cl.  and  K.O.  .  Cl.O.  If,  then,  this  liquor  be  boiled  for  some 
time,  oxygen  gas  is  given  off,  the  hypochlorite  being  decomposed, 
and  chloride  of  potassium  and  chlorate  of  potash  being  formed  ', 
9(K.O.  .  Cl.O.)  producing  120.  with  8K.C1.  and  K.O. .  Cl.O,.  If  car- 
bonate  of  potash  has  been  employed,  the  tibsorption  of  the  chlorme 
is  rapid  until  half  of  the  salt  has  been  decomposed  und  the  remain- 


CHLORATE     OF     POTASH.  425 

der  converted  into  bicarbonate,  from  combining^  with  the  evolved 
carbonic  acid,  as  described  under  the  preceding  head  ;  but  a  high 
temperature  and  a  great  excess  of  chlorine  being  necessary  to  com- 
plete the  reaction,  render  the  operations  tedious  and  very  trouble- 
some ;  and  as,  owing  to  the  large  quantity  of  oxygen  evolved,  there 
is  but  one  equivalent  of  chlorate  of  potash  obtained  by  the  action 
of  eighteen  equivalents  of  chlorine  on  eighteen  of  potash,  the  pro- 
cess is  one  of  considerable  expense. 

We  owe  to  Graham  a  method  which  is  free  from  these  disadvan- 
tages. If  an  equivalent  of  carbonate  of  potash  be  mixed  with  one 
of  hydrate  of  lime  (by  weight  about  2  of  K.O.  .  CO  to  1  of  Ca.O. . 
H.O.),  and  exposed  to  a  current  of  chlorine,  the  gas  is  absorbed  with 
avidity,  and  the  solid  mass  becomes  very  hot,  while  water  is  given 
off  abundantly.  When  saturated,  it  may  be  gently  heated  to  com- 
plete the  decomposition.  No  oxygen  is  given  off,  the  reaction  being 
that  6(K.O.  .  C.OJ  and  6(Ca.O.  .  H.O.),  acted  on  by  6Cl.,  produce 
5K.C1.,  6Ca.O.  .  C.O^,  and  K.O.  .  Cl.O,,  while  6H.0.  are  evolved. 
By  digesting  the  mass  in  water,  the  potash  salts  are  dissolved  out, 
carbonate  of  lime  remaining,  and  the  chlorate  of  potash  may  be 
separated  from  the  chloride  of  potassium  by  crystallization.  By  this 
means  three  times  as  much  product  may  be  obtained  from  the  same 
materials  as  by  the  older  process. 

This  salt  crystallizes  in  rhomboidal  tables  of  a  pearly  lustre  :  it  is 
anhydrous :  100  parts  of  water  dissolve  but  3*5  parts  at  32^,  and  60 
parts  at  219^.  It  tastes  sharp  and  cooling,  like  nitre  j  when  heated, 
it  melts  and  evolves  oxygen  gas,  being  decomposed  into  chloride  of 
potassium  and  hyperchlorate  of  potash  ;  on  increasing  the  heat,  this 
also  is  decomposed,  and  chloride  of  potassium  remains  pure.  Its 
uses  in  preparing  oxygen,  and  the  compounds  of  chlorine  and  oxy- 
gen, have  been  already  noticed.  From  its  supplying  oxygen  still 
more  readily  than  nitre,  it  is  the  basis  of  a  variety  of  deflagrating 
mixtures.  When  rubbed  in  a  mortar  with  sulphur  or  with  sulphu- 
ret  of  antimony,  it  explodes  violently.  Placed  in  contact  with  a 
minute  bit  of  phosphorus  on  an  anvil,  and  struck  by  a  hammer,  it 
gives  a  dangerous  detonation.  The  ordinary  lucifer  matches  are 
formed  by  mixtures  of  chlorate  of  potash  with  sulphur  and  charcoal, 
or  sulphuret  of  antimony  or  of  cinnabar,  made  into  a  paste  with 
gumarabic,  and  applied  to  the  extremity  of  a  bit  of  stick,  previously 
smeared  with  sulphur.  Students  should  be  very  cautious  how  they 
employ  this  salt  in  such  experiments  as  those  now  noticed. 

Perchloratc  of  Potash — K.O.  .Cl.O?;  Eq.  1732-6  or  138-8 — is  of  importance  only 
from  being  one  of  the  least  soluble  salts  of  potash,  and,  consequentl}^,  that  the  per- 
chloric acid  may  be  used  as  a  test  for  the  presence  of  potash  in  solution,  it  giving 
a  granular  crystalline  precipitate  if  that  alkali  be  present.  Its  preparation  is  su^ 
ficiently  noticed  in  page  306. 

Tlie  Sihcaie  of  Potash  is  of  considerable  importance  as  a  constituent  of  glass,  and 
will  be  noticed  as  such  hereafter. 

lodate  of  Potash. — K.O. .  I.O5.  This  salt,  which  is  but  sparingly  soluble  in  water, 
may  be  obtained  by  neutralizing  the  perchloride  of  iodine  with  caustic  potash ;  I, 
CI5  and  6K.0.  produce  5K.C1.  and  K.O. .  I.O5.  This  last  separates  in  crystalline 
grains.  It  may  also  be  obtained  by  adding  iodide  of  potassium  10  fused  chlorate  of 
potash ;  the  mass  froths  up,  the  oxygen  passing  to  the  iodine,  and  there  is  obtained  a 
mixture  of  chloride  of  potassium  and  iodate  of  potash,  which  may  be  separated  by 
crystallization.  This  salt  has  a  remarkable  tendency  to  form  acid  and  double  salts, 
of  which,  however,  none  are  specially  interesting. 

H  H  H 


426  CHLORIDE     OF     SODIUM. 

Salts  of  Sodium. 

Chloride  of  Sodium.  Common  Salt.  Sea  Salt— Nn.Cl  j  Eq.  733-6 
or  58*8 — exists  in  great  abundance  in  nature  ;  solid,  as  rock  salt^ 
and  in  solution  in  the  water  of  the  ocean,  and  of  many  inland  seas 
and  lakes.  The  deposites  of  rock  salt  occur  only  among  the  more 
recent  (secondary)  geological  formations,  lying  above  the  coal,  and 
in  connexion  with  the  new  red  sandstone,  as  in  Cheshire.  The  beds 
of  salt  are  sometimes  of  great  magnitude;  thus,  at  Northwich,  the 
bed  now  worked  is  supposed  to  be  not  less  than  60  feet  thick,  a  mile 
and  a  half  long,  and  1300  yards  wide  ;  and  the  deposites  at  Wie- 
liczka,  in  Poland,  appear  to  be  still  larger.  The  origin  of  these  de- 
posites of  salt  is  probably  to  be  found  in  the  gradual  drying  up,  by 
evaporation,  of  salt  lakes,  to  which  fresh  quantities  of  salt  were  con- 
tinually supplied  by  the  surrounding  springs.  Owing  to  admixture 
of  earthy  matters,  the  rock  salt,  as  quarried,  is  generally  brownish- 
coloured,  and  hence  requires  to  be  dissolved  in  water  and  crystal- 
lized for  use.  The  expense  of  extracting  the  salt  may  be  in  many 
cases  lessened,  by  simply  boring  down  to  the  bed  with  a  pipe  a  few 
inches  in  diameter,  and  letting  thereby  water  run  in  upon  the  salt ; 
a  strong  solution  of  salt  is  thus  produced,  which  is  pumped  up  and 
evaporated.  The  expense  of  sinking  a  shaft  and  quarrying  out  the 
solid  salt  is  thus  avoided. 

In  warm  countries,  as  on  the  coasts  of  Portugal  and  of  the  south  of 
France,  salt  is  obtained  by  the  spontaneous  evaporation  of  sea-wa- 
ter, which  is  allowed,  on  the  rise  of  the  tide,  to  flow  into  shallow 
basins,  being  passed  from  one  to  another,  according  as  it  becomes 
more  concentrated,  and,  finally,  the  evaporation  being  finished  by 
means  of  artificial  heat.  The  sea-water  is  not  evaporated  to  dry- 
ness, as  its  other  saline  ingredients  would  in  that  case  be  mixed 
with  the  common  salt.     The  sea-water  is  generally  composed  of 

Chloride  of  sodium     .     .     .  2*50 

Chloride  of  magnesium  .     ,  0*35 

Sulphate  of  magnesia      .     .  0*58 

Carbonate  of  lime  and    >  q.^^  \  100-00, 
Carbonate  of  magnesia  ) 

Sulphate  of  lime    ....  0-01 

Water 96-54  J 

vvith  generally  some  traces  of  iodide  and  bromide  of  magnesium. 
According  as  the  evaporation  proceeds,  the  common  salt  is  depos- 
ited in  crystals,  and  the  mother  liquor,  or  bittern^  being  rich  in  salts 
of  magnesia,  is  preserved  for  the  manufacture  of  Epsom  salts. 

In  addition  to  these  sources,  chloride  of  sodium  may  be  obtained 
by  the  direct  combination  of  its  elements,  or  by  decomposing  car- 
bonate of  soda  by  muriatic  acid.  In  practice,  however,  this  is  never 
done. 

Chloride  of  sodium  crystallizes  in  cubes.  Its  taste  is  purely  sa- 
line. It  is  equally  soluble  in  water  at  all  temperatures,  100  of  wa- 
ter dissolving  36'.5  ;  by  a  very  strong  heat  it  may  be  volatilized. 
Its  crystals  are  anhydrous,  but  are  generally  fissured,  containing 
water,  which,  when  heated,  bursts  the  crystal,  producing  loud  de« 


427 

crepitation.  A  strong  solution  of  salt  does  not  freeze  at  0^,  but  de- 
posites  crystals  in  rhombic  plates,  which  are  a  hydrated  chloride 
of  sodium.  If  these  crystals  be  heated  beyond  15°  they  give  out 
water,  and  are  changed  into  minute  cubes. 

The  uses  of  chloride  of  sodium  are  very  numerous  and  important. 
Besides  being  employed  in  seasoning  food,  it  is  now  universally  the 
source  from  whence  the  other  compounds  of  sodium,  such  as  the 
carbonate  and  sulphate,  are  obtained.  It  is  employed  also  in  the 
manufacture  of  glass  and  of  porcelain,  and  as  a  manure. 

The  bromide  and  iodide  of  Sodium  resemble,  in  properties  and  mode 
of  preparation,  the  corresponding  compounds  of  potassium,  and  do 
not  require  special  notice. 

Sulphate  of  Soda.  Glauber's  Salt.—Na.O. .  S.O3+ 10  Aq.  Eq.  892-1 
4-1125  or  71'48+90.  So  named  after  its  discoverer:  exists  in  some 
mineral  waters,  and  may  be  prepared  by  neutralizing  carbonate  of 
soda  by  dilute  sulphuric  acid.  For  the  purposes  of  commerce,  it  is 
manufactured  in  great  quantities  from  common  salt,  as  described 
under  the  head  of  muriatic  acid  (p.  307). 

As  it  is  not  the  object  of  the  process  to  economize  the  muriatic 
acid  gas,  the  decomposition  is  carried  on  in  a  reverberatory  furnace 
similar  to  that  figured  in  p.  333.  Three  or  four  hundred  weight  of 
salt  being  spread  over  the  floor  of  the  furnace,  forming  a  layer  three 
or  four  inches  deep,  the  equivalent  quantity  (an  equal  weight)  of 
sulphuric  acid,  of  the  strength  1*600,  as  taken  from  the  chambers,  is 
poured  in  through  an  aperture  in  the  dome,  and  a  moderate  fire  kept 
up  until  the  materials  begin  to  dry ;  the  fire  is  then  increased  grad- 
ually until  all  the  muriatic  acid  gas  has  been  expelled,  and  the  reside 
ual  sulphate  of  soda  begins  to  fuse.  The  acid  gas  passes  up  the 
chimney,  and  is  either  allowed  to  pass  away  into  the  air,  or  is  con- 
densed by  meeting  with  a  stream  of  water,  and  the  weak  liquid  acid 
thus  formed  is  suffered  to  run  to  waste.  The  greater  part  of  the 
sulphate  of  soda  thus  produced  is  immediately  used  to  make  car- 
bonate of  soda ;  but  to  form  Glauber's  salt,  it  is  only  necessary  to 
dissolve  it  in  warm  water,  and  let  it  crystallize  by  cooling. 

The  sulphate  of  soda  crystallizes  in  six-sided  prisms,  as  in  the 
figure,  very  much  channelled  at  the  sides.  It  is 
easily  soluble  in  water,  having  a  point  of  maxi- 
mum solubility  at  93  \  as  figured  in  page  22.  Its 
ordinary  crystals  contain  56  per  cent,  of  water ; 
by  exposure  to  the  air  it  loses  all  its  water  by 
eftlorescence,  and  falls  into  a  white  powder  j  from 
a  hot  saturated  solution  opaque  rhombic  octohe- 
dral  crystals  are  deposited,  which  are  anhydrous. 
The  isomorphism  of  these  crystals  with  permanganate  of  barytes, 
and  the  speculations  founded  on  it,  have  been  noticed  p.  224.  A 
bisulphate  and  a  sesquisulphate  of  Soda  may  be  formed  by  adding 
oil  of  vitriol  to  a  solution  of  the  neutral  salt,  and  crystallizing  by- 
evaporation.  They  are  much  less  determinate  than  the  acid  sul- 
phates of  potash. 

Xitrate  of  Soda.  Cubic  JViVre.— Na.O. .  N.O,.  Eq.  1067-5  or  85-57. 
The  spontaneous  formation  of  this  salt  by  the  atmospheric  influence, 
probably  on  a  soil  containing  chloride  of  sodium,  has  been  noticed 


428  PHOSPHATES     OF      SODA. 

p.  277.  It  may  also  be  obtained  by  means  of  nitric  acid  and  carbon- 
ate of  soda.  It  crystallizes  in  rhombs,  isomorphous  with  calc  spar 
(p.  224).  It  is  very  soluble  in  water,  and  is  slightly  deliquescent ; 
hence  it  cannot  be  employed  in  the  manufacture  of  gunpowder.  It 
(s  used  for  the  manufacture  of  nitric  and  sulphuric  acids,  and  as  a 
manure. 

Hyposulphite  of  Soda. — Na  O.  .  S^O^H-  10  Aq.  This  salt,  which 
oas  become  of  some  practical  interest,  from  its  use  in  dissolving 
off  the  sensitive  silver  compounds  in  making  photogenic  drawings, 
may  be  made  by  boiling  together  three  parts  of  dry  carbonate  of 
soda  with  one  of  sulphur  until  this  last  is  dissolved,  and  then  pass- 
ing a  stream  of  sulphurous  acid  gas  through  the  liquor  until  it  smells 
strongly  of  it.  Na.O.  .  C.O^,  with  S.  and  S.O2,  produce  Na.O.  .  S.Oz, 
while  C.O2  is  evolved.  If  the  three  parts  of  carbonate  of  soda  be 
boiled  with  two  of  sulphur,  and  the  deep  yellow  liquor  be  exposed 
to  the  air  until  it  yields  a  colourless  liquor  on  filtration,  the  salt  is 
more  simply  produced,  the  necessary  quantity  of  oxygen  being  ab- 
sorbed from  the  air.  The  hyposulphite  of  soda  thus  formed  is  easily 
soluble  in  water.  Its  resemblance  to  Glauber's  salt  in  form,  and  its 
other  properties,  are  noticed  in  p.  291. 

Hypochlorite  of  Soda.  Chloride  of  Soda.  Disinfecting  Liquor  of 
Labaraque — Is  produced  by  treating  a  solution  of  carbonate  of  soda 
with  chlorine  as  long  as  this  is  absorbed,  but  no  carbonic  acid 
evolved.  For  farther  observations,  see  the  hypochlorites  of  potash 
and  of  lime. 

A.  Tribasic  Phosphate  of  Soda. — The  common  phosphate  of  soda 
of  the  shops  is  a  tribasic  salt,  containing  (P.O-  +  2Na.O. -hH.0.)4- 
24<  Aq.  It  is  prepared  by  decomposing  the  solution  of  acid  tribasic 
phosphate  of  lime  obtained  from  bones  (as  described  in  p.  295)  by 
means  of  carbonate  of  soda.  Carbonate  of  lime  is  thrown  down, 
and  phosphate  of  soda  formed.     It  is  easily  soluble  in  water,  and 

crystallizes  in  oblique  rhombic  prisms,  as  in  the  fig- 
ure, which   react   alkaline.     When   exposed  to  the 
air,  it  .loses  some  of  its  water  by  efflorescence  (ten 
atoms  1),  but  the  crystals  retain  their  form.     If  this 
salt  be   mixed  with  an  excess  of  caustic  soda,  the 
atom  of  basic  water  is  displaced,  and  the  subphos- 
phate  of  soda  (P.O-,  +  3Na.O  +  24  Aq.)  crystallizes  in 
long  prisms  ;  and  by  the  addition  of  hydrated  phos- 
phoric acid  to  its  solution,  and  cautious  evaporation, 
the   acid  tribasic  phosphate  (P.05  4-Na.O.-i-2H.O.)  +  2  Aq.,  which 
crystallizes  in  oblique  rhombic  prisms,  is  formed :  it  is  dimorphous. 
The  characteristic  of  these  three  salts  is  to  give  with  nitrate  of 
silver  a  yellow  precipitate  of  tribasic  phosphate  of  silver. 

B.  Bibasic  Phosphate  of  Soda. — Of  these  salts,  that  termed  the  Py- 
rophosphate of  Soc/«,(P.O:^-|-2Na.O.)-[-  10  Aq.,  is  of  interest,  as  its  dis- 
covery led  the  way  to  the  true  history  of  these  bodies.  It  is  form- 
ed by  fusing  the  common  phosphate  of  soda,  (P.05-l-2Na.O.  +  H.O.) 
-1-24  Aq.,  at  a  red  heat.  All  the  water  of  crystallization  is  given 
off  at  a  very  moderate  heat ;  but  by  a  red  heat  the  twenty-fifth  or 
basic  atom  is  expelled,  and,  when  the  salt  is  then  redissolved,  the 
phosphoric  acid  does  not  recombine  with  basic  water,  but  remains 


BORATES  OF  SOD  A. S  ALTS  OF   BARIbM.    429 

united  only  with  the  soda.  '  It  is  recognised  by  giving  a  white  pre- 
cipitate with  nitrate  of  silver. 

C.  The  Monobasic  Phosphate  of  Soda,  P.05-fNa.O.,  is  obtained  by 
heating  the  acid  tribasic  or  bibasic  phosphates  of  soda  to  redness. 
All  the  volatile  base  being  thus  expelled,  the  phosphoric  acid  re- 
mains combined  with  one  equivalent  of  soda.  This  salt  fuses  into 
a  transparent  glass  j  is  deliquescent ;  its  solution  does  not  crystal- 
lize. It  is  easily  recognised  by  throwing  down  from  solutions  of 
lead  and  silver,  precipitates,  which  are  not  powders,  but  soft,  tena- 
cious pastes. 

Borates  of  Soda. — Boracic  acid  combines  with  soda  in  many  pro- 
portions, forming  salts,  of  which  the  most  important  is  the  biborate, 
the  borax  of  commerce  (Na.O.-f^B.O^)-!- 10  Aq.  It  exists  in  the 
water  of  several  lakes  in  Thibet  and  China,  also  in  Hungary,  and 
was  imported  thence  in  small  crystals,  smeared  with  a  fatty  matter, 
under  the  name  of  tinkal.  The  borax  of  commerce  is  now  obtained 
by  treating  the  native  boracic  acid  obtained  from  Tuscany,  p.  326, 
by  carbonate  of  soda.  On  the  application  of  heat,  the  acid  dissolves 
with  the  evolution  of  carbonic  acid  and  ammonia ;  the  liquor  is  run 
into  large  vats  lined  with  lead,  where  it  cools  very  slowly,  and  the 
borax  gradually  crystallizes  in  oblique  rhombic  prisms,  as  z,  w,  My 

in  the  hgure.     If  a  strong  solution  of  borax  be  kept  at         

SS"",  the  salt  crystallizes  in  regular  octohedrons  with  f(T_f_~p 
only  five  atoms  of  water.  Although  this  salt  contains  1 
two  equivalents  of  acid,  it  has  an  alkaline  reaction :  i 
when  heated,  it  froths  up  very  much,  abandoning  its  |>- 
water.  The  dry  salt  melts  at  a  red  heat  into  a  colour-  ^ 
less  glass,  which  dissolves  most  metallic  oxides  very  readily,  and 
hence  is  serviceable  in  experiments  with  the  blowpipe,  as  enabling 
the  metals  to  produce  the  coloured  glasses  by  which  they  are  rec- 
ognised ;  under  the  head  of  glass  and  porcelain,  its  use  in  these 
branches  of  art  will  be  again  noticed. 

The  remaining  compounds  of  boracic  acid  with  soda,  as  the  neu- 
tral borate,  Na.O. .  B.O3  +  8  Aq.,  and  acid  salts,  as  Na.O.-{-4.B.03  and 
Na.O.+6'B.03,  are  not  important. 

Silicate  of  Soda  will  be  described  under  the  head  of  glass. 

Salts  of  Lithium. — From  the  rarity  of  this  body,  its  salts  require  no  farther  notice 
than  that  its  carbonate  is  but  very  sparingly  soluble  in  water,  yet  its  solution  pos- 
sesses an  alkaline  reaction.  It  thus  serves  to  connect  the  alkaline  with  the  earthy 
bases. 

Salts  of  Barium, 

Chloride  of  Barium.— Bsi.Cl-^^  Aq.  Eq.  1299-64-225  or  104-8-h 
18.  This  salt  may  be  prepared  by  decomposing  the  native  carbon 
ate  of  barytes  with  dilute  muriatic  acid,  or,  more  economically,  by 
decomposing  the  sulphuret  of  barium,  the  preparation  of  which  is 
described  in  p.  342,  by  dilute  muriatic  acid.  In  the  former  case, 
carbonic  acid,  in  the  latter,  sulphuretted  hydrogen,  is  given  off. 
The  chloride  of  barium  crystallizes  from  a  hot  solution  in  rhom- 
boidal  tables  which  contain  14'7  of  water. 

Sulphate  of  Barytes.— Ba.O. .  S.O3.  Eq.  1458  or  119-5.  This  salt 
exists  native,  in  great  abundance,  being  the  most  common  source 
of  barytes.     It  is  very  generally  associated  with  sulphuret  of  lead, 


430  SALTS  OF  BARIUM,  STRONT 


and  serves  as  an  indication  of  the  prol)able  proximity  of  that  ore. 
It  is  totally  insoluble  in  water.  Its  crystalline  form  is  an  oblique 
rhombic  prism,  generally  very  flat,  as  in  the 
figure  ;  derived  from  an  octohedron  of  which 
i  and  e  are  planes  ;  the  secondary  planes,  p 
and  w,  belong  to  the  prism.  It  is  one  of  the 
heaviest  of  saline  bodies,  its  specific  gravity 
being  4*3;  hence  its  name  of  heavy  spar  and  terra ponderosa.  WheA 
ground  to  fine  powder,  it  is  used  as  a  cheap  substitute  for  white 
lead  in  painting,  for  which  large  quantities  of  it  are  employed ;  but 
its  crystalline  texture  prevents  it  having  the  opacity  or  body  neces- 
sary in  a  good  pigment.  It  may  be  prepared  artificially  by  adding 
sulphuric  acid  to  any  solution  containing  barytes  ;  it  falls  as  a  heavy 
white  crystalline  powder.  Its  total  insolubility  renders  its  constit- 
uents excellent  reagents  for  each  other. 

Mtrate  of  Barytes^Ba.O.-{-'N.O,;  Eq.  1633-9  or  130-9— may  be 
produced  by  acting  on  carbonate  of  barytes  with  dilute  nitric  acid, 
or,  more  cheaply,  by  mixing  strong  hot  solutions  of  sulphuret  of  ba- 
rium and  nitrate  of  soda.  The  sparingly  soluble  nitrate  of  barytes 
crystallizes  as  the  mixed  liquors  cool,  but  the  sulphuret  of  sodium 
remains  dissolved.  In  this  process,  from  Ba.S.  and  Na  0.  .  N.O5  we 
obtain  Ba.O.  .  N.O5  and  Na.S.  This  salt  requires  twelve  parts  of 
cold  water  for  solution,  but  dissolves  in  four  of  boiling  water,  from 
which  it  crystallizes  on  cooling  in  octohedrons.  These  crystals  are 
anhydrous.  When  heated,  they  yield  pure  barytes. 
The  other  salts  of  barytes  do  not  require  notice. 

Salts  of  Strontium. 

Chloride  of  Strontium.— Sr. CI +  6  Aq.  Eq.  989-9  or  79-32.  This 
salt  is  obtained  from  the  native  carbonate  or  sulphate  of  strontia, 
exactly  as  chloride  of  barium  is  obtained  from  the  native  salts  of 
barytes.  It  Crystallizes  in  long  needles  which  deliquesce.  It  is 
very  soluble  in  water. 

Sulphate  of  Strontia.— -Sr.O. .  S.O3.  Eq.  1148-4  or  91-9.  This,  the 
most  abundant  source  of  strontia,  is  found  native  crystallized,  iso- 
morphous  with  sulphate  of  barj'^tes.  It  may  be  produced  artificial- 
ly as  a  white  powder,  by  adding  sulphuric  acid  to  any  solution  con- 
taining strontia.  It  is  dissolved  by  3600  parts  of  boiling  water,  and 
remains  dissolved  after  cooling.  It  is  fused  by  a  strong  heat  j  with 
charcoal  it  gives  sulphuret  of  strontium. 

JV-itrate  of  Strontia — Sr.O.  .  N.O- — crystallizes  in  octohedrons^ 
which  dissolve  in  five  parts  of  cold,  and  one  half  part  of  boiling 
water.  Mr.  Scanlan  has  observed,  that  during  the  crystallization 
of  this  salt  bright  flashes  of  light  are  emitted.  It  is  anhydrous,  but 
decrepitates  when  heated,  owing  to  mechanically  included  water. 
On  the  application  of  heat,  these  crystals  evolve  oxygen  and  nitro- 
gen, and  leave  pure  strontia. 

Salts  of  Calcium, 

Chloride  of  Calcium— C'd.C].-\- 6  Aq. ;  Eq.  698-7  +  675  or  55984- 
54 — is  obtained  by  decomposino-  carbonate  of  lime  with  muriatic 
acid.    In  the  laboratory  it  is  abundantly  procured  as  the  residue  of 


FLUORIDE     OF     CALCIU  M. S  ULPHATE     OF     LIME.  431 

the  preparation  of  carbonic  acid,  ammonia,  &c.  It  is  very  soluble 
in  water  j  its  solution,  evaporated  to  the  consistence  of  a  sirup, 
gives,  by  cooling,  long,  striated,  rhombic  prisms,  which  deliquesce 
with  great  rapidi'v,  and  when  heated  undergo  watery  fusion,  soon 
after  which  it  abandons  two  thirds  of  its  water  of  crystallization, 
and  a  powder  is  obtained,  Ca.Cl.-[-2  Aq.,  in  which  form  it  is  best 
adapted  for  freezing  mixtures.  Heated  still  farther,  it  becomes  an- 
hydrous, and  at  a  red  heat  fuses.  In  this  state  it  is  phosphorescent 
in  the  dark,  forming  Homberg's  pyrophorus.  It  has  a  very  great 
affinity  for  water,  combining  with  two  atoms  of  it,  with  the  evolu- 
tion of  much  heat,  and  is  hence  employed  to  dry  gases  for  experi- 
mental purposes,  and  to  remove  water  from  liquids,  as  in  the  recti- 
fication of  alcohol. 

This  salt  combines  with  lime,  forming  an  oxychloride  of  calci 
um,  Ca.Cl.  l-3Ca.O.,  which  is  obtained  by  boiling  a  solution  of  it 
with  an  excess  of  lime,  and  filtering.  The  new  substance  crystal- 
lizes, on  cooling,  in  small  flat  rhombs,  which  contain  forty-nine  per 
cent.,  or  fifteen  atoms  of  water. 

The  bromide  or  iodide  of  Calcium  do  not  present  any  interest. 

Fluoride  of  Calcium^  Ca.F.,  is  an  abundant  mineral  known  as  fluor 
spar,  found  crystallized  in  cubes  and  octohedrons,  but  principally 
massive.  When  first  extracted  from  the  earth  it  is  moderately 
tough  and  soft,  and  is  cut  into  ornaments, which  present  a  beautiful 
variety  of  colours.  Its  crystals  become  strongly  phosphorescent 
by  heat  or  by  electricity.  It  is  insoluble  in  water ;  from  it  all  the 
other  preparations  of  fluorine  are  derived,  as  noticed  in  p.  319,  324, 
and  327.  It  appears  as  a  gelatinous  precipitate  when  hydrofluoric 
acid  is  added  to  any  soluble  salt  of  lime.  When  heated  in  contact 
with  silicious  or  aluminous  minerals,  it  forms  easily  fusible  com- 
pounds, and  being  thus  of  use  as  a  flux  in  the  smelting  of  metallic 
ores,  its  name  of  fluor  spar  was  thence  derived. 

Sulphate  of  Lime— Ca.O. .  S.O3+2  Aq. ;  Eq.  857-2-f-225  or  68-69  + 
18 — may  be  prepared  artificially,  by  mixing  a  solution  of  any  solu- 
ble salt  of  lime  with  Fulphuric  acid.  It  forms  a  crystalline  powder, 
nearly  equally  soluble  in  hot  and  cold  water,  requiring  461  times  its 
weight  for  its  solution.  It  occurs  in  nature  abundantly,  and  in  vari- 
ous forms :  1st,  in  distinct  colourless  crystals  j  2d,  in  semi-transpa- 
rent masses  of  crystalline  structure,  constituting  alabaster,  and  in 
amorphous  masses,  forming  extensive  rocky  strata,  in  many  places, 
in  which  state  it  is  called  common  gypsum.  From  this  plaster  of  Paris 
is  prepared,  bj'^  calcining  the  gypsum,  broken  into  small  pieces,  in 
ovens  at  a  temperature  below  300 \  until  its  water  of  crystallization 
is  expelled.  In  this  operation  it  falls  to  powder,  and  is  to  be  put  up 
in  tight  vessels  so  as  to  exclude  the  air.  When  mixed  with  water 
it  rapidly  recombines  with  the  two  atoms,  evolving  heat  and  expand- 
ing in  becoming  solid,  so  as  to  fill  up  all  interstices  of  the  mould 
into  which  it  may  be  poured.  On  this  property  is  founded  the  art 
of  casting  in  plaster  and  the  formation  of  the  various  kinds  of  stucco, 
or  artificial  stone,  in  which  a  solution  of  glue,  or  of  various  earthy  salts, 
may  be  substituted  for  pure  water.  If  the  gypsum  be  heated,  in  ba- 
king, above  300  ,  it  is  changed  in  nature,  and  no  longer  combines 
with  water  so  as  to  set ;  it  is  then  converted  into  a  form  which  exists 
in  nature  crystallized,  and  which  is  termed  anhydrite. 


432 


MANUFACTURE     OF     CHLORIDE     OF     LIME. 


A  double  salt  of  sulphate  of  lime  and  sulphate  of  soda  is  found 
native,  and  termed  Glauberite.  It  is  insoluble  in  water,  by  which 
it  is  also  decomposed.     It  cannot  be  formed  artificially. 

The  Hyposulphite  of  Lime  is  a  soluble  salt,  the  mode  of  preparing 
which  is  described  p.  291. 

The  Mitrate  of  Lime  is  very  deliquescent,  and  is  decomposed  by 
a  moderate  heat. 

Phosphoric  acid  combines  with  lime  in  several  proportions,  of 
which  the  most  important  is  the  Basic  trihasic  Phosphate  of  Lime^  or 
Earth  of  Bones.  This  salt,  which  constitutes  the  inorganic  portion 
of  the  skeletons  of  the  mammalia,  mixed  only  with  small  quantities 
of  carbonate  and  sulphate  of  lime,  and  of  fluoride  of  calcium,  has  the 
formula  8Ca.O. -f  3P.O5.  It  may  be  obtained  precipitated  by  dis- 
solving bone  earth  in  muriatic  acid,  and  exactly  neutralizing  the  so- 
lution by  caustic  ammonia.  It  falls  as  a  gelatinous  powder  contain- 
ing four  atoms  of  water.  As  the  phosphoric  acid  of  bones  is  in  its 
tribasic  condition,  Graham  considers  it  to  be  a  combination  of  two 
phosphates,  thus,  2(3Ca.O.  .  P.O,-f  Aq.)-}-(H.O.  .  2Ca.O.  .  P.O,-f 
Aq.).  Each  of  these  tribasic  phosphates  of  lime  may  be  obtained 
separate,  by  decomposing  solutions  of  chloride  of  calcium  by  solu- 
tion of  the  ordinary  phosphate,  or  of  the  subphosphate  of  soda. 

Hypochlorite  of  Lime.  Chloride  of  Lime.  Bleaching  Salt. — When 
speaking  of  the  oxygen  compounds  of  chlorine,  and  of  the  chlorate 
and  hypochlorite  of  potash,  I  have  had  occasion  to  notice  the  diver- 
sity of  opinion  regarding  the  nature  of  the  bleaching  substance^ 
formed  by  the  action  of  chlorine  on  the  alkalies  and  on  lime.  Ot 
these  the  chloride  of  lime  is  by  far  the  most  important  in  the  arts 
It  is  prepared  by  generating  chlorine  in  a  large  still,  a,  b.  Iij,  as  described  p.  301 
the  materials  being  kept  constantly  mixed  by  means  of  an  ngitator  moved  round  b^ 
the  handle  d.  The  gas  is  conducted  by  the  tube  e  e  \o  the  upper  part  of  a  wood;- 
en  reservoir  or  apartment,  as  in  the  iigure,  made  very  tight,  i,  i,  on  the  floor 

11 


of  which  pure  hydrate  of  lime  is  exposed  to  the  action  of  the  gas.  The  lime  is 
introduced  by  the  door  A:,  ^,  and  the  surface  is  changed  occasionally  by  stirring 
with  rakes  by  means  of  the  apertures  /,  Z,  /:  the  absorption  should  take  place  so  slow- 
ly as  no.  to  evolve  any  sensible  heat.  In  this  way  100  parts  of  slacked  lime  combine 
generally  with  from  fifty  to  sixty  of  chlorine.  If  the  process  be  carried  on  too  rap- 
idly, a  quantify  of  lime  is  decomposed,  chlorate  of  lime  and  chloride  of  calcium  be- 
ing formed,  which  may  be  recognised  by  the  product  getting  damp  when  exposed 
to  the  air 


VALUATION     OF      CHLORIDE     OF     LIME.  433 

The  best  bleaching  powder  thus  prepared  by  the  dry  way  does  not  contain  more 
than  forty  per  cent,  of  chlorine ;  this  does  not  correspond  to  any  exact  atomic  con- 
stitution ;  but  if  lime  be  diffused  through  water  so  as  to  form  a  thin  cream,  it  then 
absorbs  more  than  its  own  weight  of  gas,  and  is  totally  dissolved.  It  is  probably 
the  mechanical  disadvantages  of  the  dry  way  which  prevents  the  absorption  of  the 
gas  reaching  this  limit,  and  the  best  bleaching  powder  may  be  looked  upon  as  a  mix- 
ture of  true  chloride  of  lime,  with  about  eighteen  per  cent,  of  hydrate  of  lime  in  ex- 
cess. Accordingly,  when  ordinary  bleaching  powder  is  treated  with  water,  the  true 
atomic  compound  is  dissolved  out,  and  the  excess  of  lime  remains.  The  composi- 
tion of  the  theoretical  and  best  practical  substances  may,  therefore,  be  expressed  as 
follows : 


Theoretical.  _  Best  practical 

1  atom  chlorine,  3547  48-63 

1     "     lime,        28-57  39-04 

I     "     water,       9-00        12-33 

73-04  100-00 


Chlorine 4032 

Lime 4540 

Water 14-28 

100-00 


But  the  generality  of  good  samples  in  commerce  will  be  found  not  to  exceed  thirty 

per  cent,  of  chlorine. 

The  solution  of  this  chloride  of  lime  has  a  marked  alkaline  reaction ;  it  is  without 
any  bleaching  power  except  an  acid  be  present,  which  liberates  chlorine,  and  enables 
it  to  destroy  the  colouring  matter.  It  is  thus  that  the  colour  can  be  removed  from 
certain  points  without  injuring  others,  which  is  of  very  great  importance  in  calico 
printing;  thus  a  piece  of  cloth  being  dyed  uniformly  with  madder  (as  Turkey  red), 
the  pattern  is  printed  on  with  tartaric  acid  thickened  with  gum,  and  the  whole  being 
immersed  in  a  bath  of  chloride  of  lime,  the  chlorine  is  liberated  by  the  acid  at  every 
point  of  the  pattern,  and  the  cloth  is  there  bleached,  giving  a  white  ground,  on  which 
other  colours  may  be  applied,  while  the  general  surface  remains  deep  red.  A  solu- 
tion of  bleaching  powder  in  water  exhales  a  sensible  odour  of  chlorine,  owing  to  the 
absorption  of  carbonic  acid  from  the  air,  and  obtains  thereby  weak  bleaching  prop- 
erties. 

As  the  technical  value  of  bleaching  powder  depends  on  the  total  quantity  of  chlo- 
rine which  it  contains,  this  may  be  determined  without  reference  to  its  theoretical 
constitution.  For  this  purpose  a  variety  of  methods  have  been  proposed,  and  the 
process  is  termed  Chloromctry.  The  earliest  method  employed  consisted  in  prepa- 
ring a  standard  solution  of  sulphate  of  indigo,  which,  being  of  a  deep  blue  colour,  was 
bleached  by  the  chlorine  expelled  from  the  lime  by  the  sulphuric  acid,  and  evidently, 
the  richer  the  bleaching  powder  was  in  chlorine,  the  more  solution  of  indigo  a  certain 
weight  of  it  could  bleach.  The.  action  of  chlorine  on  indigo  is,  however,  so  com- 
plex, that  this  method  was  found  exposed  to  numerous  fallacies,  and  may  be  con- 
sidered as  now  obsolete.  Latterly,  Gay  Lussac  has  proposed  to  substitute  for  this 
the  more  definite  action  of  chlorine  in  acidifying  arsenic.  He  prepares  a  solution 
of  arsenious  acid  in  muriatic  acid,  and  dilutes  this  with  water.  On  adding  thereto 
a  solution  of  chloride  of  lime,  the  muriatic  acid  takes  the  lime,  and  the  chlorine,  de- 
composing water,  converts  the  arsenious  acid  into  arsenic  acid,  and  itself  forms  hy- 
drochloric acid;  As.Oa  with  2C1.  and  2H.0.  producing  As.Os  and  2H.CI.  The 
proportions  which  I  employ  in  this  reaction  are  as  follows :  100  grains  of  arsenious 
acid  are  to  be  dissolved  in  2000  grains  of  strong  spirits  of  salt,  and  this  liquor  diluted 
with  distilled  water  till  it  occupies  the  volume  of  7000  grains  of  water.  This  is  the 
standard  test  liquor;  to  employ  it,  100  grains  of  the  bleaching  powder  to  be  tested 
are  to  be  diifused  through  lOOO  grains  of  water,  and  the  test  liquor  to  be  gently 
poured  from  a  graduated  glass  on  it,  in  a  deep  jar,  continually  stirring  the  mixture . 
A  drop  of  weak  solution  of  sulphate  of  indigo  is  to  be  occasionally  applied,  by  means 
of  a  glass  rod,  to  the  surface  of  the  liquor ;  as  long  as  any  chlorine  remains  unalter- 
ed, the  blue  colour  of  the  drop  is  instantly  destroyed,  and  the  addition  of  the  arsenic 
liquor  is  to  be  continued  until  the  blue  drop  remains  unaltered.  Then  the  quantity 
of  chlorine  present  in  the  100  grains  of  bleaching  powder  is  represented  by  j^-^iYi  of 

tthe  quantity  of  the  test  liquor  employed ;  thus,  if  there  were  2565  grains  of  the  test 
liquor  necessary  to  destroy  the  bleaching  power  of  the  100  grains  of  chloride  of  lime, 
tlie  quantity  of  chlorine  would  be  25-65.  This  is  not  absolutely  correct ;  for  in  theo- 
ry, the  true  quantity  of  chlorine  indicated  would  be  26-08 ;  but  as  a  few  drops  of  the 
solution  are  always  employed,  more  than  what  should  by  theory  be  necessary,  the 
practical  proportion  of  -J^^th  comes  very  close  to  the  truth.  Even  one  half  part  per 
cent.,  which  is  the  limit  of  error,  is  quite  unimportant  in  practice. 
Another  method,  which  is  simple  and  rapid  in  execution,  is  nearly  the  same  as 
that  described  in  p.  355  for  determining  the  technical  value  of  black  oxide  of  man- 


434     CONSTITUTION    OFTHE     BLEACHING     SALTS. 

ganese  by  means  of  copperas  (green  sulphate  of  iron).  The  proportion  and  meth- 
od of  testing  which  I  employ  are  as  follows :  390  grains  of  clean  and  dry  crystals  of 
green  sulphate  of  iron  are  to  be  dissolved  in  as  much  water  as  will  bring  the  solu- 
tion to  the  volume  of  5000  grains  of  water.  On  the  other  hand,  100  grains  of  the 
chloride  of  lime  are  to  be  diffused  through  1000  grains  of  water,  and  the  solution  of 
copperas  is  to  be  added  thereto,  until  the  presence  of  a  trace  of  the  protosulphate  of 
iron  in  excess  is  indicated,  by  the  mixed  liquor  striking  a  full  blue  colour  when  a 
drop  of  it  is  placed  on  a  slip  of  paper,  imbibed  with  red  prussiate  of  potash.  The 
quantity  of  chlorine  present  in  the  100  grains  of  the  bleaching  powder  isyl^th  of  the 
quantity  of  the  standard  copperas  liquor  employed;  thus,  if  2783  grains  measure  of 
the  volume  of  the  solution  be  foynd  necessary,  the  sample  contains  2783  of  chlorine 
per  cent.  For  the  27-83  of  liquor  contains  217  grains  of  sulphate  of  iron,  which  is 
peroxidized  by  the  action  of  27*6  grains  of  chlorine ;  here,  also,  the  limit  of  error  need 
not  exceed  one  half  per  cent.  Other  processes  have  been  proposed,  founded,  some 
on  the  change  of  yellow  prussiate  into  red  prussiate  of  potash,  by  means  of  the  chlo- 
rine of  the  bleaching  powder;  and  others,  by  decomposing  the  bleaching  powder  by 
means  of  an  excess  of  water  of  ammonia,  and  measuring  the  nitrogen  gas  evolved; 
but  these  are  more  troublesome  and  less  exact  than  the  processes  already  detailed, 
which  are  those  most  worthy  of  confidence  from  the  manufacturer. 

As  to  the  theoretical  nature  of  bleaching  powder,  chemists  are 
not  as  yet  able  to  decide  positively.  The  original  and  simple  idea 
of  a  direct  combination  between  the  chlorine  and  the  lime  has  been 
revived  by  Millon,  who  advanced  that,  by  decomposing  the  salts  of 
lead,  iron,  and  copper  by  solution  of  chloride  of  lime,  precipitates 
were  obtained,  which  were  compounds  of  the  protoxide  of  the  metal 
united  with  as  much  chlorine  as  was  equivalent  to  the  oxygen  ne- 
cessary to  form  peroxide.  Thus,  that  with  lead,^  a  chloroxide  Pb.O. 
CI. ;  that  with  iron,  a  chloroxide  FcaOaCl.  The  chloride  of  lime, 
Ca.O.Cl.,  would  thus  be  equivalent  to  deutoxide  of  calcium,  Ca.0.0. 
It  has  been  found,  however,  that  the  evidence  is  not  yet  satisfac- 
tory. The  peroxide  of  potassium  is  K.O3,  while  chloride  of  potash 
is  not  K.O.CI2,  but  K.O.Cl.  The  composition  of  all  these  bleaching 
compounds  appears  to  be  an  atom  of  chlorine  united  to  an  atom  of 
a  protoxide,  and  this  may  be  explained  by  supposing  a  hypochlorite 
and  a  metallic  chloride  to  be  formed  ;  thus  2Ca.O.  and  2C1.  may 
give  Ca.O.  +  Cl.O.  and  Ca.Cl.  But,  if  this  happens,  the  chloride  of 
calcium  certainly  remains  combined,  forming  a  double  salt  5  for  the 
bleaching  powder,  if  properly  prepared,  has  no  tendency  to  deli- 
quesce, and  only  becomes  damp  when  long  kept ;  and  then  chlorate 
of  lime  and  free  chloride  of  calcium  are  formed,  and  all  its  bleach- 
ing qualities  are  lost.  There  are  thus  two  views  equally  tenable  : 
first,  that  the  bleaching  compounds  are  chlorides  of  oxides^  corre- 
sponding to  peroxides ;  and,  second,  that  they  are  double  salts  of  a 
hypochlorite  with  a  chloride  ;  but  there  is  no  reason  to  consider 
that  the  chlorous  acid,  CI.O4,  comes  into  play  in  their  manufacture, 
although  the  salts  of  that  acid,  when  otherwise  prepared,  do  possess 
bleaching  properties. 

Salts  of  Magnesium. 

Chloride  of  Magnesium — Mg.Cl. ;  Eq.  600  9  or  48.16— may  be  ob- 
tained in  solution  by  acting  on  the  carbonate  of  magnesia  with  mu- 
riatic acid  ;  by  evaporation,  it  may  be  obtained  in  prisms  with  6 
Aq.,  which  are  very  deliquescent.  These  crystals  cannot  be  de- 
prived of  water  without  total  decomposition,  the  chlorine  passing 
off  as  muriatic  acid,  and  magnesia  remaining  behind.  The  chloride 
may,  however,  be  obtained  anhydrous,  by  previously  mixing  its  so- 


SALTS    OF     MAGNESIUM     AND     ALUMINUM. 


435 


lution  with  sal  ammoniac,  with  which  it  forms  an  anhydrous  double 
salt,  which,  when  heated  to  redness,  gives  off  sal  ammoniac,  and 
the  pure  chloride  of  magnesium  remains  melted,  and  forms  a  clear 
crystalline  mass  when  cold.  The  chloride  of  magnesium  exists  in 
sea-water. 

Sulphate  of  Magnesia.^Ug.O. .  S.O3.  Eq.  759-4  or  SO-8.  This  salt 
exists  abundantly  in  saline  mineral  springs,  as  those  of  Seidlitz,  Sel- 
lers, and  Epsom,  from  whence  it  derives  its  common  name  of  Epsom 
salt.  It  is  extracted  principally  from  the  magnesian  limestone, 
which  is  calcined,  and  the  mixed  lime  and  magnesia  treated  with 
dilute  sulphuric  acid  ;  the  sulphate  of  lime,  being  very  sparingly  sol- 
uble, is  easily  separated  from  the  sulphate  of  magnesia  by  washing 
with  water ;  the  latter  is  dissolved  out,  and  the  liquor  evaporated 
and  crystallized.  A  great  deal  is  also  made  from  the  mother  liquor 
of  sea-water,  or  bittern  (p.  426).  This  is  decomposed  by  sulphuric 
acid,  and  the  salt  formed  separated  by  crystallization. 

The  sulphate  of  magnesia  crystallizes  in  eight  rhombic  prisms, 
as  in  the  figure,  containing  seven  atoms  of  water, 
of  which  one  is  constitutional,  and  the  other  six 
crystalline  ;  its  formula  is  therefore  Mg.O.  .  S.O3 . 
H.O. +  6  Aq. ;  when  heated  to  212^  it  easily  aban- 
dons the  6  Aq.,  but  retains  the  seventh  atom  of  wa- 
ter even  at  400^.  It  combines  with  the  sulphate 
of  potash  to  form  a  double  salt,  (Mg.O. .  S.O3+K. 
O. .  S.03)-t-6  Aq.,  the  atom  of  constitutional  water 
being  replaced  by  the  alkaline  sulphate.  The  sul- 
phates of  soda  and  of  ammonia  act  in  the  same  way. " 

Nitrate  of  MagTiesia,  Mg.O. .  N.O5,  is  very  soluble  and  deliquescent.  It  cannot  be 
obtained  dry,  as  it  crystallizes  with  six  equivalents  of  water,  of  which  five  are  ex- 
pelled by  a  moderate  heat,  and  by  a  higher  temperature  the  nitric  acid  itself  passes 
off,  and  magnesia  remains  behind ;  Mg.O. .  N.O5 .  H.O.  producing  Mg.O.  and  H.O. . 
N.O5. 

The  Borate  of  Magnesia  constitutes  the  mineral  boracite,  whose  electrical  and 
crystalline  properties  have  been  already  noticed. 

There  exists  a  great  number  of  combinations  of  silicic  acid  with  magnesia,  con- 
stituting the  steatite,  or  soapstone ;  the  meerschaum,  of  which  pipe-bowls  are  cut ;  oli- 
vine and  serpentine,  which  exist  abundantly  in  the  green  marble  of  Galway :  these 
are  simple  silicates  of  magnesia ;  others,  as  amphibole  and  pyroxene,  are  double  sili- 
cates of  magnesia  and  lime,  more  or  less  replaced  by  protoxide  of  iron. 

Salts  of  Aluminum. 

Chloride  of  Aluminuvi.—AhCh.  Eq.  1670-3  or  133-84.  In  a  hydrated  form  this 
salt  may  be  prepared  by  dissolving  alumina  in  muriatic  acid,  a  solution  being  ob- 
tained, which,  when  evaporated,  yields  very  deliquescent  crystals,  containing  twelve 
atoms  of  water.  On  applying  heat  to  this,  the  salt  itself  is  decomposed,  muriatic 
acid  is  given  off,  and  pure  alumina  remains.  The  dry  chloride  of  aluminum  is 
formed  only  by  a  process  analogous  to  that  described  for  chloride  of  silicon,  p.  323. 
Pure  alumina  is  mixed  with  lampblack  and  ignited  in  a  porcelain  tube,  while  a 
stream  of  dry  chlorine  is  passed  over  it :  the  oxygen  of  the  alumina  combines  witlT 
the  carbon,  and  forms  carbonic  oxide,  and  the  chlorine  combines  with  the  aluminum. 
The  resulting  chloride,  being  volatile,  sublimes,  and  is  condensed  in  the  cool  portion 
of  the  tube,  which  is  allowed  to  project  some  distance  beyond  the  furnace  for  that 
purpose,  or  a  wide  glass  tube  is  adapted  to  receive  the  salt. 

The  chloride  of  aluminum  thus  formed  is  a  palcrgreen  crystalline  mass.  Exposed 
to  the  air,  it  fumes  and  deliquesces.  Once  combined  with  water,  it  cannot  be  freed 
from  it.     It  is  used  to  obtain  metallic  aluminum,  as  described  p.  349. 

The  Fluoride  of  Aluminum  is  found  in  the  mineral  kingdom.  The  beautiful  gem, 
the  topaz,  is  a  double  fluoride  and  silicate  of  alumina. 


436  MANUFACTURE     OF     ALUM. 

4 

Sulphate  of  Alumina  (AI2O3  +  SS.Og)-}- 18  Aq. — This  salt  is  obtain- 
ed by  dissolving  alumina  in  dilute  sulphuric  acid  ;  it  has  a  sweetish 
styptic  taste,  is  very  soluble  in  water,  and  crystallizes  in  thin  flexi- 
ble plates ;  when  heated,  it  abandons  its  water,  and  at  a  red  heat 
its  sulphuric  acid,  alumina  remaining  pure.  The  sulphuric  acid 
unites  with  alumina  in  many  other  proportions,  of  which  that  con- 
stituting the  mineral  aluminite  is  the  most  important ;  its  formula  is 
AI2O34-S.O34-3  Aq.,  the  base,  acid,  and  water  each  containing  the 
same  quantity  of  oxygen.  This  salt  is  produced,  also,  by  adding 
an  excess  of  caustic  ammonia  to  a  solution  of  alum  \  hence  caustic 
ammonia  cannot  be  used  to  prepare  pure  alumina  (p.  351). 

The  sulphate  of  alumina  combines  with  the  alkaline  sulphates  to 
form  the  remarkable  double  salts,  the  common  alums.  The  most 
ordinary  kind  is  the  double  sulphate  of  alumina  and  potash^  the  for- 
mula of  which  is  (K.O. .  S.03-L-A1A4-3S.03)  +  24<  Aq. 

From  the  large  quantities  of  this  salt  employed  in  the  processes  of  dyeing,  its  man- 
ufacture is  conducted  upon  the  great  scale.  In  the  coal  districts,  and  underlying 
the  beds  of  good  coal,  strata  of  clay-slate  are  generally  found,  containing  a  certain 
quantity  of  coally  material,  and  through  which  abundance  of  bisulphuret  of  iron  is 
disseminated  in  the  instable  rhombic  form  (see  p.  332  and  358).  When  this  alum 
slate  is  exposed  to  the  air,  the  sulphuret  of  iron  rapidly  absorbs  oxygen  and  forms 
copperas,  with  an  excess  of  sulphuric  acid,  which  reacts  on  the  clays,  with  the 
alumina  of  which  it  combines.  This  effect  is  accelerated  by  the  application  of  heat, 
which  is  applied  by  building  up  the  mineral  into  pyramidal  heaps,  with  some  fuel 
underneath,  and  channels  through  the  interior,  by  which  a  draught  may  be  establish- 
ed ;  the  fuel  below  being  set  on  fire,  the  slate  contains  coal  enough  to  maintain  its 
own  combustion,  and  the  mass  changes  in  colour  as  it  bums,  becoming  brick  red ; 
according  as  the  process  is  carried  through,  successive  quantities  of  mineral  are  ad- 
ded to  the  burning  heap,  until  it  often  acquires  a  height  of  sixty  or  eighty  feet.  When, 
the  mass  thus  calcined  has  become  quite  cold,  it  is  powdered  and  lixiviated  with 
water ;  a  large  quantity  of  sulphate  of  alumina  and  sulphate  of  iron  dissolve  out, 
and  the  liquor  is  brought  by  evaporation  to  a  certain  degree  of  strength.  A  solution 
of  some  salt  of  potash  is  then  added,  generally  the  waste  chloride  of  potassium  from 
soap-boilers,  and  the  sulphate  of  iron  being  decomposed,  forms  sulphate  of  potash, 
which  unites  with  the  sulphate  of  alumina,  and  crystallizes  out  as  alum,  while  the 
iron  remains  as  chloride  in  the  liquor. 

In  some  volcanic  countries,  as  Italy,  a  mineral  is  found  already  containing  potash 
and  sulphuric  acid  united  to  alumina,  from  which  is  obtained  a  very  pure  alum, 
rock-alum,  which  is  valued  very  much  by  dyers,  on  account  of  its  total  freedom  from 
sulphate  of  iron,  of  which  English  alum  generally  contains  a  small  trace,  which  in- 
jures the  colours  of  the  dyes. 

Alum  crystallizes  in  regular  octohedrons,  the  solid  angles  being 
often  replaced  by  the  surfaces  of  a  cube.  When  heated,  the  water 
is  first  expelled,  and  at  a  red  heat  it  parts  with  most  of  its  sulphuric 
acid,  sulphate  of  potash  and  pure  alumina  remaining.  The  taste  of 
alum  is  sweet  and  astringent ;  it  reacts  acid,  and  is  soluble  in  18*4< 
parts  of  cold,  and  in  0-75  parts  of  boiling  water.  A  remarkable  py- 
rophorus,  that  of  Homberg,  is  prepared  from  alum  ;  three  parts  of 
dried  alum  and  one  of  lampblack  well  mixed  are  to  be  placed  in  a 
stout  glass  bottle,  and,  being  bedded  with  sand  in  a  crucible,  are  to 
be  carefully  heated  to  redness,  until  a  blue  flame  appears  at  the 
mouth  of  the  bottle ;  when  this  has  lasted  a  few  minutes,  the  bottle 
is  to  be  stoppered  with  a  bit  of  chalk,  and  the  whole  cautiously 
cooled.  The  bottle  contains  a  black  powder,  a  mixture  of  lamp- 
black, alumina,  and  sulphuret  of  potassium,  which  last,  being  in  a 
ytate  of  exceedingly  minute  division,  takes  fire  when  a  little  of  the 
product  is  shaken  out  of  the  bottle,  and  emits  considerable  light. 
Basic  Mum.     Cubical  Mum.—M^O^  .  SS.Og-f  K.O.  .  S.O3.     This 


GLASS     AND    PORCELAIN.  437 

substance,  which  is  preferred  as  a  mordant  to  ordinary  alum,  is  pre- 
pared by  adding  carbonate  of  potash  to  a  solution  of  alum,  as  long 
as  the  precipitate  which  first  forms  is  redissolved  by  agitation.  It 
crystallizes  in  cubes  which  have  no  acid  reaction. 

The  sulphate  of  soda  combining  with  sulphate  of  alumina,  forms 
the  soda  alum^  which  is  not  much  used.  The  ammonia  alum  will  be 
hereafter  noticed. 

The  Phosplmte  of  Alumina  constitutes  a  remarkable  mineral  found  in  Cork  and 
Tipperary,  the  wavellite. 

The  simple  and  double  silicates  of  alumina  constitute  probably  the  majority  of  all 
known  minerals;  such  of  them  as  possess  technical  or  pharmaceutic  value  are 
noticed  under  the  heads  of  the  uses  to  which  they  are  applied.  For  a  description  of 
the  others,  I  refer  to  the  ordinary  works  on  mineralogy. 

One  substance,  however,  of  which  the  constitution  is  very  curious,  may,  from  its 
technical  importance,  here  be  noticed,  the  Mpis-lazuli,  ultramariTie.  It  is  found  in 
veins  in  igneous  rocks  in  Siberia,  but  particularly  in  China.  It  is  of  a  rich  blue 
colour,  not  crystalline,  and  being  powdered,  serves  in  painting  as  the  richest  and 
most  permanent  blue  ;  its  composition  has  been  found  to  be,  in  100  parts,  silica,  35-8; 
alumina,  34-8;  soda,  23-2;  sulphur,  3-1 ;  carbonate  of  lime,  3-1 :  it  is  difficult  to  de- 
duce a  formula  from  these  numbers,  and  the  state  of  combination  of  the  sulphur  is 
not  well  understood.  Attempts  at  imitating  the  composition  of  this  body  have  been 
partially  successful,  and  a  large  quantity  of  artificial  ultramarine  is  now  made  for 
painters'  use  by  the  following  process :  freshly  precipitated  silicic  acid  and  alumina 
are  mixed  with  sulphur  in  a  solution  of  caustic  soda,  all  in  the  proportions  above 
given,  and  the  mixture  dried  down ;  the  resulting  mass  is  placed  in  a  covered  cruci- 
ble and  exposed  to  a  white  heat ;  it  gives  a  dark  and  pure  blue  mass,  to  which,  for 
the  perfect  bringing  out  of  the  colour,  the  air  must  have  had  partial  access  during 
its  ignition.  The  product  is  reduced  to  impalpable  powder  by  the  same  process 
adopted  for  the  native  substance. 

Constitution  of  Glass  and  Porcelain, 

1  deferred  the  description  of  the  silicates  of  potash,  soda,  and 
lime,  because  they  stand  so  closely  allied  with  the  silicate  of  alumi- 
na, in  relation  to  the  important  manufactures  of  glass  and  earthen- 
ware, that  their  properties  could  only  be  well  understood  when 
studied  in  connexion  with  it. 

Silicic  acid  combines  with  the  alkalies  in  many  proportions,  of 
which  those  that  contain  a  considerable  excess  of  base  are  soluble 
in  water.  Thus  is  prepared  the  liquo?-  of  flints^  by  melting  together 
one  part  of  powdered  quartz  and  two  of  carbonate  of  potash  ;  the 
carbonic  acid  is  expelled,  and  a  glassy  mass  is  obtained,  which  de- 
liquesces in  the  air,  and  is  very  soluble  in  water.  It  reacts  strongly 
alkaline,  and  gives,  with  acids,  a  precipitate  of  silica  in  its  soluble 
form,  as  described  p.  321.  In  this  preparation,  soda  may  be  substi- 
tuted for  potash  in  a  proportion  one  third  less,  and  a  mixture  of 
seventy  parts  of  carbonate  of  potash,  fifty-four  of  dry  carbonate  of 
soda,  and  152  of  fine  quartz  sand,  gives  a  still  more  fusible  and  sol- 
uble product.  This  substance,  under  the  name  of  soluble  glass, 
has  been  employed  to  render  wood  incombustible,  several  coats  of 
a  strong  solution  of  it  being  applied  under  the  paint. 

When  the  quantity  of  silicic  acid  is  greater,  the  resulting  alkaline 
silicate  is  insoluble  in  water,  and  possesses  the  qualities  which  give 
to  glass  its  peculiar  value.  These  are,  first,  to  solidify,  after  bein^ 
melted,  very  gradually,  and  to  pass  through  a  condition  of  pasti- 
ness, which  admits  of  its  being  blown  out,  cut,  and  fashioned  in  ev- 
ery way  ;  and,  second,  to  remain,  when  solid,  quite  transparent,  and 
destitute  of  any  tendency  to  crystalline  structure.     Its  composition 


438 


MANUFACTURE     OF     GLASS. 


should  also  be  such  as  to  resist  completely  the  action  of  air  and 
water. 

The  materials  used  in  the  manufacture  of  glass  are,  1st,  quartz 
sand,  as  free  as  possible'from  iron  ;  2d,  lime,  used  sometimes  pure, 
sometimes  slacked  j  occasionally  chalk  is  employed  in  place  of  lime  j 
3d,  carbonate  of  potash  (pearl  ashes  of  commerce)  ;  4th,  carbonate 
of  soda,  or  a  salt  of  soda,  as  Glauber's  salt  or  common  salt  j  5th, 
old  broken  glass,  technically  termed  cullet ;  6th,  red  lead,  which 
must  be  extremely  pure  ]  and  for  corrective  purposes,  arsenious  acid 
sometimes,  but  more  frequently  black  oxide  of  manganese. 

These  materials  are  by  no  means  all  employed  together ;  the  composition  of  va- 
rious kinds  of  glass  difiering  very  much,  as  is  shown  in  the  following  table  of  th« 
best  analyses  of  glass. 


Constituents. 

Hard  while 
Glass. 

Crown  Glass.  |    Bottle  Glass. 

Crys- 
tal. 

Flint  Glass.    1 

No.  1. 

No.  2. 

No.  3. 

No.  4.  No.  5. 

No.  6. 

53-5 

No.  7. 

59-2 

No.  8. 

No.  9. 

Silicic  Acid      .    .    . 

71-7 

69-2 

62-8 

69-260-4 

51-9 

42-5 

Potash 

12-7 

158 

221 

80   3-2 

5-5 

90 

13-8 

11-7 

Soda 

2-5 

30 

30!  .  . 

Lime 

10-3 

7-6 

12-5 

130:20-7 

29-2 

05 

Alumina      .... 

0-4 

1-2 

) 

36 

10-4 

60 

1-8 

Magnesia    .... 

20 

^2-6 

0-6 

0-6 

.  . 

.  . 

,  , 

Oxide  of  Iron  .     .    . 

b-3 

0-5 

S 

1-6 

3-8 

5-8 

0-4 

.  . 

,  .  . 

Oxide  of  Manganese 

0-2 

10 

.  . 

Oxide  of  Lead     .    . 

990 

991 

1000 

28-2 
97-8 

33-3 
99-0 

43-5 
1000 

981 

99-3 

1000 

Although  in  some  of  these  analyses  a  slight  loss  occurred,  yet  they  are  sufficiently 
accurate  for  all  purposes.  No.  1  is  the  hard  Bohemian  glass,  so"  valuable  to  the 
chemist,  from  the  high  temperature  it  bears  without  softening.  No.  2,  also  a  Bohe- 
mian glass,  is  much  more  fusible,  and  is  that  in  ordinary  use.  No.  3  is  English 
plate,  and  No.  4  German  plate  glass,  Nos.  5  and  6  are  both  French.  Nos.  7  and 
§  are  English  glass  for  table  use  and  chemical  apparatus  ;  and  No.  9  is  the  glass  so 
celebrated  for  optical  purposes,  made  by  Guinaud. 

It  is  difficult  to  trace  any  definite  relation  between  the  acid  and  bases  in  these 
glasses ;  indeed,  we  cannot  look  upon  the  difierent  silicates  as  being  really  combined 
with  each  other ;  they  are  rather  in  a  state  of  intimate  mechanical  mixture ;  hence, 
if  the  glass  be  kept  soft,  but  not  liquid,  for  a  considerable  time,  the  silicates  gradu- 
ally separate ;  the  less  fusible  crystallizing,  and  rendering  the  glass  opaque  white. 
This  takes  place  most  easily  with  such  glass  as  contains  much  silicate  of  lime  oi 
alumina.  In  this  form,  the  mass  is  so  hard  as  to  strike  fire  with  steel,  and  becomes 
almost  infusible.    From  the  name  of  its  discoverer,  it  is  termed  lieaumur's  Porcelain. 

The  arrangement  of  the  furnaces  for  the  manufacture  of  glass  varies  according  to 
the  materials  and  the  kind  of  product.  The  materials,  reduced  to  the  state  of  very 
fine  powder,  are  intimately  mixed,  and  fused  in  crucibles  of  very  refractory  clay. 
The  silica  decomposes  the  carbonates  of  lime  and  potash  or  soda,  and,  expelling  the 
carbonic  acid,  combines  with  the  alkali  and  earth.  If  sulphate  of  soda  had  been 
used,  a  certain  quantity  of  carbon  is  added,  by  which  the  sulphuric  acid  is  decom- 
posed, sulphurous  and  carbonic  acids  being  evolved  (p.  292),  otherwise  the  silica 
could  not  completely  expel  the  sulphuric  acid.  From  the  presence  of  minute  quan- 
tities of  protoxide  of  iron  in  the  materials,  the  glass  has.  at  first,  a  pale-greenish  tint, 
which  is  counteracted  by  the  addition  of  a  little  nitre  or  arsenious  acid,  these  agents 
giving  oxygen  to  the  iron,  which  does  not  colour  when  peroxidized ;  with  the  latter 
body  the  metallic  arsenic  is  evolved  in  vapour,  the  bad  effects  of  which  should  pre- 
vent its  employment.  More  generally  peroxide  of  manganese  is  used,  which,  acting 
on  protoxide  of  iron,  produces  peroxide  of  iron  and  protoxide  of  manganese,  neither 
of  which  bodies  gives  any  sensible  tint  to  glass.  If  there  be  too  much  manganese 
employed,  the  glass  acquires  a  violet  tint.  There  is  reason  to  suspect  that  soda 
glass  is  greenish  even  when  absolutely  free  from  iron. 

The  general  arrangement  of  a  glass  furnace  may  be  illustrated  by  reference  to  the 
figures,  which  represent  the  essential  parts  of  one  of  the  most  perfect  forms  employ- 
ed in  the  manufacture  of  the  fine  crown  glass  of  Germany.  In  the  oval  furnace 
A.  which  is  covered  by  a  dome,  the  crucible.s  are  arranged  in  two  rows,  on  barJcs, 


MANUFACTURE     OF     GLASS. 


439 


of  which  one  is  represented  in  the  sectional  figure.  These  crucibles  are  left  open  < 
but  if  employed  for  a  glass 
containing  lead,  they  should 
be  covered  by  a  hood,  pre- 
senting only  an  aperture  ex- 
ternal to  the  furnace  for 
the  workman,  as  the  glass 
would  require  to  be  thus  pro- 
tected from  the  smoke  and 
combusti])le  gases  of  the  fur- 
nace, which  would  reduce 
the  lead  to  the  metallic  state. 
Between  the  banks  is  a  rec- 
tangular space  for  the  fire, 
resting  on  the  gratings  b  b, 
which  are  separated  by  the 
partition  wall  F,  and  have 
apertures  at  the  sides  for  the 
introduction  of  the  fuel.  By 
means  of  the  passage  D,  there  is  access  beneath  the  grate  for  the  purpose  of  clearing 
it,  and  the  draught  is  regulated  by  the  opening  or  closing  of  the  doors  e  e.  The 
flame  of  the  fuel,  which  should  be  either  wood  or  a  very  bituminous  coal,  issues 
partly  through  the  apertures  in  front  of  the  crucibles  o  o,  and  partly  passes  by  g  into 
the  wings  and  chimney ;  by  means  of  the  wings,  a  great  quantity  of  the  heat  is 
economized  for  preparatory  operations.    Next  the  furnace  are  placed  the  fresh  cru- 


r 


cibles  e  e,  which,  being  always  made  in  the  glass-house,  are  there  dried,  baked,  and 
ultimately  brought  to  a  full  red  heat,  so  as  to  be  fit  for  introduction  into  the  furnace 
with  a  charge  of  glass.  The  draught  passing  in  the  direction  of  the  arrows  over 
the  low  partition,  the  flame  and  hot  air  acts  on  the  space  k,  on  the  floor  of  which  are 
spread  the  materials  for  the  next  charge  of  glass,  well  mixed,  and  introduced  by  the 
apertures  1 1;  these  being  brought  to  a  dull  red  heat,  undergo  a  commencement  of 
vitrefaction,  and  are  thus  fritted,  or  prepared  for  the  perfect  combination  by  fusion 
in  the  crucibles.  This  operation  of  fritting  was  formerly  performed  in  a  separate 
reverberatory  furnace.  The  draught  escapes  partly  from  the  small  chimney  x;  but 
a  portion  of  the  hot  air,  having  passed  over  the  partition  m,  is  conducted  into  the 
chamber  w,  which  is  filled  with  wood  supported  on  the  grating ;  the  hot  air,  in  pass- 
ing off,  carries  away  the  moisture  of  the  wood,  which  is  thus  brought  to  a  state  of 
perfect  desiccation,  so  as  to  give  the  greatest  possible  effect  in  the  furnace. 

For  the  perfect  combination  of  the  materials,  and  obtaining  a  mass  free  from 
streaks  and  air-bubbles,  it  is  essential  that  the  glass  should  be  brought  into  a  state 
of  perfect  liquidity,  so  as  to  allow  the  gases  to  pass  off  freely,  and  then  be  suffered 
to  cool  until  it  acquires  the  pasty  consistence  which  fits  it  for  being  worked  into  the 
necessary  fonns.  In  thus  cooling  down,  however,  those  glasses  which  contain 
oxide  of  lead  frequently  separate  into  two  or  more  layers  of  glass  of  different  den- 
sities, which,  when  stirred  up  by  the  tools  of  the  workman,  give  by  their  imperfect 
mixture  a  clouded  and  streaked  appearance  to  the  articles  made  from  such  glass. 
This  impefection  is  peculiarly  fatal  to  glass  for  optical  purposes,  as  each  layer  may 
have  a  different  refractive  power,  and  thus  give  distorted  images. 

The  great  use  of  glass  in  the  arts  and  in  ordinary  life  depends  upon  its  plasticity 
at  a  red  heat,  which  renders  it  capable  of  being  moulded  into  every  form ;  its  insol- 


440  COMPOSITION     OF     CLA'^. 

ubility  in  water ;  its  resisting  the  action  of  acids  and  the  generality  of  chemical  re- 
agents under  all  ordinary  circumstances ;  its  transparency  and  lustre,  and  the  rela- 
tions to  heat,  to  light,  and  to  electricity,  which  have  been  already  fully  noticed.  From 
the  low  conducting  power  of  glass  for  heat,  thick  portions  of  it  are  liable  to  break 
when  suddenly  warmed,  the  part  to  which  the  heat  is  directly  applied  expanding,  and 
thereby  separating  from  that  which  remains  cold.  When  a  lump  of  glass  is  sudden- 
ly cooled,  as  by  being  laid,  while  soft,  on  a  i)late  of  cold  iron,  or  being  dropped  into 
water,  the  internal  portions  being  prevented  from  contracting,  remain  in  a  state  of  in- 
stable arrangement,  on  which  depends  its  double  refracting  and  polarizing  properties 
(p.  230).  When  the  molecules  of  such  a  piece  of  chilled  glass  are  made  to  vibrate,  by 
being  scratched,'  or  a  little  fragment  being  broken  off,  they  change  totally  their  dis- 
position, and,  flying  asunder,  the  mass  crumbles  into  powder  with  an  explosion. 
Priiice  Rupert's  drops,  with  which  this  property  of  glass  may  be  exemplified,  are  pre- 
pared by  taking  up  on  an  iron  rod  a  little  melted  glass,  and  allowing  the  drops  of  it 
to  fall  into  a  vessel  of  cold  water;  when  one  is  held  in  the  hand,  and  the  long  pro- 
jecting tail  broken  off,  a  smart  blow  is  felt  with  a  dull  noise,  and  the  drop  is  found 
to  be  reduced  to  fine  powder.  As  this  excessive  frangibility  would  render  glass  un- 
fit for  most  household  and  chemical  purposes,  it  is  necessary  to  lessen  it  as  much  as 
possible,  which  is  done  by  allowing  it  to  cool  very  slowly.  For  this  purpose,  the 
vessels,  when  formed,  are  placed  in  the  aiinealing  fiirnace,  or  leer,  which  is  a  long  gal 
lery  containing  a  number  of  iron  trays  moveable  along  it  by  means  of  an  endless 
chain ;  the  hot  glass  articles  are  placed  in  the  trays  at  one  end,  where  a  strong  fire 
is  made,  the  flame  of  which  sweeps  to  a  certain  distance  into  the  gallery.  Accord- 
ing as  new  trays  come  up,  those  already  full  are  drawn  down  into  the  cooler  part 
of  the  gallery  by  the  chain,  and  finally  issue  at  the  other  end  quite  cold.  The  pas- 
sage down  occupying  from  twenty-four  to  forty-eight  hours,  the  particles  of  the  glass, 
in  cooling,  have  time  to  assume  their  most  stable  arrangement,  and  may  then  be  ex- 
posed, if  not  very  thick,  to  changes  of  temperature,  provided  they  be  not  very 
sudden. 

The  specific  gravity  of  glass  varies  with  its  composition  from  2*4 
to  3-6,  the  latter  being  that  of  flint  glass,  containing  40  per  cent,  of 
oxide  of  lead.  The  lighter  glasses  are  generally  those  which  are 
hardest,  and  resist  the  action  of  water  and  of  reagents  best.  The 
oxide  of  lead  in  flint  glass  is  acted  on  by  a  variety  of  chemical  sub- 
stances, which  unfits  it  for  many  laboratory  uses.  Where  alkali 
predominates,  the  glass  is  rapidly  acted  on  by  the  air,  attracting 
moisture,  and  thus  frequently  embarrassing  electrical  experiments. 
Bottle  glass  which  contains  much  alumina  is  so  rapidly  corroded 
by  the  cream  of  tartar  in  wine,  as  sometimes  to  become  opaque, 
and  spoil  the  wine  in  the  course  of  a  few  days. 

I  have  had  frequent  occasion  to  notice  the  various  coloured  glasses  produced  by 
the  addition  of  metallic  oxides  (see  p.  37) ;  on  this  principle  is  founded  the  art  of 
painting  on,  or  staining  glass,  and  also  the  manufacture  of  artificial  gems.  These 
arts  I  shall  have  to  notice  farther  on,  and  any  detail  of  their  methods  would  be  foreign 
to  a  work  like  the  present. 

The  manufacture  of  porcelain  and  earthenware  depends  on  two 
principles,  first,  that  of  the  plasticity  and  fusibility  of  clay,  and,  sec- 
ondly, the  fusibility  of  a  glass  by  which  the  substance  of  the  porous 
clay  may  be  imbibed,  and  thus  rendered  water-tight.  Clay,  when 
perfectly  pure,  is  a  neutral  silicate  of  alumina,  Al203H-3Si.03 ;  but 
as  the  great  deposites  of  clay  used  for  the  purposes  of  the  arts  are 
produced  by  the  weathering  (decomposition)  of  a  variety  of  rocks, 
a  number  of  foreign  ingredients  are  intermixed  in  small  quantity, 
and  produce  varieties  which  influence  very  much  the  proportions 
used  in  the  manufacture.  The  purest  porcelain  clay  is  formed  by 
the  decomposition  of  the  feldspar  contained  in  granitic  and  syenitic 
rocks.  The  feldspar  has  the  formula  K.O. .  Si.03-{-(AlA+3*Si.03)  i 
by  the  action  of  water,  the  silicate  of  potash  is  dissolved  out  as  sol- 
uble glass  (p.  437),  and  the  silicate  of  alumina  remains  as  a  fine 


MANUFACTURE     OF     EARTHENWARE. 


441 


powder,  perfectly  white,  impalpable,  forming  with  water  a  paste 
capable  of  being  moulded  into  any  form,  and,  when  heated,  abandon- 
ing the  water  and  contracting  in  volume,  but  retaining  the  form 
which  had  been  given  to  it.  The  pure  porcelain  clay  is  seldom 
found,  and  hence  is  used  only  for  the  finest  objects  j  other  clays  of 
greater  or  less  purity  are  therefore  used,  either  alone,  or  mixed  with 
porcelain  clay,  for  such  objects  as  stone-china  and  delft  ,•  and  clays 
in  which  a  quantity  of  alumina  is  replaced  by  iron,  and  which,  con- 
sequently, when  burned,  assume  a  red  or  yellow  colour,  are  em- 
ployed for  common  earthenware.  In  the  clays  which  contain  very 
little  iron,  and  hence  burn  white,  there  are  present,  almost  univer- 
sally, certain  quantities  of  alkali,  remaining  from  the  decomposed 
feldspar ;  this  is  generally  potash,  but  may  be  soda  when  the  clay 
is  formed  from  albite  (Na.O. .  Si.O  -fSAlaOa-f-SSi.Oa)  ;  and  when  the 
source  of  the  clay  is  not  a  pure  granitic  rock,  the  associated  miner- 
als generally  yield  a  certain  quantity  of  lime  which  mixes  with  it. 
Hence  the  composition  of  the  following  clays,  from  various  coun- 
tries, used  in  the  manufacture  of  porcelain,  can  easily  be  account- 
ed for : 


Clay  from 

Mori. 

Schnee- 
berg. 

Limoges. 

Silica      .... 

71-42 

436 

46-8 

Alumina      .     .    . 

26  07 

377 

373 

Lime      .... 

0  13 

Potash   .... 

045 

25 

Water    .... 

120 

13-0 

Oxide  of  Iron  .     . 

1-93 

1-5 

If  clay  alone  were  used  in  the  fabrication  of  earthenware,  al- 
though, from  its  plasticity,  it  would  assume  perfectly  the  required 
form,  yet,  from  its  infusibility,  it  would,  when  baked,  have  so  little 
coherence,  and,  from  its  great  contraction,  be  so  liable  to  crack, 
that  in  practice  it  could  not  be  beneficially  employed.  The  paste 
of  which  the  china  and  delft  articles  are  made,  consists,  therefore, 
of  clay,  to  which  is  added  silica,  lime,  and  potash — in  other  words, 
the  constituents  of  crown  glass — which,  being  fusible  at  a  high  tem- 
perature, cement  together  the  particles  of  clay,  and  enable  the  dif- 
ferent portions  of  the  vessel  to  hold  together  during  the  bakings. 
Thus,  to  form  the  body  of  ironstone  chinaware,  forty  parts  of  Dev- 
onshire clay  are  mixed  with  from  forty  to  sixty  of  feldspar,  and 
generally  about  five  parts  of  flint  glass  and  ten  of  quartz. 

It  would  not  be  within  the  object  of  the  present  work  to  detail  the  mechanical  pro- 
cess of  fashioning  articles  of  earthenware.  When  formed,  they  are  first  dried  in  the 
air,  and  then  heated  moderately,  to  expel  as  much  water  as  will  fit  them  for  the  re- 
ception of  the  glaze.  This  consists  in  covering  them  perfectly  with  a  sheet  of  easily- 
fusible  glass,  which,  by  entering  into  all  their  pores,  and  varnishing  their  surface, 
renders  the  vessels  impervious  to  water;  the  glassy  constituents  of  the  paste  having, 
in  quantity  and  fusibility,  only  sufficient  power  to  cement  the  particles  of  the  clay 
together,  without  depriving  the  mass  of  its  porosity.  The  composition  of  the  glaze 
may  vary  much  in  different  establishments ;  an  ordinary  one,  for  ironstone  china, 
consists  of  feldspar  36,  quartz  20,  white  lead  40,  flint  glass  8.  These  materials  are 
flitted  together,  and  then,  being  reduced  to  impalpable  powder,  are  diffused  through 
water,  into  which  the  vessel  to  be  glazed  is  dipped,  and  is  then  taken  out  again.  The 
clayey  substance  of  the  vessel  rapidly  imbibes  the  water,  and  the  fine  powder  of  the 
glaze  remains  uniformly  spread  upon  the  surface.  The  articles  so  prepared  are  ar- 
ranged in  capsules  of  a  very  refractory  ware,  and  placed  in  the  kiln  or  furnace  to  be 
baked.     The  construction  of  the  porcelain  kiln  is  represented  in  the  figure.    It  is  a 

K  K  K 


442    BAKING     AND     GLAZING     OF     EARTHENWARE. 


Taulted  building,  generally  of  three  stories,  provided  with  five  fireplaces,  from  which 

the  flames  pass  into  the 
kiln  by  the  passages  b,  m, 
a,  p,  marked  with  the  ar- 
rows ;  from  the  third  story 
the  chimney  issues.  The 
highest  floor  is  reserved 
for  drying  the  capsules  in 
which  the  articles  to  be 
baked  are  arranged ;  on  the 
floor  of  the  sec;ond,  the  ar- 
ticles are  dried  to  the  de- 
gree which  fits  them  for  the 
reception  of  the  glaze ;  and 
in  the  lowest  chamber,  by 
the  full  action  of  the  fire, 
the  final  baking  is  perform- 
ed. The  operation  com- 
mences, first,  with  a  moder- 
ate fire,  the  fuel  being  in- 
troduced into  the  cavity  A, 
and  supplied  with  air  by 
the  apertures  e  s;  the  heat 
being  allowed  to  rise  grad- 
ually for  six  or  eight  hours, 
the  space  becomes  full  of 
ignited  fuel,  and  a  strong 
draught  is  established.  The  apertures  are  then  closed,  fuel  (and  for  this,  as  for 
glass-making,  wood  answers  best)  is  heaped  on  the  rest  b,  and  the  air  admitted  to 
the  kiln  only  after  having  passed  through  k.  The  temperature  is  thus  kept  uniform- 
ly intense  for  seventeen  or  eighteen  hours,  and  then,  the  kiln  being  allowed  to  cool 
slowly  for  three  or  four  days,  the  articles  are  extracted  in  their  finished  state. 

The  glaze  on  earthenware  being  a  transparent  glass,  it  may  be 
coloured  by  various  metallic  oxides,  and  thus  the  patterns  produced 
which  give  to  the  finer  kinds  of  ware  so  much  popularity.  The 
coloured  glass,  being  reduced  to  fine  powder,  is  mixed  up  with  oil 
of  spike,  and  either  laid  on  with  a  brush,  as  in  ordinary  painting, 
or  printed,  in  a  very  ingenious  manner,  by  having  the  pattern  en- 
graved on  copper,  and  printing  it  with  the  glaze  made  with  oil  into 
a  very  thin  ink  on  damp  tissue  paper.  The  paper  with  the  figure 
thus  formed  is  laid  evenly  on  the  vessel,  which,  from  its  porosity, 
immediately  absorbs  the  liquid  materials  of  the  ink,  and  leaves  the 
powder  of  the  glaze  on  the  surface  in  all  the  fine  tracings  of  the  de- 
sign. The  paper  is  then  cautiously  rubbed  off  by  the  finger  in  a 
vessel  of  cold  water,  and  the  uniform  glazing  applied  over  all,  as 
before  described.  The  blue  patterns  are  produced  by  cobalt  ;  the 
black  by  a  mixture  of  oxides  of  iron  and  manganese  j  the  crimson 
by  gold ;  and  gold  and  platina  are  applied  also  in  their  metallic 
state,  by  dissolving  their  chlorides  in  oil  of  turpentine,  and  apply- 
ing this  varnish  with  a  pencil,  then  burning,  and  burnishing  the  me- 
tallic surface. 

A  coarse  kind  of  glazing,  given  to  the  common  articles  of  earth- 
enware, is  produced  by  throwing  into  the  kiln,  when  intensely  hot, 
a  few  handfuls  of  common  salt ;  by  means  of  the  watery  vapour 
produced  by  the  combustion  of  the  fuel,  the  silicic  acid  on  the  sur- 
face of  the  earthenware  decomposes  the  common  salt,  which  is  con- 
verted into  vapour  by  the  heat ;  Si.Og  with  Na.Cl.  and  H.O.,  produ- 
cing Na.O.  .  Si.Oa,  which  forms  a  transparent  glassy  varnish  on  their 
surface,  while  H.Cl.  passes  off  with  the  excess  of  w^atery  vapour, 
forming  copious  white  fumes. 


SALTS     OF     MANGANESE.  443 

The  general  characters  of  the  salts  of  glucinum,  thorium,  yttrium,  zirconium,  Ixm- 
thanum,  and  ceiium  have  been  noticed  under  the  heads  of  these  respective  metals 
(p.  351,  et  seq.)f  and  do  not  require  farther  detail. 

Salts  of  Manganese. 

Manganese  may  give  origin  to  four  classes  of  salts,  in  two  of 
which  it  constitutes  the  base,  and  in  the  others  forms  an  element 
of  the  acid  ;  these  last,  the  manganates  and  'permanganates^  have  been 
noticed  in  p.  356,  and  it  remains  only  to  describe  the  former. 

Protochloride  of  Manganese. — Mn.Cl.-l-4  Aq.  Eq.  788-5-1-450  or 
63- 19-1-36.  This  salt  maybe  obtained  by  digesting  the  commercial 
black  oxide  in  muriatic  acid  until  all  the  excess  of  chlorine  has 
been  expelled,  then  evaporating  to  dryness,  and  fusing  the  mass,  at 
a  bright  red  heat,  in  a  crucible.  The  chloride  of  iron,  which  is  form- 
ed by  the  impurities  of  the  ore,  is  decomposed  by  the  last  portions 
of  water,  and  muriatic  acid  being  given  off,  oxide  of  iron  remains. 
Hence,  on  digesting  the  melted  mass  in  water,  protochloride  of 
manganese  dissolves,  and  all  the  iron  remains  insoluble.  The  solu- 
tion, which  is  of  a  pale  pinkish  tint,  is  to  be  evaporated,  and  the  salt 
crystallized.  The  crystals  are  rhombic  tables,  rose  coloured;  by 
heat  they  lose  their  water  of  crystallization,  but  are  not  otherwise 
altered.  It  is  known  to  be  free  from  iron  when  its  solution  gives, 
with  yellow  prussiate  of  potash,  a  pure  white  precipitate. 

Perchloride  of  Manganese^  Mn.Cl2,  appears  to  be  formed  when 
strong  muriatic  acid  is  digested  on  peroxide  of  manganese  without 
heat.     A  gentle  heat  resolves  it  into  protochloride  and  free  chlorine. 

Protosulphate  of  Manganese. — Mn.O. .  S.O3-I-7  Aq.  This  salt  may 
be  obtained  pure  from  the  commercial  oxide  by  mixing  this  into  a 
thick  cream  with  oil  of  vitriol,  and  heating  it  in  a  shallow  dish 
until  it  becomes  quite  dry,  oxygen  being  given  off.  The  dry  mass 
which  contains  the  mixed  sulphates  of  iron  and  manganese  is  to  be 
then  placed  in  a  crucible,  and  heated  to  bright  redness  ;  the  sulphate 
of  iron  is  decomposed,  its  sulphuric  acid  being  expelled  by  the  heat ; 
but  the  sulphate  of  manganese  is  not  altered,  and  on  digesting  the 
resulting  mass  in  water,  dissolves,  and  is  obtained  crystallized  by 
evaporation  and  cooling.  This  salt  crystallizes  in  oblique  rhombic 
prisms  with  7  Aq.,but  is  also  found  with  5  Aq.  and  with  4  Aq.,  its 
form  changing  in  each  case.  In  all,  one  equivalent  of  water  is  con- 
stitutional, and  may  be  replaced  by  an  alkaline  sulphate,  with  which 
the  sulphate  of  manganese  forms  double  salts,  like  those  of  sulphate 
of  magnesia. 

Sesquisulphate  of  Manganese,  Mn2034-3S.03  may  be  obtained  by 
dissolving  the  sesquioxide  in  sulphuric  acid.  The  solution  is  of  a 
rich  crimson  colour :  when  heated,  it  becomes  colourless,  giving 
off  oxygen,  and  it  is  instantly  bleached  by  sulphurous  acid  or  any 
deoxidizing  agent.  Its  most  important  property  is  that  of  forming 
with  the  sulphate  of  potash  or  of  ammonia  double  salts,  crystallizing 
in  octohedrons,  which  are  manganese  alums,  similar  in  constitution 
to  the  ordinary  alum,  but  with  AI2O3  replaced  by  MuaOa. 

No  other  salt  of  manganese  requires  special  notice. 


444  SALTSOFIRON. 

Salts  of  Iron. 

There  are  two  series  of  iron  salts,  corresponding  to  the  two  ox- 
ides, proto-salts  and  sesqui-salts. 

Protochloride  of  Iron. — Fe.Cl.+4H.O.  This  salt  is  formed  when 
metallic  iron  is  dissolved  in  muriatic  acid,  hydrogen  being  evolved  j 
the  solution,  which  is  of  a  pale  bluish-green  colour,  yields,  on  evap- 
oration, rhombic  crystals  of  the  hydrated  chloride,  which  are  slightly 
deliquescent.  This  solution  absorbs  oxygen  from  the  air  with  great 
avidity,  and  becomes  dark-green  coloured.  When  these  crystals 
are  heated  they  lose  water,  and,  if  the  air  have  not  access,  a  white 
mass  of  dry  protochloride  of  iron  is  obtained,  but  otherwise  per- 
chloride  is  formed  and  the  whole  decomposed.  The  anhydrous 
protochloride  is  very  elegantly  prepared  by  passing  a  stream  of  dry 
chloride  of  hydrogen  over  fine  iron  wire,  coiled  up  in  a  tube  of  hard 
Bohemian  glass,  and  heated  to  bright  redness :  hydrogen  gas  ia 
evolved,  and  protochloride  of  iron  formed,  which  sublimes  into  the 
cold  part  of  the  tube  as  brilliant  white  spangles.  By  the  action  of 
the  air  it  is  rapidly  decomposed. 

Sesquichloride  of  Iron. — FeaClg.  This  salt  is  formed  when  iron  is 
dissolved  in  aqua  regia ;  a  deep  brown  solution  is  obtained,  which, 
when  evaporated  to  the  consistence  of  a  sirup,  gives  large  red  crys- 
tals of  hydrated  chloride,  which  are  very  deliquescent.  On  the  ap- 
plication of  heat,  this  salt  is  totally  decomposed  j  muriatic  acid  is 
given  off,  and  the  red  oxide  of  iron  remains  behind,  with  some  un- 
altered chloride,  as  a  basic  salt.  To  obtain  the  anhydrous  sesqui- 
chloride, a  stream  of  dry  chlorine  gas  is  to  be  passed  over  iron  wire 
heated  to  redness  in  a  tube  of  Bohemian  glass.  The  iron  burns  in 
the  chlorine,  and  the  salt  sublimes  into  the  cool  portion  of  the  tube, 
where  it  forms  a  dark  olive  crystalline  mass,  which  rapidly  attracts 
moisture  from  the  air.     This  salt  is  very  soluble  in  alcohol. 

The  sesquichloride  of  iron,  when  dissolved  along  with  sal  ammo 
niac,  may  form  a  true  double  salt,  containing  an  equivalent  of  each 
salt  ;  but  the  crystals  which  are  generally  thus  obtained,  although 
deeply-coloured  red,  contain  but  two  or  three  per  cent,  of  the  chlo- 
ride of  iron. 

Protoiodide  of.Iron,  Fe.I.,  is  formed  by  digesting  iodine  in  wa 
ter  on  an  excess  of  iron  filings.  Considerable  heat  is  evolved,  and 
a  colourless  solution  is  obtained,  which,  when  evaporated,  yields  a 
crystalline  mass  containing  water  of  crystallization,  and  which  is 
decomposed  by  a  farther  action  of  the  heat,  iodine  being  evolved. 
It  absorbs  oxygen  very  rapidly.  A  solution  of  protoiodide  of  iron 
dissolves  iodine  abundantly,  becoming  brown,  and  possibly  contain- 
ing the  sesqui-iodide,  Fcala ;  but  it  is  more  likely  that  the  iodine  is 
not  combined,  as  it  is  sensible  to  the  test  of  starch. 

The  bromides  of  Iron  resemble  perfectly  the  iodides. 

Protosulphate  of  Iron.  Green  Copperas. — Fe.O. .  S.Oa-f  7  Aq.  The 
manufacture  of  this  salt  is  conducted  on  the  large  scale  for  the  pur- 
poses of  the  arts,  by  exposing  to  the  action  of  air  and  moisture  the 
nodules  of  bisulphuret  of  iron,  which  are  found  abundantly  in  the 
strata  of  alum-slate-clay  (p.  436).  Oxygen  is  rapidly  absorbed  both 
by  the  iron  and  the  sulphur,  sulphuric  acid  and  oxide  of  iron  being 


SALTS    OF     IRON.  445 

formed,  and  the  liquor  which,  holding  these  in  solution,  drains  from 
the  beds  of  decomposing  pyrites,  is  run  into  tanks,  where  it  is  put 
in  contact  with  pieces  of  old  iron,  which  serve  to  neutralize  the  ex- 
cess of  acid  produced  from  the  pyrites,  being  a  bisulphuret,  and 
also,  by  means  of  the  hydrogen  evolved,  to  retain  all  the  iron  in  the 
state  of  protoxide;  after  proper  evaporation,  the  salt  is  obtained 
crystallized  from  these  solutions.  On  the  small  scale,  it  may  be 
prepared  by  dissolving  iron  wire  in  dilute  sulphuric  acid,  as  in  the 
process  for  preparing  hydrogen  gas  (page  247).  The  protosulphate 
of  iron  generally  crystallizes  with  seven  atoms  of  water,  of  which 
one  is  constitutional,  and  may  be  replaced  by  an  alkaline  sulphate, 
forming  double  salts.  The  form  of  its  crystal  is  a  short  oblique 
rhombic  prism,  z,  w,  u,  with  numerous  secondary  faces,  as  j3,  c,  in 
the  fig.  Its  taste  is  styptic  and  metallic ;  it  dissolves 
in  1-64  parts  of  water  at  50%  and  in  0-30  parts  at  212°. 
Like  the  other  protosalts  of  iron,  it  is  but  very  spa- 
ringly soluble  in  alcohol.  When  heated,  it  abandons 
first  its  water,  and  at  full  red  heat  its  sulphuric  acid,  _ 

of  which  a  portion  is  decomposed  into  sulphurous  acid  and  oxygen, 
by  which  the  iron  becomes  peroxidized.  The  peroxide  of  iron  thus 
formed  is  used  in  the  arts,  under  the  names  of  rouge  and  colcothar^ 
as  a  polishing  material.  On  these  properties  is  founded  the  manu- 
facture of  fuming  oil  of  vitriol,  described  in  page  247.  The  proto- 
sulphate of  iron  absorbs  oxygen  rapidly  even  when  dry,  and  becomes 
covered  with  a  reddish  crust  of  basic  persulphate,  whence  its  com- 
mercial name.  In  solution,  the  absorption  of  oxygen  proceeds 
quickly,  until  two  thirds  of  the  iron  are  peroxidized  and  a  reddish 
solution  obtained,  from  which  alkalies  throw  down  the  black  mag- 
netic oxide  (see  page  363).     This  solution  does  not  crystallize. 

Se^^w^w/pAa^e  o//ro?^.— FeA+3S.03.  Eq.  2481-9  or  198  9.  This 
salt  is  found  native  in  large  quantities  in  Chili,  combined  with  9  Aq. 
It  may  be  prepared  artificially  by  pouring  oil  of  vitriol  on  red  oxide 
of  iron,  stirring  the  mass  well,  and  applying  a  moderate  heat  to  ex- 
pel the  excess  of  acid.  The  salt  may  then  be  dissolved  in  water, 
forming  a  red  solution,  and  giving,  when  evaporated,  a  deliquescent 
mass  scarcely  crystallized.  In  this  way  it  retains  an  excess  of  acid, 
which  may  be  driven  off  by  a  heat  just  below  redness.  The  persul- 
phate then  appears  as  a  white  powder,  which  dissolves  but  very 
slowly  in  water.  By  a  strong  heat  this  salt  is  totally  decomposed. 
The  protosulphate  may  be  converted  into  persulphate  by  adding  to 
a  boiling  solution  nitric  acid  in  small  quantities,  as  long  as  any  ni- 
tric oxide  gas  is  given  off.  There  are  several  basic  persulphates 
of  iron,  of  which  the  most  important  is  the  rust-coloured  powder, 
which  precipitates  from  a  solution  of  protosulphate  of  iron  when 
oxidized  by  exposure  to  the  air  ;  its  formula  is  2Fe203-(-S.03-f-3  Aq. 

The  persulphate  of  iron  combines  with  the  alkaline  sulphates  to 
form  a  class  of  alums^  which  contain  FegOg  in  place  of  AL2O3.  These 
iron  alums  are  generally  pale  red  in  colour,  but  have  the  form,  sol- 
ubility, and  nearly  the  taste  of  common  alum. 

Protonitrate  of  Iron  may  be  formed  by  dissolving  sulphuret  of  iron 
in  cold  dilute  nitric  acid ;  it  crystallizes  in  pale-green  rhombs, 
which,  when  heated,  evolve  nitric  oxide  gas,  and  form  a  basic  ni- 


446  SALTS     OF     IRON,     NICKEL,     AND     COBALT. 

trate  of  the  peroxide.  Metallic  iron  dissolves  in  dilute  nitric  acid 
without  the  evolution  of  any  gas,  water  and  nitric  acid  being  si* 
multaneously  decomposed,  and  oxide  of  iron  and  ammonia  produced. 
Thus  N.O3  with  3H.0.  and  6Fe.,  give  6Fe.O.  and  N.H3. 

Pernitrate  of  Iron  is  produced  when  iron  is  dissolved  in  hot  nitric 
acid  ;  the  solution  is  reddish  brown,  and  gives,  by  drying,  a  deli- 
quescent mass  easily  decomposed  by  heat.  When  a  solution  of 
this  salt  is  decomposed  by  carbonate  of  potash  added  in  excess,  the 
oxide  of  iron,  which  first  precipitates,  is  redissolved,  and  a  deep  red 
liquor  obtained,  which  is  sometimes  used  in  medicine  under  the 
name  of  StahVs  alkaline  tincture  of  Iron. 

Protophosphate  of  Iron^  Tribasic — H.O.  .  2Fe.0.4-P-03 — may  be 
formed  by  decomposing  a  solution  of  protosulphate  of  iron  with  tri- 
basic phosphate  of  soda.  It  is  a  white  powder,  which  rapidly  be- 
comes blue  by  exposure  to  the  air,  a  portion  of  the  iron  becoming 
peroxidized.  This  blue  phosphate  of  iron  is  a  double  salt,  which 
exists  in  nature,  forming  the  bog  iron  ore^  and  may  be  produced  ar- 
tificially by  adding  solution  of  phosphate  of  soda  to  the  solution  of 
mixed  sulphate  of  iron,  from  which  alkalies  precipitate  the  black 
oxide  (p.  363).  The  precipitate  which  forms  is  of  a  rich  blue  col- 
our, and  is  not  changed  by  exposure  to  the  air.  Its  formula  is  (H. 
0..2Fe.O.-(-P.05)  +  (2FeA.P.05).     It  is  used  in  medicine. 

Sesquiphosphate  of  Iron,  2Fe203+P.05,  is  obtained  by  decompo- 
sing a  solution  of  sesquisulphate  of  iron  by  phosphate  of  soda.  It 
is  a  white  powder,  insoluble  in  water.     It  is  used  in  medicine.. 

The  salts  of  the  protoxide  of  iron  are  remarkable  for  absorbing 
nitric  oxide  in  considerable  quantity,  and  forming  therewith  a  deep 
olive-coloured  liquor,  which  rapidly  attracts  oxygen  from  the  air. 
The  quantity  of  gas  absorbed  is  one  atom  for  two  atoms  of  salt, 
and  the  nitric  oxide  may  be  considered  as  replacing  the  third  atom 
of  oxygen,  which  forms  the  sesquioxide.  Thus  the  protochloride 
gives  Fe,  +  Cl^ .  N.O2,  and  the  protosulphate  (Fe24-  O,  •  N.O,)  -f  2S.O3, 
analogous  to  Fez  +  Cl.a  and  (Fca-j- 03)4-28.03.  The  utility  of  this 
olive  liquor  as  a  test  for  nitric  acid  and  in  eudiometry,  has  been 
noticed  in  p.  264^  and  281. 

Salts  of  JVickel  and  Cobalt. 

Chloride  of  Nickel,  Ni.Cl.,  may  be  obtained  by  dissolving  oxide  of  nickel  in  dilute, 
muriatic  acid,  or  by  acting  on  the  metal  with  the  hot  concentrated  acid.  It  crystal- 
lizes in  emerald  green  rhombs.  When  heated,  it  loses  its  water  of  crystallization, 
and  gives  a  yellow  powder,  which  by  a  red  heat  sublimes  in  crystals,  resembling 
Mosaic  gold. 

Sulp/iaie  of  Nickel. — Ni.O.  .  S.Os.  This  salt  is  obtained  by  dissolving  the  oxide 
in  dilute  sulphuric  acid,  or  by  acting  on  the  metal  with  a  mixture  of  nitric  and  sul- 
phuric acids  diluted  with  water;  the  nitric  acid  then  supplies  oxygen.  This  solu- 
tion gives  fine  emerald  green  crystals,  which  vary  in  Ibrm  according  to  the  quanti- 
ty of  water  ihey  contain.  When  they  form  below  60^,  they  are  long  rhombic  prisms, 
containing  7  Aq.,  and  isomorphouswith  the  sulphates  of  zinc  and  magnesia;  but 
when  formed  at  any  temperature  above  60°,  the  quantity  of  water  is  six  atoms,  and 
the  form  is  an  octohedron  with  a  square  base.  If  a  prismatic  crystal  be  exposed  to 
a  moderate  heat  or  to  sunshine,  it  gives  off  an  atom  of  water,  arid  becomes  oqaque 
by  breaking  up  into  a  number  of  very  minute  crystals  of  the  octohedral  form.  In 
sulphate  of  nickel  one  atom  of  water  being  constitutional,  may  be  replaced  by  the 
alkaline  sulphates,  and  double  salts  formed,  of  which  some  are  very  beautiful. 

Chloride  of  Cobalt,  Co. CI.,  is  formed  by  dissolving  oxide  of  co- 
balt, or  the  zaffre  of  commerce,  in  muriatic  acid.     The  solution  ia 


SALTS    OF     COBALT     AND     ZINC.  447 

pinkish,  and  gives,  on  evaporation,  rose-red  crystals  of  hydrated 
chloride  ;  if  the  evaporation  be  pushed  very  far,  the  liquor  becomes 
blue,  and  dark  blue  crystals  of  anhydrous  chloride  are  deposited. 
If  the  solution  contains  nickel,  which  is  always  the  case  when  pre- 
pared from  zafTre,  the  colour  becomes  green,  and  it  is  thus  that 
sympathetic  inks  of  cobalt  are  produced,  and  summer  and  winter 
scenes  in  landscapes  alternated  j  the  surface  of  a  drawing  washed 
with  a  very  dilute  solution  of  chloride  of  cobalt  being  white  until 
dried  before  the  fire,  but  then  becoming  grass  green. 

Sulphate  of  Cobalt,  Co.O.+S.Oa,  is  obtained  by  treating  zaffre  with  sulphuric  acid. 
In  its  general  characters  it  resembles  the  chloride ;  when  heated  strongly,  it  gives 
off  sulphuric  acid,  and  oxide  of  cobalt  remains ;  it  contains  six  atoms  of  water  of 
crystallization,  and  gives  a  double  salt  with  sulphate  of  potash. 

Phosphate  of  Cobalt,  H.O. .  2C0.O.+P.O5,  is  precipitated  in  dark  violet  flocks  when 
solution  of  sulphate  of  cobalt  and  phosphate  of  soda  are  mixed  together.  This  sub- 
stance is  the  basis  of  a  very  beautiful  pigment,  Thenard^s  Bliie,  which  is  prepared  by 
mixing  intimately  one  part  of  phosphate  of  cobalt  with  two  or  thr6e  of  alumina, 
and  exposing  the  mixture  to  an  intense  white  heat  in  a  wind  furnace.  The  blue 
tint  thus  given  to  alumina  serves  as  a  test  for  that  earth,  particularly  to  distinguish 
it  from  magnesia  by  the  blowpipe.    (See  p.  349  and  351). 

Silicate  of  Cobalt  constitutes  the  blue  smalts  employed  to  tinge 
paper  and  to  colour  glass ;  the  finest  kind  is  known  in  commerce 
as  azure.  Its  manufacture  is  conducted  on  the  great  scale  in  Sax- 
ony and  Sweden,  and  is  the  process  in  which  most  of  the  arsenic 
of  commerce  is  obtained,  that  being  expelled  in  the  roasting  of  the 
cobalt  ores  (p.  366,  376).  From  the  zafFre  a  sulphate  of  cobalt  is 
prepared,  and  on  the  other  hand  a  silicate  of  potash,  by  melting  to- 
gether fine  sand  and  carbonate  of  potash  ;  these  solutions  being 
mixed,  silicate  of  cobalt  i^  precipitated,  while  sulphate  of  potash 
remains  dissolved.  This  precipitate  is  the  best  material  for  colour 
ing  porcelain  and  glass ;  but  the  ordinary  smalts  are  formed  by  melt- 
ing impure  carbonate  of  cobalt  with  potash  and  quartz  into  a  blue 
glass,  which  is  then  reduced  to  impalpable  powder,  and  sorted  ac- 
cording to  the  quality,  for  commerce. 

Salts  of  Zinc  and  Cadmium. 

Chloride  of  Zim — Zn.Cl. ;  Eq.  845-9  or  67-78 — may  be  prepared  by  burning  metal- 
lic zinc  in  chlorine,  or  by  dissolving  the  metal  in  muriatic  acid.  The  solution  is 
colourless;  when  evaporated,  it  yields  rhombic  crystals,  Avhich  contain  water,  and 
deliquesce  with  extreme  rapidity.  The  dry  salt  is  white,  and  melts  a  little  above 
212°,  so  that  a  solution,  when  evaporated,  never  becomes  solid.  It  is  hence  some- 
times applied  as  a  bath  in  place  of  oil  or  fusible  metal,  in  taking  the  specific  gravity 
of  vapours  (p.  14).  From  its  fusibility  and  softness,  it  had  formerly  the  name  of 
Butter  of  Zinc.  From  its  affinity  for  water,  it  acts  powerfully  as  a  caustic  on  the  liv- 
ing tissues,  and  is  employed  in  medicine  as  such. 

Chloride  of  zinc  combines  with  oxide  of  zinc  in  many  proportions,  forming  oxy- 
chlorides,  of  which  there  are  three  worthy  of  notice  :  the  first,  which  is  long  known, 
is  formed  by  decomposing  chloride  of  zinc  by  a  small  quantity  of  ammonia;  its  for. 
mula  is  Zn.Cl.+3Zn.O.+4  Aq.  The  second  results  from  the  action  of  water  on 
the  amraoniacal  chloride  of  zinc;  its  formula  is  Zn.Cl. +6Zn.O.+10  Aq.,  and  is  that 
whose  analogies  to  the  liquid  muriatic  acid  have  been  pointed  out  in  p.  309.  The 
third  is  formed  by  acting  on  chloride  of  zinc  with  an  excess  of  potash ;  its  formula 
is  Zn.Cl.+9Zn.O.+l4  Aq. 

The  brovii'le  and  iodide  of  Zinc  resemble  completely  the  chloride  in  general  char- 
acters :  a  solution  of  iodide  of  zinc  is  capable  of  dissolving  a  large  quantitv  of  iodine. 
Sulphate  of  Zinc,  Zn.O.  .  S.O3+7  Aq.,  may  be  produced  by  dis 
solving  the  metal  in  dilute  sulphuric  acid.  For  the  purposes  of  the 
arts,  it  is  made  upon  the  great  scale  by  roasting,  in  a  current  of  hot 
air  in  a  reverberatory  furnace,  the  native  sulphuret  of  zinc,  bletide 


448  SALTS     OF      TIN. 

The  metal  and  sulphur  both  combining  with  oxygen,  a  neutral  sul- 
phate of  the  oxide  is  formed,  which  being  then  dissolved  out  by- 
water,  the  solution  is  evaporated  to  a  pellicle,  and  allowed  to  crys- 
tallize. Sometimes  the  blende,  in  place  of  being  roasted,  is  exposed 
on  sloping  beds  to  the  action  of  the  air  and  moisture,  when  it  grad- 
ually attracts  oxygen,  and  is  treated  as  has  been  described  under 
the  head  of  sulphate  of  iron.  The  crystals  which  first  form  are 
heated  until  they  undergo  watery  fusion,  and  are  then  poured  into 
conical  moulds,  where  they  solidify,  and  the  salt  is  thus  sent  into 
commerce  in  masses  like  sugar-loaves;  its  com- 
mercial name  is  white  vitriol.  The  crystals  of  sul- 
phate of  zinc  are  eight  rhombic  prisms,  as  in  the 
figure,  containing  43'9  per  cent,  of  water,  and  are 
soluble  in  two  and  a  half  times  their  weight  of  cold 
water.  It  is  permanent  in  the  air.  It  combines 
with  the  alkaline  sulphates,  which  replace  its  con- 
stitutional water,  forming  double  salts,  and  with  ox- 
ide of  zinc  to  form  basic  salts,  of  which  several  are  known,  and 
which  agree  in  constitution  with  the  oxychlorides  of  zinc.  Their 
composition  has  been  already  noticed  in  p.  368. 

Nitrate  of  Zinc,  Zn.O. .  N.O5,  is  obtained  by  dissolving  the  metal  in  dilute  nitric 
acid ;  it  crystallizes  in  flat  four-sided  prisms.    It  is  deliquescent,  and  soluble  in  al- 
cohol. 
No  other  salt  of  zinc  is  of  importance. 

Cfdm-ide  of  Cadmium,  Cd.CL,  crystallizes  in  large  four-sided  prisms ;  it  is  not  de- 
liquescent. The  other  salts  of  cadmium  resemble  completely  the  corresponding 
salts  of  zinc,  and  do  not  require  notice. 

Salts  of  Tin.* 

Protochloride  of  Tin.~Sn.Cl.  +  3  Aq.  Eq.  1 177-9  -f  337-5  or  94-39 
+27.  This  salt  is  obtained  anhydrous  by  heating  tin  in  a  current 
of  muriatic  acid  gas,  hydrogen  being  evolved  ;  or  by  distilling  a 
mixture  of  equal  parts  of  tin  and  corrosive  sublimate  in  a  glass  re- 
tort, the  metallic  mercury  first  passes  over,  and,  finally,  the  proto- 
chloride of  tin  sublimes  at  a  strong  red  heat.  It  forms  a  gray  glassy 
mass.  In  combination  with  water,  it  may  be  obtained  by  dissolving 
tin  in  strong  muriatic  acid  until  it  is  saturated,  and  on  evaporation 
the  salt  crystallizes  in  long  prisms,  which  contain  three  atoms  of 
water.  When  these  crystals  are  heated,  they  first  lose  water,  but 
afterward  muriatic  acid  passes  off,  and  a  basic  salt  remains.  This 
crystallized  protochloride,  under  the  name  o{  salt  of  tin^  is  used  ex- 
tensively in  dyeing  as  a  mordant ;  in  its  preparation  on  a  large 
scale,  copper  vessels  may  be  employed,  because,  as  long  as  any 
metallic  tin  is  present,  the  copper  is  electrically  protected  by  it, 
and  is  not  acted  on  by  the  acid.  This  salt  is  very  soluble  in  water, 
but  is  decomposed  by  a  large  quantity,  a  basic  salt,  Sn.Cl  +  Sn.O., 
being  thrown  down  ;  hence,  in  order  to  have  a  dilute  solution  clear, 
it  requires  the  addition  of  a  few  drops  of  muriatic  acid.  Protochlo- 
ride of  tin  is  remarkable  for  its  affinity  for  oxygen  and  for  chlorine  ,• 
it  reduces  the  salts  of  silver,  quicksilver,  and  gold  to  the  metallic 
state,  and  the  salts  of  copper,  iron,  and  manganese  to  the  lowest 
state  of  oxidation.  It  acts  similarly  on  many  organic  substances, 
as  indigo,  litmine,  orceine  5  forming  colourless  compounds,  which 
have  some  important  applications  in  the  art  of  dyeing. 


SALTS     OF     TIN,    CHROMIUM,    AND     VANADIUM.     449 

The  protochloride  of  tin  combines  with  chloride  of  potassium  and 
with  sal  ammoniac  to  form  double  salts,  which  were  analyzed  by 
Apjohn. 

Perchloride  of  Tin^  Sn.Cli,  is  prepared  anhydrous  by  distilling  a 
mixture  of  four  parts  of  corrosive  sublimate  and  one  of  metallic 
tin ;  at  a  very  moderate  heat,  a  colourless  liquid  distils  over,  which 
forms  dense  white  fumes  where  it  comes  into  contact  with  the  air : 
this  is  the  bichloride  of  tin,  the  fuming  liquor  of  Libavius.  Metallic 
mercury  remains  in  the  retort.  This  singular  compound  boils  at 
248^  Fah.  j  the  specific  gravity  of  its  vapour  is  9*12.  When  mixed 
with  one  third  of  its  weight  of  water,  it  solidifies  into  a  crystalline 
mass,  and  it  is  hence  that  it  forms  such  dense  fumes  by  exposure 
to  damp  air.  It  may  be  prepared  in  this  crystallized  form  by  dis- 
solving tin  in  nitromuriatic  acid  and  evaporating  the  solution,  or 
by  passing  chlorine  into  a  solution  of  protochloride  as  long  as  it  is 
absorbed.  If  the  crystals  be  heated,  they  are  decomposed,  muriat- 
ic acid  being  given  off,  and  peroxide  of  tin  remaining. 

Protoiodidc  of  Tin,  Sn.L,  may  be  formed  by  heating  together  tin  and  iodine,  or  by 
mixing  solutions  of  iodide  of  potassium  with  a  slight  excess  of  protochloride  of  tin. 
It  is  a  brownish  red  mass,  soluble  in  water,  and  crystallizing  from  the  solution  in 
long  prisms  of  a  bright  orange  colour.  It  is  decomposed  by  a  large  quantity  of  wa- 
ter. It  combines  with  the  iodide  of  potassium  to  form  a  soluble  double  iodide.  The 
biniodide  of  tin  crystallizes  in  yellow  needles,  which  are  decomposed  by  much  water. 

The  bromides  of  Tin  are  not  important. 

ProtomlpJiate  of  Tin,  Sn.O. .  S.Od,  is  formed  when  tin  is  dissolved  in  strong  sul- 
phuric acid.  A  saline  mass  is  obtained,  which  dissolves  in  water,  giving  a  brown 
solution,  from  which  the  salt  crystallizes  in  small  needles.  Bancroft's  niardant,  for 
dyers,  is  prepared  by  digesting  two  parts  of  tin  with  three  of  strong  muriatic  acid  for 
an  hoar,  and  then  adding  one  and  a  half  parts  of  oil  of  vitriol  very  cautiously.  The 
mass  becomes  hot,  and  the  tin  is  rapidly  dissolved.  The  heat  is  to  be  kept  up  on  the 
sand-bath  as  long  as  hydrogen  is  evolved.  The  solution,  on  cooling,  forms  a  crys- 
talline mass,  which  is  to  be  dissolved  in  water,  so  that  eight  parts  of  the  solution 
shall  contain  one  of  tin. 

The  sulphuric  and  nitric  acids  may  be  neutralized  by  freshly-precipitated  peroxide 
of  tin;  but  these  salts  possess  very  little  stability,  and  are  of  no  technical  or  scientific 
interest.  The  peroxide  of  tin  itself  acts  as  an  acid,  and  its  relations  to  the  alkalies 
have  been  described  in  p.  371. 

The  sulphurets  of  tin  act  as  sulphur  acids,  combining  with  the  sulphurets  of  the 
alkaline  metals.  The  bisulphuret  forms  vnth.  sulphuret  of  sodium  a  crystallizable 
salt,  2Na.S.-|-Sn.S2+12  Aq.,  sulphostannate  of  Sodium. 

Salts  of  Chromium  and  Vanadium. 

There  are  two  kinds  of  salts  of  chrome,  one  in  which  the  oxide  of  chrome  is  the 
base,  and  the  other  in  which  the  chromic  acid  is  combined  with  bases. 

A.    Salts  of  Oxide  of  Chrome. 

Cliloride  of  Ckrorrie.—Gi^Ch.  Eq.  2031-6  or  162-8.  When  oxide  of  chrome  is  mix- 
ed with  lampblack,  and  treated  by  a  current  of  dry  chlorine  at  a  red  heat,  as  de- 
scribed for  the  preparation  of  the  chlorides  of  silicon  and  aluminum,  the  chloride  is 
obtained  sublimed  in  the  cold  part  of  the  tube  in  peach-blossom-coloured  scales  of 
exceeding  beauty.  It  may  also  be  obtained  by  dissolving  oxide  of  chrome  in  muri- 
atic acid,  and  evaporating  the  solution ;  it  remains  as  a  green  mass,  in  which  it  is 
combined  with  3H.0.  When  heated  to  450°,  it  froths  up  very  much,  gives  off  that 
water,  and  forms  a  rose-coloured  mass  not  so  beautiful  as  that  obtained  by  the  pro- 
cess first  described. 

C/ilorochromic  tIciVA— Cr.Cl3-j-2Cr.O3.  This  singular  compound  is  obtained  by 
melting  together  in  a  crucible  ten  parts  of  common  salt  and  seventeen  of  bichromate 
of  potash;  the  melted  mass  is  poured  out  on  a  slab,  and  broken  into  small  pieces, 
with  which  a  tubulated  retort  may  be  filled,  and  after  a  receiver  and  condensing  ap- 
paratus have  been  attached,forty  parts  of  oil  of  vitriol  are  to  be  poured  on  the  mass. 
The  decomposition  occurs  so  violently,  that  in  a  few  minutes  all  the  produci  distils 
ever,  without  the  application  of  external  heat.    This  substance  is  a  thin  bl  od-red 

Lll 


450  CHROMATES    OF    POTASH. 

aquid  appearing  black  by  reflected  light;  it  fumes  much  by  exposure  to  the  air;  it« 
vapour  IS  red  like  nitrous  acid.  When  its  vapour  is  heated  to  redness,  it  is  decom 
posed,  as  described  in  p.  373.  It  is  decomposed  by  water.  Alcohol  placed  in  coiv 
tact  with  it  takes  fire,  burning  with  a  bright  flame ;  phosphorus  acts  in  the  same 
way.  This  substance  may  either  be  looked  upon  as  a  compound  of  perchloride  of 
chrome  with  chromic  acid,  Cr.Cla+SCr.Os,  or  as  a  compound  of  chlorine  with  a 
deutoxide  of  chrome,  Cr.OaCl.  The  analogy  of  the  sulphuric  to  the  chromic  acid 
is  supposed  to  favour  this  latter  view,  as  also  the  sp.  gr.  of  its  vapour,  which  is  5-9. 

Sulphate  of  Chrome,  Cr203+3S.03,  may  be  formed  by  dissolving  oxide  of  chrome 
in  dilute  sulphuric  acid,  but  does  not  crystallize.  Its  only  important  character  is, 
that  it  combines  with  the  sulphates  of  potash  or  of  ammonia  to  form  double  salts, 
the  chroine  alums,  which  crystallize  in  dark  purple  octohedrons,  and  which  contain 
ihe  same  proportion  of  acid,  alkali,  and  water  as  common  alum,  but  oxide  of  chrome 
in  place  of  alumina.  The  solution  of  chrome  alum  in  cold  water  is  purple,  but 
when  heated  it  becomes  green,  and  the  elements  of  the  salt  are  then  found  to  be  no 
longer  united,  as  by  evaporation  they  may  be  separated.  It  would  appear,  indeed, 
that  almost  every  salt  of  chrome  may  exist  in  either  a  green  or  a  red  condition,  and 
that  in  the  former  they  do  not  crystallize.  The  chrome  alum  is  obtained  abundant- 
ly by  setting  aside  for  a  few  days  the  residue  of  the  process  for  making  aldehyd,  as 
described  farther  on. 

The  Perjluoride  of  Chrome,  Cr.Fs,  is  formed  by  acting  with  oil  of  vitriol  on  a  mix- 
ture of  powdered  fluor  spar  and  bichromate  of  potash  in  a  platinum  retort.  It  is  a 
gas  of  a  rich  crimson  colour,  which  can  only  be  collected  in  a  platinum  crucible  in- 
verted in  the  quicksilver  trough.  Its  decomposition  by  water,  and  the  consequent 
formation  of  chromic  acid,  has  been  already  noticed,  p.  373. 

B.  Salts  of  Chromic  Acid. 

Chromates  of  Potash. — The  manufacture  of  the  bichromate  of  pot- 
ash, K.O.-)-2Cr.03,  is  carried  on  extensively,  as  it  is  from  that  salt 
that  all  the  compounds  of  the  metal  used  in  chemistry  or  in  the  arts 
are  prepared.  It  is  made  from  the  only  abundant  ore  of  chrome, 
ihe  chrovie-iron^  Fe.O.+CraOg,  by  the  following  process.  Two  parts 
oi  the  ore,  ground  to  a  fine  powder,  are  intimately  mixed  with  one 
part  of  saltpetre,  or  four  parts  of  ore  are  used  with  two  parts  of 
pearl  ashes  and  one  of  saltpetre,  and  the  mixture  exposed  for  sev- 
eral hours  on  the  floor  of  a  reverberatory  furnace  to  a  violent  heat. 
Under  the  influence  of  the  potash,  the  oxide  of  chrome  absorbs  the 
oxygen  from  the  air,  and  forms  chromic  acid.  The  calcined  mass 
is  lixiviated  with  water,  and  a  deep  yellow  liquor  is  produced,  which 
contains  neutral  chromate  of  potash,  which  may  be  obtained  crys- 
tallized by  evaporation  ;  but  as  this  salt  is  not  well  suited  for  the 
purposes  of  commerce,  it  is  generally  changed  into  the  bichromate 
by  adding  to  the  liquor  a  quantity  of  sulphuric  acid,  which  takes  one 
half  of  the  potash,  and  the  bichromate  is  then  obtained  by  crystalli- 
zation in  tanks  lined  wdth  lead. 

Bichromate  of  Potash  crystallizes  in  large  four- sided  prisms  and 
square  tables  of  a  rich  orange-red  colour.  It  melts  easily,  and  in 
cooling  crystallizes  in  another  form.  It  is  soluble  in  ten  parts  of 
cold  water.  It  is  not  decomposed  except  by  a  white  heat,  which 
expels  oxygen,  and  leaves  a  mixture  of  oxide  of  chrome  and  neutral 
chromate  of  potash. 

The  neutral  Chromate  of  Potash,  K.O.  .  Cr.O;,,  may  be  prepared  by 

t  adding  to  a  solution  of  bichromate  of  potash  as  much 
more  alkali  as  it  already  contained.  It  is  soluble  in  twice 
its  weight  of  cold  water.  Its  solution  is  intense  golden 
yellow  ;  it  crystallizes  in  rhombic  prisms,  isomorphous 
with  those  of  sulphate  of  potash,  as  in  the  figure,  of  which 
n  n  and  u,  u  are  primary,  and  z,  m  are  secondary  planes. 


SALTS     OF     TUNGSTEN,     MOLYBDENUM,     ETC.     451 

If  bichromate  of  potash  be  dissolved  in  hot  dilute  nitric  acid,  a 
terchromate  of  potash,  K.O.  .  +3Cr.03,  crystallizes  when  the  solution 
cools. 

When  bichromate  of  potash  is  dissolved  in  rather  more  than  its 
own  weight  of  strong  muriatic  acid,  with  a  very  gentle  heat,  so  that 
no  chlorine  shall  be  evolved,  and  the  liquor  shall  retain  its  clear 
,  orange  colour,  a  salt  crystallizes  on  cooling  in  fine  four-sided  prisms, 
which  is  very  remarkable  in  constitution,  consisting  of  an  equiva- 
lent of  chloride  of  potassium  united  to  two  of  chromic  acid,  K.Cl. 
i-2Cr.03. 

None  other  oi  the  chromates  of  the  metals  that  have  been  as  yet 
described  possess  interest. 

Vanadium  is  the  basis  of  several  classes  of  salts,  which,  however,  from  the  ex- 
ceeding rarity  of  the  metal,  have  been  but  little  studied.  The  salts  containing  the 
vanadic  oxide  are  generally  splendid  blue ;  those  containing  the  vanadic  add  as  basis 
are  red  or  yellow,  while  those  which  contain  vanadic  acid  as  acid  are  colourless,  or 
coloured  according  to  the  nature  of  the  base  with  which  it  may  be  combined. 

Salts  of  Tungsten^  Molybdenum^  Osmium^  and  Columbium. 

Tungsten  combines  directly  with  chlorine  in  two  proportions,  forming  the  bichlo- 
ride and  perchloride,  according  as  the  metal  or  the  gas  is  in  excess.  Both  are  vol- 
atile, and  condense  in  red  needles.  They  are  decomposed  by  water,  giving  muriatic 
acid  and  tuogstic  oxide,  W.O2,  or  tungstic  acid,  W.O3.  A  chlorotungstic  acid  exists, 
W.O2CI.,  analogous  to  the  chlorochromic  acid. 

None  of  the  compounds  of  tungsten  with  oxygen  act  as  bases.  The  nature  of  the 
salts  of  tungstic  acid  has  been  sufficiently  explained  already  in  p.  374, 

Molybdenum  takes  fire  when  heated  in  "a  stream  of  chlorine  gas,  and  forms  the  ter- 
chloride,  M0.CI3,  which  crystallizes  in  the  cold  part  of  the  tube  in  brilliant  black 
scales,  like  iodine.  Its  vapour  is  dark  red.  Two  other  chlorides  of  this  metaJ,  Mo. 
CI.  and  M0.CI2,  are  known  to  exist. 

The  protoxide  of  molybdenum  forms  salts  with  the  oxygen  acids,  which  are  pur- 
ple or  black  coloured,  and  are  very  easily  decomposed  by  heat.  Thus  the  sulphate 
is  resolved  into  sulphurous  acid  gas  and  molybdic  oxide.  The  molybdic  oxide  also 
forms  a  series  of  salts,  generally  red  coloured,  which  do  not  possess  any  special  in- 
terest. The  molybdic  acid  forms  two  series  of  salts,  in  one  of  which  it  acts  as  base, 
and  in  the  other  as  an  acid. 

Osmium  is  the  basis  of  several  salts  which  are  as  yet  very  little  known.  When 
metallic  osmium  is  heated  in  a  stream  of  dry  chlorine,  in  a  long  glass  tube,  a  volatile 
mixture  of  protochloride  and  perchloride  of  osmium  is  produced.  The  former, 
which  is  the  less  volatile,  condenses  near  the  heat  in  long  needles  of  a  fine  green 
colour;  while  the  latter,  being  carried  much  farther  by  the  current  of  gas,  is  depos- 
ited as  a  red  powder  destitute  of  any  crystalline  texture.  Both  these  salts  combine 
with  the  alkaline  chlorides,  forming  double  salts.  All  three  oxides  of  osmium  com- 
bine wi*h  the  oxygen  acids  to  form  salts  which  do  not  crystallize,  and  have  been 
very  little  studied. 

Coluvibimi  forms  a  volatile  chloride.  Its  oxide,  ^Ta,02,  does  not  combine  with 
acids,  and  the  columbic  acid  forms  salts  which  are  not  of  practical  importance. 

Salts  of  Arsenic, 

Chloride  of  Arsenic— As. Ch]  Eq.  2268-0  or  181-74 — is  formed  when  the  metal  bums 
spontaneously  in  chlorine ;  it  is  a  volatile  liquid,  which  forms  dense  white  fumes  on 
exposure  to  the  air.  It  may  be  obtained,  also,  by  mixing  intimately  one  part  of  ai» 
senious  acid  and  three  of  common  salt;  putting'them  into  a  retort  to  which  a  con 
denser  is  attached,  and  adding  four  parts  of  oil  of  vitriol.  By  a  moderate  heat  the 
chloride  of  arsenic  distils  over  as  a  dense  liquid.  By  much  water  it  is  resolved  into 
arsenious  and  muriatic  acids.     The  sp.  gr.  of  its  vapour  is  6295. 

Iodide  of  Arsenic,  As. In,  is  best  prepared  by  digesting  one  part  of  arsenic  witli 
five  of  iodine  and  fifty  of  water,  until  the  iodine  disappears;  on  cooling,  the  ioaide 
separates  in  orange-red  crystals.  It  is  decomposed  by  water  into  hydriodic  and  a^ 
senious  acids.     The  bromide  of  arsenic  may  be  similarly  formed. 

Arsenic  does  not  form  any  compound  with  chlorine,  bromine,  or  iodine  analogoui 
to  arsenic  acid. 


452  SALTS     OF     ARSENIC. 

Neither  compound  of  arsenic  with  oxygen  is  capable  of  acting  as  a  base,  and 
hence  the  only  classes  of  salts  of  arsenious  or  arsenic  acids,  are  those  in  -wiiich 
they  constitute  the  electro-negative  element. 

Arsenious  Acid  is  dissolved  in  large  quantities  by  the  caustic  and 
carbonated  alkalies,  but  the  salts  thus  formed  cannot  be  obtained 
crystallized,  and  appear  to  be  very  indefinite  in  constitution.  The 
combinations  of  arsenious  acid  with  the  earths  are  white  powders, 
of  which  the  only  one  of  interest  is  arsenite  of  Lime^  H.O.  .  2Ca.0.-f-, 
As.Os,  which  precipitates  when  arsenious  acid  is  mixed  with  lime- 
water,  or  arsenite  of  potash  with  a  salt  of  lime.  It  is  redissolved  by 
an  excess  of  any  acid. 

Arsenious  acid  is  decomposed  by  peroxide  of  iron,  an  arseniate 
of  the  protoxide  being  produced  ;  on  this  is  founded  the  efficacy  of 
the  peroxide  of  iron  as  an  antidote  to  the  poisonous  effects  of  ar- 
senious acid  (see  p.  384). 

The  arsenite  of  Cobalt  is  found  native,  as  a  rose-red  powder,  and 
the  arsenite  of  JK'ickel  exists  as  a  mineral  of  a  pale-green  colour  j  both 
contain  combined  water.  The  arsenites  of  copper  and  silver  will  be 
described  under  the  heads  of  these  metals,  and  have  been  already 
Doticed  in  p.  381,  et  seq. 

The  constitution  of  the  salts  of  arsenic  acid  has  been  already 
mentioned  in  p.  377.  They  are  all  tribasic,  and  are  isomorphous 
with  the  corresponding  tribasic  phosphates.  Some  of  them  are  of 
technical  and  medicinal  importance.  The  neutral  arseniate  of  pot- 
ash, H.O.  .  2K.O.-I-AS.O5,  forms  a  deliquescent  saline  mass.  The 
binarseniate  of  Potash^  2H.0.  .  K.O. +AS.O5,  is  formed  by  adding  to 
the  former  as  much  arsenic  acid  as  it  already  contained,  or  by  ig- 
niting in  a  crucible  equal  weights  of  arsenious  acid  and  nitrate  of 
potash  ;  red  fumes  are  given  off,  and  on  dissolving  the  residual  mass 
in  boiling  water,  the  salt  is  obtained  in  large  crystals,  which  are 
modifications  of  the  square  octohedrori. 

There  are  three  arseniates  of  Soda,  which  resemble  the  three  triba- 
sic phosphates  of  soda.  The  first,  (3Na.O.+As.05)-f  24  Aq.,  is  ob- 
tained by  igniting  arsenic  acid  wdth  an  excess  of  carbonate  of  soda. 
When  a  solution  of  arsenic  acid  is  neutralized  by  carbonate  of  soda, 
the  salt  H.O. .  2Na.0.-f  As.Oj  is  obtained,  which  may  be  had  either 
with  24  Aq.  or  14  Aq.,  according  to  the  temperature  at  which  it 
crystallizes.  The  binarseniate  of  Soda,  2H.0. .  Na.O.-f-As.Oj,  resem- 
bles the  corresponding  salt  of  phosphoric  acid. 

The  arseniates  of  the  earths  are  white  powders,  insoluble  in  wa- 
ter, but  soluble  in  an  excess  of  any  acid. 

Arseniates  of  Iron.— That  of  the  protoxide,  H.O.  .  2Fe.-l-As.O5,  is 
a  white  powder,  which,  by  exposure  to  the  air,  gradually  becomes 
green  by  absorbing  oxygen,  thereby  approaching  to  the  constitution 
of  the  native  arseniate  of  iron,  in  which  the  iron  is  in  the  state  of 
black  magnetic  oxide.  This  salt  corresponds  to  the  blue  phosphate 
of  iron,  its  formula  being  (2Fe.O. .  H.O.  -f- As.Og)  +  2Fe203 .  As.Og-f- 
12  Aq. 

The  per  arseniate  of  Iron  is  a  white  powder,  which,  when  heated, 
gives  off  12  Aq.  and  becomes  red ;  it  has  the  singular  property  of 
dissolving  totally  in  water  of  ammonia. 

ArseniaM  of  Nickel  is  a  pale  green  powder.  Arseniate  of  Cobalt  is  a  rose- red  pow- 
dor,  and  mav  be  used  in  place  of  phosphate  of  cobalt  in  preparing  Thenard's  blue 


CHLORIDE     OF     ANTIMONY.  453 

fp.  447).    It  is  prepared  on  the  large  scale  by  roasting  the  native  arseniuret  of  co- 
balt, CosAs. 

The  sulphur  salts  of  arsenic  are  some  of  the  best  characterized  among  that  class 
(p.  379).  There  are  three  sidphoarscniaks  of  Potassium,  having  respectively  the  for- 
muke  (SK.S.+As.Sj),  (SK.S.+As.Si),  and  (K.S.+As.Sa).  They  are  all  deliques- 
cent, and  crystallize  with  water.  It  would  be  very  interesting  to  find  whether  the 
second  and  third  salts  contain  basic  water,  such  as  would  keep  up  the  tribasic  char- 
acter of  the  first.  The  sulphoarseniates  of  Sodium  resemble  those  of  potassium.  The 
basic  salt  (3Na.S.+As.S5-i-15  Aq.)  crystallizes  in  large  colourless  rhomboidal  ta- 
bles. When  orpiment  is  dissolved  in  solution  of  sulphuret  of  potassium,  sulphoarse- 
mfe  of  potassium  is  obtained,  K.S.H-As.Sa,  which,  when  evaporated,  is  decomposed, 
and  deposites  a  brown  powder,  which  consists  of  K.As.Ss,  and  appears  to  contain  a 
bisulphuret  of  arsenic,  As.Sz,  combined  with  K.S.,  which  is  decomposed  when  sep- 
arated from  the  state  of  combination. 

Salts  of  Antimony. 

Sesquichloride  of  Antimony. — Sb.Clg.  Eq.  3383-5  or  271-1.  To 
obtain  this  salt  completely  pure,  sulphuret  of  antimony  in  fine  pow- 
der is  to  be  mixed  with  its  own  weight  of  corrosive  sublimate,  and 
distilled  in  a  hard  glass  retort.  The  chloride  of  antimony  distils 
over  with  a  gentle  heat  as  an  oily  liquid,  which  gradually  solidifies 
into  a  white  crystalline  mass.  It  is  very  deliquescent,  and  becomes 
soft  on  exposure  to  the  air,  whence  its  old  name  of  Butter  of  Anti- 
mony ;  it  may  be  obtained  more  cheaply  for  surgical  use,  but  not 
quite  dry,  by  mixing  together  two  parts  of  fine  common  salt  and 
one  of  crocus  of  antimony  (oxysulphuret,  see  p.  385),  and  distilling 
them  in  a  retort  with  one  part  of  strong  oil  of  vitriol.  Chloride  of 
antimony  distils  over,  and  there  remains  behind  sulphate  of  soda 
mixed  with  sulphuret  of  antimony.  In  this  operation,  the  crocus 
antimonii  being  2Sb.S3-j-Sb.O3,  the  former  remains  passive  ;  but  the 
latter,  acting  On  3Na.Cl.  and  3S.O3,  produces  Sb.Clg  and  3Na.O. .  S. 
O3.  As  there  is,  however,  some  water  supplied  by  the  oil  of  vitri- 
ol, the  product  is  not  solid.  It  is,  however,  quite  strong  enough 
for  its  successful  application  as  a  caustic. 

When  chloride  of  antimony  is  put  in  contact  with  much  water, 
both  are  decomposed,  and  a  white  oxychloride  is  precipitated,  call- 
ed Powder  of  Algarotti^  from  the  name  of  its  discoverer.  If  the  wa- 
ter be  hot,  the  precipitate  is  distinctly  crystallized.  In  it  one  fourth 
of  the  metal  is  combined  with  chlorine,  and  three  fourths  with  oxy- 
gen ;  it  contains  also  water,  its  formula  being,  according  to  Berze- 
lius,  Sb.Clj  +  SSb.Og-l-S  Aq.  The  formula  given  by  Malaguti  and 
Johnstone  is  2Sb.Cl3-l-9Sb.O3,  and  it  is  possible  that  there  are  two 
oxychlorides,  which  may  be  produced  separately  or  mixed,  accord- 
ing to  the  circumstances  of  the  precipitation.  This  oxychloride  is 
employed  to  furnish  oxide  of  antimony  in  the  preparation  of  tartar 
emetic,  and  of  some  other  salts  of  antimony. 

The  terchloride  of  antimony  combines  with  the  chlorides  of  the 
alkaline  metals,  forming  double  salts,  consisting  of  an  equivalent  of 
each  constituent. 

Perchloride  of  Antimony^  Sb.Cls,  is  formed  when  metallic  anti- 
mony is  burned  in  chlorine  gas.  It  is  a  heavy  liquid,  which  fumes 
in  the  air,  and  has  a  very  bad  smell  \  with  a  small  quantity  of  wa- 
ter it  forms  crystals  (hydrate)  ;  with  a  large  quantity  of  water  it 
gives  antimonic  and  muriatic  acids :  it  is  formed,  also,  by  heating 
sulphuret  of  antimony  in  chlorine  gas. 


454  SALTS     OF     TITANIUM,    TELLURIUM,    ETC. 

The  bromide  and  iodide  of  Aviimony  are  prepared  by  the  direct  combination  of  their 
elements;  the  operation  does  not  require  external  heat;  the  former  is  colourless, 
the  latter  orange-red.  They  are  both  easily  fusible,  volatile,  and  decomposed  by 
water. 

The  sulphurets  of  antimony  act  as  sulphur  acids  (p.  387,  388),  combining  with 
the  sulphurets  of  the  alkaline  metals  to  form  double  salts,  of  which  several  may  be 
crystallized  in  large  rhomboidal  tables,  perfectly  colourless.  The  basic  hyposulpho- 
antimo'iiite  of  Potassium  which  remains  in  solution  after  the  precipitation  of  Kermes 
by  cooling,  crystallizes  on  evaporation  in  colourless  deliquescent  plates. 

The  sesqaioxide  of  antimony  combines  with  oxygen  acids  to  Ibrm  salts,  which 
possess  but  little  interest.  Metallic  antimony  decomposes  hot  oil  of  vitriol,  evolv- 
ing sulphurous  acid  gas,  and  forming  the  sulphate  of  Anti'tnony,  a  white  salt,  which  is 
decomposed  by  water. 

Antimonial  Powder.  James's  Powder. — This  preparation,  to  which, 
at  one  time,  the  highest  medicinal  virtues  were  attached,  is  pre- 
pared by  mixing  together  equal  parts  of  sulphuret  of  antimony  and 
hartshorn  shavings,  and  calcining  them  together  in  an  iron  pot,  at  a 
dull  red  heat,  until  the  mass  becomes  ash-gray ;  this  is  to  be  then 
placed  in  a  loosely-covered  crucible,  and  exposed  to  a  white  heat 
for  two  hours,  or  until  the  mass  becomes  quite  white  j  it  is  then  to 
be  reduced  to  a  fine  powder.  In  this  process  the  sulphur,  and  the 
carbon  and  hydrogen  of  the  hartshorn,  are  burned  away,  and  the  an- 
timony is  converted  into  antimonious  acid,  of  which  a  small  quan- 
tity unites  with  the  lime  that  had  been  as  carbonate  in  the  bone  j 
the  rest  of  the  lime  remains  as  phosphate,  mixed  with  the  antimo- 
nite  of  lime  and  the  antimonious  acid.  Its  composition  varies  very 
much  J  it  seldom  contains  more  than  one  per  cent,  of  antimonite  of 
lime,  which  is  its  only  soluble  and  active  principle  ;  and  where  it 
has  been  washed,  as  is  sometimes  done,  even  this  is  removed.  It 
is  also  a  mere  mechanical  mixture  of  its  ingredients. 

Tartar  emetic  will  be  described  under  the  head  of  tartaric  acid 
and  its  salts. 

Salts  of  Titanium^  Tellurium^  and  Uranium, 

Chlmide  of  Titanium,  Ti.Cl2,  is  best  prepared  by  treating  a  mixture  of  titanic  acid 
and  lampblack  by  chlorine,  as  for  the  preparation  of  chloride  of  silicon.  It  is  a  col- 
ourless liquid,  very  volatile,  fuming  in  the  air,  resembling  closely  bichloride  of  tin; 
it  combines  with  water  so  violently  as  to  produce  explosion,  and  is  decomposed  by 
a  large  quantity. 

There  are  no  oxygen  salts  of  titanium  of  any  interest. 

Bichloride  of  Tellurium,  Te.Cl2,  is  produced  by  heating  tellurium  in  a  current  of 
dry  chlorine ;  a  thick  liquid  is  produced,  at  first  dark  red,  but  becoming  yellow  as  it 
cools,  and  at  last  solidifying  into  a  snow-white  crystalline  mass.  This  salt  is  de- 
composed by  water  into  tellurous  and  muriatic  acids,  and  combines  with  the  alka- 
line chlorides  to  form  double  salts.  The  protochloride  is  prepared  by  melting  togeth- 
er equal  weights  of  the  bichloride  and  of  tellurium,  and  distilling;  it  condenses  as 
a  deep  yellow  liquid,  which  solidifies,  but  does  not  appear  crystalline.  It  forms 
double  salts. 

The  tellurous  acid  appears  to  possess  feeble  basic  properties,  as  it  unites  with  the 
strong  acids  to  form  compounds  which  are  not  important.  The  relations  of  tellu- 
rous and  telluric  acids  to  bases  have  been  already  noticed  at  sufficient  length  (p.  389). 

The  chlorides  of  Uranium,  U.Cl.  and  U2CI3,  give  yellowish  green  solutions,  but 
do  not  crystallize.  With  the  alkaline  chlorides  they  unite,  forming  crystallizablc 
double  salts. 

Protosulphate  of  Uranium  crystallizes  in  green  prisms. 

Sesquisulphale  of  Uranium,  U2O3+3S.O3,  is  not  itself  crystallizable,  but  combine* 
vith  sulphate  of  potash  in  several  proportions  to  form  double  salts  of  very  complex 
■constitution. 

The  Sesquinitrate  of  Uraninm,  U203-F3N.05,  crvstallizes  in  large  tabular  crystab 
ti  a  bright  yellow  colour.  This  salt  is  remarkable  as  the  most  definite  nitrate  of  a 
%csquioxide  that  is  known  to  chemists. 

All  these  salts  are  prepared  by  dissolving  the  oxides  of  uranliun  in  the  dilute  acids. 


SALTS     OF     COPPER.  455 

Salts  of  Copper. 

Copper  forms  two  series  of  salts,  one  corresponding  to  the  sub- 
oxide, and  tiie  other  to  the  black  oxide.  The  former  are  generally 
white,  and  the  latter  blue  or  green. 

Chloride  of  Copper,  Cu.CL,  is  produced  by  dissolving  copper  in 
aqua  regia,  or  oxide  of  copper  in  muriatic  acid.  Its  solution  is  green, 
and  it  gives,  on  evaporation,  the  hydrated  salt  in  long,  slender  green 
prisms,  Cu.Cl.-}-2  Aq.,  which  are  slightly  deliquescent,  and  are  solu- 
ble in  alcohol.  When  heated  they  give  off  water,  and  the  dry  chlor 
ride  remains  as  a  brown  powder,  which  recombines  with  water,  with 
the  evolution  of  much  heat.  Strongly  heated,  it  fuses,  gives  off  half 
its  chlorine,  and  the  subchloride  remains,  melted  into  a  brown  resin- 
ous-looking mass,  whence  its  name  of  resina  cupri.  By  the  action 
of  an  alkali  on  a  solution  of  chloride  of  copper,  an  oxychloride  may 
be  formed,  which  precipitates  as  a  fine  green  powder,  having  the 
formula  Cu.Cl.-f3Cu.0.-|-Aq.,  and  which  is  used  as  a  pigment  by 
the  name  of  Brunswick  Green.  There  exist  two  other  oxychlorides 
of  copper,  which  have  the  formulae  Cu.Cl.-f2Cu.O.  -f  3  Aq.,  and  Cu. 
Cl.-j-4Cu.O.-l-6H.O.,  prepared  by  the  decomposition  of  the  ammo- 
niacal  chlorides  of  copper. 

The  Subchloride  of  Copper,  CuaCl.,  may  be  prepared  either  by  heat- 
ing the  chloride  as  above,  or  by  digesting  the  clippings  of  thin  cop- 
per in  a  strong  solution  of  chloride  of  copper,  to  which  some  muri- 
atic acid  had  been  added.  The  liquor  gradually  acquires  an  olive 
colour,  and  the  subchloride  is  deposited  in  the  form  of  a  white  pow- 
der. In  this  case  the  Cu.Cl.  combines  with  a  second  equivalent  of 
copper,  forming  CuaCl.  It  also  precipitates  when  chloride  of  copper 
is  acted  on  by  protochloride  of  tin,  2Cu.Cl.  and  Sn.Cl.  producing 
CU2CI.  and  Sn.Clj.  This  subchloride  is  insoluble  in  water  ;  it  dis- 
solves in  muriatic  acid,  which  lets  it  fall  by  dilution  with  water.  It 
absorbs  oxygen  rapidly  from  the  air,  and  becomes  green.  It  forms 
with  water  of  ammonia  a  colourless  solution,  which  rapidly  becomes 
blue  on  exposure  to  the  air. 

Both  chlorides  of  copper  combine  with  the  chlorides  of  the  alka 
line  metals  to  form  double  salts. 

The  Brmnide  and  Subhromide  of  Copper,  Cu.Br.  and  CuaBr.,  resemble  in  every  re- 
spect the  chlorides  just  described. 

The  Iodide  of  Copper,  Cu.L,  does  not  appear  to  exist  except  in  combination.  If  so- 
lutions of  iodide  of  potassium  and  chloride  of  copper  be  mixed,  the  subiodide  is  pre- 
cipitated, while  half  the  iodine  is  set  free,  2Cu.Cl.  and  2K.L  producing  2K.C1.  and 
CU2I.,  with  free  I.  But  if  an  excess  of  iodide  of  potassium  be  added,  these  elements 
recombine,  and  a  double  salt,  Cu.I.-f-K.L,  may  be  obtained.  The  preparation  of 
the  subiodide  of  copper  just  given  involves  the  loss  of  an  atom  of  iodine,  which  is 
avoided  by  previously  mixing  the  liquor  with  an  excess  of  solution  of  protosulphate 
of  iron,  by  which  the  copper  salt  is  reduced  to  the  state  of  suboxide,  and  all  the  io- 
dine then  precipitated  as  subiodide.  Thus  made,  it  is  a  pale  yellow  powder,  unal- 
tered by  the  air. 

Sulphate  of  Copper.— Cu.O. .  S.O3 .  H.O.  +4  Aq.  Eq.  996-9 -f  562-5 
or  79-9-1-45.  For  the  purposes  of  the  arts,  in  which  this  salt  is  ex- 
tensively employed,  it  is  prepared  by  treating  the  native  sulphuret 
of  copper  in  the  manner  described  under  the  head  of  the  sulphates 
of  iron  and  zinc.  It  may  also  be  obtained  by  boiling  oil  of  vitriol 
on  metallic  copper,  when  sulphurous  acid  gas  is  given  off,  or  by 
acting  on  the  metal  with  dilute  sulphuric  acid,  to  which  some  nitric 


456     SCHEELe's     green    and    emerald     GREEl^^ 

acid  had  been  added.  It  crystallizes  in  large  doubly-oblique 
rhombs,  of  a  fine  blue  colour,  whence  its  name,  Blue  Vitriol.  In  the 
figure,  the  primary  rhomb  and  the  most  usual 
secondary  form  are  given,  i,  «,  v  marking  the 
primary  planes  in  each.  These  crystals  dis- 
solve in  four  parts  of  cold  and  two  of  boiling 
water.  Of  the  five  atoms  of  water  which  it 
contains,  one  is  constitutional,  and  may  be  re- 
placed by  the  alkaline  sulphates,  to  form  a 
class  of  double  salts  of  great  beauty.  By  the 
action  of  a  small  quantity  of  ammonia,  a  basic 
sulphate  is  obtained,  of  which  the  formula  is  Cu.O. .  S.Og-f-SCu.O.-l- 
4  Aq.  J  and  another,  containing  Cu.O. .  S.O^-|-7Cu.O.H-12  Aq.,  is  oc- 
casionally observed  to  form. 

Jfitrate  of  Copper. — Cu.O.  .  N.O54- 3  *Aq.  This  salt  is  obtained 
when  copper  is  dissolved  in  dilute  nitric  acid ;  it  crystallizes  in  ob- 
lique rhombs  of  a  rich  blue  colour,  and  sometimes  in  paler  rhom- 
boidal  plates,  which  contain  6  Aq.  This  salt  deflagrates  violently 
when  thrown  on  burning  coals,  or  when  struck  on  an  anvil  with  a 
little  phosphorus.  If  some  of  it  be  wrapped  up  tight  in  tin  foil,  it 
becomes  very  hot,  swells  up,  fumes,  and  oxidizes  the  tin  so  rapidly, 
that  in  some  points  brilliant  sparks  are  thrown  out.  When  heated 
above  200^,  it  loses  acid,  and  a  basic  nitrate  remains,  which  may 
also  be  formed  by  adding  a  small  quantity  of  ammonia  to  a  solution 
of  the  neutral  salt.  The  formula  of  the  basic  salt  is  H.O. .  N.Os-f- 
3Cu.O. 

Phosphate  of  Copper^  H.O. .  2Cu.O.  +P.0-,  and  the  arseniate  of  Cop- 
per^ H.O. .  2Cu.O. -hAs.O,,  are  pale  green  powders,  obtained  by  dou- 
ble decomposition. 

Arsenite  of  Copper^  H.O.  .  2Cu.O-f-As.O3,  is  obtained  by  the  de- 
composition of  arsenite  of  potash  and  sulphate  of  copper  :  it  is  a 
fine  apple-green  powder,  the  importance  of  which,  as  a  test  for  ar- 
senic, has  been  already  discussed  (p.  381).  It  is  employed  in  the 
arts,  under  the  name  of  Scheele^s  Green,  as  a  pigment,  and  is  prepared 
on  the  large  scale  by  dissolving  two  pounds  of  pure  sulphate  of  cop- 
per in  twelve  quarts  of  water,  previously  heated  in  a  copper  pan. 
In  another  pan  tAvo  pounds  of  pure  calcined  pearlash  are  dissolved, 
with  eleven  ounces  of  arsenious  acid,  in  four  quarts  of  pure  water. 
Both  liquors  are  strained  through  linen,  and  then  the  arsenical  so- 
lution is  gradually  added  to  the  solution  of  copper.  The  precipi- 
tate is  collected  on  a  cloth  and  carefully  dried.  The  produce 
should  be  1  lb.  6i  oz.  A  still  more  beautiful  pigment,  which  may 
be  best  described  here,  is  prepared  under  the  name  of  Schweinfurt 
Green,  or  Emerald  Green  ;  it  is  a  compound  of  acetate  of  copper  and 
arsenite  of  copper,  Cu.O. .  a4-3(H.O.  .  2Cu.O. +  AS.O3).  It  is  pre- 
pared by  mixing  up  ten  parts  of  pure  verdigris  with  as  much  hot 
water  as  will  make  it  into  a  thin  pulp,  and  straining  it  through  a 
sieve  to  separate  the  impurities  :  -nine  or  ten  parts  of  arsenious  acid 
are  to  be  then  dissolved  in  100  parts  of  boiling  water,  and  while 
boiling,  the  verdigris  pulp  is  to  be  gradually  added  thereto,  con- 
tinually stirring.  At  first  a  mere  arsenite  of  copper  falls,  and  all 
the  acetic  acid  remains  in  the  liquor  ,•  it  being  only  after  much  agi- 


SALTS     OF     LEAD.  457 

tation  that  the  double  salt  is  produced,  which  is  known  by  the  light 
flocculent  precipitate  changing  into  a  heavy  granular  powder  of  a 
brilliant  green  colour. 

The  salts  of  the  suboxide  of  copper  with  the  oxj'^gen  acids  pos 
sess  no  practical  interest. 

'  Saks  of  Lead, 

Chloride  of  Lead^  Pb.Cl.,  may  be  produced  by  boiling  lead  in 
strong  n)uriatic  acid,  or  by  acting  on  oxide  of  lead  with  the  same 
acid  ;  but  more  simply  by  adding  to  any  soluble  salt  of  lead  a  so- 
lution of  chloride  of  sodium.  A  curdy  white  precipitate  falls,  which 
dissolves  in  boiling  water,  and,  on  cooling,  crystallizes  in  opaque 
plates  of  a  pearly  lustre,  which  do  not  contain  water.  This  salt 
requires  135  parts  of  cold  water  to  dissolve  it,  but  is  much  more 
soluble  in  boiling  water.  It  is  easily  fused,  and,  on  cooling,  forms 
a  semi-transparent  mass  like  horn,  whence  the  old  name,  plumbum 
corneum.  By  the  action  of  ammonia  on  chloride  of  lead,  several 
oxychlorides  may  be  formed,  of  which  none  are  now  of  interest. 

Bromide  of  Lead  resembles  perfectly  the  chloride. 

Iodide  of  Lead,  Pb.L,  is  formed  by  adding  iodide  of  potassium  to 
a  solution  of  nitrate  of  lead  ;  a  bright  lemon-yellow  precipitate  falls, 
which  requires  1235  parts  of  cold,  and  but  194  of  boiling  water  to 
dissolve  it.  The  solution  is  colourless,  and,  on  cooling,  deposites 
the  iodide  of  lead  in  splendid  gold-coloured  six-sided  plates,  which 
maintain  their  metallic  lustre  perfectly  in  drying.  The  iodide  of 
lead  forms  double  salts  with  the  alkaline  iodides,  and  gives,  with 
ammonia,  oxyiodides  when  the  alkali  is  not  in  excess. 

Sulphate  of  Lead. — Pb.O.  .  S.O3.  This  salt  is  found  in  the  mineral 
kingdom  in  large  transparent  rhombs,  isomorphous  with  sulphate 
of  barytes,  and  of  which  the  octohedron  z,  y,  in  the  figure,  is  the 
primary  form.  It  may  be  also  formed  by  adding  to 
any  solution  containing  lead  sulphuric  acid  or  a  sul- 
phate. It  falls  down  as  a  white  powder,  which,  from 
its  insolubility,  furnishes  a  good  test  for  lead.  When 
strongly  ignited,  it  melts  without  decomposition,  but 
with  charcoal  it  is  reduced  to  sulphuret  of  lead.  The  sulphate  of 
lead  is  soluble  in  strong  acids ;  and  hence  the  oil  of  vitriol,  manu- 
factured in  leaden  chambers,  generally  contains  a  small  quantity  of 
it  dissolved,  which  is  precipitated  on  the  addition  of  water. 

J^itrate  of  Lead,  Pb.O. .  N.O5,  is  obtained  by  dissolving  lead  in  di- 
lute nitric  acid,  and  evaporating.  It  crystallizes  in  regular  octohe- 
drons,  often  modified,  which  are  generally  opaque  j  it  is  soluble  in 
seven  and  a  half  parts  of  cold,  and  much  less  of  boiling  water.  It 
is  not  soluble  in  nitric  acid.  When  heated,  it  gives  out  a  mixture 
of  oxygen  and  nitrous  acid  gases  (p.  276),  and  leaves  melted  pro- 
toxide of  lead.  By  the  action  of  ammonia,  a  series  of  basic  salts  are 
obtained,  which  contain  two,  three,  and  six  atoms  of  oxide  of  lead 
united  to  one  of  nitric  acid. 

When  a  solution  of  nitrate  of  lead  is  boiled  on  finely-divided 
metallic  Jead,  this  dissolves,  and  on  cooling,  brilliant  yellow  plates 
are  deposited,  which  are  basic  nitrite  of  Lead,  2Pb.0.-f  N.O4.  By 
adding  sulphuric  acid  to  a  solution  of  this  salt,  a  neutral  nitrite  is 

M  M  M 


458    CHROMATES     OF     LEA  D. S  ALTS     OF     BISMUTH. 

obtained,  Pb.O.  .  N.O4+H.O.,  which  crystallizes  in  yellow  octohe- 
drons.  If  an  excess  of  lead  be  used  in  the  preparation  of  the  ni- 
trite, the  acid  is  still  farther  deoxidized,  and  a  hyponitrite  of  Lead, 
SPb.O.-j-N.Oa+S  Aq.,  is  produced,  which  crystallizes  in  rose-red 
scales.  These  salts  are  of  interest,  as  it  was  doubted  whether  the 
nitrous  acid  (N.O4)  could  combine  with  bases,  and  *it  is  only  in 
these  cases  that  we  have  obtained  positive  evidence  of  its  doing  so, 
which  we  owe  to  Peligot. 

Phosphate  of  Lead,  HO. .  2Pb.O.-|-P-05,  is  formed  by  the  action 
of  common  tribasic  phosphate  of  soda  on  a  solution  of  nitrate  of 
lead  ;  it  is  a  white  powder,  which  is  changed  by  ammonia  into  3Pb. 
O.+P.O,. 

Silicate  of  Lead  has  been  noticed  in  relation  to  crystal  and  to  flint 
glass. 

Chromate  of  Lead — Pb.O.  .  Cr.Os. — Chrome  Yellow  is  formed  by 
mixing  together  solutions  of  nitrate  of  lead  and  bichromate  of  pot- 
ash. It  precipitates  as  a  fine  lemon-yellow  powder,  insoluble  in 
water.  It  occurs  native  in  ruby-red  crystals,  constituting  the  red 
lead  ore.  This  salt  is  manufactured  largely  for  a  pigment,  which  is 
found  of  various  shades  of  yellow  and  orange  in  the  market,  being 
mixtures  of  the  true  neutral  chromate,  prepared  as  above,  with  the 
basic  chromate  of  Lead,  2Pb.O.-|-Cr.03,  which  is  of  a  bright  vermilion 
colour,  and  is  termed  Chrome  Red.  This  may  be  prepared  by  adding 
potash  to  a  solution  of  chromate  of  potash  until  this  reacts  strongly 
alkaline,  and  then  mixing  it  with  nitrate  of  lead,  or  by  digesting 
the  neutral  chromate  of  lead  in  a  warm  solution  of  potash,  which 
removes  half  the  acid.  These  give  products,  however,  inferior  in 
brilliancy  of  tint  to  the  following.  Saltpetre  is  to  be  melted  in  a 
crucible  at  a  dull  red  heat,  and  chrome  yellow  gradually  added  there- 
to, as  long  as  effervescence,  with  escape  of  red  fumes,  occurs.  The 
potash  abandons  the  nitric  acid  and  takes  half  the  chromic  acid,  and 
basic  chromate  of  lead  is  formed.  The  mass  becomes  black,  and  is 
then  to  be  allowed  to  settle,  and  the  melted  salt  poured  off  from  the 
heavy  powder  at  the  bottom  ;  this,  when  cold,  becomes  of  a  splendid 
vermilion  red,  and  is  to  be  taken  out  and  washed  with  the  smallest 
possible  quantity  of  water. 

Salts  of  Bismuth. 

Chloride  of  Bismuth,  Bi^Clg,  is  formed  by  dissolving  bismuth  in 
hot  strong  muriatic  acid;  by  evaporation  it  forms  a  crystalline  mass 
which  is  very  deliquescent,  volatile,  and  fusible.  By  water  it  is 
decomposed,  giving  the  oxychloride  of  bismuth,  a  white  powder, 
having  the  composition  BiaCla-f-^BiaOa-l-SH.O.  In  the  arts  this  pow- 
der is  sometimes  employed  under  the  name  of  Spanish  White  or  Pearl 
White. 

The  chloride  of  bismuth  combines  with  the  chlorides  of  the  alka 
line  metals,  forming  double  salts,  in  which  the  chlorine  combined 
with  the  bismuth  is  to  that  combined  with  the  other  metal  as  three 
to  two.  In  the  double  salts  formed  by  protochlorides,  this  relation 
is  never  observed,  and  hence  it  furnishes  additional  proof  that  the 
chloride  of  bismuth  is  a  sesquichloride,  on  which  idea  the  Tormulse 
■^come  2K.Cl.+Bi,Cl3+2  Aq.  and  2Na.Cl.-fBi,Cl3-f  3  Aq. 


SALTS     OF     SILVER.  459 

Sulphate  of  Bismuth^  BigOa  +  SS.Oa,  is  formed  by  dissolving  bis- 
muth in  hot  sulphuric  acid.  It  forms  a  deliquescent  mass  of  acicu- 
lar  crystals,  which  are  decomposed  by  water,  giving  a  white  pow- 
der, the  basic  sulphate  of  Bismuth^  Bi^Oa+S.Og. 

The  Mtrate  of  Bismuth^  Bi^Oa+SN.Os+O  Aq.,  is  formed  by  dis- 
solving the  metal  in  dilute  nitric  acid  ;  by  evaporation  and  cooling 
rhomboidal  crystals  are  obtained,  which  easily  deliquesce ;  when 
heated,  they  lose  water  and  nitric  acid,  and  form  a  basic  salt,  and 
finally  oxide  of  bismuth  remains  behind.  Like  the  other  salts  of 
bismuth,  this  is  decomposed  by  water,  and  may  produce  one  or  other 
of  two  basic  salts,  according  to  circumstances.  When  the  crystals, 
without  any  excess  of  acid,  are  decomposed  by  water,  the  precipi- 
tate has  the  composition  4Bi203+3N.05+9H.O. ;  while,  if  an  acid 
liquor  be  decomposed  by  water,  the  precipitate  has  the  formula  Bi. 
O3  +  N.O5.  Both  of  these  salts  yield  very  nearly  the  same  quantity 
of  oxide  of  bismuth  on  analysis,  and  were  hence  long  confounded 
together.  Many  reasons  for  considering  the  oxide  of  bismuth  to  be 
a  sesquioxide  have  been  given  (p.  398).  These  subnitrates  of  bis- 
muth are  used  indiscriminately  in  medicine,  but  the  latter  form  is 
more  generally  found  in  the  shops.  The  names  Pearl  White,  &;c., 
are  also  applied  to  these  bodies. 

Salts  of  Silver. 

Chloride  of  Silver — Ag.Cl.  ;  Eq.  1794*3  or  143*8 — exists  native  as 
an  ore  of  silver,  horn  silver,  and  may  be  formed  by  mixing  a  solu- 
tion of  common  salt  with  a  soluble  salt  of  silver.  It  forms  a  curdy 
white  precipitate,  perfectly  insoluble  in  water  and  in  acids,  but  easi- 
ly soluble  in  water  of  ammonia.  When  heated,  it  fuses  below  red- 
ness, and  on  cooling,  congeals  into  a  semitransparent  mass  of  a 
horny  aspect,  whence  its  old  name.  When  freshly  precipitated,  it 
is  exceedingly  sensible  to  the  action  of  light,  becoming  pink,  violet, 
and  ultimately  black  by  exposure  to  the  sun's  rays  ;  but  for  this  re- 
action, it  is  necessary  that  organic  matter  or  water  should  be  pres- 
ent, with  the  hydrogen  of  which  the  chlorine  may  combine,  and  that 
thus  a  thin  layer  of  subchloride  or  of  metal  may  be  produced.  The 
relations  of  chloride  of  silver  to  light  are  of  the  highest  importance 
in  photography,  and  in  examining  the  structure  of  the  solar  rays,  as 
noticed  in  p.  173,  et  seq.  The  processes  for  the  reduction  of  chlo- 
ride of  silver  to  the  metallic  state  have  been  described  in  p.  399, 
400. 

Iodide  of  Silver,  Ag.L,  is  obtained  by  decomposing  a  soluble  salt 
of  silver  by  iodide  of  potassium  ;  a  primrose-yellow  precipitate 
falls,  which  is  insoluble  in  water  and  in  ammonia  j  at  least  it  requires 
2500  parts  of  strong  water  of  ammonia  to  dissolve  one  of  iodide  of 
silver.  It  is  easily  fusible,  and  becomes  opaque  on  cooling.  In 
certain  forms  it  is  still  more  sensible  to  light  than  the  chloride,  and 
is  hence  the  basis  of  the  impression  in  the  photographic  process  of 
Daguerre  (see  p.  175).  It  is  reduced  to  the  metallic  state  by  the 
same  means  as  the  chloride. 

Bromide  of  Silver,  AgBr.,  resembles  the  chloride  in  every  par- 
ticular respect. 

Sulphate  of  Silver ^  Ag.O. .  S.O3,  is  formed  by  boiling  metallic  sil 


460  &ALTS     OF     SILVER. 

ver  in  oil  of  vitriol;  sulphurous  gas  is  given  off,  and  a  white  saline 
mass  formed,  which,  when  more  strongly  heated,  is  totally  decom- 
posed, leaving  metallic  silver.  This  salt  dissolves  in  eighty-eight 
parts  of  boiling  water,  and  crystallizes,  on  cooling,  in  small  needles. 
Hyposulphite  of  Silver. — 2Ag.O. -f  S2O2.  The  relations  of  hypo 
sulphurous  acid  to  oxide  of  silver  are  very  curious.  On  adding  a 
neutral  solution  of  nitrate  of  silver  to  a  solution  of  hyposulphite  of 
soda,  a  white  precipitate  appears,  which  at  first  redissolves,  but 
subsequently  becomes  permanent.  It  soon  loses  its  pure  colour, 
especially  if  heated,  and  at  last  becomes  black  from  sulphuret  of 
silver,  while  the  liquor  contains  sulphate  of  silver;  thus  2Ag.0.4- 
S2O2  produce  Ag.S.  and  Ag.O.  .  S.O3.  The  solution  of  this  salt  is 
extremely  sweet.  So  great  is  the  affinity  of  hyposulphurous  acid 
to  oxide  of  silver,  that  a  solution  of  it  dissolves  chloride  of  silver, 
forming  an  intensely  sweet  liquor  ;  and  the  solutions  of  the  alkaline 
and  earthy  hyposulphites  dissolve  all  the  salts  of  silver  insoluble  iu 
water,  except  the  arseniate  and  the  iodide,  and  form  double  salts 
of  exceedingly  sweet  taste.  The  double  hyposulphites  contain 
generally  one  equivalent  of  hyposulphite  of  silver  to  two  of  the 
other  salt,  but  our  knowledge  of  these  salts  is  not,  as  yet,  by  any 
means  complete. 

mtrateof  Silver.— Ag.O. .  N.O^.  Eq.  2128-5  or  170-57.  This  is 
the  most  important  salt  of  silver  ;  it  is  manufactured  on  a  very  large 
scale  in  the  Apothecaries'  Hall  of  Ireland  for  medicinal  use. 

It  is  prepared  by  dissolving  granulated  silver  in  dilute  nitric  acid, 
which  at  first  occurs  without  the  disengagement  of  any  gas,  as  the 
nitric  acid  dissolves  the  nitric  oxide  formed,  but  towards  the  end 
copious  red  fumes  are  evolved.  By  evaporation  and  cooling,  the 
salt  is  obtained  in  colourless  rhomboidal  plates,  as  in  the  figure, 
often  four  inches  across,  which  are  anhy- 
drous. It  is  soluble  in  its  own  weight  of 
cold  water.  When  heated  to  about  430^. 
it  melts  into  a  colourless  liquid,  which  is 
poured  into  cylindrical  silver  moulds,  and 
congealing,  forms  the  sticks  of  lunar  caus- 
tic used  in  surgery.  This  fused  salt  should 
be  snow-white ;  it  is  not  affected  by  light  unless  organic  matter  be 
present,  as  has  been  fully  shown  by  Scanlan  ;  but  with  organic  mat- 
ter it  soon  becomes  quite  black,  silver  being  reduced.  It  is  hence 
used  as  marking  ink,  and  for  staining  hair  black.  When  strongly 
heated,  nitrate  of  silver  is  totally  decomposed.  It  yields  its  oxy- 
gen readily  to  combustible  bodies  ;  thus,  if  a  few  grains  of  it  be  laid 
on  an  anvil  with  a  little  bit  of  phosphorus,  and  struck  with  a  ham- 
mer, it  explodes  violently.  Its  solution  is  reduced  to  the  metallic 
state  by  all  deoxidating  agents. 

Hyponitrite  of  Silver,  Ag.O.  .  N.O3,  is  obtained  in  granular  crys» 
tals  by  adding  the  soda  salt  prepared  by  melting  nitrate  of  soda  (p. 
428)  to  a  boiling  solution  of  nitrate  of  silver,  and  filtering  while 
very  hot. 

Tribasic  Phosphate  of  Silver,  SAg.O.  +  P.O^,  is  the  canary-yellow 
precipitate,  produced  by  adding  a  tribasic  phosphate  of  soau  to  a 
solution  of  nitrate  of  silver.     Its  relations  to  the  other  phosphates 


SALTS     OF     MERCURY.  461 

of  silver,  and  to  the  silver  test  for  arsenic,  have  been  noticed  in  p. 
298  and  381. 

Arseniate  of  Silver^  3Ag.0.-f  As.Og,  is  precipitated  as  a  reddish- 
brown  powder  on  adding  any  solution  of  an  arseniate  to  a  solution 
of  nitrate  of  silver.  Its  formation  is  one  of  the  most  characteristic 
properties  of  arsenic  acid. 

Arsenite  of  Silver^  H.O.  .  2Ag.O.  -f  As.Oa,  is  produced,  as  has  been 
noted  in  p.  401,  by  adding  a  solution  of  arsenious  acid  to  the  am- 
moniacal  nitrate  of  silver,  or  of  arsenite  of  potash  to  nitrate  of  sil- 
ver. It  is  a  canary-yellow  powder,  soluble  in  ammonia  and  in  ni- 
tric acid.  When  heated,  it  first  yields  water  and  becomes  brown  j 
then  it  gives  oxygen,  arsenious  acid,  and  leaves  metallic  silver. 

Salts  of  Mercury.  t 

Chloride  of  Mercury.  Corrosive  Sublimate — Hg.Cl.  j  Eq.  1708'5  or 
136'9 — may  be  prepared  by  dissolving  red  oxide  of  mercury  in  mu- 
riatic acid,  and  evaporating.  It  crystallizes  in  long  right-rhombiC 
prisms,  generally  opaque.  It  may  also  be  very  economically  pre- 
pared by  dissolving  the  basic  sulphate  (turpeth  mineral)  in  strong 
muriatic  acid,  and  crystallizing  ;  the  sulphate  of  mercury  remains  in 
the  mother  liquor,  and  may  be  again  converted  into  basic  sulphate 
by  the  action  of  water.  The  corrosive  sublimate  is,  however,  gen- 
erally prepared,  for  pharmaceutic  purposes,  by  the  dry  way,  as  fol- 
lows :  sulphate  of  mercury,  Hg.O.  .  S.O3,  is  to  be  well  mixed  with 
its  own  weight  of  common  salt,  Na.Cl.,  and  the  mixture  introduced 
into  a  wide-necked  glass  retort,  or,  on  the  large  scale,  into  a  stone- 
ware pot,  to  which  a  globular  glass  head  is  attached.  The  retort 
or  pot,  being  bedded  in  sand,  is  gradually  heated  to  redness;  decom- 
position occurs,  the  chlorine  of  the  common  salt  combining  with  Xht 
mercury,  while  the  sodium  takes  the  oxygen  and  acid  ;  we  have 
therefore  formed  Hg.Cl.,  which  sublimes  into  the  head,  forming  a 
mass  of  prismatic  crystals,  which,  being  partly  fused  by  the  heat,  co- 
here strongly  together,  and  sulphate  of  soda,  which  remains  behind ', 
Hg.O.  .  S.O3  and  Na.Cl.  giving  Hg.Cl.  and  Na.O.  .  S.O3. 

The  sublimed  chloride  of  mercury  crystallizes  in  a  right-rhombic 
prism,  as  represented  in  the  figure.  Its  specific  gravity  is  5'4< ;  it 
melts  at  509^,  and  boils  at  563\  The  specific  gravity 
of  its  vapour  is  9420.  It  dissolves  in  two  parts  of 
boiling  and  in  twenty  of  cold  water  ;  the  hot  solution 
crystallizes,  on  cooling,  in  prisms  of  a  different  form 
from  that  of  the  sublimed  salt ;  it  is  therefore  dimorph- 
ous ;  it  is  soluble  in  2^  parts  of  cold  alcohol,  and  in 
three  parts  of  cold  ether ;  it  dissolves  much  more 
readily  in  muriatic  acid  and  in  solutions  of  the  alka-  _ 

line  chlorides  than  in  pure  water,  as  it  forms  with  these  bodies 
double  salts,  which  are  very  soluble  ;  of  these,  the  double  chloride 
of  mercury  and  ammonium,  sa/  alembroth,  is  employed  in  pharmacy. 
It  will  be  specially  described  hereafter.  A  solution  of  corrosive 
sublimate  yields  all  the  reactions  of  a  salt  of  the  red  oxide  of  mer- 
cury, described  in  p.  403.  When  a  small  quantity  of  potash  is  ad- 
ded to  a  solution  of  sublimate,  a  brown  precipitate  falls,  which  by 
boiling  becomes  black  and  crystalline  ',  the  same  substance  may  be 


462 


PREPARATION     OF     CALOMEL. 


formed  by  boiling  red  oxide  of  mercury  in  a  solution  of  sublimate  } 
it  is  an  oxychloride  of  mercury^  whose  formula  is  Hg.Cl.  +  3Hg.O. 

If  a  solution  of  sublimate  be  treated  by  a  small  quantity  of  sulphu* 
ret  of  hydrogen,  a  precipitate  forms,  at  first  brownish,  but  which  ul- 
timately becomes  quite  white,  provided  there  be  sublimate  in  excess ; 
it  is  a  chlorosulphuret^  of  which  the  formula  is  Hg.C1.4-2Hg.S. 

Subchloride  of  Mercury.  Calomel.— Rg^Cl  Eq.  2974-3  or  238-3 
This  important  medicinal  agent  may  be  prepared  either  by  precipi- 
tation or  by  sublimation.  For  the  former  object,  nine  parts  of  mer- 
cury are  to  be  digested  in  eight  parts  of  nitric  acid,  sp.  gr.  1*25, 
without  heat,  until  no  more  mercury  appears  to  dissolve,  and  the 
liquor  begins  to  assume  a  yellow  colour;  eight  parts  of  common 
salt  are  next  to  be  dissolved  in  250  parts  of  boiling  water,  to  which 
« a  little  muriatic  acid  may  be  added :  these  solutions  being  mixed, 
the  calomel  immediately  precipitates,  and  thus  prepared,  it  is  abso- 
lutely pure.  The  mercury  dissolving  in  the  nitric  acid,  forms  pitrate 
of  the  suboxide,  and  by  the  chloride  of  sodium,  nitrate  of  soda  and 
subchloride  of  mercury  are  formed ;  HgaO. .  N.O5  and  Na.Cl.  giving 
Hg^Cl.  and  Na.O.  .  N.O^. 

To  obtain  calomel  by  sublimation,  four  parts  of  corrosive  subli- 
mate may  be  rubbed  up  with  three  parts  of  mercury,  so  intimately 
that  no  trace  of  metal  shall  be  visible  ;  and  the  mixture  being  intro- 
duced into  an  earthen  pot  to  which  a  glass  head  is  fitted,  heat  is 
to  be  gradually  applied  until  the  materials  have  all  sublimed.  In 
this  operation,  Hg.Cl.  combining  directly  with  Hg.,  gives  HgaCl. 
The  union  is  never  perfected  by  the  first  sublimation,  and  the  prod- 
uct is  to  be  again  powdered,  well  mixed,  and  again  sublimed.  The 
process  followed  by  the  British  pharmacopoeias  is  difl^erent,  and  is 
best  carried  on  in  the  following  proportions :  Thirty-one  parts  of 
dry  sulphate  of  the  red  oxide  of  mercury  (persulphate)  are  tobe  in- 
timately mixed  with  twenty  and  one  third  parts  of  metallic  mercury 
and  twenty  parts  of  fused  common  salt,  and  the  whole  rubbed  to- 
gether until  the  mercurial  globules  totally  disappear.  This  method 
is  the  same  as  the  former  in  principle,  except  that  the  corrosive 
sublimate  is  generated  only  when  required  to  combine  with  the  ad- 
ditional quantity  of  mercury  to  form  calomel.  The  sublimation  is 
carried  on  as  described  above.  The  sublimed  mass  is  always  con- 
taminated with  some  undecomposed  sublimate.  Hence  it  must  be 
carefully  levigated,  and  washed  with  boiling  water  as  long  as  the 
washings  give  any  milkiness  on  the  addition  of  a  few  drops  of  wa- 
ter of  ammonia. 

The  precipitated  calomel  is  a  pure  white  pow- 
der. When  sublimed,  it  forms  a  crystalline  mass, 
whose  primitive  form,  as  in  the  figure,  is  a  square 
prism.  It  is  insoluble  in  water ;  and  the  mi- 
nute division  of  the  sublimed  calomel  may  be 
elegantly  secured  by  conducting  its  vapour  into 
a  vessel  containing  boiling  water,  by  the  vapour 
of  which  it  is  suddenly  condensed,  and  falls  as 
an  excessively  fine  powder.  Its  specific  gravi- 
ty is  6-5.  The  presence  of  sublimate  in  the  cal- 
omel of  the  shops  is  detected  by  boiling  for  a  fev/ 
minutes  in  alcohol,  and  adding  to  the  alcoholic  li* 


^  IODIDES     OP     MERCURY.  463 

quor  some  water  of  ammonia,  which  gives  a  white  precipitate  if 
corrosive  sublimate  be  present.  By  boiling  with  muriatic  acid,  or 
with  solution  of  common  salt  or  sal  ammoniac,  calomel  is  gradually- 
decomposed  into  sublimate,  which  dissolves,  and  metallic  mercury, 
which  remains  behind. 

T/ie  Bromide  and  Subbromide  of  Mercury,  Hg.Br.  and  Hg2Br.,  may  be  prepared, 
the  first  by  acting  directly  on  mercury  with  bromine,  when  a  colourless  solution  is 
obtained,  which  gives  prismatic  crystals  by  evaporation ;  the  second,  by  decompo- 
sing nitrate  of  the  suboxide  by  bromide  of  potassium.  These  bodies  resemble  com- 
pletely sublimate  and  calomel  in  their  properties. 

Iodide  of  Mercury.  Red  Iodide— Kg.l. ;  Eq.  2845-0  or  228-0— may 
be  formed  by  the  direct  combination  of  its  elements,  even  without 
heat,  by  trituration  together  with  a  few  drops  of  alcohol.  It  is  then 
dark  red,  but  may  be  obtained  of  a  brilliant  red  colour  by  precipi- 
tating a  solution  of  corrosive  sublimate  with  an  equivalent  of  iodide 
of  potassium.  An  excess  of  the  latter  redissolves  the  precipitate, 
as  it  forms  a  double  salt  (K>I.  +  Hg.I.),  soluble  in  water,  and  crystal 
lizable  in  octohedrons.  The  iodide  of  mercury  is  insoluble  in  wa- 
ter;  when  heated,  it  fuses  and  sublimes,  condensing  in  a  crystalline 
mass,  formed  of  rhomboidal  plates,  which,  when  broken  or  scratch- 
ed, gradually  become  red,  breaking  up  into  a  number  of  minute 
crystals  of  a  different  form.  It  is  somewhat  soluble  in  alcohol,  and 
abundantly  in  aqueous  hydriodic  acid.  A  hot  solution  of  iodide  of 
potassium  dissolves  much  more  than  the  atomic  proportion  of  it  j 
the  excess  crystallizes  in  long,  red,  square  prisms,  according  as  the 
solution  cools.  It  dissolves  also  in  a  strong  solution  of  corrosive 
sublimate,  with  which  it  combines  in  two  proportions.  It  forms  a 
class  of  double  salts,  equally  extensive  with  that  produced  by  cor- 
rosive sublimate. 

Subiodide  of  Mercury^  Hg2l.,  may  be  formed  by  triturating  iodine 
with  mercury,  or  by  precipitating  a  solution  of  iodide  of  potassium 
by  a  slight  excess  of  nitrate  of  the  suboxide  of  mercury.  It  is  an 
olive-green  powder,  which  is  resolved  by  heat  into  metallic  mercu- 
ry and  iodide,  and  is  similarly  decomposed  by  a  solution  of  iodide 
of  potassium,  with  which  the  iodide  of  mercury  formed  combines. 

Sesquiodide  of  Mercury^  or  Yellow  Iodide. — Hg4l3  or  2Hg.I. -J- Hggl. 
To  obtain  this  substance,  a  solution  of  iodide  of  potassium,  to  which 
half  as  much  iodine  as  it  already  contained  has  been  added,  is  to  be 
decomposed  by  a  slight  excess  of  a  solution  of  the  subnitrate  of 
mercury.  The  bright  yellow  powder  which  precipitates  must  be 
dried  cautiously  with  little  exposure  to  light.  By  means  of  a  solu- 
tion of  iodide  of*'potassium,  it  is  resolved  into  red  iodide  and  me- 
tallic mercury.  The  reaction  by  which  it  is  formed  is  that,  of  the 
subiodide  first  produced,  by  the  K.I.  and  Ug^O.  .  ISi.O^,  one  half  is 
converted  into  red  iodide  by  the  additional  atom  of  iodine  which 
is  supplied;  2(K.I.)-f  I.  and  2(Hg20.  .  N.O,)  giving  2(K.O.  .  N.O5) 
and  Hg.2l.-{-2Hg.I.     This  preparation  is  employed  in  pharmacy. 

A  preparation  which  has  been  proposed  by  Donovan,  under  the 
name  of  lodo-hydrargyrate  of  Arsenic^  is  prepared  by  rubbing  togeth- 
er 6-08  grs.  arsenic,  15-38  grs.  of  mercury,  and  50  grs.  iodine,  v/ith 
a  few  drops  of  alcohol,  until  they  combine,  and  then  adding  eight 
ounces  of  water  with  a  few  drops  of  hydriodic  acid ;  a  solution  18 
obtained,  at  first  colourless,  but  soon  becoming  yellowish-brown  by 


464  OXYGEN  SALTS  OF  MERCURY.  *' 

light,  from  iodine  being  set  free.  This  preparation  is  not  a  cnem- 
ical  compound  ;  but  the  iodide  of  arsenic  being  decomposed  by  the 
water,  the  iodide  of  mercury  is  dissolved  by  the  hydriodic  acid 
formed,  while  arsenious  acid  exists  free  in  the  solution. 

Sulphate  of  Mercury— Eg. 0.  .  S.O3;  Eq.  1867  or  149-6— is  produ- 
ced by  boiling  oil  of  vitriol  on  mercury,  until  it  is  converted  into  a 
white  saline  mass,  which  requires  to  be  finally  heated  nearly  to  red- 
ness to  expel  the  excess  of  acid.  Sulphurous  acid  is  evolved,  Hg. 
and  ^S.Og  giving  Hg.O.  .  S.O3  and  S.O2  j  but  this  may  be  avoided 
by  adding  from  time  to  time  a  small  quantity  of  nitric  acid,  by  which 
oxygen  will  be  supplied.  This  salt  forms  a  white  powder,  not  crys- 
talline ;  at  a  full  red  heat  it  is  resolved  into  merc+iry,  sulphurous 
acid,  and  oxygen.  Its  use  is  extensive  in  preparing  calomel  and 
sublimate.  By  a  large  quantity  of  water  it  is  decomposed  into  free 
acid  and  basic  sulphate^  turpeth  mineral^  SHg.O.  +  S.Og,  which  is  a 
bright  yellow  powder,  which,  when  heated  with  muriatic  acid,  gives 
neutral  sulphate  and  corrosive  sublimate,  2H.C1.  and  (3Hg.0.-t-S. 
O3)  producing  2Hg.Cl.  and  Hg.O. .  S.O3,  water  being  formed  (see 
p.  461). 

Subsulphate  of  Mercury— Eg^O. .  S.O3 — Sulphate  of  the  Black  Ox- 
ide may  be  formed  by  heating  metallic  mercury  with  oil  of  vitriol, 
provided  the  heat  do  not  pass  beyond  212"  ;  or  by  mixing  strong 
solutions  of  "nitrate  of  the  black  oxide  and  of  sulphate  of  soda.  It 
is  a  white  powder,  very  sparingly  soluble  in  water,  by  which  it  is 
not  decomposed,  and  is  thereby  distinguished  from  the  preceding 
salt. 

Kitrute  of  Mercury.  J^itrate  of  the  Red  Oxide. — 2Hg.O.  .  N.O5+ 
2  Aq.  This  salt  is  formed  when  mercury  is  dissolved  in  an  excess 
of  nitric  acid  with  heat.  It  crystallizes  in  rhomboidal  plates,  which 
are  deliquescent,  and  soluble  in  a  small  quantity  of  water.  Its  so- 
lution is  decomposed  when  diluted,  a  basic  nitrate  of  the  Red  Oxide 
being  precipitated  of  a  bright  canary  colour,  and  having  the  formu- 
la HO.  .  N.Oj-I-SHg.O.  If  this  powder  be  boiled  with  much  water, 
a  still  more  basic  salt  is  formed,  which  has  the  formula  N.05-]-6Hg. 
O.  Both  this  salt  and  the  sulphate,  when  heated  by  sulphuretted 
hydrogen  not  in  excess,  give  white  basic  compounds,  like  the  chlo- 
rosulphuret  (p.  464),  having  the  formulae  Hg.O.  .  N.05H-2Hg.S.  and 
Hg.O..S.03  +  2Hg.S. 

Subnitrate  of  Mercury.  J^itrate  of  the  Black  Oxide. — When  mercu- 
ry is  dissolved  in  dilute  nitric  acid,  without  any  heat,  or  with  only 
as  much  as  sustains  a  very  moderate  action,  the  black  oxide  formsj 
and  may  unite  with  the  nitric  acid  in  various  proportions.  1st.  If 
there  be  nitric  acid  in  excess,  the  solution  gives  by  cautious  evapo- 
ration clear  transparent  rhombs  of  neutj-al  subnitrate,  huviug  the  for- 
mula HgaO.  .  N.O5+2H.O.  2d.  If  there  be  an  excess  of  mercury, 
large  opaque  white  rhombic  prisms  sometimes  form,  which  have  the 
composition  (3Hg.,0.  +  2N.O,,+3H.O.).  3d.  By  letting  this  solution 
stand,  these  crystals  gradually  disappear,  and  very  small  canary- 
yellow  crystals,  nearly  spherical,  with  numerous  brilliant  facets,  are 
produced:  this  is  a  basic  salt,  the  formula  being  H.O.  .  N.05-l-2Hg, 
O.  This  salt  may  also  be  formed  by  the  action  of  water  on  either 
the  first  or  second  j  both  being  decomposed  into  free  acid,  and  the 


SALTS  OF  GOLD  AND  PALLADIUM.        465 

basic  salt,  which  is  not  farther  altered  even  by  boiling  water.  The 
second  salt  may  be  looked  upon  as  a  compound  of  the  first  and  third, 
since  (3Hg,0.4-2N.05+3H.O.)=(Hg,0. .  N.03+2H.O.)  +  (:H.O.  .N. 
0,+  2Hg,0.). 

S'.ibchromate  of  Mercury,  Hg20.+Cr.03,  produced  by  mixing  solutions  of  chro- 
mate  of  potash  and  subriitrate  of  mercury,  is  a  bright  orange  powder,  insoluble  in 
water;  when  heated  to  redness,  it  gives  off  mercury  and  oxygen,  and  chromic  oxide 
of  a  fine  green  colour  remains  (p.  372). 

Red  nitrate  of  mercury  combines  with  iodide  of  mercury  to  form  a  double  salt, 
which  is  formed  by  half  precipitating  a  solution  of  the  mercuric  salt  by  iodide  of  po- 
tassium, and  boiling  until  the  precipitate  redissolves ;  on  cooling,  the  new  salt  is  de- 
posited in  brilliant  red  crystalline  scales,  which  are  decomposed  by  much  water. 

Salts  of  Gold. 

Perchloride  of  Gold. — Au.Clg.  When  gold  is  dissolved  in  nitro- 
muriatic  acid,  and  the  solution  evaporated  very  cautiously  to  dry- 
ness, this  salt  remains  as  a  ruby-red  crystalline  mass,  which  dissolves 
with  a  yellowish-red  colour  in  water.  Its  solution  is  acid,  and  is 
decomposed  by  the  light,  and  by  all  deoxidizing  agents.  It  combines 
with  muriatic  acid,  and  forms  a  deep  yellow  liquor,  from  which 
the  acid  chloride  of  Gold  crystallizes  in  long  yellow  needles.  It  is 
soluble  in  alcohol  and  in  ether,  from  which  last  solution  it  is  depos- 
ited in  the  metallic  state  on  evaporation,  the  chlorine  combining  with 
the  ether.  In  this  way  some  forms  of  gilding  are  effected,  as  on 
steel.  The  chloride  of  gold  combines  with  many  other  chlorides, 
forming  double  salts.  The  chloride  of  gold  and  potassium,  AU.CI3+ 
K.C1.-I-5  Aq.,  crystallizes  in  orange-red  striated  rectangular  prisms. 
It  efhoresces  in  the  air,  and  may  be  obtained  anhydrous;  it  is  then 
ruby-red.  Chloride  of  gold  and  sodium  (Na.Cl.  +  Au.Cl3+4  Aq.) 
forms  crystals  of  the  same  form  and  colour,  but  which  do  not  ef- 
floresce :  when  heated,  they  fuse  in  their  water  of  crystallization. 

Subchloride  of  Gold,  Au.Ch,  is  produced  by  heating  the  chloride  to 
about  450^  in  a  porcelain  dish,  stirring  it  very  carefully  until  no 
more  chlorine  is  given  off.  It  is  a  yellowish-white  mass,  insoluble 
in  water,  by  which  it  is  gradually  decomposed  into  chloride  and 
metallic  gold.  It  is  in  this  way  only  that  a  solution  of  chloride  of 
gold  perfectly  free  from  an  excess  of  acid  can  be  obtained. 

Iodides  of  Gold. — When  solutions  of  chloride  of  gold  and  iodide  of  potassium  are 
mixed,  a  greenish  precipitate  occurs  of  subiodid^  of  Gold,  Au.L,  while  two  thirds  of 
the  iodine  become  free.  If  the  iodide  of  potassium  be  in  great  excess,  however,  the 
iodine  and  subiodide  are  both  redissolved,  and  a  double  salt  obtained,  which  crystal- 
lizes, and  which  contains  iodide  of  Gold;  its  formula  is  K.I.-fAu.Ia;  by  the  cautious 
addition  of  chloride  of  gold  to  a  solution  of  this  salt,  a  greenish  precipitate  may  be 
obtained  without  any  liberation  of  iodine,  and  which  hence  must  be  the  iodide. 

The  oxides  of  gold  do  not  act  as  bases,  and  the  general  nature  of  the  salts  which 
they  form,  as  acids,  has  been  noticed  in  p.  406. 

Salts  of  Palladium. 

Chloride  of  Palladntm,  Pd.Cl.,  is  formed  by  dissolving  palladium  in  nitromuriatic 
acid.  Its  solution  is  deep  brown,  and  it  forms,  by  evaporation,  a  crystalline  mass; 
by  the  action  of  a  small  quantity  of  caustic  alkali,  a  basic  salt,  or  oxycMoride  of  Pal- 
ladium, Pd.Cl.+3Pd.O.+4  Aq.,  is  produced  ;  it  is  a  brown  powder,  insoluble  in  wa- 
ter. The  chloride  of  palladium  combines  with  other  chlorides  to  form  double  salts ; 
when  heated  to  about  600°,  it  abandons  half  its  chlorine,  and  subcfdffride  of  Palladi- 
um remains,  an  olive-brown  powder  insoluble  in  water.  By  a  strong  red  heat  this 
is  totally  decomposed. 

Deutockloride  of  Palladium,  Pd.Cla,  is  formed  when  the  chloride  of  palladium  is 
gently  heated  with  aqua  regia ;  it  forms  a  dark  brown  liquor,  which  gives,  with  a 

N  N  N 


466   SALTS     OF     PLATINUM,    IRIDIUM,     AND    RHODIUM. 

solution  of  chloride  of  potassium,  a  sparingly  soluble  double  salt,  K.Cl.+Pd.Cla. 
This  deutochloride  cannot  be  obtained  solid,  its  solution  giving  off  chlorine,  and 
chloride  remaining. 

Iodide  of  Palladium,  Pd.I.,  is  a  black  powder,  obtained  by  double  decomposition. 
It  forms  double  salts  with  other  iodides.  By  heat  it  is  decomposed,  without  form- 
ing  any  subiodide. 

Sulphate  of  PaUadium,  Pd.O. .  S.O3,  is  produced  by  dissolving  the  metal  in  a  mix- 
ture of  nitric  and  sulphuric  acids.  By  evaporation,  a  saline  mass  is  obtained, 
which  is  decomposed  by  water. 

Nitrate  of  Palladium;'?  A. O. .  N.O5,  is  obtained  by  acting  on  the  metal  with  nitric 
acid.  At  first  it  dissolves  without  any  evolution  of  gas,  forming  a  deep  olive  liquor; 
but  when  heated,  it  gives  off  N.O2,  and  becomes  brown.  The  nitrate  of  palladium 
is  decomposed  by  water,  giving  basic  salts. 

Salts  of  Platinum. 

Protochloride  of  Platinum,  Pt.Cl.,  is  formed  by  exposing  the  bi-' 
chloride,  in  fine  powder,  to  a  temperature  of  about  500"^  in  a  porce- 
lain dish,  and  frequently  stirring- ;  one  half  of  the  chlorine  being 
evolved,  a  greenish  olive  powder  is  produced,  which  is  the  proto- 
chloride. It  is  insoluble  in  water  ;  by  a  red  heat  it  .is  resolved  into 
chlorine  and  metallic  platinum.  If  the  bichloride  be  exposed  only 
to  a  temperature  of  about  400^,  water  dissolves  from  out  of  the  re- 
sulting mass,  a  substance  which  colours  it  intensely  brown,  and 
which  is,  probably,  a  sesquichloride,  PtaCla. 

Bichloride  of  Platinum. — Pt.Cl2.  This  salt  is  produced  by  dis- 
solving platinum  in  nitromuriatic  acid.  The  solution,  when  free 
from  excess  of  acid,  is  intensely  yellow :  on  evaporation,  it  gives  a 
crystalline  deliquescent  mass.  This  salt  is  very  soluble  in  alcohol, 
and  is  so  used  for  the  detection  of  potash  (p.  339).  It  combines 
with  other  chlorides,  forming  double  salts,  of  which  some  possess 
considerable  interest.  Those  with  chloride  of  potassium,  K,C1.4- 
Pt.Cli,  and  with  sal  ammoniac,  N.H4C1.H- Pt.Cl,,  are  precipitated  as 
yellow  powders  from  strong  solutions,  or  as  minute  octohedral  or- 
ange-red crystals  from  dilute  solutions  of  those  alkalies,  and  are 
hence  used  for  their  detection.  These  salts  are  insoluble  in  alco- 
hol. The  sodium  double  salt  (Na.Cl.+Pt.Cy  is,  on  the  contrary, 
easily  soluble  both  in  alcohol  and  water. 

The  Iodides  of  Platinum  are  black  powders,  insoluble  in  water,  formed  by  the 
double  decomposition  of  iodide  of  potassium  with  the  respective  chlorides.  The 
biniodide  combines  with  iodide  of  potassium  to  form  a  double  salt  K.I.-fPt.Iz,  which 
dissolves  in  water,  giving  a  solution  so  deeply  claret-coloured  that  it  may  serve  to 
detect  a  very  minute  trace  of  platinum  in  solution. 

Although  many  oxygen  salts  of  platinum  are  described  in  the  systematic  books 
(sulphate,  nitrate,  &cl),  I  consider  that  we  possess  no  accurate  knowledge  whatever 
of  that  class  of  combinations. 

Salts  of  Iridium  and  Rhodium. 

There  are  four  chlorides  of  iridium.  The  pytochloride,  Ir.Cl.,  is  prepared  by 
heating  metallic  iridium  to  redness  in  chlorine ;  it  is  an  olive-green  body,  which  is 
insoluble  in  water,  but  combines  with  other  chlorides  to  form  double  salts.  The 
sesquichloride,  IraCla,  is  formed  by  dissolving  the  sesquioxide  in  muriatic  acid.  It  iJ 
a  brown  crystalline  substance,  volatile,  and  forming  double  salts.  The  bichloride^ 
Ir.Cl2,  is  produced  when  a  concentrated  solution  of  the  former  is  treated  with  aqua 
regia.  It  forms  a  dark  brown  solution,  giving,  when  dried,  a  black  mass.  It  gives 
with  chloride  of  potassium  a  sparingly  soluble  double  salt  in  black  octohedral  crys- 
tals. The  perchloride,  I.CI3,  is  not  known  except  in  the  state  of  a  double  salt,  K.Cl. 
+I.CI3,  which  is  produced  by  processes,  for  which  I  refer  to  the  larger  systematic 
works. 

The  protoxide,  sesquioxide,  and  deutoxide  of  iridium  form  salts  with  the  oxygen 


ELEMENTS     OF      ORGANIC     BODIES.  467 

acids;  the  solutions  of  the  first  class  being  green  or  purple,  those  of  the  second  class 
blood- red,  and  those  of  the  third  orange,  produce  the  variety  of  tints  which  gives  the 
name  Indium  to  the  metal;  they  are  not  otherwise  important. 

Sesquichloride  of  Rhodium,  R2CI3,  is  prepared  by  decomposing  the  double  chloride 
of  rhodium  and  potassium  by  hydrofluosilicic  acid.  The  filtered  liquor  gives,  when 
evaporated,  a  brown-red  mass,  destitute  of  crystalline  structure ;  by  heat  it  is  com- 
pletely decomposed.  It  combines  with  other  chlorides  to  form  well-defined  double 
salts,  such  as  that  2K.Cl.+R2Cl3-f  2  Aq.  formed  by  acting  on  metallic  rhodium  and 
chloride  of  potassium  by  aqua  regia.  When  metallic  rhodium  alone  is  treated  by 
chlorine,  a  rose-red  powder  is  obtained,  insoluble  in  water  and  acids,  which  is  a  sim- 
ilar compound  of  protochloride  and  sesquichloride  of  rhodium,  R4Cl5=2R.Cl.+ 
R2CI3. 

By  igniting  metallic  rhodium  with  bisulphate  of  potash,  a  double  salt  is  obtained, 
which  does  not  crystallize.  The  nitrate  of  rhodium  is  a  dark  red  deliquescent  salt, 
which  gives  with  nitrate  of  soda  a  double  salt  in  dark  red  crystals. 


k 


CHAPTER  XVI. 

ON  THE  GENERAL  PRINCIPLES  OF  THE  CONSTITUTION  OF  ORGANIC  BODIES. 

Organic  bodies  are  distinguished  generally  by  a  much  greater 
complexity  of  composition  than  occurs  in  substances  of  mineral  or- 
igin. Except  in  the  case  of  carbonic  oxide,  there  is  no  example  of 
an  atom  of  an  organic  compound  containing  but  two  simple  atoms ; 
and  carbonic  acid  and  cyanogen  are  the  only  examples  of  an  organ- 
ic atom  being  formed  by  three  elementary  atoms.  On  the  contrary, 
the  number  of  simple  atoms  entering  into  the  composition  of  an  or- 
ganic body  is  sometimes  very  great :  thus  an  equivalent  of  oleic  acid 
contains  270  simple  atoms  j  an  atom  of  albumen  is  formed  of  883 
simple  atoms;  an  atom  of  spermaceti  includes  468  simple  atoms; 
Clumbers  to  which  we  find  no  form  of  combination  approaching  in 
inorganic  compounds. 

Besides  this  greater  complexity  of  constitution,  organic  bodies 
ure  distinguished  by  the  nature  of  their  elements.  I  have  had  oc- 
casion already  to  describe  as  inorganic  fifty-four  undecompounded 
bodies,  which,  by  their  reunion  in  various  proportions,  generate  the 
compound  substances  which  constitute  the  mineral  crust  of  the 
globe  ;  but  among  organic  bodies  we  meet  with  few  of  these.  Al- 
though equalling  in  number  and  surpassing  in  variety  of  properties 
the  mineral  species,  the  products  of  the  animal  and  vegetable  king- 
dom may  be  looked  upon  as  consisting  almost  exclusively  of  six 
elements,  of  which  two,  sulphur  and  phosphorus,  are  met  with  but 
seldom  ;  nitrogen  is  much  more  extensively  found,  especially  in 
animal  substances  ;  oxygen  and  hydrogen  exist  in  almost  all ;  but 
the  element  which  is  peculiarly  organic,  and  which,  with  the  one 
exception  of  ammonia,  exists  in  all  bodies  derived  from  an  animal 
or  vegetable  source,  is  Carbon,  It  is  henco  that  I  have  deferred  the 
description  of  carbon  and  its  compounds  until  I  could  pass  directly 
from  it  to  the  great  variety  of  organic  bodies  of  which  it  is  the  ba- 
sis. With  the  constituents  of  inorganic  bodies  it  has  but  an  acci- 
dental connexion  ;  for,  as  I  shall  hereafter  show,  there  is  no  form  o{ 


468  CLASSES     OF     ORGANIC     BODIES. 

carbon  which  has  not  at  some  time  made  part  of  an  organized  being. 
Besides  these  six  elements  of  organic  bodies,  there  are  many  which 
enter  into  the  structure  of  animals  and  plants,  and  are  subservient 
in  an  important  degree  to  the  proper  performance  of  their  func- 
tions, without  being  really  constituents  of  their  organic  tissues  or 
secretory  products.  Thus  iodine  and  bromine  exist  in  many  ma- 
rine plants  and  sponges;  common  salt  and  oxygen  salts  of  potash, 
soda,  lime,  and  magnesia  exist  in  most  animal  and  vegetable  juices  ; 
phosphate  of  lime  constitutes  the  bony  skeleton  of  one,  and  carbo- 
nate of  lime  the  testaceous  covering  of  another  tribe  of  animals, 
while  silica  forms  the  solid  basis  of  some  of  the  lower  tribes  of  zo- 
ophytes. In  the  red  colouring  matter  of  the  blood,  iron  is  an  essen- 
tial element,  and  the  same  metal  has  been  found  in  minute  quantity 
in  other  parts  of  animals  ;  indications  of  fluorine  and  of  silica  have 
been  found  in  the  bones  and  teeth ;  but  in  all  these  instances,  ex- 
cept the  one  fact  of  the  iron  element  of  red  blood,  we  find  these 
saline  substances  to  be  contained  in  fluids  in  a  condition  of  mere 
physical  solution,  or  to  be  deposited  as  solids  in  the  bones  or  teeth 
in  a  purely  inorganic  form,  clearly  to  be  distinguished  from  the 
proper  state  of  organic  combination,  in  which  the  carbon,  hydro- 
gen, oxygen,  and  nitrogen  of  the  tissues  and  secretory  products  are 
united. 

Among  organic  bodies,  it  is  necessary  to  distinguish  three  class- 
es, which  differ  no  less  in  complexity  of  composition  than  in  the 
circumstances  under  which  they  are  formed,  and  their  relation  to 
organic  bodies.  These  are,  first,  those  bodies  which  are  directly 
elements  of  an  organized  and  living  being,  and  which,  while  in  con- 
nexion with  it,  appear  to  possess  the  power  of  elaborating,  from 
certain  nutritious  juices,  additional  material  similar  to  themselves. 
Such  are  the  organic  constituents  of  the  animal  and  vegetable  tis- 
sues and  of  the  blood,  which,  while  in  connexion  with,  and  form- 
ing portions  of  the  animal  or  plant,  participate  to  a  certain  degree 
in  its  vitality,  and  do  not  obey  the  laws  of  ordinary  affinity,  unless 
by  being,  in  the  first  instance,  killed;  these  bodies  should  be  more 
properly  called  organized  than  merely  organic  ;  their  chemical  rela- 
tions commence  only  when  they  have  been  deprived  of  their  most 
essential  character,  life.  They  are  organs ;  their  constitution  can- 
not be  expressed  in  formulse,  nor  their  properties  accounted  for  by 
analysis.  After  their  death  we  may  obtain  from  them,  by  chemical 
treatment,  a  variety  of  organic  bodies  ;  but  that  they  were  composed 
of  these  bodies,  and  that  their  properties  resulted  from  the  combi- 
nation of  such  elements  as  we  extract  from  them,  it  would  be  false 
philosophy  to  imagine.  The  fibrine  and  albumen  of  the  blood,  the 
muscles,  and  the  cellular  tissues,  the  fatty  matter  of  the  brain,  per- 
form their  functions  in  virtue  of  vital  power,  and  not  of  any  chen>- 
ical  properties  they  possess.  The  albumen  of  the  egg  is  not  a  chem- 
ical substance,  but  a  delicatelj^-constructed  mass,  destined  to  be 
transmuted  into  the  organs  of  the  chick,  and  by  participating  in  its 
life,  protected  from  putrefaction.  But  when  albumen  is  precipitated 
by  corrosive  sublimate,  it  is  killed,  and  the  product  of  its  decompo- 
sition combines  with  the  oxide  of  mercury. 

This  class  of  bodies  have  their  origin,  therefore,  in  actions  purely 


RELATION    OF     ORGANIC     FORCE     TO     AFFINITY.  469 

vital.  They  have  a  structure  organic-molecular,  totally  different 
from  crystallization,  and  for  the  most  part  consisting  of  minute 
cells.  When  dead,  these  tissues  undergo  spontaneous  decomposi- 
tion, with  more  or  less  rapidity,  according  as  their  composition  is 
more  complex  ;  but  for  this  water  must  be  present.  Some  forms 
of  animal  tissue,  which  appear  to  lose  the  organized  structure  and 
vitality  with  which  they  were  at  first  formed,  are  capable  still  of 
remaining  in  connexion  with  the  living  system,  and,  although  dead, 
have  no  tendency  to  putrefy,  probably  from  not  being  in  any  de- 
gree soluble  in  water.  The  formation  and  growth  of  nails  and 
hoofs,  hair  and  horns,  are  examples  of  the  important  uses  of  this 
property. 

It  is  by  virtue  of  the  vital  forces  of  the  bodies  of  this  first  class, 
not  individually,  but  united  together  so  as  to  constitute  the  tissues, 
glands,  &c.,  of  plants  and  animals,  that  the  organic  bodies  of  the 
second  class  have  their  origin.  These  are  substances  produced  (se- 
creted) from  the  elements  by  which  organized  bodies  are  nourished, 
probably  by  the  union,  under  peculiar  conditions,  of  such  portions 
of  the  constituents  of  the  food  as  were  not  proper  or  proportioned 
to  be  assimilated  to  the  organized  tissues  of  the  living  being  itself. 
It  is  thus  that,  by  a  plant  which  uses  water,  carbonic  acid,  and  at- 
mospheric air  as  nutriment,  after  the  assimilation  of  a  certain  quan- 
tity of  their  constituents  to  its  proper  tissues,  sugar,  starch,  and  al- 
bumen, adapted  for  the  nutrition  of  its  young,  may  be  formed  as 
secreted  products,  and  oils,  resins,  colouring  matters,  &c.,  rejected 
as  useless  or  injurious. 

The  third  class  of  organic  bodies  contains  those  which  are  evolv- 
ed by  the  chemical  decompositions,  whether  spontaneous  or  arti- 
ficial, to  which  substances  of  the  first  and  second  class  are  subject- 
ed. Thus  sugar,  by  fermentation,  yields  alcohol  and  carbonic  acid  ; 
alcohol,  by  oxidation,  yields  acetic  acid,  or  aldehyd  ;  acetic  acid, 
variously  treated,  produces  acetone,  or  alkarsin ;  while  ligneous 
fibre  gives  origin,  when  heated,  to  a  crowd  of  organic  products,  of 
which  pyroxylic  spirit  is  an  example. 

It  is  very  interesting  to  contrast  these  classes  of  bodies  with  each 
other,  in  relation  to  the  forces  by  which  their  constitution  is  regu- 
lated, as  compared  with  the  simpler  forms  of  affinity  by  which  the 
actions  of  inorganic  elements  are  controlled.  In  the  first  there  is 
found  nothing  referrible  to  chemical  attraction  ;  all  affinity  is  an- 
nulled by  the  supremacy  of  life  and  organization.  Hence  it  is  only 
when  dead  that  such  bodies  can  be  analyzed,  and  by  treatment  with 
reagents  a  crowd  of  products  belonging  to  the  third  class  be  obtain- 
ed from  their  more  or  less  evident  decomposition.  No  matter, 
therefore,  how  perfect  our  mediate  or  immediate  analyses  of  such 
substances  may  be,  the  synthesis  of  such  bodies,  or  their  production 
by  the  union  of  their  elements,  is  strictly  impossible  to  the  chemist. 
The  formation  of  a  molecule  of  albumen  would  not  be  a  case  of 
chemical  combination,  but  of  the  formation  of  a  portion  of  an  or- 
ganized cell  ;  it  would  require  not  merely  the  combination  of  its  el- 
ements, but  also  that  the  compound  should  have  life  imparted  to  it. 

In  relation,  however,  to  the  second  and  third  classes,  the  circum- 
stances are  quite  different  j  although  we  cannot  trace,  precisely, 


470  THEORY     OF     COMPOUND     RADICALS. 

the  force  by  which  the  organized  tissues  act  in  eliminating  from  a 
liquid  of  uniform  composition,  such  as  the  blood  or  sap,  the  various 
secretions  which  constitute  the  second  class,  yet  the  circumstan- 
ces of  their  formation  admit  of  being  examined,  and  already  some 
insight  has  been  obtained  as  to  the  way  in  which  organic  bodies 
may  separate,  or  be  converted  into  others,  without  reference  to  the 
mere  affinities  of  their  elements,  by  means  of  the  influence  that  has 
been  already  described  as  catalytic  (p.  236,  et  seq.)  ;  in  this  way  the 
functions  of  organized  tissues  may  be  imitated,  and  a  true  synthesis 
of  organic  bodies  of  the  second  class  may  be  effected.  With  the 
bodies  of  the  third  class  we  find,  also,  that  the  circumstances  of 
their  formation  are  either  purely  artificial,  or  capable  of  being  easi- 
ly imitated,  and  the  reactions  by  which  they  are  evolved,  although 
often  catalytic,  fall,  in  the  majority  of  cases,  under  the  rules  of  or- 
dinary affinity.  In  structure,  also,  the  bodies  of  the  second  and 
third  class  range  themselves  with  inorganic  compounds  ;  those 
which  are  solid  may,  for  the  most  part,  be  obtained  crystallized,  and 
the  liquid  substances  possess  definite  freezing  and  boiling  points. 

Between  such  organic  bodies  and  mineral  substances  we  find  the 
greatest  similarity,  not  merely  in  their  physical  relations,  but  in 
chemical  properties  also.  The  great  classes  of  acids  and  bases  ex- 
ist, well  marked,  among  organic  bodies,  and  in  their  combinations 
with  each  other,  the  same  principles  of  multiple  and  equivalent 
combination  are  followed  as  hold  for  inorganic  compounds.  So 
perfect  is  the  analogy  of  general  characters,  that  it  has  long  been 
an  object  with  chemists  to  unite,  under  one  principle,  the  laws  of 
composition  of  organic  and  inorganic  bodies  ;  and  as  the  character- 
istic distinction  of  mineral  substances  is  to  consist  of  a  series  of  el- 
ements which  are  respectively  combined,  two  and  two,  in  virtue  of 
their  opposite  affinities,  attempts  have  been  made  to  reduce  the 
complex  constitution  of  organic  bodies  to  the  same  principle  of  bi- 
nary union,  by  supposing  that  certain  of  the  elements  are,  in  the 
first  instance,  grouped  together  so  as  to  form  a  single  molecule, 
and  that  this,  acting  as  a  simple  body,  combines  with  the  element 
which  remains.  It  is  from  the  discovery  of  cyanogen,  and  the  dis- 
cussions as  to  the  nature  of  the  ethers  and  of  the  ammoniacal  salts, 
that  we  must  date  the  positive  introduction  of  this  theory  of  com- 
pound radicals  into  chemistry.  Its  utility  has  not  been  limited  to 
the  explanation  of  the  constitution  of  organic  bodies ;  on  the  con- 
trary, it  has  been  applied  successfully  to  explain  the  phenomena  pre- 
sented by  numerous  classes  of  inorganic  compounds,  such  as  the 
compounds  of  sulphur  and  oxygen,  noticed  p.  292,  and  especially 
to  the  foundation  of  the  binary  theory  of  salts,  as  described  in  the 
fifteenth  chapter. 

Were  we,  however,  to  apply  the  theory  of  compound  radicals  in- 
discriminately to  explain  the  constitution  of  organic  bodies,  we 
should  be  liable  to  fall  into  continual  error.  The  criterion  which  1 
would  assume  as  decisive  of  the  constitution  of  an  organic  body  is, 
whether  certain  of  its  elements  may  be  exchanged  for  others,  in  ac- 
cordance with  the  ordinary  laws  of  substitution  of  inorganic  bodies, 
and  thus  a  series  of  compounds  be  produced,  through  which  some 
elements  of  the  original   substance  shall  have  passed  untouched, 


THEORY     OF     COMPOUND     RADICALS.  471 

and  from  which  again,  by  suitable  reactions,  the  original  substance 
can  be  obtained  unaltered.  In  such  case  I  would  consider  those 
elements  which  remain  unaffected  as  being  strictly  united  with  each 
other,  and  constituting  a  compound  radical,  which,  combining  with 
other  bodies,  gives  origin  to  a  series  of  compounds  more  or  less  ex- 
tensive. Thus,  if  we  treat  oil  of  bitter  almonds,  C14H6O2,  by  chlorine, 
we  obtain  a  compound  C^Ji:iOJ^\.J  which  gives,  with  iodide  or  sul- 
phuret  of  potassium,  bodies  whose  formulae  are  respectively  C14H3O2 
I.  and  0,4115028.  Again  acted  on  by  oxygen,  it  gives  crystallized 
benzoic  acid,  C,4Ho04,  or,  rather,  C,4H503-|-Aq.  Now  it  will  be  seen 
that,  throughout  this  whole  series,  the  element  C,4H502  has  remained 
unaltered.  In  the  oil  it  was  combined  with  hydrogen ;  in  benzoic  acid 
it  unites  with  oxygen  ;  in  the  other  bodies  it  is  united  with  chlorine, 
iodine,  &c.,  and  from  these  the  oil  may  be  recovered  by  processes 
by  no  means  indirect.  Now  when  we  state  that  in  these  compounds 
the  elements  C,4H502  are  united,  first  with  each  other,  by  an  affin- 
ity which  ordinary  reagents  cannot  overcome,  and  that  this  com- 
pound  group  unites  with  the  simple  bodies,  hydrogen,  oxygen,  &c., 
by  an  affinity  so  much  weaker  that  they  can  be  readily  substituted 
for  each  other,  we  state  only  an  established  fact,  and  in  denomina- 
ting the  group,  0,411^02,  the  root  or  radical  of  the  series  of  bodies 
thus  produced,  we  involve  no  hypothetical  idea.  For  brevity,  we 
express  that  compound  radical  by  the  symbol  Bz.,  and  we  term  it 
Benzyle  ;  we  write  the  formula  of  its  combinations,  respectively,  Bz. 
H.,  Bz.Cl.,  Bz.L,  and  Bz.O.+Aq. 

But  we  must  not  be  induced,  by  the  brilliancy  shed  on  certain 
branches  of  organic  chemistry  through  the  application  of  this  prin- 
ciple, to  transgress  the  boundaries  of  sound  induction.  There  are 
numerous  organic  compounds  in  which  I  believe  that  no  binary 
structure  exists,  and,  consequently,  to  which  the  theory  of  organic 
radicals  should  not  be  applied.  It  is  the  class  of  bodies  character- 
ized by  a  remarkable  indifference  to  combination,  and  which,  when 
decomposed  by  the  influence  of  reagents,  lose  not  merely  one  con- 
stituent and  gain  another  in  its  place,  but  are  totally  transformed 
into  new  compounds,  into  which  all  of  their  original  components 
enter,  and  towards  which  the  reagent  that  had  been  applied  fre- 
quently appears  indifferent,  so  that  the  action  appears  to  have  more 
the  character  of  catalysis  than  of  true  chemical  affinity.  Such  bod- 
ies are  gum,  sugar,  starch,  some  of  the  oily  and  colouring  matters, 
urea,  and  many  others :  treat  these  bodies  as  you  will,  there  are  no 
phenomena  of  true  replacement ;  they  may  be  decomposed,  but  bod- 
ies of  a  totally  different  type  are  formed,  and  the  original  substances 
cannot  be  regenerated. 

The  organic  radical  which  is  thus  assumed  as  the  basis  of  a  se- 
ries of  compounds,  acts  as  a  simple  body,  but  it  does  so  only  in  re- 
lation to  the  nature  and  intensity  of  the  forces  that  act  upon  it ;  it 
may  be  decomposed,  and  frequently  it  cannot  be  separated  from 
combination  without  total  decomposition  ;  hence  iew  compound 
radicals  can  be  isolated.  But  they  can  be  decomposed,  even  while 
still  in  combination,  by  the  intervention  of  powerful  affinities ;  and 
this  decomposition  may  be  either  total,  so  as  to  leave  no  trace  of 
the  original  constitution  of  the  substance,  or  by  giving  origin  to 


472  ITS     APPLICATION     LIMITED. 

another  series  of  combinations,  may  indicate  a  still  more  intimate 
constitution,  and  unveil  an  organic  radical  of.  a  simpler  structure 
acting  as  the  basis  of  the  first. 

Thus  we  have  seen  what  positive  grounds  there  are  for  admit 
ting  benzyle,  C^HiO.,  to  be  the  radical  of  the  oil  of  bitter  almondis 
and  of  benzoic  acid  ;  but  if  we  digest  oil  of  bitter  almonds  with 
ammonia,  all  oxygen  is  removed,  and  we  obtain  a  compound  of  ni 
trogen  with  the  body,  C  H^,  which  may  also  be  obtained  in  other 
forms  of  combination.  Now  this  organic  substance,  C14H5,  acts  as 
the  basis  of  benzyle,  for  the  oil  of  bitter  almonds  can  be  reproduced 
from  it ;  and  we  thus  obtain  evidence  of  three  stages  of  constitution 
in  benzoic  acid,  whose  formula  should  be  written,  therefore,  as  (Cj^ 
H5-I-O2)  [-0.  The  considerations  described  in  p.  291  point  out  a 
perfect  analogy  to  this  in  the  constitution  of  sulphuric  acid.  Ee- 
duced  to  its  ultimate  elements,  its  formula  is  S.O3 ;  but  powerful  evi- 
dence shows  that  its  real  basis  is  sulphurous  acid,  and  not  sulphur, 
its  rational  formula  being  S.O2+O.  Now  here  the  primary  radical, 
CiJi^y  corresponds  to  sulphur,  and  benzyle  to  sulphurous  acid  ;  the 
total  quantity  of  oxygen  in  such  acids  being  divided  into  two  por- 
tions, differing  in  order  and  intensity  of  combination  with  the  ulti- 
mate radical.  If  we  add  to  these  considerations  the  view  of  salt- 
radicals,  and  consider  the  salts  of  benzoic  acid  as  expressed  by  the 
formula  Bz.Oa+M.,  as  that  of  the  sulphates  has  been  shown  to  be 
S.O2 .  02+^.,  we  observe  even  a  fourth  degree  to  which  the  mole- 
cular structure  of  the  complex  organic  radical  may  be  traced. 

It  is,  indeed,  when  applied  to  explain  the  constitution  of  the  or- 
ganic acids,  that  the  theory  of  compound  radicals,  as  employed  in 
the  new  views  of  the  constitution  of  oxygen  salts,  appears  most  in- 
teresting, as  the  anomalies  of  properties  and  composition  presented 
by  the  salts  of  the  organic  acids  were  more  numerous  and  more  ex- 
traordinary than  any  which  the  mineral  acids  presented,  and  were, 
indeed,  totally  unintelligible,  until  illustrated  by  the  conjoined  in- 
vestigations of  Dumas  and  of  Liebig.  An  example  of  this  may  easi- 
ly be  selected.  Of  the  organic  acids,  the  majority  are  monobasic, 
but  there  are  also  many  bibasic  and  tribasic  ;  thus  the  citric  acid, 
whose  formula  is  C|2H^0,,,  combines  with  three  atoms  of  base  ;  the 
meconic  acid,  C14H.O,,,  is  also  tribasic;  the  tartaric  acid,  0^1140,0, 
and  the  mucic  acid,  C,2HgO|4,  are  bibasic.  In  these  instances,  the 
quality  of  combining  with  many  atoms  of  base,  which  is  so  anoma- 
lous on  the  older  view,  necessarily  follows  from  the  formulae  of  the 
hydrated  acids,  which  become  respectively,  for  citric  acid,  C12H5O14 
.-f-Haj  for  meconic  acid,  C14H.O  4+H3;  for  tartaric  acid,  C^jOia+Hj; 
and  for  mucic  acid,  CijHsOie-fHi.  By  its  means  many  other  singu- 
lar properties  of  organic  acids  are  explained :  thus  there  appear  to 
exist  three  acids,  having  absolutely  the  same  composition  of  C2N. 
O.,  viz.,  the  cyanic,  the  fulminic,  and  the  cyanuric  acids ;  they  are 
isomeric  ;  they  possess  excessively  different  properties.  Whence 
has  that  difference  its  rise  '(  If  we  say  that  the  cyanic  acid  contains 
cyanogen  ready  formed,  and  that  the  others  do  not,  it  still  remains 
to  explain  the  isomerism  of  the  others ;  and  we  find  that  the  cyanic 
and  cyanuric  acids  are  transformed  into  each  other  by  the  slightest 
causes.     We  obtain,  however,  at  once  the  key  to  this  isomerism, 


CONSTITUTION     OF     COMPOUND     RADICALS.      473 

when  we  study  the  salts  formed  by  these  acids.  The  cyanic  acid 
is  monobasic ;  its  hydrate  is  C2N.O.  +  H.O. :  the  fulminic  acid  is  bi- 
basic;  its  hydrate  is  C4N2O2+2H.O. :  the  cyanuric  acid  is  tribasic ; 
its  formula  is  CsNaOg+SH.O.  These  acids  are  thus  found  to  have 
different  atomic  weights ;  their  molecular  groups  are  ascertained  to 
contain  different  numbers  of  molecules,  and  hence  to  admit  of  to- 
tally distinct  internal  structure.  When  expressed  in  formulae  on 
the  binary  theory,  we  have  C2N.O2+H.  for  the  cyanic,  C4N2O4+H2 
for  the  fulminic,  and  CyNaOe+Hg  for  the  cyanuric  acid;  and  not 
merely  the  difference  in  nature  of  the  acids,  but  also  the  distinctive 
characters  bf  their  salts  necessarily  result. 

Although  chemists  are  unanimous  in  regarding  the  principle  of  com- 
pound radicals  as  the  basis  of  the  philosophy  of  organic  chemistry, 
yet  science  has  not  yet  arrived  at  the  point  w^hen  the  principle  is 
adopted  by  all  in  the  same  form  of  detailed  application.  On  the 
contrary,  there  are  few  specific  examples  of  that  principle  that  are 
not  still  open  to  discussion.  The  views  of  Berzelius  on  this  subject 
are  specially  of  importance.  He  considers  that  the  compound  rad- 
icals of  organic  bodies  consist  only  of  carbon  and  hydrogen,  or  of 
carbon  and  nitrogen  :  that  they  never  contain  oxygen.  Hence  he 
does  not  admit  the  existence  of  benzyle  in  benzoic  acid  or  in  oil 
of  bitter  almonds  j  he  considers  the  only  radical  to  be  the  carbo- 
hydrogen,  Ci4H5,  and  benzoic  acid  to  be  directly  C,4H5-f-03.  He 
looks  upon  the  oil  of  bitter  almonds  as  containing  ready-formed 
benzoic  acid,  combined  with  the  true  hydruret  of  the  radical,  as  3 
(C,4HA)==2(C»4H5-f  03)4-(C,4H5+H3).  The  chloride  of  benzyle  he 
looks  upon  as  an  oxychloride,  3(C,4H5 .  O2CI.)  being  equal  to  2(C,4Hs 
-}'Oj)-|-(Ci4H5-f  CI3).  This  is  evidently  the  same  difference  of  view 
that  exists  as  to  the  nature  of  the  sulphurous  acid  compounds,  which 
Berzelius  also  regards  as  more  complex.  Thus  the  chlorosulphu- 
rous  acid  is,  according  to  him,  a  compound  of  sulphuric  acid  with 
a  terchloride  of  sulphur,  3(S.02Cl.)=2S.03  +  S.Cl3;  and  so  in  all 
other  bodies  similarly  circumstanced. 

The  opinions  of  a  man  to  whose  extraordinary  industry  and  ge- 
nius we  owe  some  of  thennost  important  additions,  both  theoretical 
and  practical,  that  science  has  received  since  the  epoch  of  Lavoisier, 
should  not  be  rejected  without  much  consideration  j  but  on  apply- 
ing those  ideas  to  express  the  constitution  of  the  crowd  of  bodies, 
containing  four  or  five  elements,  which  have  recently  been  discov- 
ered, we  are  led  to  suppositions  destitute  of  experimental  proof,  and 
yet  which,  assuming  the  existence  of  numerous  hypothetic  bodies 
of  anomalous  constitution,  and  combined  in  very  unusual  ways, 
would  require  for  their  legitimate  admission  into  science  a  very 
strong  body  of  experimental  evidence.  It  would  be  impossible  here 
to  discuss  the  principles  of  his  opinion  in  detail ;  I  am  led  to  con- 
clude, from  the  consideration  of  the  whole  body  of  facts  which  bear 
upon  it,  that  it  is  inferior  in  power,  and  simplicity  of  explanation  of 
known  facts,  and  as  an  instrument  of  discovery,  to  the  simpler  view 
of  the  constitution  of  organic  bodies  which  has  been  described  ;  and 
being:  thus  deficient  in  all  the  important  duties  of  a  sound  theory,  I 
do  not  hesitate  to  reject  it. 

The  proposition  of  the  theory  of  types  by  Dumas  (see  p.  234) 

Ooo 


474  THEORY     OF     CHEMICAL     TYPES. 

will  probably  constitute  an  epoch  in  science,  by  fixing  attention  on 
the  permanent  equivalency  of  an  organic  atom,  notwithstanding 
complete  alteration  in  the  nature  of  its  elements.  This  did  not  fol- 
low necessarily  from  the  theory  of  compound  radicals,  nor  does  the 
conservation  of  the  type  require  that  the  radical  be  preserved  unal- 
tered, but  only  the  type  of  the  radical.  Thus,  when  aldehyd  is 
changed  into  chloral  (C4H4O2  into  C4H. .  CI3O2),  the  type  is  preserved, 
since  the  hydrogen  is  replaced  by  an  equivalent  of  chlorine  ;  the 
radical  is  altered,  since  acetyl,  C4H3,  is  changed  into  C4CI5,  but  the 
new  radical  is  still  constructed  on  the  type  of  the  original.  The 
theory  of  types,  so  far  from  being  inconsistent  with  the  theory  of 
compound  radicals,  is  in  perfect  harmony  with  it,  at  least  as  I  un- 
derstand it,  and  as  I  believe  it  to  have  been  proposed  by  Dumas. 
The  bases  u^on  which  it  rests  may  be  announced  as  follows : 

1st.  That  the  hydrogen  of  a  compound  radical  may  be  replaced 
by  chlorine  or  by  oxygen,  &c.,  equivalent  for  equivalent,  and  a  new 
radical  thus  produced,  which,  being  constructed  on  the  same  type 
as  the  original,  will  have  the  same  general  laws  of  combination,  and 
will  hence  form  compounds  of  the  same  type  as  those  containing 
the  original  radical.  Thus,  from  C4H3  may  be  formed  040)3,  and 
these,  combining  with  oxygen  and  water,  form  04H3O.-j-Aq.  or  O4 
HgOg-l-Aq.,  and  O4OI3O  -j-Aq.  or  O4OI3O34- Aq. :  also,  by  uniting 
with  chlorine,  they  produce  C4H3OI.  and  C4OI3OI. 

2d.  That  when  bodies  of  the  same  type,  and  containing  radicals 
of  the  same  type,  are  subjected  to  the  action  of  strong  affinities,  by 
which  their  constitution  is  broken  up,  the  resulting  products  are 
constituted  also  upon  the  same  plan,  although  differing  in  composi- 
tion 5  thus  C4H4O4,  when  heated  with  potash,  gives  2C.O2  and  CJi^ ; 
and  C4H.  .  CI3O4,  similarly  treated,  gives  2C.O2  and  C2H.CI3  j  the 
types  of  C2H.H3  and  C2H.CI3  being  the  same,  and  containing  equiv- 
alent radicals. 

3d.  When  bodies  of  the  same  chemical,  though  of  different  me- 
chanical types,  or,  as  I  would  term  them,  bodies  of  the  same  natural 
families,  as  the  alcohols,  are  submitted  to  the  action  of  affinities  of 
equal  power,  the  bodies  generated  have  *he  same  relation  to  one 
another  as  the  original  bodies  had ;  and  the  radicals  are  either  un- 
changed, or  all  changed  in  a  similar  degree.  Thus  from  wine  alco- 
hol (C4H6O2),  methylic  alcohol  (C2H4O2),  essential  oil  of  potato 
spirit,  CioHiaOj,  and  ethal,  C32H34O2,  there  are  produced  by  the  ac- 
tion of  potash  a  series  of  acids,  each  having  the  same  type  and 
containing  the  same  radical  as  its  alcohol  ;  thus  the  acetic  acid  (C4 
H4O4),  the  formic  acid  (C2H2O4),  the  valerianic  acid  (CJ0H10O4),  and 
the  ethalic  acid,  C32H32O4. 

Considered  in  this  way,  the  theory  of  types  is  an  important  ad- 
dition to  our  ideas  on  the  constitution  of  organic  bodies.  It  serves 
to  attach,  under  a  few  very  simple  principles,  numerous  classes  of 
compounds,  whose  composition  would  otherwise  appear  very  com- 
plex and  anomalous,  and  will  probably,  when  applied  to  the  study 
of  such  bodies  as,  not  containing  compound  radicals,  give  only  their 
molecular  group  as  a  mass  to  our  examination,  become  a  source  o{ 
still  more  important  additions  to  our  knowledge. 

Although  each  organic  substance  gives,  when  acted  on  by  re- 


PRINCIPLE     OF     ACTION     OF     REAGENTS.  475 

agents,  products  which  are  characteristic  of,  and  often  peculiar  to 
itself,  yet  there  are  some  general  rules  which,  being  now  noticed, 
will  obviate  the  necessity  of  much  detail  hereafter. 

When  an  organic  substance  is  treated  with  dry  chlorine,  it  eithei 
combines  directly  with  the  gas,  or,  as  more  frequently  happens,  hy- 
drogen is  removed  to  an  amount  equivalent  to  that  of  the  chlorine 
absorbed.  Even  in  the  first  case,  the  direct  union  is  often  but  ap- 
parent, and  arises  from  the  muriatic  acid  formed  combining  with 
the  true  product.  Thus  olefiant  gas,  C4H4,  gives  the  oily  liquid  C4 
H4CI2 ;  but  this,  in  place  of  being  a  direct  combination,  consists  of 
C4H^C1.,  which  is  the  true  product  formed  by  substitution  of  CI. 
for  H.,  but  is  united  with  the  H.Cl.  thus  generated. 

If  water  be  present,  it  influences  the  reaction  very  much,  being 
generally  decomposed.  In  some  cases,  all  the  chlorine  unites  with 
its  hydrogen,  while  the  oxygen  combines  with  the  organic  sub- 
stance ;  but,  generally,  the  chlorine  unites  with  both  elements  of 
the  water,  forming  muriatic  acid,  which  remains  free,  and  hypochlo- 
rous  or  chlorous  acids,  which  enter  into  the  composition  of  the  or- 
ganic product.  In  other  cases,  again,  the  presence  of  water  does 
not  appear  to  exercise  any  influence. 

When  an  organic  substance  is  treated  with  nitric  acid,  it  is  always 
raised  to  a  higher  degree  of  oxidation.  Very  rarely  does  the  action 
stop  there.  Hydrogen  is  usually  separated,  and  oxygen  put  in  its 
place  ;  while  the  new  products  formed  contain  usually  a  smaller 
number  of  molecules  than  the  original  organic  substance.  Thus 
gum  (CioHioOio),  when  acted  on  by  nitric  acid,  gives,  first,  by  sim- 
ple oxidation,  mucic  acid  (C,2H,oO,6)  ;  but,  if  the  action  of  the  acid 
be  more  violent,  all  hydrogen  is  removed,  and  two  atoms  of  oxygen 
substituted,  thus  producing  CijOig,  the  elements  of  six  atoms  of  ox- 
alic acid. 

In  many  cases,  the  action  of  nitric  acid  is  not  limited  to  the  oxi- 
dation, whether  direct  or  indirect,  of  the  organic  substances ;  but, 
by  the  removal  of  some  hydrogen  from  it,  in  combination  with  some 
of  the  oxygen  of  the  nitric  acid,  water  is  formed,  and  the  nitrogen, 
or  nitric  oxide,  or  nitrous  acid,  combines  with  the  remaining  organ- 
ic elements,  and  forms  new  products.  Thus,  from  napthaline  and 
benzine,  numerous  substances  containing  nitrogen  are  derived. 
This  fixation  of  nitrogen  may  occur  even  with  bodies  which  already 
contain  it ;  thus  indigo,  treated  with  iwtric  acid,  produces  bodies, 
the  indigotic  and  the  picric  acids,  which  contain  a  larger  proportion 
of  nitrogen  than  the  indigo  itself. 

The  peroxides  of  manganese  and  lead  often  serve  to  oxidize  or- 
ganic bodies  in  a  more  regulated  manner  than  nitric  acid,  the  new 
substance  combining  with  the  protoxide  of  the  metal ;  thus,  by  Pb. 
O2,  uric  acid  is  decomposed  into  allantoin,  urea,  and  oxalic  acid. 

By  fusion  with  hydrate  of  potash,  the  oxidizement  of  organic 
substances  is  very  powerfully  effected  ;  water  being  decomposed, 
its  hydrogen  evolved,  and  the  oxygen  uniting  with  the  organic  body 
to  form  an  acid^  which  remains  combined  with  the  potash.  Thus 
alcohol,  C4H6O2  and  2H.0  ,  produce  acetic  acid,  C4H4O4,  and  H4  be- 
comes free.  Often  the  organic  substance  is  merely  broken  up  into 
other  bodies  of  simpler  constitution,  as  when  tartaric  acid,  C8H4OJ0, 


476 


ORGANIC     ORIGIN     OF      CARBON. 


by  fusion  with  potash,  is  decomposed  into  acetic  acid,  C4H4O4,  and 
oxalic  acid,  2(C203).  In  every  case,  if  the  temperature  be  much 
raised,  carbonic  acid  is  one  of  the  products  j  thus  acetic  acid  (C4H4 
O4)  separates  into  C4H4  and  2C.O2. 

The  action  of  sulphuric  acid  on  organic  bodies  may  be  very  dif- 
ferent, according  to  circumstances  j  thus  from  starch  we  may  ob- 
tain, by  a  merely  catalytic  influence,  gum,  grape-sugar,  and  ulti- 
mately sacchulmine.  In  these  cases,  the  sulphuric  acid  remains 
totally  unchanged  and  free,  but  generally  it  enters  into  combination 
with  the  organic  body,  either  without  decomposition,  as  in  the  sul- 
phovinic  and  sulphomethylic  acids,  or  else  water  is  formed  by  its 
reaction  on  the  organic  body,  which,  thus  deprived  of  an  atom  of 
hydrogen,  combines  with  hyposulphuric  acid,  S2O5.  It  is  thus  that 
the  sulphurous  element  exists  in  the  *sulphobenzoic  acid,  the  isethi- 
onic  acids,  &c. 

If  an  organic  substance  containing  nitrogen  be  acted  on  by  these 
reagents  at  a  high  temperature,  this  is  generally  separated  under 
the  form  of  ammonia ;  water  being  decomposed,  and  its  hydrogen 
so  applied,  while  its  oxygen  forms  the  ordinary  oxidized  organic 
products.  If  potash  be  the  reagent,  the  ammonia  is  expelled,  and  a 
salt  of  potash  with  the  new  organic  acid  remains ;  if  sulphuric  acid 
be  the  reagent,  the  organic  acid  is  set  free,  and  a  sulphate  of  am 
monia  remains. 

By  the  action  of  heat  upon  fixed  organic  compounds,  a  variety  of 
products  are  formed,  which  may  generally  be  described  as  formed 
by  the  abstraction  of  a  portion  of  carbon  and  oxygen,  as  carbonic 
acid,  and  of  hydrogen  and  oxygen,  as  water.  Hence  such  pyrogen- 
ic  products  are  always  richer  in  hydrogen  and  carbon  than  the  bod- 
ies they  are  formed  from,  and  of  less  acid  characters.  This  kind 
of  decomposition  will,  however,  require  to  be  described  in  a  dis- 
tinct chapter. 


CHAPTER  XVII. 

OF  CARBON,  AND  ITS  COMPOUNDS   WITH  OXYGEN,  SULPHUR,  AND  CHLORINE. 

Carbon  exists  in  large  quantities,  and  very  extensively  distributed 
in  nature,  as  a  constituent  of  all  vegetable  and  animal  bodies.  It  is 
found,  also,  in  the  mineral  kingdom,  under  forms,  however,  which 
may  be  shown  to  have  originally  been  derived  from  organic  bodies. 
Thus  the  difl^erent  varieties  of  coal  have  been  produced  by  the  ag- 
gregation of  great  quantities  of  wood,  the  materials  of  primeval  for- 
ests, which,  being  submerged  in  water,  and  covered  by  the  gradual- 
ly-deposited layers  of  sand  and  mud,  have  been  elevated,  in  connex- 
ion with  the  strata  of  clay  and  sandstone  so  produced,  to  their  pres- 
ent situations.  The  wood  thus  circumstanced  has  undergone  a  kind 
of  decomposition,  which  shall  be  hereafter  fully  noticed,  and  the 
mixture  of  fixed  and  volatile  organic  products,  which  constitute  our 


NATURE     OF     LIMESTONE     ROCK. DIAMOND.     477 

coal,  has  thus  its  origin.  This  formation  of  coal,  as  well  as  the 
formation  of  peat  and  turf  at  the  present  day,  almost  at  the  surface, 
is  accompanied  by  a  disengagement  of  carbonic  acid  in  large  quan- 
tity, and  hence  the  probable  source,  in  the  air  and  in  mineral  wa- 
ters, of  that  substance,  of  which,  also,  much  may  be  derived  from 
the  respiration  of  animals. 

A  more  strictly  mineral  form  of  carbon  is  that  of  carbonic  acid 
united  to  lime,  and  to  other  metallic  oxides,  forming  the  numerous 
class  of  native  carbonates.  Of  these  the  most  abundant  is  the  car- 
bonate of  lime,  which,  under  the  form  of  chalk,  oolite,  coral,  mount- 
ain limestone,  &c.,  constitutes  a  large  proportion  of  the  geological 
formations  of  our  globe.  In  all  these  cases,  the  rock  is  formed  of 
shells  of  animals,  aggregated  together  in  great  masses ;  these  geo- 
logical formations,  resulting  from  the  collection,  at  the  bottom  of  a 
sea  or  lake,  of  the  spoils  of  myriads  of  generations  of  those  animals, 
which,  by  superincumbent  pressure,  may  be  more  or  less  densely 
aggregated  ;  or  by  proximity  of  igneous  rocks,,  may  be  partially  or 
completely  fused,  and  their  organic  characters  obliterated  to  a  great- 
er or  less  degree.  In  this  way  the  crystalline  marbles  are  formed, 
in  which  few  or  no  traces  of  organic  origin  remain.  The  compara- 
tively small  quantity  of  carbonate  of  lime,  which  is  found  separately 
and  distinctly  crystalline,  either  as  arragonite  or  calc  spar,  may  be 
traced  to  the  solvent  action  of  water  impregnated  with  carbonic  acid, 
filtering  through  strata  containing  shells,  and  then  gradually  depos- 
iting, in  favourable  situations,  the  matter  it  had  thus  taken  up,  in 
crystals,  the  form  of  which  depends  upon  the  temperature  at  which 
they  are  produced  (page  225).  The  other  native  carbonates,  ol 
which  the  quantity  is  very  small  in  comparison  with  that  of  the  car- 
bonate of  lime,  may  have  been  produced  by  double  decomposition. 
Thus  a  water,  holding  carbonate  of  lime  in  solution,  filtering  across 
a  stratum  containing  oxidized  iron  or  copper  pyrites,  would  give 
origin  on  the  spot  to  a  crystalline  deposite  of  sulphate  of  lime,  and, 
at  a  certain  distance,  carbonate  of  iron  or  of  copper  would  be  sep- 
arated. Those  instances  suffice  to  point  out  the  reasons  for  consid- 
ering carbon  as  truly  the  organic  element,  and  that  its  appearance 
in  a  mineralized  condition  arises  from  secondary  actions. 

Carbon  presents  itself  in  a  great  variety  of  forms.  Absolutely 
pure,  it  constitutes  the  diamond,  which,  from  its  exceeding  hardness, 
brilliancy,  and  rarity,  ranks  as  the  first  of  gems.  It  is  found  dis- 
seminated in  alluvial  strata  in  Golconda,  Brazil,  &;c.,  and  is  separa- 
ted from  the  sand  and  mud  by  processes  of  washing.  No  deposition 
of  diamond  in  rocks  has  ever  yet  been  found.  It  crystallizes  in 
forms  of  the  regular  system,  generally  having  a  great  number  of 
sides,  bounded  by  curved  edges,  in  virtue  of  which  it  splits  glass 
like  a  wedge,  in  place  of  scratching  it  as  a  file.  Its  crystals  are 
generally  hemihedral,  and  frequently  rough  and  discoloured  at  the 
surface.  These  crystals  all  cleave  parallel  to  the  faces  of  a  regular 
octohedron  (fig./,  p.  26),  but  the  properties  of  the  diamond  separate 
it  completely  from  the  proper  mineral  crystals  of  the  regular  system. 
Thus  it  possesses  double  refraction  in  some  cases  ,•  it  polarizes  light 
elliptically ;  its  structure  has  been  found  by  Brewster  to  consist  in 
layers,  sometimes  containing  cavities,  indicating  that  the  crystal  had 


478  ORIGIN     AND     NATURE    OP    PLUMBAGO. 

been  originally  soft,  and  only  concreted  by  degrees ;  and  in  the  re* 
cent  researches  of  Dumas  on  the  atomic  weight  of  carbon,  it  was 
found  that,  when  burned,  diamonds  generally  leave  behind  a  minute 
skeleton  of  inorganic  matter.  These  considerations  fulJy  show  that 
the  diamond  derives  its  origin  from  the  decomposition  of  organic 
matter.  The  diamond  is  the  hardest  body  known ;  it  cuts  every 
other,  and  can  be  ground  only  by  means  of  its  own  powder.  It  is 
usually  colourless,  but  sometimes  brown  or  rose-coloured ;  its  re- 
fractive power  is  very  great  (2*439),  whence  its  great  brilliancy. 
It  conducts  heat  and  electricity  very  badly  j  it  resists  most  chemi- 
cal agents,  but  burns  in  melted  nitre  brilliantly,  forming  carbonate 
of  potash ;  it  burns,  also,  when  heated  to  redness  in  oxygen  gas,  and 
evolves  sufficient  heat  to  maintain  the  continuance  of  the  combus- 
tion; its  specific  gravity  is  about  3*5. 

Another  very  remarkable  form  of  carbon  is  that  of  plumbago  or 
graphite.  This  is  found  in  many  localities,  but  sufficiently  pure  for 
the  purposes  of  the  arts  only  in  Borrodale,  in  Cumberland.  It  is 
perfectly  opaque,  crystallized  in  rhombohedrons,  or  six-sided  ta- 
bles ;  but  its  usual  appearance  is  in  brilliant  leaves  or  spangles ;  it 
is  soft  and  unctuous  to  the  touch,  and  gives,  on  paper,  a  continuous 
gray  streak,  whence  its  name  of  blacklead^  and  its  use  in  making  pen- 
cils. Its  formation  appears  to  be  connected  with  the  action  of  iron, 
and  with  a  high  temperature  :  it  is  found  only  in  igneous  rocks,  as 
granite  and  mica  slate,  and  contains  almost  always  a  large  quantity 
of  iron  intermixed  in  the  metallic  state,  so  that  it  was  once  sup- 
posed to  be  a  carburet  of  iron.  Graphite  may  be  formed  artificial- 
ly by  adding  charcoal  to  melted  cast  iron ;  the  charcoal  dissolves 
largely,  but  on  cooling  is  found  to  separate  in  brilliant  flexible 
plates,  more  or  less  regularly  six-sided.  Graphite  is  lighter  than 
diamond,  its  specific  gravity  being  2*5,  and  it  conducts  heat  and 
electricity  much  better.  It  is  very  hard  to  set  on  fire,  and  does  not 
continue  to  burn  unless  heat  be  applied  from  without. 

Carbon,  in  a  form  more  or  less  mixed  with  foreign  matters,  is 
obtained  by  the  application  of  a  very  high  temperature  to  animal 
or  vegetable  substances  in  close  vessels.  The  kinds  of  carbon  thus 
produced  still  difl^er  very  much.  Thus  coke  is  obtained  by  heating 
coal  in  iron  retorts  until  all  the  volatile  products  are  driven  off, 
and  the  excess  of  carbon  remains  mixed  with  the  earthy  matter 
which  all  coal  contains.  The  properties  of  coke  approximate  more 
or  less  to  those  of  graphite,  according  to  the  temperature  at  which 
it  has  been  produced.  By  the  proximity  of  igneous  rocks  to  coal 
under  the  earth,  a  similar  expulsion  of  its  volatile  matters  may  be 
effected,  and  a  form  of  carbon  nearly  pure,  anthracite^  results.  These 
fuels  are  difficult  to  light,  but,  when  once  ignited,  give  out  an  in- 
tense heat  by  their  combustion. 

If  an  organic  substance,  which  contains  hydrogen  and  carbon,  be 
set  on  fire,  and  there  be  a  copious  supply  of  air,  it  is  totally  con- 
verted into  water  and  carbonic  acid  ;  but  if  the  supply  of  air  be 
limited,  the  affinity  of  the  hydrogen  for  the  oxygen  preponderates, 
and  no  carbon  is  consumed  until  all  hydrogen  is  converted  into  wa- 
ter. By  this  method  of  imperfect  combustion,  several  forms  of  car- 
bon are  prepared,  such  as  wood-charcoal  and  lampblack.     If  we 


CHARCOAL  AND  LAMPBLACK.  479 

take  a  splinter  of  wood  and  set  it  on  fire,  we  observe  that  at  first 
only  the  volatile  products  of  the  wood  burn  with  flame,  and  that  n 
mass  of  charcoal  forms  inside,  and  remains  unaltered  as  long  as,  be- 
ing surrounded  by  flame,  it  is  protected  from  the  air ;  but  when  the 
end  projects  beyond  the  flame,  it  ignites  and  burns  away,  leaving 
only  a  trifling  ash.  If,  however,  a  tube  be  taken,  and,  as  in  the  fig- 
ure, as  the  combustion  advances  along  the  stick  b,  the  burn- 
ed portion  a  be  gradually  plunged  into  a  narrow  tube,  this  J 
becomes  filled  with  carbonic  acid,  which  does  not  support 
combustion,  and  the  cylinder  of  charcoal  formed  may  thus 
be  permanently  preserved  ;  on  this  principle  wood-charcoal  is 
prepared.  Billets  of  wood  are  heaped  together  regularly,  so 
as  to  form  a  hemispherical  mass  of  about  forty  feet  diameter  j 
in  the  centre  a  hole  reaches  from  the  top  to  the  bottom,  form- 
ing a  chimney.  The  outside  is  then  coated  with  sods,  so  as 
to  render  it  impervious  to  air  except  at  the  bottom,  where 
some  apertures  are  left.  Burning  charcoal  is  then  thrown  into  the 
chimney,  and  the  fire  communicating  to  the  billets,  these  burn  with 
a  supply  of  air  so  limited  that  the  charcoal  remains  unconsumed, 
the  combustion  commencing  at  the  top  and  proceeding  down.  The 
outside  of  the  heap  is  then  covered  with  denser  sods,  so  as  to  cut 
off'  the  supply  of  air  as  the  combustion  proceeds.  When  the  car- 
bonization has  been  completed,  the  whole  mass  is  covered  up  and 
allowed  to  cool  perfectly  before  being  opened.  In  this  country, 
most  of  the  charcoal  used  is  obtained  in  the  preparation  of  vinegar 
by  the  destructive  distillation  of  wood,  as  will  be  hereafter  noticed. 
The  quantity  of  charcoal  produced  from  wood  varies  very  much 
with  the  rapidity  of  the  process  ;  the  generality  of  fresh  woods 
yielding  but  thirteen  or  fourteen  per  cent,  by  a  rapid  decomposition, 
while,  when  slowly  charred,  they  may  yield  twenty-five  or  twenty- 
six.  The  mode  of  conducting  the  process,  therefore,  must  be  chan- 
ged according  as  the  residual  charcoal,  or  the  volatile  materials,  are 
the  most  valuable  products.  The  charcoal  preserves,  in  a  remark- 
able manner,  the  structure  of  the  wood  from  which  it  is  produced, 
so  that  by  the  microscope  some  of  the  most  delicate  forms  of  vege- 
table organization  may  be  traced  in  charcoal  that  has  been  slowly 
prepared. 

Lampblack  is  formed  by  a  still  more  direct  application  of  the  principle  of  imper- 
fect combustion.  In  the  apparatus  represented  in  the  figure,  a  is  a  pot  placed  in  a 
furnace  which  is  vaulted  over,  so  that  all  vapour  from  it 
may  pass  into  the  chamber  b,  c,  while  by  some  apertures 
a  small  quantity  of  air  is  allowed  to  sweep  over  its  sur- 
face ;  the  sides  of  the  round  chamber  are  lined  with  leath- 
er, and  above  is  a  conical  cover  of  coarse  linen,  d, 
through  which  the  draught  from  the  furnace  passes,  and 
which  may  be  lowered  or  raised  by  the  cord  and  pulley. 
A  quantity  of  pitch  or  tar  is  placed  in  the  pot  and  made 
t9  boil ;  it  takes  fire,  and,  as  the  quantity  of  air  which 
has  access  to  it  is  very  smaH,  the  hydrogen  alone  bums, 
and  the  carbon,  being  carried  up  by  the  current  in  a  very 
finely-divided  state,  is  deposited  on  the  sides  and  cover 
as  an  impalpable  powder, 

jJnimal  charcoal  is  produced  by  the  decom- 
position of  animal  mafters  in  close  vessels. 
From  its  properties,  which  I  shall  just  now  notice,  it  is  manufactured 


480 


PROPERTIES  OF'  ANIMAL  CHARCOAL. 


in  large  quantities  for  the  arts,  especially  from  bones,  and  is  hence 
called  Ivory-black  or  Bone-black.  The  bones  are  placed  in  iron  cyl- 
inders, which  are  arranged,  vertically  or  horizontally,  in  a  furnace, 
in  connexion  with  a  series  of  condensing  vessels  containing  water  ; 
the  volatile  constituents  of  the  animal  matter  being  expelled  prin- 
cipally as  carbonate  of  ammonia,  of  which  a  large  quantity  is  thus 
made,  the  excess  of  carbon  remains  in  a  state  of  very  minute  divis- 
ion, mixed  with  the  earth  of  bones  (phosphate  of  lime). 

Some  of  the  most  important  uses  of  carbon  are  founded  on  prop- 
erties which  the  various  forms  of  it  possess  in  different  degrees. 
Its  inflammability  varies  with  its  density  and  closeness  of  aggrega- 
tion ;  being  least  in  graphite,  and  becoming  so  great  when  wood 
charcoal,  prepared  at  a  low  temperature,  has  been  reduced  to  pow- 
der for  the  preparation  of  gunpowder,  as  to  inflame  sometimes  spon- 
taneously, and  give  rise  to  destructive  accidents.  Carbon  possesses 
a  remarkable  tendency  to  unite  with  colouring  and  odorous  substan- 
ces. This  property  is  specially  possessed  by  ivory-black,  in  conse- 
quence of  the  extreme  degree  of  division  of  its  particles.  When  a 
purely  organic  body  yields  carbon,  the  molecules  of  the  latter  ag- 
gregate themselves  to  a  degree  which  depends  on  the  temperature ; 
and  if,  as  in  wood,  there  be  a  fusible  ash  present,  this  acts  as  a  ce- 
ment, and  diminishes  the  porosity  very  much.  If  the  organic  sub- 
stance be  fusible,  as  starch  or  sugar,  the  closeness  of  texture  of  the 
charcoal  becomes  still  greater,  and  its  utility  less  ;  but  in  bones,  the 
molecules  of  organic  matter  are  separated  by  an  infusible  earthy 
salt,  and  when  carbonized,  the  charcoal  is  obtained  in  the  greatest 
po'ssible  state  of  comminution.  A  still  more  efficient  charcoal  is 
formed  by  calcining  dried  blood,  hoofs,  or  horns,  with  carbonate  of 
potash,  which  prevents  the  aggregation  of  the  particles  of  carbon, 
which,  the  alkaline  salt  being  washed  out  with  water,  is  left  in  the 
most  active  condition  possible.  In  the  arts,  this  property  is  applied 
to  the  purification  of  sugar  ;  to  clearing  solutions  of  many  organic 
substances  j  and  barrels  in  which  water  is  to  be  kept  are  charred  on 
the  insides,  in  order  to  remove  any  organic  matter  described  in  the 
water,  which  might  be  liable  to  putrefy. 

The  following  table  contains  some  numerical  results  of  the  rela- 
tive decolorizing  power  of  equal  quantities  of  carbon  in  various 
forms ;  the  first  column  containing  the  number  expressing  the  pow- 
er of  removing  the  colour  of  a  solution  of  indigo,  and  the  second 
column  that  of  a  solution  of  coarse  sugar.  The  power  of  ivory- 
black  is  taken  as  the  standard : 


Kind>  of  Charcoal. 

Common  ivory-black 

Well  ignited  lampblack 

Lampblack  ignited  with  pot  ashes 

Charcoal  from  the  decomposition  of  acetate  of  potash  . 

Starch  ignited  with  pot  ashes 

Blood  ignited  with  phosphate  of  lime 

Ivory-black  digested  in  muriatic  acid 

Ivory-black  digested  in  muriatic  acid,  and  afterward 

ignited  v^^ith  pot  ashes 

Blood  ignited  with  pot  ashes 


Sugar. 


1 

10 
44 
89 

10 
1-7 

20 
20 


ATOMIC     WEIGHT     OF     CARBON.  481 

The  decolorizing  power  is  thus  not  the  same  for  all  bodies.  If 
charcoal  that  had  once  been  used  be  again  ignited,  it  does  not  re- 
cover its  activity,  as  the  colouring  matter  fuses  before  charring,  and 
thereby  lessens  its  porosity.  Charcoal  possesses  also  a  remarkable 
power  of  absorbing  gases.  If  a  fragment  of  wood  charcoal,  which 
had  been  strongly  heated,  and  allowed  to  cool  without  access  of 
air,  be  introduced  into  a  tube  containing  ammoniacal  gas,  in  the 
mercurial  pneumatic  trough,  an  immediate  absorption  occurs,  to 
the  amount  of  ninety  times  the  volume  of  the  charcoal.  In  other 
cases  the  absorption  is  not  so  great ;  a  cubic  inch  of  boxwood  char 
coal,  which  is  the  most  active,  absorbing 


90  cubic  inches  of  ammonia. 
85    "  "  muriatic  acid. 

65     "  "  sulphurous  acid. 

55     "  "  sulphuretted  hydro- 

35     "  "  olefiant  gas.    [gen. 


40  cubic  inches  of  nitrous  oxide 
35    "  "  carbonic  acid. 

9-25  "  oxygen. 

75  "  nitrogen. 

175  "  hydrogen. 


These  gases  in  this  absorption  undergo  no  chemical  change,  but 
appear  to  be  retained  on  the  surface  of  the  pores  of  the  charcoal  by 
powerful  cohesion,  and  probably  in  the  liquid  form,  as  it  is  such 
gases  as  may  be  rendered  liquid  by  pressure  that  are  absorbed  in 
larger  quantity. 

The  number  expressing  the  atomic  weight  of  carbon  is  not  at 
present  exactly  known.  By  Drs.  Prout  and  Thompson  it  was  fixed 
at  seventy-five  upon  the  oxygen,  and  six  upon  the  hydrogen  scale  j 
but  the  investigations  of  Berzelius  and  Dulong  induced  the  majority 
of  chemists  to  adopt  a  higher  number,  76'4<  or  6-13.  The  latest 
experiments  of  Dumas  and  Stass  directed  to  the  determination  of 
this  point,  induce  those  eminent  chemists  to  recur  to  the  original 
number,  75  ;  while  Liebig  and  Redtenbachar  have  deduced  from 
their  researches  the  numbers  75-8.  Dr.  Clarke,  from  a  re-exami- 
nation of  Berzelius's  results,  finds  that  they  give,  when  corrected 
for  some  minute  sources  of  error,  75*6  ;  and,  until  opinion  becomes 
more  unanimous  upon  this  important  point,  I  shall  assume  as  the 
number  expressing  the  equivalent  of  carbon,  75'6  upon  the  oxygen, 
and  6-05  upon  the  hydrogen  scale. 

If  we  admitted  the  truth  of  Dulong  and  Petit's  law  (p.  66,  219), 
connecting  the  specific  heat  with  the  atomic  weights  of  bodies,  we 
should  consider  the  ei^uivalent  of  carbon  to  be  double  that  above 
given,  as  Regnault  has  found  the  specific  heat  to  be  0'241.  This 
idea  appears  favoured  by  the  fact,  that  it  is  doubtful  whether  there 
really  exists  a  combination  of  carbon  containing  an  odd  number  of 
equivalents,  taking  the  number  as  6-05.  But  the  force  of  this  result 
is  totally  obviated  by  the  fact  that  the  specific  heat  of  carbon  varies 
with  its  state  of  aggregation  so  much,  that  for  poplar  charcoal  it  is 
0-296,  and  for  diamond  but  0-147;  hence  we  cannot  connect  these 
numbers  with  the  chemical  equivalent  of  the  body. 

Notwithstanding  that  carbon  is  absolutely  infusible  and  fixed,  yet, 
from  the  variety  of  gaseous  and  volatile  compounds  into  which  it 
enters,  and  whose  constitution  is  remarkably  illustrated  by  the  ap- 
plication of  the  theory  of  volumes,  carbon  vapour  is  frequently  spo- 
ken of  by  chemists,  although  its  existence  is  purely  hypothetical. 
I  have  mentioned  (p.  215)  the  difference  of  opinion  as  to  its  specific 

Ppp 


482  ANALYSIS    OF     ORGANIC     BODIES, 

gravity,  which  I  assume  at  843.  The  new  results  would  appear  to 
show  that  it  is  really  but  836*8  upon  the  one,  or  4184  upon  the 
other  view. 

General  Principles  of  Organic  Analysis. 

Substances  which  contain  much  carbon  are,  in  general,  easily  recognised,  by  their 
being  more  or  less  combustible,  and  forming  carbonic  acid  when  burned,  besides 
often  leaving  a  carbonaceous  residue.  Even  where  the  bodies  are  not  inflammable 
simply,  they  deflagrate  more  or  less  violently  when  heated  with  nitre,  and  form  car- 
bonate of  potash. 

Altliough  it  is  not  within  the  scope  of  the  present  work  to  embrace  the  details  ol 
chemical  analysis,  it  would  yet  be  improper  to  omit  a  general  description  of  the 
methods  adopted  for  the  determination  of  the  quantities  of  carbon,  hydrogen,  and  ni- 
trogen, which  enter  into  the  constitution  of  organic  bodies.  The  general  principle 
npon  which  this  process  is  carried  out,  consists  in  supplying  oxygen  so  abundantly 
to  the  organic  substance,  as  that  all  its  carbon  shall  be  converted  into  carbonic  acid, 
and  all  its  hydrogen  into  water,  and  yet  the  supply  of  oxygen  shall  be  so  graduated, 
and  the  decomposition  so  regularly  progressive,  as  to  admit  of  the  products  being 
collected  with  accuracy.  The  nitrogen  is  always  determined  by  an  independent 
operation,  in  w^hich  the  other  elements  are  neglected ;  and,  although  processes  have 
been  proposed  which  provided  for  a  direct  valuation  of  the  oxygen,  it  is  found  in 
practice  better  to  obtain  its  value  by  subtracting  the  weight  of  all  the  other  constit- 
uents from  that  of  the  substance  employed.  For  the  analysis  of  an  organic  sub- 
stance, there  are,  therefore,  two  processes ;  the  first,  to  determine  the  carbon  and  hy- 
drogen, and  the  second  to  determine  the  amount  of  nitrogen. 

The  substance  generally  used  to  supply  oxygen  is  the  black  oxide  of  copper,  pre- 
pared by  gently  igniting  the  nitrate.  Sometimes  chromate  of  lead  is  employed,  par- 
ticularly for  bodies  rich  in  chlorine.  Where  the  substance  to  be  analyzed  bums 
with  difficulty,  it  is  often  necessary,  in  order  to  be  certain  of  the  complete  combus- 
tion of  the  carbon,  to  pass  a  stream  of  oxygen  gas  over  it  at  the  termination  of  the 
process. 
A  straight  tube  of  hard  Bohemian  glass,  of  about  sixteen  inches  long,  and  from 

one  third  to  half  an  inch 

I  I  ''  yj    ^  diameter,  is  to  be  drawn 

I  i  I  y^    out  at  one  end  to  a  point, 

{^^^^y|j]|]jnpj|[[|jCT  which  is  to  be  sealed  and 

.  turned  up,  as  in  the  fig- 

ure. Some  oxide  of  copper  (or  chromate  of  lead,  as  the  case  may  be)  is  to  be  then 
poured  in  so  as  to  occupy  about  two  inches  of  the  tube  next  the  bottom.  As  much 
Dxide  of  copper  as  will  occupy  about  six  inches  of  the  tube  is  to  be  then  intimately 
mixed  with  the  substance  to  be  analyzed,  if  it  be  solid,  by  rubbing  in  a  mortar,  and 
this  mixture  then  introduced.  The  mortar  is  next  to  be  rinsed  out  with  as  much  ox- 
ide of  copper  as  will  fill  two  or  three  inches;  and,  finally,  pure  oxide  of  copper  is  to 
be  placed  for  about  three  inches  in  front  of  all.  The  whole  materials  thus  intro- 
duced will  occupy  about  fourteen  inches  of  the  tube,  when  it  is  shaken  down  by  tap- 
ping it,  nearly  horizontally  on  the  edge  of  a  table,  so  as  to  leave,  as  in  the  figure, 
where  the  dotted  lines  mark  the  spaces  of  the  several  portions,  a  free  passage  above 
the  materials  from  end  to  end  of  the  tube.  In .  these  operations  the  greatest  care 
must  be  taken  to  avoid  all  access  of  moisture;  the  tube,  the  mortar,  and  the  sub- 
stance must  be  made  absolutely  dry,  and  the  oxide  of  copper,  being  powerfully  hy- 
groscopic, should  be  ignited  before  each  operation,  and  allowed  to  cool  under  a  bell 
glass  with  a  capsule  of  oil  of  vitriol,  or  by  being  placed  while  very  hoi  in  a  long  dry 
tube,  which  is  then  to  be  corked  completely  tight.  After  the  substance  and  oxide  of 
copper  have  been  placed  in  the  tube,  it  is  generally  necessary  to  remove  even  the  tra- 
ces of  damp  which  might  have  been  absorbed  by  exposure  to  the  air  during  the  mix- 
ing in  the  mortar.  This  is  done  by  means  of  a  small  exhausting  syringe,  which  is 
attached  to  the  combustion  tube  by  a  cork,  a  tube  containing  fused  "chloride  of  cal- 
cium being  interposed.  The  combustion  tube  is  bedded  in  warm  sand,  and  by 
means  of  the  syringe,  the  damp  air  it  contains  is  withdra\^m,  and  replaced  by  air, 
which,  passing'over  the  chloride  of  calcium,  becomes  completely  dry.  After  a  lew 
repetitions  of  this  process,  all  moisture  is  removed,  and  the  combustion  tube  is 
ready  to  be  attached  to  the  other  parts  of  the  apparatus. 

a  6  ton  wool  is  dropped  at  «,  and  it  is  then  filled 


ANALYSIS     OP     ORGANIC     BODIES.  483 

with  recently-fused  chloride  of  calcium  in  fragments  of  the  size  of  a  split  pea.  At  *  a 
little  cotton  wool  is  also  placed,  and  a  small  lube  is  connected  with  it  by  a  cork. 
To  its  smallei  end  a  cork  is  adapted,  which  accurately  fits  the  end  of  the  combus- 
tion tube,  and  which  has  been  carefully  dried.  This  apparatus  (but  without  the  last 
cork)  is  carefully  weighed  before  the  operation. 

The  second  apparatus  is  ihe  potash  bulb4ube,  the  invention  of  which  by  Liebigwas 
the  great  cause  of  the  rapid  progress  of  organic  chemistry  within  the 
last  few  years,  as  it  facilitated  the  analysis  of  organic  bodies  in  a  re- 
markable degree.  It  consists  of  a  tube  on  which  are  blown  five 
bulbs;  the  three  interior  communicating  by  pretty  wide  openings, 
but  each  outer  bulb  separated  from  the  others  by  a  couple  of  inches 
of  tube.  The  proportions  of  the  respective  bulbs  may  be  collected 
from  the  figure,  which  represents  also  the  form  into  which  the  tube 
is  bent.  The  three  central  bulbs  are  to  be  nearly  filled  with  a  strong 
solution  of  caustic  potash  (sp.  gr.  1-25),  and  the  apparatus  attached  to  the  small 
tube,  b,  of  the  v^ater  tiibe  by  a  caoutchouc  connector  tied  very  carefully  on.  It  is  to 
be  allowed  to  incline,  at  the  angle  represented  in  the  next  figure,  so  that  the  carbonic 
acid  gas,  when  passing  through  it,  shall  bubble  from  bulb  to  bulb,  without  any  dan- 
ger of  expelling  any  portion  of  the  liquor. 

The  combustion  tube  is  to  be  placed  in  a  sheet  iron  furnace,  the  form  and  size  of 
which  may  be  collected  from  the  figure,  its  open  end  so  far  projecting  Q.\  inches)  a*! 


that  the  cork  by  which  the  water  tube  is  attached  shall  not  be  in  any  danger  of  be- 
ing charred,  but  yet  shall  be  so  hot  that  no  water  can  condense  upon  it.  The  joint- 
ings being  found  to  be  completely  tight,  and  the  water  tube  and  potash  bulbs  being 
attached,  and  arranged  as  in  the  figure,  the  analysis  may  be  proceeded  with.  Some 
ignited  charcoal  is  to  be  placed  round  the  first  three  inches  of  the  tube,  and 
when  the  pure  oxide  of  copper  is  completely  red-hot,  the  next  portion,  which,  having 
rinsed  out  the  mortar,  contains  some  traces"  of  the  organic  substance,  is  to  be  simi- 
larly ignited.  The  hydrogen  of  the  substance  reduces  the  oxide  of  copper,  and  forms 
water,  which  is  collected  by  the  chloride  of  calcium  in  the  water  tube,  and  the  car- 
bon, also  reducing  the  oxide  of  copper,  is  converted  into  carbonic  acid,  which,  being 
dried  in  passing  over  the  chloride  of  calcium,  is  totally  absorbed  by  the  potash  in  the 
bulbs.  By  the  addition  of  burning  charcoal,  the  combustion  of  the  organic  matter 
is  made  to  progress  down  the  tube,  the  operator  being  directed  in  his  proceedings  by 
the  rate  at  which  the  evolution  of  carbonic  acid  and  its  absorption  proceed,  until  he 
arrives  within  two  inches  of  the  end  of  the  tube.  He  then  stops  until  he  has  made 
the  point  and  the  pure  oxide  of  copper  near  it  red-hot,  and  then  closes  in  the  char- 
coal on  the  remaining  space. 

The  combustion  being  thus  completed,  the  tube  remains,  ho\^ever,  occupied  by  a 
mixture  of  watery  vapour  and  carbonic  acid,  which  must  not  be  lost;  for  this  the 
point  of  the  tube  serves.  It  is  broken  with  a  nippers,  and  then  a  current  of  air  is 
gently  sucked,  by  means  of  a  tube  fitted  to  the  potash  bulb-tube,  through  the  whole 
apparatus;  this  carries  the  v/ater  vapour  to  the  water  tube,  and  the  carbonic  acid  to 
the  potash,  so  that  all  the  products  of  the  combustion  are  obtained.  The  apparatus 
is  then  taken  asunder,  and  the  potash  tube  and  water  tube  weighed ;  the  increase  of 
weight  gives,  of  course,  the  quantities  of  carbonic  acid  and  of  water  collected,  and 
hence,  by  simple  calculation,  the  proportions  of  carbon  and  hydrogen  contained  in 
the  quantity  of  substance  that  had  been  operated  on. 

If  the  substance  had  been  one  very  difficult  to  burn,  and  hence  requiring  oxygen 
to  finish  its  combustion,  the  tube  is  not  drawn  out  at  the  end,  but  widened  a  little,  so 
as  to  form  a  small  bulb,  in  which  some  chlorate  of  potash  is  placed.  At  the  end  of 
the  process,  this  being  heated  evolves  oxygen,  which  not  only  burns  any  traces  of  car- 
bon that  might  remain,  but  serves  also  "to  carry  the  carbonic  acid  and  vapour  fully 
into  the  water  tube  and  bulbs. 

There  are  a  variety  of  circumstances  to  be  attended  to  in  this  operation,  in  order  to 
obtain  the  high  degi'ee  of  accuracy  which  alone  confers  value  on  numerical  results. 
These  can  be  learned  omy  in  the  laboratory,  and  not  even  from  the  most  detailed  <Ip- 


484 


DETERMINATION     OF     NITROGEN. 


O 


scription.    My  object  is  merely  to  afford  an  idea  of  the  general  principles  of  the 
method. 

If  the  substance  to  be  analyzed  be  liquid  and  vol- 
atile,  it  is  introduced  into  small  bulbs  of  the  size  of 
the  figure,  by  the  method  given  in  page  11.    There 
are  generally  two  of  these  bulbs,  one  placed  about 
two  and  the  other  about  six  inches  from  the  sealed  end  of  the  tube,  as  shown  in  the 

,    figure ;  the  little  stem  is  broken 

Jj    across  in  the  act  of  introducing 

•H,  mmsms\'^^(  ^  >^«kmm%%%w^^\#.a^  them,  so  that  the  liquid  may 

f  <  easily  flow  out,  when,  by  the 

approach  of  a  piece  of  red-hot  charcoal,  it  is  gently  heated,  so  as  to  form  a  vapour. 
The  peculiar  precautions  necessary  in  the  management  of  the  analysis  of  such  bod- 
ies, and  the  methods  adopted  for  non-volaiile  liquids  and  other  bodies  of  peculiar 
Sroperties,  can  only  be  learned  by  experience,  and  do  not  fall  within  my  purpose  to 
escribe. 

To  determine  the  nitrogen  of  an  organic  substance,  a  long  combustion  tube  is 
taken  (2  or  25  feet),  sealed  at  one  end,  but  not  drawn  out,  as  in  the  figure.    Next 


tne  sealed  end  is  placed  carbonate  of  copper  for  a  space  of  six  or  eight  inches,  and 
then  the  pure  oxide  of  copper,  the  mixture,  the  rinsing  of  the  mortar,  and  again 
pure  oxide,  occupying  fourteen  or  fifteen  inches,  exactly  as  in  the  former  case ;  in 
front  of  all,  five  or  six  inches  are  occupied  by  clean  metallic  copper  in  a  finely-di- 
vided state,  either  as  reduced  by  hydrogen  from  the  oxide,  or  as  very  thin  turnings. 
These  divisions  and  the  general  form  of  the  tube  are  given  by  the  figure.  To  the 
combustion  tube  there  is  fitted  by  a  tight  cork  a  quill  tube,  which  is  in  connexion 
on  the  one  hand  with  an  exhausting  syringe,  and  then,  by  a  vertical  tube  more  than 
thirty  inches  long,  passes  to  the  mercurial  pneumatic  trough.  All  the  joinings  being 
found  tight,  and  the  combustion  tube  arranged  in  the  furnace,  red-hot  charcoal  is  ap- 
plied to  the  closed  end  of  the  tube,  where  it  disengages  carbonic  acid  from  the  carbon- 
ate of  copper,  which,  sweeping  through  the  apparatus,  expels  the  atmospheric  air. 
To  render  this  the  more  effectual,  the  whole  apparatus  is  exhausted  by  the  syringe, 
and  again  filled  Math  carbonic  acid,  and  this  is  continued  until  the  bubbles  of  gas 
which  come  over  are  perfectly  absorbed  by  solution  of  potash.  In  this  expulsion  of 
the  air  of  the  apparatus,  not  more  than  one  half  of  the  carbonate  of  copper  should 
have  been  used. 

The  fire  is  now  to  be  withdrawn  from  the  closed  end  of  the  tube,  and  applied  to 
the  part  occupied  by  the  metallic  copper.  When  this  is  red  hot,  the  combustion  is 
carried  backward,  just  as  in  the  former  example ;  and  when  all  the  substance  has 
been  burned,  the  coals  are  applied  to  the  remaining  carbonate  of  copper,  which, 
evolving  carbonic  acid,  clears  out  all  the  nitrogen  of  the  apparatus,  just  as  it  had  in 
the  commencement  cleared  out  all  the  atmospheric  air.  The  mixed  gases  that  are 
produced  in  this  operation  are  received  in  a  bell-glass  which  contains  some  strong 
solution  of  potash,  by  which  the  carbonic  acid  is  absorbed,  and  the  nitrogen  remain- 
ing may  then  be  measured.  The  volume  of  gas  is  next  to  be  corrected  for  temper- 
ature and  pressure,  as  directed  in  p.  57  and  20,  and  its  weight  then  calculated. 

The  use  of  the  metallic  copper  in  the  front  of  the  mixture  requires  notice;  when 
nitrogen  passes  over  red-hot  oxide  of  copper,  there  is  always  some  nitric  oxide  form- 
ed, which  would  falsify  the  result,  as  its  volume  is  double  that  of  the  nitrogen  it  con- 
tains ;  but  nitric  oxide  is  completely  decomposed  by  red-hot  metallic  copper,  pure 
nitrogen  being  evolved,  and  hence  the  purity  of  the  resulting  gas  is  secured  by  this 
arrangement.  Indeed,  in  all  combustions  of  an  azotized  body,  the  mixture  should 
have  some  bright  metallic  copper  in  front  of  it. 

The  direct  valuation  of  nitrogen  is  thus  a  very  delicate  operation,  and  occupies 
several  hours.  If  the  substance  contain  a  large  quantity  of  nitrogen,  its  amount 
may  be  indirectly  ascsrtained  in  a  much  simpler  way.  The  quantity  of  carbon  in 
the  substance  is  first  learned  by  an  ordinary  analysis,  then  another  combustion  tube 
is  arranged  with  very  clean  copper  in  front ;  but,  in  place  of  adapting  the  water  tube 
and  bulbs,  the  water  is  taken  no  count  of,  and  the  gases  evolved  are  collected  in 
narrow  graduated  tubes,  over  mercury.  In  order  to  clear  out  the  air  from  the  tube, 
"ome  of  the  mixture  next  the  sealed  end  is  first  ignited,  and  the  gas  allowed  to  es- 
cape, the  tubes  being  filled  from  the  products  of  the  subsequent  periods  of  combus- 
tion. In  this  case  no  weights  need  be  attended  to,  as  it  is  only  the  analysis  of  the 
gas  in  the  ti>bes  that  is  required  for  the  result.    The  volume  of  gas  in  a  tube  being 


CARBONIC     ACID,     ITS     PREPARATION,     ETC.    485 

marked,  some  solution  of  potash  is  introduced  and  agitated  in  it.  The  carbonic 
acid  is  absorbed,  and  the  nitrogen  remains,  the  volume  of  which  is  read  off,  taking 
care  that  the  level  of  the  mercury  is  the  same  inside  as  outside  the  tube.  The 
relative  volumes  of  the  carbonic  acid  and  nitrogen  gases  are  thus  found ;  and  as  cin 
equal  volume  represents  an  atom  for  each,  the  relative  number  of  atoms  of  carbon 
and  nitrogen  is  thus  determined ;  and  as  the  total  quantity  of  carbon  is  known  by  a 
previous  experiment,  the  total  quantity  of  nitrogen  may  be  calculated.  When  the 
relation  of  the  number  of  atoms  of  carbon  to  those  of  nitrogen  is  simple,  as  occurs 
in  cyanogen  and  oxamide,  C2N.,  mellon,  C3N2,  caffeine  and  taurine,  C4N.,  this  method 
gives  very  accurate  results. 

Where  the  organic  substance  contains  chlorine,  sulphur,  arsenic,  &c.,  it  is  to  be 
destroyed  by  nitric  acid,  or  by  ignition  with  potash  or  lime,  and  the  inorganic  con- 
stituents "then  determined  in  the  ordinary  way.  In  organic  salts  the  metallic  basis 
is  determined  by  igniting  the  substance,  burning  away  the  organic  element,  and  de- 
termining the  quantity  of  inorganic  base  by  whatever  method  is  best  suited  to  its 
individual  nature. 

Carbon  combines  with  oxygen  in  several  proportions,  of  which 
three,  those  in  which  it  forms  the  carbonic  oxide,  and  the  carbonic 
and  oxalic  acids,  are  the  most  important,  and  deserve  the  most  de- 
tailed description. 

Of  Carbonic  Acid.    Eq.  275-6  or  22-05. 

Carbonic  acid  exists  in  the  atmosphere  as  a  product  of  combus- 
tion and  of  the  respiration  of  animals.  Combined  with  metallic 
oxides,  it  forms  the  numerous  class  of  native  earthy  and  metallic 
carbonates,  of  which  the  carbonate  of  lime  is  much  the  most  impor- 
tant. It  is  a  result,  also,  of  the  slow  decomposition  of  most  vege- 
table substances,  and  is  evolved  in  great  quantity  from  the  ground 
in  volcanic  countries.  In  the  fermentation  of  sugar  it  is  produced 
in  abundance  along  with  alcohol.  For  the  purposes  of  the  chemist, 
it  is  generally  prepared  by  decomposing  marble  or  calc  spar  by 
means  of  any  stronger  acid  \  from  its  cheapness,  and  the  solubility 
of  the  residual  salt,  muriatic  is  generally  employed.  Some  frag- 
ments of  white  marble  being  placed  in  a  wide-necked  bottle,  the 
acid,  diluted  with  its  own  volume  of  water,  is  poured  in  by  a  funnel 
tube,  as  in  the  figure,  p.  247,  and  the  gas  which  is  evolved  is  con- 
ducted by  the  bent  tube,  to  be  made  use  of  as  required.  The  re- 
action consists  in  H.Cl.  and  Ca.O.  .  C.O2  producing  H.O.  and  Ca.Cl., 
which  remains  in  the  bottle,  while  C.O2  is  driven  off.  Carbonic  acid 
being  dissolved  by  water,  and  it  being  generally  required  in  larger 
quantity  than  it  is  convenient  to  collect  over  mercury,  we  take  ad- 
vantage of  the  density  of  the  gas  to  collect  it  in  dry  jars,  as  de- 
scribed and  figured  for  chlorine  in  p.  301.  The  jar  is  known  to  be 
full  when  a  lighted  taper,  applied  near  the  mouth,  is  instantly  ex- 
tinguished. 

The  properties  of  carbonic  acid  are  very  remarkable  ;  it  is  per- 
fectly colourless  and  invisible  ;  it  is  irrespirable,  producing,  when 
an  attempt  is  made  to  breathe  it,  violent  spasms  of  the  glottis.  If 
it  be  inspired,  mixed  with  air,  even  in  the  proportion  of  1  to  10,  it 
gradually  produces  stupor  and  death,  acting  as  a  narcotic  poison. 
Its  specific  gravity  is  1-521.  It  hence,  when  disengaged  in  large 
quantities,  whether  by  natural  operations  or  in  processes  of  manu- 
facture, accumulates  in  all  cavities  within  its  reach,  and  may  cause 
fatal  accidents  to  animals  who  enter  unadvisedly.     Thus  workmen 


486  LIQUID     AND     SOLID     CARBONIC     ACID. 

engaged  in  cleaning  out  dry  wells  or  vaults,  or  the  large  vats  from 
which  fermenting  liquors  have  been  run  off,  should  carefully  ob- 
serve whether  a  candle  can  remain  for  some  time  burning  brightly 
at  the  bottom.  In  volcanic  countries,  caverns  are  frequently  occu- 
pied to  the  level  of  their  surface  by  this  gas,  exhaled  from  the 
ground  ;  and  an  experiment  often  tried,  to  amuse  the  traveller,  con- 
sists in  walking  into  such  a  cavern  with  a  dog,  which,  holding  the 
head  near  the  floor,  is  almost  instantly  asphixiated  by  the  layer  of 
carbonic  acid,  while  the  men,  whose  heads  are  above  its  level, 
breathe  pure  air ;  the  dog,  on  being  thrown  immediately  into  a 
neighbouring  pond,  recovers  from  his  stupor.  Carbonic  acid  does 
not  support  combustion.  A  taper  plunged  into  a  jar  full  of  the  gas 
is  instantly  extinguished,  and  the  high  specific  gravity  of  the  gas 
may  be  well  shown  by  placing  a  lighted  taper  at  the  bottom  of  a  jar 
containing  air,  and  taking  in  the  hand  another  jar  containing  car- 
bonic acid  ;  on  inclining  this  jar,  the  heavy  gas  pours  over  the  edge, 
nearly  as  water  would  do,  into  that  in  which  the  taper  is  placed, 
and,  falling  to  the  bottom,  extinguishes  it. 

Water  dissolves  its  own  volume  of  carbonic  acid  gas,  forming  a 
solution  of  an  agreeably  acidulous  taste,  which  sparkles  when  agi- 
tated J  it  colours  blue  litmus  paper  of  a  wine-red,  which  disappears 
on  exposure  to  the  air  or  by  heat.  By  means  of  pressure,  water 
can  be  made  to  absorb  a  large  quantity  of  carbonic  acid,  which  es- 
capes with  effervescence  when  the  pressure  is  removed,  and  is  thus 
the  basis  of  a  variety  of  agreeable  effervescing  beverages.  Solution 
of  carbonic  acid  in  water  precipitates  solutions  of  lime  and  barytes 
white,  forming  carbonates,  which  redissolve  in  an  excess  of  the  car- 
bonic acid. 

Under  a  pressure  of  thirty-six  atmospheres,  carbonic  acid  may 
be  liquefied.  It  then  forms  a  colourless,  exceedingly  mobile  liquid, 
of  specific  gravity  0'83  at  32^,  which  is  remarkable  for  its  exces- 
sive expansibility  by  heat,  it  having  four  times  that  of  air,  or  nearly 
one  per  cent,  for  each  degree  of  Fahrenheit.  When  the  pressure 
is  suddenly  removed  from  this  liquid  acid,  it  gasefies  with  such  ra- 
pidity that,  one  portion  absorbing  heat  from  the  other,  this  latter  is 
rendered  solid  (see  page  86).  Solid  carbonic  acid  can  thus  be  ob- 
tained in  large  quantity  by  the  apparatus  contrived  by  Thilorier. 
It  is  a  white  body,  in  filamentous  masses,  like  asbestus  ;  it  evaporates 
but  slowly  ;  it  is  very  soluble  in  alcohol  and  ether  ;  the  ethereal  so- 
lution produces  by  its  evaporation  the  most  intense  cold  known,  es- 
timated at  — 180  degrees  of  Fahrenheit. 

The  composition  of  carbonic  acid  may  be  determined 
by  very  simple  experiments.  If  into  a  bottle  of  pure  ox- 
ygen gas  we  insert  a  little  bit  of  charcoal,  ignited  at  one 
point,  at  the  end  of  the  wire  a,  as  in  the  figure,  it  burns 
with  vivid  scintillations,  and  the  oxygen  is  all  converted 
into  carbonic  acid.  The  stopper  of  the  bottle,  through 
which  the  wire  passes,  being  perfectly  tight,  it  will  be 
found  that  the  volume  of  the  gas,  when  cold,  has  not 
sensibly  altered,  and  thus  that  carbonic  acid  contains  its 
own  volume  of  oxygen.     It  co'nsists,  therefore,  of 


MANUFACTURE     OF     POTASHES. 


487 


Two  volumes  of  oxygen     .     1102-6x2=2205  2 

One  volume  of  carbon  vapour    ....     8430 

Forming  two  volumes  of  carbonic  acid    2-^-3048-2 

Of  which  one  volume  weighs,  therefore,    =1524- 1 

The  corrected  specific  gravity  of  carbonic  acid,  1*521,  indicates 
that  the  theoretical  density  of  carbon  vapour  should  rather  be  taken 
as  83G  than  843. 

To  demonstrate  the  existence  of  carbon  in  carbonic  acid  gas,  it 
is  sufficient  to  heat  to  dull  redness,  in  a  current  of  the  gas,  a  small 
globule  of  potassium.  The  metal  takes  fire,  burning  with  a  brilliant 
violet  flame,  and  forms  potash,  while  carbon  is  abundantly  deposit- 
ed as  a  brilliant  jet-black  film  on  the  interior  of  the  tube. 

Carbonic  acid  combines  with  the  bases,  forming  a  very  important 
class  of  salts,  the  carbonates.  It  forms  neutral,  basic,  and  acid  salts, 
which  last  are  really  double  salts,  containing  carbonate  of  water, 
which,  however,  exists  only  in  combination,  as  the  carbonic  acid 
does  not  combine  with  water  directly  in  definite  proportions.  All 
salts  of  carbonic  acid  are  known,  by  yielding,  when  acted  on  by 
muriatic  acid  in  the  cold,  the  gas  possessing  the  properties  now 
described. 

Carbonate  of  Potash.— K.O. .  CO,.  Eq.  866-3  or  694.  This  salt, 
which  is  the  great  source  of  all  other  combinations  of  this  alkali,  is 
obtained  for  the  purposes  of  commerce  from  the  ashes  of  plants 
growing  at  a  distance  from  the  sea.  The  vegetable  juices  contain 
potash,  combined  with  various  acids,  as  the  nitric,  oxalic,  acetic, 
malic,  &c.,  which,  by  the  burning  of  the  wood,  are  converted  into 
carbonates.  The  produce  differs  according  to  the  kind  of  wood, 
and  with  the  season.  The  softer  and  more  juicy  the  plants  are,  the 
more  potash  they  yield.  Plants  of  the  natural  families  compositas 
and  crucifera3  are  the  richest ;  the  grasses  rank  next ;  and  among 
the  woods,  the  leaves  yield  more  than  the  small  branches,  and  these, 
again,  more  than  the  stems.  In  countries  where  there  are  large 
forests,  as  America  and  Russia,  the  small  wood  is  burned,  and  the 
ashes  collected  ;  these  are  boiled  with  water  in  large  iron  pans  or 
pots,  from  whence  the  name  potash  is  derived.  By  this  means,  a 
large  quantity  of  insoluble  salts  is  separated,  and  the  carbonate  of 
potash,  which  dissolves,  is  obtained  in  a  purer  form  by  evaporation 
to  dryness.  It  then  constitutes  the  pearlashes,  or  refined  potashes 
of  commerce.  Even  these  still  retain  much  silica,  sulphate  of  potash, 
and  chloride  of  potassium,  so  that  the  best  American  pearlashes  sel- 
dom contain  more  than  eighty-five  per  cent.,  and  Russian  potash 
often  not  sixty  per  cent,  of  true  carbonate  of  potash. 

The  purification  of  pearlashes  being  difficult,  carbon- 
ate of  potash  is  best  prepared  for  chemical  purposes  by 
calcining  cream  of  tartar  ;  the  tartaric  acid  which  it  con- 
tains is  decomposed,  and  carbonic  acid  formed,  which 
combines  with  the  potash ;  the  mass  is  digested  with 
water,  filtered  to  separate  the  excess  of  charcoal,  and 
evaporated  to  dryness  in  a  clean  iron  vessel.  A  white 
granular  mass  is  obtained,  the  salt  of  tartar  of  the  older 
pharmacopoeias.  It  is  very  deliquescent,  soluble  in  half 
its  weight  of  water,  and  crystallizes  with  two  atoms  of  water  in 


488 


CARBONATE      OF      SODA. 


N 

1 

! 

I 
1 

i 

1 

oblique  rhombic  octohedrons,  a,  a\  a",  a"\  as  in  the  figure  (K.O. 
C.O2+2  Aq.).     It  reacts  strongly  alkaline.     It  is  almost  insoluble  in 
alcohol,  and  when  added  to  weak  spirit,  combines  with  the  excess 
of  water,  forming  a  heavy  fluid,  which  remains  separated  from  the 
lighter  and  stronger  alcohol  above. 

As  it  is  only  the  carbonate  of  potash  that  constitutes  the  value  of 
pearlashes  in  the  manufactures  to  which  it  is  applied,  it  is  important 
to  be  able  to  determine,  by  a  single  and  simple  operation,  the  relative 
worth  of  commercial  samples.  This  process  is  termed  alkalimetry. 
The  best  method  of  performing  it  will  be  described  under  the  head 
of  "Carbonate  of  Soda." 

Bicarbonate  of  Potash,  K.O. .  C.O2  +  H.0. .  C.O2,  is  formed  by  passing 

a  current  of  carbonic  acid  gas  through  a  saturated 

solution  of  the  neutral  carbonate,  the  temperature 

of  which  should  not  be  above  100\     On  cooling, 

it  crystallizes  in  right  rhombic   prisms   of  eight 

sides,  as  in  the  figure.     It  dissolves  in  four  parts 

of  cold  water,  and  in  much  less  when  hot.     If  its 

solution  be  boiled,  it  abandons  its  second  atom  of 

carbonic  acid,  and  becomes  neutral  carbonate.     Its 

reaction  on  vegetable  colours  is  feebly  alkaline. 

Carbonate    of  Soda—lSi^.O.  .  C.O^+IO  Aq.  5  Eq.  667-3  +  1125  or 

53*4i7-f-90  — is  manufactured  upon  a  very  large  scale,  for  the  purposes 

of  commerce,  from  common  salt,  which  must  first  be  converted  into 

sulphate  of  soda  in  the  manner  described  in  page  427. 

The  dry  sulphate  of  soda  is  to  be  mixed  with  its  own  weight  of 
limestone  or  chalk,  and  half  its  weight  of  small  coal,  and  the  mix- 
ture being  reduced  to  fine  powder,  is  introduced  into  a  reverbera- 
tory  furnace,  such  as  is  figured  in  page  333,  in  charges  of  about  2  cwt. 
each.  After  being  exposed  to  a  full  red  heat  for  about  an  hour,  on 
the  floor  of  the  furnace,  the  mass  fuses,  and  being  well  stirred  for  a 
few  minutes,  is  raked  off'  through  the  opening  in  the  side,  and  re 
ceived  in  metal  boxes.  It  forms  a  black  mass,  which  is  known  iv 
commerce  as  black-ash,  or  British  barilla.  The  theory  of  this  process 
is  very  remarkable  ;  the  sulphate  of  soda  being  melted  in  contact 
with  the  coally  matter,  is  deoxidized,  its  oxygen  being  carried  off  by 
the  carbon,  and  sulphuret  of  sodium  remaining.  This  is  immediately 
decomposed  by  the  carbonate  of  lime,  sulphuret  of  calcium  and 
carbonate  of  soda  being  produced.  S.O3  .  Na.O.  and  2C.  form 
aCO^and  Na.S.,  which,  vvith  Ca.O. .  C.O^,  gives  Ca.S.  and  Na.O. .  C. 
Og.  As,  however,  much  of  the  carbonic  acid  of  the  chalk  is  expelled 
by  the  heat,  a  certain  quantity  of  the  soda  remains  caustic  in  the 
produce,  and  also  some  sulphuret  of  sodium  undecomposed.  This 
black-ash  generally  contains  about  22  per  cent,  of  real  alkali.  To 
obtain  the  soda  under  a  purer  form,  the  masses  of  black-ash  are 
broken  up,  and  digested  in  warm  water  until  all  soluble  matter  is 
extracted.  The  residue  consists  of  sulphuret  of  calcium  and  the 
excess  of  coally  matter.  The  liquor  is  then  evaporated  to  dryness, 
and  the  saline  mass  obtained  is  calcined  in  a  reverberatory  furnace 
with  one  fourth  of  its  weight  of  sawdust,  in  order  to  convert  all  of 
the  alkali  into  carbonate,  and  to  burn  out  some  traces  of  sulphur 
which  still  remain  j  on  being  then  redissolved  in  water,  and  the  clear 


METHOD     OF     ALKALIMETRY.  489 

solution  dried  down,  it  constitutes  white-ash^  or  soda-ash  of  the  best 
quality,  containing  from  45  to  50  per  cent,  of  real  alkali. 

For  the  preparation  of  the  crystallized  carbonate,  the  soda-ash  is 
dissolved  in  boiling  water,  and  the  solution  being  evaporated  to  a 
pellicle,  is  left  to  crystallize  for  some  days.  The  mother  liquor, 
when  drained  off  the  crystals,  yields,  when  dried  down,  an  inferior 
soda-ash,  which  is,  however,  applied  to  many  manufacturing  uses. 
The  pure  carbonate  of  soda  crystallizes  in  flat,  oblique  rhomboidal 
prisms,  as  in  the  figure,  which  contain 
ten  atoms  of  water,  Na. .  C.O.-f- 10  Aq. 
In  a  dry  atmosphere,  they  lose  by  efflo- 
rescence all  their  water,  and  fall  into  a  ^"x^x^V^^  ^ — Ili^ 
white  powder.  It  dissolves  in  five  parts 
of  cold,  and  in  less  than  one  of  boiling  water.  By  a  gentle  heat» 
the  salt  undergoes  aqueous  fusion,  and  when  dried,  gives  a  white 
powder,  soda  siccata.  By  a  strong  heat,  the  carbonate  of  soda  melts, 
but  is  not  otherwise  affected. 

Prior  to  the  invention  of  the  soda  process  described  above,  the 
carbonate  of  soda  was  obtained  from  the  ashes  of  marine  plants,  as 
the  salsola,  and  various  fuci,  which  were  burned  in  large  quantities 
on  the  west  coast  of  Ireland,  in  the  Orkneys,  and  on  the  coasts  of 
France  and  Spain,  The  saline  products  thus  obtained  were  known 
in  commerce  as  kelp^  barilla^  varec  ;  but  these  sources  of  alkali  may 
now  be  considered  as  extinct.  Graham  states,  on  the  authority  of 
Mr.  Muspratt,  that  in  1838  there  were  manufactured  from  common 
salt  50,000  tons  of  soda-ash  and  20,000  tons  of  crystallized  carbon- 
ate, and  the  manufacture  is  continually  on  the  increase. 

To  the  practical  chemist  and  the  manufacturer,  it  is  important  to  be  able  to  deter- 
mine, by  a  rapid  and  easily  executed  process,  the  real  quantity  of  alkali  present  in 
any  sample  of  pearlashes  or  soda-ash  that  may  be  in  the  market.  All  such  pro- 
cesses* depend  on  measuring  the  quantity  of  sulphuric  acid  necessary  to  produce  a 
neutral  salt  with  a  certain  weight  of  the  sample;  but  in  the  management  of  the  de- 
tails considerable  difference  may  exist.  A  mode  which  I  have  found  to  be  very  ac- 
curate, and  easily  executed  even  by  ordinary  persons,  consists  in  preparing  before- 
hand a  stock  of  a  dilute  sulphuric  acid,  of  sp.  gr.  1-068  at  a  temperature  of  60°.  This 
acid  may  be  formed  by  mixing  one  ounce  of  the  strongest  oil  of  vitriol  with  nine 
ounces  of  water;  but  its  sp.  gr.  should  be  verified  by  trial  before  being  used. 

One  hundred  grains  of  the  sample  to  be  tried  are  then  to  be  powdered  and  stirred 
up  in  a  capsule  with  an  ounce  of  water.  A  glass  jar  about  a  foot  high  and  an  inch 
wide,  provided  with  a  lip  to  pour  from  and  a  steady  foot,  and  graduated  into  400 
parts,  of  which  each  part  indicates  five  grains  of  the  standard  acid,  is  to  be  filled 
with  the  acid  up  to  the  400th  mark,  and  then,  by  pouring  very  cautiously  from  the 
lip  a  few  drops  at  a  time,  the  alkaline  liquor  in  the  capsule  is  to  be  exactly  neutral- 
ized. A  little  bit  of  litmus  paper  may  be  left  in  it,  and  stirred  about  well  after  each 
addition  of  a  few  drops  of  acid.  A  drop  of  acid  in  excess  reddens  the  litmus  paper 
permanently ;  and  as  this  does  not  injure  the  result  sensiblv,  it  may  be  done  in  order 
to  secure  complete  neutralization.  The  graduations  of  the  glass  being  numbered 
from  above  downward,  simple  inspection  shows  how  much  acid  has  been  employed ; 
and  it  is  only  necessary  to  multiply  the  number  of  divisions  by  thirty-one  if  the  al- 
kali be  soda,  or  forty-seven  if  the  alkali  be  potash,  and  divide  in  each  case  by  100, 
to  obtain  the  quantity  of  real  alkali  present  in  the  100  grains  examined. 

The  principle  of  this  method  is,  that  100  grains  of  the  standard  acid  contain  eight 
grains  of  dry  sulphuric  acid,  and  hence  100  measures  contain  forty  grains,  which 
number  being  that  of  the  equivalent  of  the  acid,  neutralizes  almost  exactly  thirty- 
one  grains  of  soda  or  forty-seven  grains  of  potash,  which  are  the  equivalent  weights 
also.  To  find,  therefore,  the  quantity  of  either  alkali  in  a  sample  neutralized  by, 
for  example,  137  measures  of  acid,  we  say, 

For  potash,      100  :  47  :  :  137  :  .'C=[3ix 47=64-4 ; 
And  for  soda,  100  :  31  :  :  137  :  x=\p^x3l=^-5,  , 

Qqq 


490 


CARBONATE     OF     LIME. 


A.  table  may  easily  be  constructed  beforehand  on  those  principles,  so  as  to  save 
even  this  little  calculation.  Tiie  greatest  amount  of  error  at  all  likely  to  occur  in 
this  process  is  one  division  of  acid  in  excess.  The  difference  made  by  this,  however, 
does  not  influence  the  result  for  commercial  purposes ;  thus,  in  the  examples  above 
taken,  if  the  quantity  of  acid  had  been  measured  wrongly  at  138,  the  indications 
would  be,  for  potash,  64-9,  and  for  soda,  42-8;  the  error  in  no  case  exceeding  half  a 
part  per  cent.,  and  being  exactly  counterbalanced  by  taking  the  numbers  31  and  47 
instead  of  the  correct  equivalents,  31-3  and  47-3. 

Bicarbonate  of  Soda^  H.O.  .  C.Oa  +  Na.O. .  C.Oj,  is  formed  by  pass- 
ing a  current  of  carbonic  acid  gas  through  a  cold  solution  of  carbon- 
ate 'y  the  new  salt  precipitates  in  small  opaque  crystals,  having  the 
appearance  of  starch.  It  requires  fifteen  parts  of  cold  water  for  its 
solution  j  it  has  an  alkaline  reaction,  but  is  not  disagreeable  to  the 
taste. 

Sesquicarbonate  of  Soda  occurs  native  on  the  banks  of  certain  lakes 
in  northern  Africa,  whence  it  is  exported  under  the  name  of  trona. 
Its  formula  is  2Na.O.  .  C.02  +  3C.024-4H.O.  It  cannot  be  formed 
at  will. 

Carbonate  of  Barytes. — Ba.O. .  C.O2.  This  salt  exists  native,  crys- 
tallized in  oblique  rhombic  prisms;  it  is  insoluble  in  pure  water,  but 
dissolves  in  water  containing  carbonic  acid.  It  is  very  poisonous. 
It  may  be  prepared  artificially  by  mixing  solutions  of  chloride  of 
barium  and  carbonate  of  ammonia;  a  white  precipitate  falls,  which, 
being  well  washed  and  dried,  is  pure  carbonate  of  barytes.  It  is 
used  in  the  analysis  of  minerals  containing  alkali,  and  for  the  prep- 
aration of  various  salts  of  barytes.  It  has  been  used  in  the  manu 
facture  of  glass. 

Carbonate  of  Strontia  resembles  perfectly  the  former. 

Carbonate  of  Lime.—Csi.O.  .  CO,.  Eq.  632-5  or  50-7.  The  cir- 
cumstances and  forms  under  which  this  salt  exists  in  nature  have 
been  so  frequently  noticed  (p.  477,  225),  and  the  molecular  consti- 
tution and  peculiar  relations  to  light  of  its  crystals  so  fully  described, 
that  it  is  not  necessary  to  enter  upon  its  history  here  farther.  It 
may  be  prepared  pure  by  decomposing  chloride  of  calcium  by  means 
of  carbonate  of  ammonia  ;  it  forms  then  a  white  powder  insoluble  in 
pure  water,  but  dissolving  in  water  containing  carbonic  acid.  This 
is  not  due  to  the  formation  of  a  bicarbonate  of  lime,  but  owing  to  a 
specific  solvent  power  which  a  solution  of  carbonic  acid  in  water 
has  on  many  bodies,  as  silica,  phosphate  of  lime,  &c.,  which  are  in- 
soluble in  pure  water.  It  is  thus  that  carbonate  of  lime  is  held  dis- 
solved in  most  waters,  and  is  deposited  as  a  crust  on  the  interior 
of  any  vessels  in  which  such  water  may  be  boiled.  By  the  gradual 
dissipation  of  the  carbonic  acid  on  exposure  to  the  air,  the  carbonate 
of  lime  may  be  slowly  deposited,  and  then  crystallizes  ;  thus  are 
formed  the  remarkable  stalactites,  &c.,  of  limestone  caverns. 

Carbonate  of  Magnesia. — Mg.O. .  CO,.  This  salt  exists  anhydrous 
in  nature,  crystallized  in  rhombohedrons  like  calc  spar. 
By  dissolving  magnesia  in  water  by  a  stream  of  car- 
bonic acid,  it  may  be  formed,  and  is  gradually  deposit- 
ed in  rhomboidal  prisms  of  six  or  eight  sides,  as  »»,  «, 
«,  in  the  fisfure,  which  contain  three  atoms  of  water.  It 
is  this  salt,  Mg.O. .  C.O.-fS  Aq.,  which  exists  in  Mur- 
ray's solution  of  magnesia.  When  acted  on  by  pure  hot 
water,  this  salt  is  decomposed,  carbonic  acid  escaping, 


CARBONATE     OF     IRON,     ETC. 


491 


and  basic  carbonate  of  magnesia  being  produced.  It  is  this  basic  car- 
bonate which  constitutes  the  magnesia  alba,  or  common  carbonate  of 
magnesia  of  the  shops.  It  is  prepared  by  mixing  boiling  solutions 
of  sulphate  of  magnesia  and  carbonate  of  soda,  leaving  the  former 
slightly  in  excess.  The  precipitate  is  very  light  and  bulky,  and  al- 
most totally  insoluble  in  water.  One  fourth  of  the  carbonic  acid  is 
given  off  in  this  reaction,  and  the  precipitate  is  found  to  be  a  com- 
pound of  carbonate  and  of  hydrate  of  magnesia,  Mg.O.  .  H.O. -f-3 
(Mg.O.  .  C.O,.H.O.),  or  4Mg.O.  +  3C.O,  +  4  Aq. 

The  nature  of  dolomite  or  magnesian  limestone  has  been  already 
sufficiently  noticed  (p.  348). 

Carbonate  of  Manganese,  Mn.O.  .  C.O2,  is  a  white  powder  formed 
by  double  decomposition,  and  decomposed  by  a  red  heat. 

Protocarbonate  of  Iron,  Fe.O.  .  C.O2,  exists  native  in  rhombs  iso- 
morphous  with  calc  spar.  It  may  be  prepared  by  decomposing 
protosulphate  of  iron  by  carbonate  of  soda  ;  it  forms  a  white  pre- 
cipitate, which,  by  exposure  to  the  air,  rapidly  absorbs  oxygen  and 
gives  out  carbonic  acid,  becoming  green,  and  ultimately  red,  being 
then  mere  peroxide  of  iron.  The  carbonate  of  iron  can  therefore 
scarcely  be  obtained  pure  ;  but  by  mixing  the  fresh  precipitate  with 
sugar,  and  evaporating  to  dryness  with  constant  agitation,  a  quantity 
of  the  carbonate  remains  undecomposed,  being  protected  from  the 
air  by  a  varnish  of  sugar  on  its  particles,  and  thus  constitutes  the 
carbonas  ferri  cum  saccharo  of  pharmacy.  The  carbonate  of  iron  is 
soluble  in  water  containing  carbonic  acid,  and  exists  thus  dissolved 
in  chalybeate  spas. 

When  solutions  of  sulphate  of  zinc  and  carbonate  of  soda  are 
mixed  together,  a  basic  carbonate  of  Zinc  is  formed,  consisting  of  2 
(Zn.O. .  C.02)4"3Zn.O.  .H.O.  if  the  solutions  were  warm,  but  of  Zn. 
O. .  C.02+2Zn.O.  .H.O.  if  cold  j  carbonic  acid  gas  is  given  off  in 
both  cases. 

There  are  two  carbonates  of  Copper,  both  basic  ',  the  green  carbon- 
ate exists  native  (malachite),  and  is  used  as  a  pigment.  It  may  be 
formed  by  mixing  solutions  of  a  salt  of  copper  and  an  alkaline  car- 
bonate 5  the  precipitate  is  at  first  flocculent,  and  of  a  fine  pale  blue, 
but  when  boiled  it  becomes  dense,  granular,  and  bright  green :  its 
formula  is  2Cu.O.  +  C.024-H.O.  The  blue  carbonate  exists  also 
native  (Copper-azure),  but  cannot  be  prepared  artificially  so  as  to  be 
permanent:  its  formula  is  SCu.0. 4-20.02 H-H.O. 

Carbonate  of  Lead,  Pb.O.  .  C.O2,  exists  native,  crystallized  in 
forms  isomorphous  with  those  of  the  carbonate  of  barytes,  and  may 
be  formed  as  a  finely-crystalline  powder  by  decomposing  solution 
of  nitrate  of  lead  by  carbonate  of  soda.  There  are  several  basic 
carbonates  of  lead,  which,  in  a  greater  or  less  degree  of  mixture, 
constitute  the  White  Lead,  or  Ceruse  of  commerce,  so  much  used  in 
painting.  The  composition  of  white  lead  generally  falls  between 
those  given  by  the  formulae  3Pb,0.  +  2C.024-H.O.  and  4Pb.O+3C. 
O2  +  H.O. 

For  the  manufacture  of  white  lead,  very  thin  sheets  of  the  metal 
are  exposed  to  the  fumes  arising  from  vessels  containing  weak  vin- 
egar, which  are  kept  moderately  warm  by  being  imbedded  in  fer- 
menting tan  J  the  lead,  absorbing  oxygen  from  the  air,  combines 


492  CARBONIC     OXIDE. 

with  the  acetic  acid,  forming  a  basic  acetate  of  lead,  which  is  de- 
composed by  the  carbonic  acid  of  the  surrounding  air,  basic  carbon- 
ate of  lead  being  produced,  and  neutral  acetate  of  lead  remaining; 
this,  under  the  action  of  the  air,  takes  up  a  new  quantity  of  lead, 
and  the  same  decomposition  is  renewed,  a  minute  quantity  of  acet- 
ic acid  thus  serving  to  produce  a  very  large  quantity  of  ceruse. 
This  process  has  lately  been  much  improved  by  exposing  litharge, 
finely  ground  and  mixed  with  one  per  cent,  of  acetate  of  lead,  to  a 
stream  of  carbonic  acid,  generally  derived  from  the  fermenting  vats 
of  a  brewery  ;  the  one  portion  of  neutral  acetate  successively  unites 
with  all  the  litharge  to  form  basic  acetate,  the  successive  portions 
of  which  are  decomposed  by  the  carbonic  acid,  white  lead  being 
formed,  and  the  original  quantity  of  neutral  acetate  remaining  un- 
combined  at  the  end. 

The  carbonates  of  the  other  metals  are  unimportant. 

Carbon  combines  with  the  metals  to  form  carburets^  of  which  the 
best  known  are  those  of  iron  and  silver ;  the  former  has  been  fully 
noticed  in  the  description  of  cast-iron  and  steel  (p.  360),  and  the 
carburet  of  silver  is  a  gray  powder,  which  remains  when  certain 
silver  salts  of  organic  acids,  as  the  citrate  and  tartrate,  are  imper- 
fectly burned  away. 

Carbonic  Oxide. — CO.     Atomic  Weight  14i'05  % 

If  carbonic  acid  gas  be  passed  through  a  tube  containing  red-hot 
charcoal,  it  takes  up  as  much  more  carbon  as  it  already  contained, 
and  forms  carbonic  oxide  ]  its  volume  being  thereby  doubled.  The 
gas  may  also  be  prepared  by  heating  to  redness,  in  an  iron  retort, 
a  mixture  of  charcoal  and  chalk,  when  the  carbonic  acid  evolved 
from  the  latter  combines  with  the  excess  of  carbon,  and  forms  car- 
bonic oxide  5  in  place  of  charcoal,  iron  filings  or  zinc  may  be  used ; 
the  metal,  in  this  case,  takes  half  of  the  oxygen  from  the  carbonic 
acid,  C.O2  and  Zn.  giving  Zn.O.  and  CO. 

A  very  simple  and  elegant  way  of  obtaining  this  gas  consists  m 
warming  strong  oil  of  vitriol  with  crystals  of  oxalic  acid,  in  a  flask, 
o  6,  from  which  a  tube,/,  passes  to  a  bottle  containing  solution  of 

caustic   potash,  «,   as   in  the   figure ; 
^1/  from   this  another  tube  conducts  to 

the  pneumatic  trough.  The  oxalic 
acid,  C2O3-I-H.O.,  yields  up  its  basic 
water  to  the  sulphuric  acid,  and,  as 
the  oxalic  acid  cannot  exist  except 
in  combination  with  some  base,  it  is 
resolved  in  carbonic  oxide  and  car- 
bonic acid  (CA^C.O.  +  CO.),  which 
are  evolved  as  gases,  mixed  in  equal 
volumes  ;  in  bubbling  through  the 
bottle  containing  potash,  the  carbonic  acid  is  completely  absorbed, 
and  the  pure  carbonic  oxide  may  be  collected  over  water. 

It  is  a  colourless,  inodorous  gas,  and  has  no  action  on  vegetable 
colours;  it  extinguishes  a  taper,  but  is  combustible,  and,  burning 
with  a  pale  blue  flame,  forms  carbonic  acid.  It  is  this  gas  which 
produces,  on  the  top  of  a  clear  coke  fire,  a  blue  flame,  which  ap- 


MANUFACTURE     OP      OXALIC     ACID.  493 

pears  purple  when  seen  with  the  red  background  of  the  glowing 
cinders.  It  contains  half  its  volume  of  oxygen  j  its  specific  gravity- 
is  972'8.  Carbonic  oxide  appears  to  enter  into  union  with  a  great 
variety  of  bodies,  and  to  act  in  such  compounds  as  a  compound 
radical. 

Oxalic  Acid.—Qfi^  or  2(C.0.)  +  0.     Eq.  451-2  or  36-1. 

Oxalic  acid  is  one  of  the  most  important  organic  bodies.  It  is 
found  combined  with  potash,  forming  the  Salt  of  Sorrel,  in  several 
plants  of  the  genera  oxalis  and  rumex,  and  combined  with  lime  in 
the  roots  of  rhubarb,  and  in  a  variety  of  lichens.  It  was  formerly 
extracted  principally  from  the  oxalis  acetosella,  from  whence  its 
name  is  derived,  but  is  now  manufactured  in  larger  quantities  arti- 
ficially. It  is  generally  a  product  of  the  oxidation  of  vegetable  sub- 
stance^ by  nitric  acid,  on  which  fact  its  mode  of  preparation  is 
founded.  The  substances  employed  are  usually  starch  or  sugar,  a 
quantity  of  which  is  placed  in  an  earthen  pipkin,  of  which  a  great 
number  are  arranged  in  a  shallow  vessel  containing  warm  water ; 
about  four  parts  of  nitric  acid,  specific  gravity  1*42,  are  poured  into 
each  pipkin.  The  starch  is  rapidly  oxidized,  and  nitrous  fumes  giv- 
en off  abundantly  ;  when  the  action  has  become  slow,  one  part  more 
of  acid  is  to  be  added,  and  the  heat  increased.  The  liquors  so  ob- 
tained, are  mixed,  evaporated  to  a  pellicle,  and  set  aside  to  crystal- 
lize, and  the  crystals  are  purified  by  re-solution  and  crystallization. 
From  the  mother  liquors  new  quantities  of  oxalic  acid  may  be  ob- 
tained by  heating  with  more  nitric  acid. 

If  we  consider  the  sugar  in  its  dryest  form  as  being  CiaHgOg,  the 
action  of  the  nitric  acid  should  consist  in  first  removing  the  nine 
equivalents  of  hydrogen,  and  substituting  for  them  nine  equivalents 
of  oxygen;  thus  CizHgOg  and  6N.O5  should  give  6(CA)  with  9H.0. 
and  6N.O2.  But  the  action  is  not  so  simple,  as  other  products,  es- 
pecially the  Saccharic  Acid,  are  at  the  same  time  formed.  By  means 
of  permanganate  of  potash,  however,  the  carbon  of  sugar  may  be 
very  elegantly  and  directly  changed  into  oxalic  acid,  CjaHgOg  and 
6(Mn20,+K.O.)  producing  12(Mn.O,)  with  9H.0.  and  6(C203+K. 
O.),  the  oxalic  acid  formed  exactly  neutralizing  the  potash  of  the 
manganic  salt  employed. 

The  oxalic  acid  crystallizes  from  its  solution  in  oblique  rhombic 

prisms,  of  which  those  planes  marked  i  c  are  prima-     k- ■. ^^^ 

ry,  and  af  secondary  :  the  summit  is  often  dihedral,     /K""" — '\'  \ 
in  which  case  the  plane  a,  and  that  vertically  oppo-    kKX     0   \     % 

site  to  it,  are  absent.     These  crystals  contain  three  (j^-A^- \jj 

atoms  of  water,  of  which  one  is  basic  :  CaOa-f  H.O.  A^iZZI—J 
H-2  Aq.  When  warmed,  they  give  off"  2  Aq.,  and  the  hydrate  of 
oxalic  acid  remains  as  a  white  powder,  which  melts  at  350^,  and 
when  heated  farther  sublimes,  a  portion  being,  however,  decompo- 
sed; the  products  of  the  reaction  of  oil  of  vitriol  on  oxalic  acid  have 
been  already  noticed  (p.  492).  Oxalic  acid  is  converted  into  car- 
bonic acid  by  contact  with  many  peroxides,  as  the  peroxide  of  man- 
ganese, by  which  means  the  technical  value  of  manganese  ores  may 
be  determined  (see  p.  355).  By  contact  with  a  great  excess  of  hot 
nitric  acid  or  of  chlorine,  it  is  also  converted  into  carbonic  acid. 


494  OXALATES     OP     POTASH. 

The  acidity  of  oxalic  acid  is  very  great ;  a  grain  of  it  dissolved 
in  30,000  grains  of  water  will  still  affect  litmus  paper.  It  neutrali- 
zes the  alkalies  perfectly,  and  forms  with  them  two  series  of  acid 
salts.  In  the  neutral  oxalates,  the  oxygen  of  the  acid  to  that  of  the 
base  is  3  :  1.  By  heat,  those  of  the  metals  proper  are  generally  con- 
verted into  carbonic  acid  and  metal,  C^Oa+M.O.  giving  C204andM. 
Those  of  the  earths  and  alkalies  evolve  carbonic  oxide,  and  produce 
a  carbonate,  CA+M.O.  giving  CO.  and  C.O^+M.O.  The  former 
action  is  usefully  applied  to  obtain  cobalt  and  nickel  in  the  metal- 
lic state. 

Oxalic  acid  is  detected  easily  by  its  strong  acidity,  and  its  not 
leaving  a  carbonaceous  residue  when  heated.  Its  solution  gives, 
with  lime-water,  a  precipitate  which  is  insoluble  in  an  excess  of  ox- 
alic acid,  or  of  any  organic  acid.  It  precipitates,  also,  the  solu- 
tions of  barytes  and  lead.  It  acts  violently  on  animals  as  a  poison  j 
for  an  antidote  magnesia  is  the  best,  but  chalk  or  whiting  is  the  most 
readily  procured. 

Several  of  the  oxalates  deserve  special  notice.  There  are  three 
oxalates  of  Potash,  remarkable  as  being  the  bodies  by  which  Wollas- 
ton  satisfied  himself  of  the  truth  of  the  law  of  multiple  combination, 
p.  208,  their  proportions  of  acid  being  as  1  :  2  :  4. 

The  neutral  Oxalate  of  Potash,  K.O.  .  CaOg  +  Aq.,  may  be  formed 
by  acting  on  sugar  by  permanganate  of  potash,  or  by  heating  any 
fixed  organic  matter,  as  sawdust  or  paper,  with  an  excess  of  potash, 
below  redness.  It  is  more  simply  produced  by  neutralizing  oxalic 
acid,  or  the  following  salt,  with  carbonate  of  potash  ]  it  crystallizes 
in  rhombic  prisms,  of  a  bitter  taste,  which  dissolve  in  three  parts 
of  water,  and  are  insoluble  in  alcohol. 

Binoxalate  of  Potash,  K.O. .  C2O3+H.O. .  C2O3  +  2  Aq.,  exists  nat- 
urally in  the  various  kinds  of  sorrel,  from  whence  it  was  originally 
extracted  under  the  name  of  Salt  of  Sorrel,  but  is  now  artificially 
made.  One  part  of  oxalic  acid  is  exactly  neutralized  by  potash, 
and  then  exactly  as  much  more  oxalic  acid  is  added  to  the  solution, 
from  which,  by  evaporation  and  cooling,  the  salt  crystallizes  in  ob- 
lique rhombic  prisms,  which  are  soluble  in  forty  parts  of  cold  and 
in  six  parts  of  boiling  water.  Its  taste  is  strongly  acid  and  saline, 
and  it  is  poisonous,  though  less  so  than  the  acid  uncombined. 
When  heated,  the  salt  is  decomposed,  evolving  carbonic  acid  and 
carbonic  oxide,  and  leaving  a  residue  of  carbonate  of  potash,  which 
should  be  scarcely  coloured  if  the  salt  were  pure. 

Quadroxalate  of  Potash,  K.O.  .C2O3+3H.O. .  CaOg-f^  Aq.,  is  form- 
ed by  neutralizing  one  part  of  oxalic  acid  by  potash,  and  adding  to 
the  solution  three  times  as  much  oxalic  acid  more.  It  may  also  be 
prepared  by  dissolving  the  binoxalate  in  muriatic  acid,  which  takes 
half  of  the  alkali,  and  the  quadroxalate  crystallizes  out.  This  and 
the  last  salt  are  indiscriminately  sold  in  commerce  as  salt  of  sor- 
rel, and  also  often  as  Salt  of  Lemons,  for  removing  iron  moulds  and 
stains  of  ink,  which  they  do  by  forming,  with  the  peroxide  of  iron, 
a  soluble  double  salt. 

There  is  but  one  oxalate  of  Soda  ;  it  is  not  important. 

Oxalate  of  Lime,  Ca.O. .  C2O34-2  Aq.,  exists  abundantly  in  nature, 
forming  the  hard  earthy  basis  of  many  lichens,  and  may  be  prepared 


DOUBLE  OXALATES  OP  POTASH,  ETC.     495 

by  mixing  solutions  of  oxalate  of  ammonia  and  of  any  soluble  salt 
of  lime.  It  forms  a  white  flocculent  precipitate,  which,  by  boiling, 
becomes  heavy  and  granular.  It  is  totally  insoluble  in  water,  and 
is  hence  used  as  a  means  of  removing  lime  from  solutions,  and  de- 
termining its  quantity.  It  dissolves  in  the  mineral  acids,  but  is  in- 
soluble in  all  organic  acids,  even  the  acetic.  When  heated,  it  leaves 
a  perfectly  white  residue  of  carbonate  of  lime. 

The  remaining  simple  oxalates  are  not  important,  except  the  ox-. 
alate  of  Silver,  which  is  a  white  powder,  prepared  by  double  decom- 
position, and  remarkable  for  being  decomposed  by  a  moderate  heat, 
with  a  slight  explosion,  into  carbonic  acid  and  metallic  silver. 

There  are  several  double  oxalates  of  interest. 

Oxalate  of  Potash  and  Peroxide  of  Iron,  (Fe203+3C203)+3K.O.  .  C2O3+6  Aq., 
is  prepared  by  dissolving  peroxide  of  iron  in  solution  of  binoxalate  of  potash ;  it 
crystallizes  in  fine  grass-green  tables,  which  are  permanent  in  the  air.  There  exists 
a  similar  salt  containing  soda. 

Oxalate  of  Potash  and  Chrmne,  (Cr203+3C203)+3K.O.  .  C2O3+6  Aq.,  is  prepared 
by  dissolving  together  in  hot  water  one  part  of  bichromate  of  potash,  two  of  crys- 
tallized oxalic  acid,  and  two  of  binoxalate  of  potash,  A  copious  evolution  of  car- 
bonic acid  occurs,  the  chromic  acid  being  deprived  of  half  its  oxygen  by  a  part  of 
the  oxalic  acid,  with  the  remainder  of  which  the  oxide  of  chrome  unites.  The  li- 
quor assumes  a  fine  purple  colour,  and  on  cooling,  yields  prisms  of  a  splendid  blue 
colour,  so  deep  as  to  be  perfectly  opaque,  unless  the  crystals  be  very  thin. 

Oxalate  of  Copper  and  Potash,  K.O.  .  C2O3+CU.O.  .  CaOs-f-S  Aq.,  is  formed  by  di- 

gesting  a  solution  of  binoxalate  of  potash  on  oxide  of  copper.    It  crystallizes  in  fine 
lue  prisms.     It  may  be  obtained  with  4  Aq. 

Ckloro-carbonic  ^cid. —CO. -\- CI  Eq.  619-1  or  49-5.  When 
equal  volumes  of  carbonic  oxide  and  chlorine  are  exposed  for  some 
hours  to  the  light,  they  gradually  combine,  forming  a  colourless  gas, 
which  was  termed  by  J.  Davy,  its  discoverer.  Phosgene  Gas.  Its 
odour  is  very  irritating ;  the  volume  being  diminished  to  one  half, 
its  density  is  3412.  It  is  decomposed  by  water,  carbonic  and  mu- 
riatic acids  being  formed.  It  is  decomposed  by  most  metals,  which 
unite  with  the  chlorine  and  liberate  carbonic  acid.  Its  action  on 
ammonia  and  on  alcohol  will  be  hereafter  noticed. 

Combination  of  Carbonic  Oxide  and  Potassium,  and  the  Products 
of  its  Decomposition. 

If  potassium  be  heated  in  a  current  of  carbonic  oxide,  the  gas  is 
rapidly  absorbed,  but  no  charcoal  is  separated,  as  occurs  with  car- 
bonic acid  gas.  The  metal  is  converted  into  a  blackish-green  po- 
rous mass.  If  the  air  be  admitted  to  this  while  hot,  it  inflames  j 
when  brought  into  contact  with  water,  it  is  immediately  decomposed, 
a  peculiar  gas  being  given  ofl^,  and  a  rhodizonate  of  potash  formed. 
This  oxycarburet  of  potassium  is  obtained  in  quantity  in  the  process 
by  which  potassium  is  procured,  and  constitutes  the  great  obstacle 
to  obtaining  that  metal,  as  described  in  page  337.  It  is  also  formed, 
but  very  impure,  by  merely  brightly  igniting  cream  of  tartar  in  a 
covered  crucible  for  an  hour.  The  composition  of  this  body  is  not 
yet  known,  and  hence  the  mode  of  its  decomposition  cannot  be  ex- 
pressed in  formulae.  The  gas  which  it  evolves  by  solution  in  water 
has  been  examined  by  Mr.  Davy.  It  is  colourless  and  inflammable, 
and  burns  more  brightly  than  olefiant  gas.  Its  characteristic  prop- 
erty is  to  detonate  with  a  brilliant  flash,  and  deposite  charcoal  when 
mixed  with  chlorine,  even  in  the  dark.  He  assigns  to  it  the  formula 
C.H. 


496  ISOMERIC     OXIDES     OF     CARBON. 

Rhodizonic  Acid. — This  is  formed  when  the  oxycarburet  of  potas- 
sium is  dissolved  in  cold  water.  It  is,  when  dry,  isomeric  with 
carbonic  oxide,  C7O7,  but  it  appears  to  be  a  tribasic  hydracid,  and 
its  formula  CvOio-j-Hs.  Its  salts  are  of  a  fine  scarlet  red  colour, 
whence  its  name. 

Croconic  Acid,  C5O4,  is  formed  when  a  solution  of  rhodizonate  of 
potash  is  boiled  ;  an  atom  of  potash  becomes  free,  and  croconate 
and  oxalate  of  potash  are  produced;  C^Ot+SK.O.  giving  K.O.  and 
CaOg-f  K.O.,  with  C5O4+K.O.  The  salts  of  croconic  acid  are  bright 
yellow  coloured,  but  do  not  require  other  notice. 

Mellitic  Acid,  C4O3,  when  dry,  is  found  only  native,  combined 
with  alumina,  in  a  very  rare  mineral,  mellite  or  honeystone.  It  crys- 
tallizes with  water,  C403-fH.O.,  and  from  its  characters,  especially 
the  properties  of  the  mellate  of  silver,  it  appears  to  be  properly  a 
hydrogen  acid,  having  carbonic  oxide  as  its  radical,  and  its  formula 
to  be  C4O4-J-H.  When  its  ammonia  salt  is  decomposed  by  heat,  it 
is  resolved  into  two  very  singular  bodies,  paraban  and  euchroic  acid, 
whose  history,  however,  is  not  important  here. 

In  concluding  this  account  of  the  oxygen  compounds  of  carbon,  it 
is  proper  to  notice  the  peculiar  function  which  the  carbonic  oxide 
appears  to  play.  From  the  composition  of  its  chlorine  compound, 
it  is  certain  that  the  equivalent  of  the  gas  is  CO.,  and,  combining 
with  oxygen,  it  forms  carbonic  acid,  C.O2.  But  I  consider  that  we 
cannot  look  upon  oxalic  acid  as  being  a  lower  degree  of  oxidation 
of  the  same  radical  as  carbonic  acid.  On  the  contrary,  the  body 
C2O2,  which  is  the  basis  of  it,  enters  into  a  completely  distinct  series 
of  compounds,  such  as  oxamide,  and  is  probably  merely  isomeric 
with  carbonic  oxide,  into  which  it  may  be  changed  by  a  variety  of 
reactions.  Still  less  is  carbonic  oxide  the  basis  of  the  rhodizonates, 
C  O7,  or  of  the  croconates  or  mellates  ;  but  the  gas  is  changed  into 
these  more  complex  bodies  by  an  isomeric  action,  which  appears  to 
occur  at  the  moment  that  it  combines  with  the  potassium.  I  look 
upon  the  carbonic  oxide  gas,  therefore,  as  being  the  basis  only  of 
carbonic  acid  and  phosgene  gas,  and  that  the  radicals  of  the  oxalic 
acid  and  the  bodies  of  its  series,  as  well  as  of  the  rhodizonic  and 
other  acids,  are  compounds  of  carbon  and  oxygen,  isomeric  with 
carbonic  oxide,  but  not  yet  isolated. 

OfSulphuret  of  Carbon.— CS^.     Eq.  478-7  or  38-3. 

This  remarkable  substance  is  formed  whenever  sulphur  comes 
into  contact  with  red-hot  charcoal.  It  may  be  prepared  by  means 
of  the  apparatus  figured  in  page  323 ;  the  tube  a,  c  being  filled  with 
pieces  of  charcoal  about  the  size  of  almonds,  and  bits  of  sulphur 
introduced  from  time  to  time  at  h,  which  is  to  be  then  tightly  clo- 
sed with  a  cork.  The  sulphur  fuses,  and  the  tube  being  a  little  in- 
clined, runs  down  upon  the  ignited  charcoal,  combines  with  it,  and 
the  product  passing  as  vapour  into  the  long  glass  tube  e, /,  is  con- 
densed, and  collected  as  a  liquid  in  the  bottle. 

In  large  quantity,  it  is  more  conveniently  prepared  by  fixing,  air  tight,  into  an  iron 
cylinder  about  a  foot  high  (such  as  a  quicksilver  boiile),  two  iron  tubes,  one  long,  b, 
reaching  nearlv  to  the  bottom,  and  projecting  a  foot  above  the  top,  and  the  other 
short,  c,  and  bent  at  a  right  angle,  serving  to  convey  the  product  to  the  condensing 
apparatus.    By  means  of  the  tube  c,  the  bottle  may  be  filled  with  small  fragments 


SULPHURET     OF     CARBON. 


497 


of  charcoal,  and  then,  being  placed  in  a  furnace,  the  wide  glass  tube  c,  and  the  nai- 
rower  /,  are  to  be  attached  by  corks.  From  the  cock  d  a  stream  of  water  flows^ 
which,  gl^ided  by  the  tin-plate  gTitter  o,  cools  the  tube/,  and  is  conducted  by  the 
thread  h  to  the  basin  x.  When  the  bottle  is  bright  red,  small  pieces  of  sulphur  are 
to  be  dropped  in  by  the  long  tube,  the  end  of  which  is  to  be  then  carefully  closed  up 
by  a  cork.  The  sulphur,  being  vaporized,  acts  on  the  charcoal,  and  the  sulphuret  of 
carbon  formed  being  condensed  in  the  narrow  tube  cf,  collects  in  the  bottle  n,  which 
is  half  filled  with  ice  in  order  more  perfectly  to  preserve  it.  Any  incondensible  gas- 
es that  may  be  formed  escape  by  the  tube  m.  The  process  might  be  continued  until 
all  the  charcoal  in  the  bottle  had  been  converted  into  sulphuret ;  but  if  sulphur  were 
allowed  to  be  present  to  excess,  it  would  melt  the  bottom  of  the  bottle.  The  process, 
therefore,  should  not  be  pushed  so  far. 

The  sulphuret  of  carbon  thus  obtained  contains  an  excess  of  sul- 
phur dissolved  in  it,  and  must  be  purified  by  redistillation  at  a  very 
moderate  heat  (in  a  water  bath) ;  when  about  nine  tenths  have  dis 
tilled  over,  by  allowing  the  residue  to  evaporate  spontaneously  in  a 
capsule,  very  fine  right  rhombic  crystals  of  sulphur  may  be  obtain- 
ed (p.  284). 

The  sulphuret  of  carbon  is  a  colourless  liquid,  of  a  very  disagree- 
able garlic  smell.  It  does  not  mix  with  water,  but  dissolves  in  al 
cohol  and  ether.  It  dissolves  sulphur  and  phosphorus  in  large 
quantity.  Its  specific  gravity  is  1272.  It  boils  at  108"^  "Fah.,  and 
forms  a  colourless  vapour,  whose  specific  gravity  is  2*621.  From 
its  volatility,  it  obtained  the  name  of  Alcohol  of  Sulphur.  In  evap- 
orating it  produces  great  cold  ;  mercury  may  be  frozen  by  suspend- 
ing under  a  bell-glass  a  thermometer,  the  bulb  of  which  is  envel- 
oped by  cotton  moistened  by  this  fluid,  and  rapidly  exhausting  the 
air.  It  is  very  inflammable,  burning  with  a  blue  flame,  and  producing 
carbonic  and  sulphurous  acids.  If  a  few  drops  of  it  be  let  fall  into 
a  strong  bottle  containing  oxygen,  so  much  of  it  evaporates  as  to 
form  an  explosive  mixture  with  the  gas,  which  then  detonates  when 
touched  with  a  lighted  taper,  like  a  mixture  of  oxygen  and  hydro- 
gen. When  the  sulphuret  of  carbon  is  heated  in  contact  with  a 
metal,  carbon  is  separated,  and  a  metallic  sulphuret  produced.  It  is 
thus  found  to  consist  of  one  atom  of  carbon  united  to  two  of  sul- 
phur, and  its  formula  to  be  C.So. 

It  is  a  powerful  sulphur  acid,  combining  with  the  sulphurets  of 
the  alkaline  metals  and  forming  sulphur  salts,  which  are  crystalli- 
zable  ;  with  the  sulphurets  of  lead,  silver,  copper,  &;c.,  it  forms  in- 

R  PvR 


498  CHLORIDES     OF     CARBO  N. A  M  M  O  N  I  A. 

soluble  compounds,  which* correspond  closely  in  composition  to  the 
ordinary  carbonates.  This  substance  is,  in  fact,  exactly  equivalent 
to  carbonic  acid,  C.O2,  the  sulphur  being  replaced  by  oxygen,  with 
which  its  analogies  have  been  already  noticed  in  p.  291.  The  sul- 
phuret  of  carbon  is  hence  often  called  Sulphocarbonic  Jlcid. 

Moist  chlorine  converts  this  body  into  a  crystalline  substance  ]iike 
camphor  j  but  this,  as  well  as  the  products  of  the  action  of  nitric 
acid  and  of  strong  alkalies,  have  not  yet  been  accurately  examined 

Chlorides  of  Carbon, 

Subchloride  of  Carbon,  C2CI.,  is  formed  by  passing  the  vapour  of  the  protochlorirte 
many  times  through  an  ignited  glass  tube ;  chlorine  is  given  off,  ana  the  subchlo- 
ride  deposited  in  silky  crystals,  which  are  fusible,  and  sublime  at  about  300^  un- 
changed. 

Protochloride  of  Carbon,  C2CI2,  is  also  formed  from  the  sesquichloride  of  carbon 
by  heating  its  vapour  to  redness,  when  chlorine  is  given  off;  or  better  by  distilling 
the  sesquichloride  with  an  alcoholic  solution  of  sulphuret  of  potassium,  which  re- 
moves one  third  of  the  chlorine.  It  is  a  limpid  fluid,  boiling  at  160° ;  the  sp.  gr.  of 
its  vapour  is  2862.    By  a  strong  heat  it  gives  subchloride  and  free  chlorine, 

Sesquichloride  of  Carbon,  C2CI3,  is  produced  by  the  action  of  a  great  excess  of  chlo- 
rine in  bright  sunshine  on  olefiant  gas  or  on  muriatic  ether;  all  the  hydrogen  of 
these  bodies  is  removed,  and  the  carbon  remains  united  with  chlorine.  It  forms  a 
white  crystalline  mass  like  camphor,  which  is  insoluble  in  water,  but  soluble  in  al- 
cohol and  ether.  It  melts  at  320'',  and  sublimes  at  360"^  unchanged ;  at  a  red  heat  it 
abandons  chlorine,  and  forms  the  bodies  last  described. 

Bichlaride  of  Carbon,  C2CI4,  is  formed  by  exposing  a  body  termed  chloroform, 
whose  formula  is  C2H.CI3,  or  marsh  gas,  C2H4,  to  an  excess  of  chlorine  in  bright  sun- 
light. The  hydrogen  is  gradually  removed  and  replaced  by  chlorine.  It  is  liquid; 
its  sp.  gr.  is  1-6;  it  boils  at  192°.    The  sp.  gr.  of  its  vapour  is  5302. 


CHAPTER  XVIII. 

OF    THE    COMPOUNDS  OF  NITROGEN  AND  HYDROGEN.      AMMONIA,  ITS  DERIV- 
ATIVES   AND    COMPOUNDS. 

Although  there  is  very  perfect  evidence  that  hydrogen  and  ni- 
trogen unite  in  two,  perhaps  in  three  proportions,  we  as  yet  know 
but  one  of  these  in  an  isolated  form,  which  is  the  volatile  alkah\ 
Ammonia.  This  was  known  to  the  earliest  chemists,  but  the  im- 
portance of  its  history  to  the  progress  of  chemical  philosophy  has 
been  but  lately  felt  to  its  just  extent. 

Ammonia  is  produced  in  almost  all  reactions  where  nitrogen  and 
hydrogen  are  brought  together,  one  or  both  being  nascent.  Thus, 
when  an  electric  spark  is  passed  through  damp  air,  nitric  acid  and 
ammonia  are  both  formed,  and  hence  the  rain  which  falls  after  thun- 
der-storms contains  nitrate  of  ammonia.  It  is  evolved  in  large 
quantities  in  the  putrefaction  of  organic  substances  containing  ni- 
trogen, and  is  formed  also  by  their  distillation  at  high  temperatures, 
whence  the  greater  supply  of  ammonia  used  in  the  arts  is  derived. 
When  any  oxide  of  nitrogen  is  mixed  with  hydrogen,  and  passed 
through  a  tube  containing  red-hot  spongy  platinum,  ammonia  is 
formed  j  and,  lastly,  it  is  produced  abundantly  when  iron  or  tin  is 


PREPARATION     OF     AMMONIA.  499 

oxidized  violently  by  nitric  acid,  the  oxygen  being  taken  both  from 
the  acid  and  water,  the  nascent  hydrogen  and  nitrogen  unite.  Am- 
ttionia  is  also  a  product  of  organization,  being  contained  in  the 
sweat  of  animals,  and  being  exhaled  by  the  flowers  of  many  plants, 
and  by  the  leaves,  also,  of  the  cruciferse. 

For  the  purposes  of  the  chemist,  ammonia  is  obtained  from  the 
muriate  of  ammonia,  or  sal  ammoniac,  which  is  manufactured  in 
large  quantities  for  commerce,  by  processes  to  be  hereafter  de- 
scribed. Equal  parts  of  the  s^l  ammoniac,  in  powder,  and  slacked 
lime  are  to  be  intimately  mixed  and  heated  in  a  flask,  from  which 
a  bent  tube  passes ;  the  gas  which  issues  is  to  be  conducted  through 
a  tube,  as  in  the  figure  (p.  310),  containing  dry  lime  or  fused  pot- 
ash, by  which  adhering  moisture  is  removed,  and  it  may  then  be 
collected  over  mercury.  It  is  colourless  and  transparent.  Its  odour 
is  strong,  pungent,  and  irritating,  well  known  as  the  smell  of  harts- 
horn. When  perfectly  dry,  it  has  no  action  on  vegetable  colours ; 
but  if  damp,  it  reacts  powerfully  alkaline.  The  brown  colour  which 
it  produces  on  turmeric  disappears  when  heat  is  applied,  by  which 
it  is  distinguished  from  the  browning  by  the  fixed  alkalies  or  earths. 
By  a  pressure  of  6i  atmospheres^  or  at  a  temperature  of  — 61°,  gas 
eous  ammonia  is  liquefied.  When  inspired  pure,  it  proves  excess 
ively  caustic  and  poisonous. 

Ammonia  is  slightly  combustible.  It  does  not  support  combus 
lion.  When  a  series  of  electric  sparks  is  passed  through  a  quan 
tity  of  the  gas  confined  over  mercury,  its  volume  enlarges,  and  ul- 
timately becomes  double.  It  is  then  totally  decomposed,  and  the 
resulting  gas  consists  of  three  volumes  of  hydrogen  and  one  of  ni- 
trogen: tJhe  specific  gravity  of  ammonia  is  therefore  591*5,  as  de- 
duced in  p.  215,  and  its  formula  N.H3.  If  a  current  of  ammoniacal 
gas  be  passed  through  a  red-hot  tube  filled  with  iron  wire,  it  is  de- 
composed in  the  same  way  as  by  electricity.  If  the  tube  contain 
red-hot  charcoal,  carbon  is  taken  up,  and  prussiate  of  ammonia  and 
carburet  of  hydrogen  produced. 

Ammoniacal  gas  is  rapidly  absorbed  by  water,  which  takes  up 
780  times  its  volume  at  32^.  Great  heat  is  thereby  evolved,  and 
the  solution,  which  augments  two  thirds  in  volume,  has  a  specific 
gravity  of  0*872,  and  boils  at  120°.  It  contains  then  about  32  per 
cent,  of  ammonia,  and  approximates  to  the  formula  N.Hg-f  4  Aq. 
This  solution  is  termed  Water  of  Ammonia^  or,  improperly,  Liquid 
Ammonia,  To  prepare  it  upon  a  larger  scale,  the  matrass  and  se- 
ries of  three-necked  bottles,  described  and  figured  in  p.  308,  may 
be  employed.  Five  parts  of  lime,  slacked,  and  mixed  with  as  much 
water  as  will  convert  it  into  a  thin  paste,  are  to  be  introduced,  witli 
four  parts  of  powdered  sal  ammoniac,  into  the  matrass,  which  is 
then  to  be  placed  upon  the  sand-bath,  and  connected  with  the  range 
of  bottles.  The  first  bottle  is  left  empty,  in  order  to  catch  any  wa- 
ter or  mixture  that  may  be  carried  over,  and  it  should  be  allowed 
to  grow  warm,  in  order  that  it  may  retain  no  gas;  in  the  other  bot- 
tles water  is  placed,  by  which  the  gas  is  absorbed,  and  they  are 
kept  cool  by  damp  cloths  applied  to  their  surface.  For  ordinary 
purposes,  water  of  ammonia  need  not  contain  more  than  18  per 
cent,  of  gas  j  it  then  has  a  specific  gravity  of  0-930. 


500  CONSTITUTION     OF     AMMONIA, 

The  watery  solution  of  ammonia  possesses  all  the  characters  of 
the  gas  in  a  strong  degree.  It  neutralizes  the  strongest  acids,  and 
acts  in  all  respects  as  a  strong  base,  ranking  next  to  lime.  It  forms 
many  classes  of  combinations,  in  some  of  which  it  exists  unaltered, 
but  in  others  it  first  undergoes  peculiar  decomposition.  Its  action 
on  chlorine  is  very  violent,  and  accompanied  by  flame ;  sal  ammo- 
niac is  formed  and  nitrogen  set  free,  as  described  in  p.  261. 

Ammonia  is  very  easily  recognised :  its  odour,  the  brown  colour 
given  to  turmeric  paper,  which  is  removed  by  a  gentle  heat,  and  its 
forming  dense  white  fumes  on  the  approach  of  a  glass  rod  moisten- 
ed with  strong  muriatic  acid,  characterize  it  when  free  ;  all  sub- 
stances which  contain  ammonia  are  either  volatilized  by  heat,  or 
decomposed,  the  ammonia  being  generally  liberated  j  in  all  cases, 
by  heating  the  body  with  moist  caustic  potash,  ammonia  is  evolved 
as  gas,  and  may  be  known  by  the  properties  now  described. 

The  real  nature  of  ammonia  has  recently  been  the  subject  of 
much  inquiry ;  its  equivalent  is  satisfactorily  determined  to  be 
17*1,  and  hence  its  formula  is  N.Hg,  and  its  equivalent  volume  4.  It 
may  enter  into  combination  directly  with  dry  oxygen  acids,  but  it 
does  not  then  form  the  proper  ammoniacal  salts,  which  all  contain 
an  atom  of  water  essential  to  their  constitution.  It  combines  with 
a  great  number  of  saline  bodies,  and  then  resembles,  in  its  functions, 
their  water  of  crystallization.  Its  most  remarkable  property,  how- 
ever, is,  that,  in  acting  on  metallic  compounds,  and  on  certain  or- 
ganic acids,  it  abandons  an  atom  of  hydrogen,  and  the  remaining 
N.Hg  combines  with  the  metal,  or  with  the  radical  of  the  acid.  Thus, 
with  Hg.Cl.  and  N.Hg  there  result  Hg.N.H2  and  H.Cl.  j  with  Pt.Cl^ 
and  2N.H3  there  are  formed  Pt.  +  SN.H^  and  2H.C1. ;  from  Hg. .  N.O, 
and  N.H3  are  produced  Hg.N.Ha  and  H.N.Og.  Of  organic  bodies, 
oxalate  of  ammonia  gives,  when  heated,  C2O2  +  N.H2,  and  benzoate 
of  ammonia  produces  similarly  C,4H502  +  N.H2.  It  is  hence  evident 
that  the  third  atom  of  hydrogen  is  not  so  intimately  combined  with 
the  nitrogen  as  the  remaining  two ;  it  may  be  eliminated  by  the 
simplest  reactions,  but  the  N.  and  H2  remain  much  more  firmly 
united,  and  separate  only  when  the  constitution  of  the  ammonia  is 
totally  broken  up.  I  hence  concluded  that  the  N.H2  should  be  con- 
sidered as  the  radical  of  ammonia,  and  proposed  to  term  it  Amido- 
gene,  and  its  symbol  Ad.  The  ammonia  is  then  Jlmidide  of  Hydro- 
gen, and  its  rational  formula  N.H2H.  or  Ad.H.  Ammonia  is  thus 
assimilated  to  water,  and  to  chloride  of  hydrogen  in  constitution, 
the  radical  amidogene  having  the  closest  analogy  to  oxygen  and 
chlorine.  These  conclusions  have  been  almost  unanimously  adopt- 
ed by  chemists. 

These  views  are  remarkably  illustrated  by  the  action  of  ammonia 
on  potassium ;  when  this  metal  is  heated  in  the  dry  gas,  hydrogen 
is  disengaged,  and  a  fusible  olive-green  substance  is  obtained.  The 
quantity  of  hydrogen  evolved  is  the  same  as  that  which  the  metal 
should  evolve  from  water,  that  is,  one  atom,  and  the  olive  body  con- 
sists of  K.N.H2.  It  is  Amidide  of  Potassium.  When  put  into  water, 
potash  and  ammonia  are  produced,  K.Ad.  and  H.O.  giving  K.O.  and 
H.Ad.  When  this  olive  substance  is  heated  nearly  to  redness,  am- 
monia is  expelled  and  Jfitruret  of  Potassium  remains,  3K. .  N.H,  giv- 


COMPOUNDS     OF     AMIDOGENE.  ,  501 

ing  2N.H3  and  K3N.  The  phenomena  are  exactly  the  same  with 
sodium,  an  amidide  and  a  nitruret  of  sodium  being  thus  formed. 

In  describing  the  compounds  of  ammonia,  it  is  necessary  to  dis- 
tinguish those  in  which  ammonia  acts  simply  as  amidide  of  hydro- 
gen, resembling  in  its  functions  the  oxide  or  chloride  of  hydrogen, 
from  the  class  of  bodies  in  which  the  ammonia  is  associated  with 
water,  the  proper  salts  of  ammonia,  which,  as  already  noticed,  are 
isomorphous  with  those  of  potash.  I  shall  have  occasion  to  discuss 
the  theory  of  these  bodies  farther,  but  shall  first  describe  the  most 
important  members  of  the  former  class. 

Ammonia  and  Chlorine. — If  a  bottle  full  of  chlorine  gas  be  in- 
verted in  a  cup  containing  a  solution  of  sulphate  or  muriate  of  am- 
monia, it  is  gradually  absorbed,  and  a  heavy  yellow  liquid  collects 
in  globules  in  the  bottom  of  the  cup.  This  substance  must  be  treated 
with  the  utmost  caution ;  if  strongly  rubbed  or  struck,  or  if  it  be 
touched  with  any  creasy  body,  or  with  phosphorus,  it  explodes  with 
intense  violence  j  a  globule  as  large  as  a  pin-head,  on  being  exploded 
in  a  teacup,  shatters  it  to  pieces.  Almost  every  chemist  who  has 
examined  it  has  been  severely  hurt,  and  hence  its  composition  is 
not  yet  well  known.  Sir  Humphrey  Davy  found  that,  when  decom- 
posed over  mercury,  it  gives  nitrogen  and  chlorine  in  the  propor- 
tions by  volume  of  1:3,  and  hence  it  was  concluded  to  be  Chloride 
of  Azote^  N.CI3,  under  which  name  it  is  described  in  most  books.  It 
has  been  observed,  however,  that  traces  of  sal  ammoniac  are  formed 
when  it  is  decomposed ;  it  consequently  must  contain  hydrogen, 
and  it  may  probably  be  bichloride  of  Amidogene^  Ad.Cl2,  which,  when 
decomposed,  should  produce  N.  and  CI3,  besides  Ad.H. .  H.Cl. 

Iodine  and  Ammonia. — When  the  semi-fluid  compound  of  iodine 
and  ammonia  is  put  into  water,  it  is  decomposed  into  hydriodato 
of  ammonia,  and  a  brown  powder  which  is  usually  described  as  Io- 
dide of  Azote ^  N.I3.  This  substance  may  also  be  prepared  by  digest- 
ing iodine  in  water  of  ammonia,  the  iodine  gradually  changing  into 
the  brown  substance,  and  the  solution  containing  hydriodate  of  am- 
monia :  this  body  must  be  collected  on  filters  in  very  small  quantity, 
and  dried  merely  by  exposure  to  the  air  j  if  it  be  rubbed,  even  un- 
der Avater,  it  explodes  with  a  violent  detonation,  though  not  so  pow- 
erfully as  the  previous  body.  The  cloud  of  hydriodate  of  ammonia, 
formed  by  its  decomposition,  is  very  evident ;  it  therefore  contains 
hydrogen,  and  I  look  upon  it  as  a  hiniodide  of  Amidogene^  Ad.l2« 

A  corresponding  compound  containing  bromine  has  been  formed. 

By  the  action  of  ammonia  on  metallic  oxides,  a  numerous  class 
of  bodies  may  be  formed,  which  all  possess  more  or  less  violent 
detonating  properties  ;  they  all  contain  combined  water.  It  is  im- 
possible to  say,  positively,  whether  the  ammonia  exists  undecom- 
posed  in  tiiese  bodies  5  I  rather  think  it  does,  and  I  shall  hence 
term  them  ammoniurets. 

Ammoniuret  of  Silver. — This  is  the  most  violent  of  all  these  com- 
pounds :  it  is  prepared  by  digesting  recently-prepared  oxide  of  sil- 
ver in  water  of  ammonia,  or  by  dissolving  nitrate  of  silver  in  an  ex- 
cess of  water  of  ammonia,  and  precipitating  the  solution  by  caustic 
potash.  It  is  a  brown  powder,  which  detonates  violently  by  the 
slightest  shock  or  friction  j  when  exploded,  it  is  said  to  produce 


502  NITRURETS     AND     AMMONIURETS. 

water,  azote,  and  metallic  silver,  which  should  give  for  its  formula 
N.Ha+BAg.O.-f-Aq.  But  the  facility  of  its  decomposition,  which 
has  been  the  cause  of  many  serious  accidents,  has  prevented  it  be- 
ing accurately  analyzed. 

Ammoniuret  of  Gold^  Au.Oa-f-SAd.H.,  is  produced  by  the  action 
of  water  of  ammonia  on  peroxide  of  gold.  It  is  a  brown  powder, 
nearly  as  explosive  as  the  former  body,  but  it  has  been  accurately 
analyzed  by  Dumas.  These  bodies  are  known  as  Fulminating  Gold 
or  Silver. 

The  Ammoniuret  of  Platinum  is  formed  by  digesting  hydrated 
oxide  of  platinum  in  water  of  ammonia.  It  is  a  light-brown  powder, 
not  yet  analyzed,  and  quite  different  from  the  impure  substance 
described  in  books  as  Davy's  fulminating  platinum. 

I  have  examined  the  ammoniurets  of  Copper  aiui  Mercury  formed  by  digesting  the 
oxides  of  these  metals  in  water  of  ammonia :  the  first  is  blue,  the  second  yellow ; 
their  formulae  are  3Cu.O.+2Ad.H.+6  Aq.,  and  3Hg.O+Ad.H.+2  Aq.  They  de- 
tonate feebly  when  heated.  There  exist,  also,  compounds  of  ammonia  with  the  ox- 
ides of  uranium,  of  iron,  and  of  osmium,  which  have  not  been  accurately  examined. 

By  the  action  of  heat  on  some  metallic  compounds  of  ammonia,  true  nitrurets  of 
the  metals  have  been  obtained,  of  which  the  most  remarkable  are  those  of  copper 
and  mercury.  The  nitruret  of  Copper  was  formed  by  passing  ammonia  over  anhy- 
drous oxide  of  copper  at  a  temperature  of  480°  Fah. ;  water  is  evolved,  and  the 
nitrogen  and  copper  unite,  forming  a  black  powder,  which,  at  the  temperature  of 
540°,  is  decomposed,  with  the  evolution  of  a  red  light,  into  its  elements.  Its  formula 
appears  to  be  CueN.,  which  corresponds  to  the  suboxide  CU2O.,  as  w^hen  replacing 
oxygen  |  is  equivalent  to  O.  (see  p.  262)  and  CueN.— 3(Cu2+|).  Schrseter,  to  whom 
the  discovery  of  the  above  compound  is  due,  formed  also  a  7iitrurd  of  Chrome,  whose 
formula  is  not  quite  ascertained. 

Ammonia  is  absorbed  in  large  quantities  by  the  chlorides  of  phosphorus  and  of 
sulphur,  and  substances  produced  which  possess  singular  properties. 

Ammoniacal  Protochloride  of  Phosphorus,  P.Cl3+5Ad.H.,  is  obtained  by  exposing  the 
liquid  chloride  of  phosphorus  to  a  current  of  dry  ammonia.  It  forms  a  white  pow- 
der, which,  when  put  in  contact  with  water,  produces  sal  ammoniac,  and  an  insol- 
uble white  substance  that  has  not  been  analyzed;  the  reaction  is  probably  that 
S(C1.H. .  Ad.H.)  and  P.N2H3  result.  If  the  ammoniacal  protochloride  of  phosphorus 
be  calcined  without  access  of  air,  a  very  remarkable  body,  phosphwret  of  Azote,  the 
formula  of  which  is  P.Nz,  is  produced,  while  phosphorus,  hydrogen,  ammonia,  and 
sal  ammoniac  are  expelled.  The  phosphuret  of  azote  is  insoluble  in  water,  and  re- 
sists the  action  of  the  most  powerful  acids  and  alkalies.  The  composition  of  the 
ammoniacal  perchlorides  of  Phosphorus  is  not  quite  certain,  as  these  bodies  appear  to 
decompose  each  other.  The  formula  is  P.Cl5H-2Ad.H.  When  calcined  they  yield 
phosplmret  of  azote. 

Gaseous  ammonia  and  chloride  of  sulphur  combine  in  two  proportions,  according 
as  each  ingredient  is  in  excess.  The  formulae  of  these  bodies  are  S.Cl.-fAd.H.  and 
8.Cl.-|-2Ad.H.  The  former  is  a  brown  powder,  soluble  in  alcohol  and  ether ;  the 
latter  is  a  citron-yellow  powder.  They  are  remarkable  for  delivering  as  a  product 
of  their  decomposition,  by  water  or  by  heat,  the  sulphuret  of  Azote  (S3N.),  which  is  a 
volatile  yellow  powder,  decomposed  "by  the  prolonged  action  of  water  into  ammonia 
r;nd  hyposulphurous  acid,  2(S3N.)  and  6H.0.  giving  3S2O2  and  2Ad.H. 

When  chloride  of  sulphur  is  digested  with  water  of  ammonia,  a  brown  substance 
is  formed,  whose  composition  is  CI.S4  .  N3H6.  It  is  probably  formed  of  chloride  and 
amidide  of  sulphur,  S.Cl.-K3(S.Ad.) 

Ammoniacal  gas  is  absorbed  in  great  quantity  by  the  volatile  chlorides  of  boron, 
arsenic,  tin,  and  titanium.  The  compounds  formed  are  white  and  crystalline  ;  they 
are  decomposed  by  water,  and  the  solution  contains  sal  ammoniac,  and  the  metal 
or  the  boron,  in  combination  with  oxygen. 

There  are  few  metallic  salts  which  do  not  absorb  ammonia  when  exposed  to  a 
current  of  the  dry  gas;  but  certain  metals  are  specially  distinguished  by  the  charac- 
ter that  ammonia  added  to  their  solutions  produces  precipitates  which  either  contain 
ammonia  or  amidogene,  as  is  the  case  with  mercury,  palladium,  and  platinum,  or 
by  an  excess  of  the  ammonia  the  precipitate  is  redissolved,  and  soluble  compounds 
containing  ammonia  are  produced,  as  occurs  with  zinc,  copper,  nickel,  cobalt,  and 
also  palladium  and  platinum.     The  number  of  combinations  thus  formed  is  so  very 


AMMONIA-SALTS     OF     ZINC,    COPPER,     ETC.       503 

great  that  it  would  be  tedious  to  describe  all,  and  I  shall  hence  notice  only  such  aa 
possess  scientific  or  pharmaceutical  importance. 

1.  Ammonia-Salts^of  Zinc. 

Dry  sulphate  of  zinc  exposed  to  a  current  of  dry  ammonia  absorbs  it,  producing  a 
white  powder,  2(Zn.O.  .  S.03)+5Ad,H.,  which  dissolves  perfectly  in  water. 

If  water  of  ammonia  be  added  to  a  solution  of  chloride  of  zinc,  a  basic  chic  ride  is 
precipitated,  which  being  redissolved  by  an  excess  of  ammonia,  a  colourless  solu- 
tion js  obtained,  which  crystallizes  on  cooling.  According  to  the  proportion  of  am- 
monia in  excess,  I  have  found  that  one  or  other  of  two  compounds  may  be  formed, 
one  in  long  and  brilliant  prisms,  the  other  in  fine  pearly  tables.  The  latter  salt  con- 
sists of  Zn.Cl.+2Ad.H.+H.O.,  the  former  of  2(Zn.Cl.)+2Ad.H.+H.O.  In  these 
salts,  as  in  ail  such  as  are  produced  by  the  action  of  an  excess  of  ammonia  on  a 
metallic  salt,  I  consider  that  the  acid  exists  combined  with  ammonia,  and  not  with 
the  metallic  oxide,  in  which  they  differ  essentially  from  those  produced  by  the  di- 
rect absorption  of  ammonia  by  a  salt,  in  which  I  conceive  the  union  of  the  acid  and 
oxide  not  to  be  distuibed.  Hence  I  write  the  formula  of  the  tabular  ammonia-chloride 
of  Zinc  as  Ad.H.  .  H.Cl.+Ad.H.  .  Zn.O.  When  heated  it  gives  off  ammonia  and 
water,  and  a  white  powder,  Ad.H.  .  Zn.Cl.,  remains. 

By  the  action  of  an  excess  of  ammonia  on  a  solution  of  sulphate  of  zinc,  the  am- 
monia sulphate  of  Zinc  is  formed :  its  formula  is  Ad.H.  .  H.O.  .  S.Og+Ad.H.  .  Zn.O. 
It  crystallizes  in  short  prisms ;  when  heated  it  evolves  Ad.H,  .  H.O.,  and  a  wliite 
powder,  Ad.H.  .  Zn.O.  .  S.O3  remains.  In  crystals  it  contains  3  Aq.,  of  which  it 
loses  two  by  efilorescence,  and  the  third  by  a  moderate  heat. 

2.  Ammonia-Salts  of  Copper. 

Chloride  of  copper  absorbs  dry  ammonia,  forming  a  blue  compound,  Cu.Cl,-4-3Ad. 

H.,  soluble  in  water. 

When  ammonia  is  added  to  a  strong  and  hot  solution  of  chloride  of  copper,  until 
the  precipitate  which  first  forms  is  perfectly  redissolved,  a  deep  purple  liquor  is 
produced,  from  which  octohedral  crystals  are  deposited  on  cooling.  Their  for- 
mula is  Ad.H.  .  H.Cl.+Ad.H.  .  Cu.O.  When  heated,  these  crystals  evolve  am- 
monia and  water,  and  a  blue  powder,  Ad.H. .  H.Cl.,  remains,  which  is  totally  decom- 
posed by  a  strong  heat. 

Dry  sulphate  of  copper  exposed  to  a  current  of  dry  ammonia  forms  a  fine  purple 
powder,  whose  formula  is  2(Cu.O.  .  S.03)+5Ad.H. 

An  excess  of  ammonia  gives,  with  a  strong  solution  of  sulphate  of 
copper,  a  rich  purple  liquor,  from  which  the  ammoniucal  sulphate  of  Cop- 
per cr3^stallizes  on  cooling  in  large  right  rhombic  prisms,  u,  u\  with 
dihedral  summits,  ?",  i,  as  in  the  figure,  m  being  a  secondary  plane.  I 
consider  these  crystals,  however,  to  be  macles.  The  formula  of  this 
salt  is  Ad.H.  .  H.O.  .  S.Oa+Ad.H.  .  Cu.O.  When  heated,  it  gives  off 
ammonia  and  water,  and  a  green  powder,  Ad.H. .  Cu.O. .  S.O3,  remains. 

Under  the  name  of  cuprum  ammoniatum,  the  ammoniacal  sulphate  of  copper  is  em- 
ployed in  medicine.  It  is  then  prepared  by  rubbing  together  sulphate  of  copper  and 
carbonate  of  ammonia  in  a  mortar.  The  mass  becomes  pasty,  owing  to  the  water 
of  crystallization  of  the  sulphate  of  copper  becoming  free,  and  carbonic  acid  is  giv- 
en off.  The  purple  mass  which  results  is  soluble  in  water,  and  generally  contains 
carbonate  of  ammonia  in  excess. 

When  a  hot  and  strong  solution  of  nitrate  of  copper  is  decomposed  by  an  excess 
of  ammonia,  and  allowed  to  cool,  the  ammoniacal  nitrate  of  Copper  crystallizes  in 
rhombic  octohedrons  of  a  fine  purple  colour:  its  formula  is  Ad.H.  .  H.O.  .N.Os-H 
Cu.  Ad.  In  this  body  there  is  no  doubt  of  the  metal  being  combined  with  amidogene, 
and  not  the  oxide  with  ammonia ;  hence  probably  arises  its  remarkable  character 
of  deflagrating  violently  when  heated  until  it  begins  to  melt. 

The  iodide  and  fluoride  of  copper  produce  compounds  resembling  those  of  the 
chloride. 

3.  Ammonia-Salts  of  J^ickel  and  of  Cobalt. 

These  resemble  the  corresponding  salts  of  copper  so  perfectly,  that  it  is  sufficient 
to  refer  to  the  foregoing  for  their  properties ;  and  their  composition  is  obtained  bf 
substituting  Ni.  or  Co.  for  Cu.  in  the  formulae. 


504     AMMONIA-SALTS     OF     SILVER,    PALLADIUM,    ETC. 

4.  Ammonia-^ alts  of  Silver. 

The  chloride  of  silver  is  soluble  in  water  of  ammonia.  The  solution  gives  opaque 
white  rhombic  crystals,  which  exhale  ammonia  when  exposed  to  the  air,  and  leave 
chloride  of  silver. 

When  the  sulphate  or  the  nitrate  of  silver  is  treated  with  an  excess  of  water  of 
ammonia,  colourless  solutions  are  obtained,  which  yield  by  evaporation  double  salts, 
in  rhombic  prisms,  having  the  formulce  Ad.H. .  H.O. .  S.Oa+Ag.Ad,  and  Ad.H, .  H. 
O. .  N.Os+Ag.Ad.  In  both  salts  the  silver  is  combined  with  amidogene,  Chromate 
of  silver  and  ammonia  gives  a  similar  salt.  The  ammonia-nitrate  of  silver  is  employ- 
ed in  testing  for  arsenic  and  in  preparing  fulminating  silver.  A  remarkable  prop- 
erty of  it  is,  that  when  fused  it  evolves  ammonia  and  nitrogen,  and  metallic  silver 
remains  mixed  with  ordinary  nitrate  of  ammonia,  and  coats  the  sides  of  the  glass 
containing  it  with  a  brilliant  mirror  surface.  By  a  higher  temperature  the  nitrate 
of  ammonia  is  decomposed,  and  nitrous  oxide  evolved. 

5.  Ammonia-Salts  of  Palladium. 

This  metal  is  remarkable  for  giving  with  ammonia  two  series  of  salts,  of  which 
one  is  soluble  and  the  other  insoluble  in  water. 

When  ammonia  is  added  to  a  solution  of  protochloride  of  palladium,  a  flesh-col- 
oured precipitate  is  produced,  having  fhe  formula  Pd.Cl. .  Ad.H.  When  more  am- 
monia is  added,  it  dissolves,  and  from  the  solution  the  second  salt  crystallizes  in 
long  rectangular  prisms,  having  the  formula  Ad.H. .  H.Cl.-fPd.O. .  H.Ad.  By  a 
gentle  heat,  an  atom  of  water  is  given  off,  and  the  metal  exists  then  in  the  salt  as 
amidide.  If,  in  a  solution  of  this  salt,  the  excess  of  ammonia  be  neutralized  by  mu- 
riatic acid,  a  yellow  crystalline  precipitate  forms,  which  has  the  same  formula  as  the 
first  salt,  Pd.Cl.+H.Ad. 

With  solution  of  sulphate  of  palladium  and  water  of  ammonia,  a  precisely  similar 
series  of  salts  is  formed;  the  first  being  flesh-red,  Pd.O. .  S.Oa-l-H.Ad. ;  the  second 
salt  in  colourless  prisms,  Ad.H. .  H.O. .  S.Oa+Pd.O. .  H.Ad.,  and,  when  dried,  the 
last  member  becoming  Pd.Ad. ;  and  by  a  small  quantity  of  an  acid,  a  crystalline 
precipitate,  which  consists  also  of  Pd.O. .  S.Os+H.Ad, 

The  iodide  of  palladium  gives  similar  salts.  With  the  nitrate  no  other  than  the 
cokurless  crystalline  salt  can  be  obtained,  whose  form  is  thin  rhombic  plates.  Ad. 
H..H.O. .N.Os+Pd.Ad.  When  heated,  it  deflagrates  like  loose  gunpowder,  and 
leaves  behind  metallic  palladium  as  a  black  powder. 

In  the  red  and  yellow  insoluble  ammonia-salts  of  palladium,  although  the  experi- 
mental composition  is  the  same,  I  consider  that  an  important  difierence  of  constitu- 
tion exists.  The  red  salts  are  formed  by  adding  ammonia  to  a  simple  salt  of  the 
metal;  direct  union  then  occurs,  and  we  have,  for  example,  Pd.Cl.+H.Ad.  But 
when  we  form  the  yellow  salt  by  adding  an  acid  to  a  solution  of  the  soluble  ammo- 
nia-salt, I  conceive  that  the  acid  unites  directly  with  the  amidide  of  the  metal,  and 
thus  forms,  for  example,  Pd.Ad.+H.Cl.  The  yellow  ammonia-iodide,  Pd.Ad. -fH.L, 
gradually  changes  itself  b^ck  into  the  red  substance,  Pd.I,-f-H,Ad. 

6.  Ammonia-Salts  of  Mercury. 

From  the  great  influence  these  bodies  have  had  on  the  theory  of  ammonia,  and 
their  importance  in  pharmacy,  the  mercurial  compounds  containing  ammonia  de- 
serve more  detailed  notice  than  those  of  any  other  metal. 

A.  Action  of  Ammonia  on  the  Haloid  Salts  of  Mercury. 

When  corrosive  sublimate  is  heated  in  a  current  of  dry  ammoniacal  gas,  it  unites 
therewith,  forming  a  white  compound,  fusible  and  volatile,  having  the  composition 
2Hg.C1.4-H.Ad.  By  contact  with  water,  this  body  is  decomposed  into  sal  alem- 
broth  and  white  precipitate ;  the  former,  a  compound  of  sublimate  and  sal  ammo- 
niac,  dissolving,  and  the  latter,  whose  composition  will  be  next  studied,  separating 
as  a  whi:e  powder. 

If  we  add  to  a  cold  solution  of  corrosive  sublimate  a  very  slight  excess  of  ammo- 
nia, a  copious  white  precipitate  is  produced,  and  the  liquor  is  found  to  contain  exact- 
ly half  the  chlorine  of  the  sublimate  combined  with  hydrogen  and  ammonia  as  sal 
ammoniac ;  the  v/hite  powder,  which  had  been  known  to  the  early  chemists  as  White 
Precipitate  of  Mercury,  contains  all  the  mercury  and  the  remaining  half  of  the  chlo- 
rine of  the  sublimate.  It  was  supposed  to  contain,  also,  ammonia  and  oxygen,  but  I 
have  proved  that  it  contains  only  the  elements  of  amidogene  and  no  oxygen ;  that  its 


PRECIPITATES     OF     MERCURY.  505 

formula  is  Hg.Cl.+Hg.Ad.,  it  being  a  true  chloro-amidide  of  mercury.  The  theory 
of  its  formation  is  very  simple,  2Hg.Cl.  and  2H.Ad.  producing,  by  interchange  of 
the  elements  of  one  equivalent  of  each  body,  Hg.Cl.+Hg.iVd.,  which  precipitates, 
and  H.Cl.+H.Ad.,  which  remains  dissolved.  This  was  the  first  instance  in  which 
amidogene  was  discovered  to  be  combined  with  a  metal,  and  from  its  establishment, 
the  true  constitution  of  ammonia  was  first  recognised. 

W/iitc  Precipitate  is  insoluble  in  cold  water.  It  is  decomposed  by  boiling  water, 
two  atoms  of  which,  reacting  on  two  of  white  precipitate,  produce  sal  ammoniac, 
which  dissolves,  and  a  heavy  yellow  powder,  which  is  insoluble  in  water,  and  has 
the  formula  Hg.Cl.+2Hg.0.+Hg.Ad.  This  body  is  completely  analogous  to  the 
oxychloride  of  mercury,  Hg.Cl.+3Hg.O.,  from  which  it  may  be  prepared  by  the  ac- 
tion of  ammoniacal  gas,  the  third  atom  of  Hg.O.  and  H.Ad.  giving  Hg.Ad.  and 
H.O.,  which  is  expelled.  When  white  precipitate  is  heated  suddenly,  it  is  totally 
converted  into  calomel,  nitrogen,  and  ammonia,  but  by  careful  management  of  the 
heat,  sublimate  and  ammonia  are  given  ofi",  and  a  red  powder  remains,  which  is  a 
compound  of  chloride  and  nitruret  of  mercury,  Hg.Cl.+HgaN. ;  or,  rather,  as  the  ni- 
trogen here  replaces  oxygen,  and  has  hence  the  one  third  atomic  weight,  Hg.Cl.4- 
3Hg.j,  exactly  analogous  to  the  oxychloride  j  by  careful  management,  all  the  subli- 
mate may  be  expelled,  and  the  azoturd  of  Mercury,  Hg.f ,  is  obtained  as  a  brown  pow- 
der, which  detonates  with  great  violence  when  struck. 

The  white  precipitate  which  has  been  now  described  must  be  distinguished  from 
another  body  which  has  been  confounded  with  it  in  the  pharmacopoeias,  until  the 
difference  was  shown  by  Woehler's  observations  and  my  analysis.  This  second  or 
beta-white  precipitate  is  prepared  by  adding  caustic  potash  to  a  cold  solution  of  the 
double  salt  formed  by  corrosive  sublimate  and  sal  ammoniac.  It  may  also  be  form- 
ed by  boiling  alpha- white  precipitate  in  a  solution  of  sal  ammoniac.  It  has  a  crys- 
talline aspect,  and  is  not  decomposed  by  boiling  water ;  when  heated,  it  fuses,  and 
gives  off  ammonia  and  azote,  while  a  mixture  of  calomel,  sublimate,  and  sal  ammo- 
niac sublimes.  Its  formula  is  very  simple,  Hg.Cl.+H.Ad. ;  but  it  may  also  be  look- 
ed upOn  as  a  compound  of  alpha-white  precipitate  and  sal  ammoniac,  (Hg.Cl.-f- 
Hg.Ad.)+(H.Cl.+H.Ad.)=2(Hg.C].-t-H.Ad.). 

When  calomel  absorbs  dry  ammonia,  it  forms  a  dark  gray  powder,  which  is  2 
HgaCl.+H.Ad. ;  by  a  gentle  heat  all  ammonia  may  be  expelled,  and  the  calomel 
remains  quite  white. 

If  the  calomel  be,  however,  digested  in  water  of  ammonia,  one  half  of  its  chlorine 
is  converted  into  sal  ammoniac,  and  a  dark  gray  powder  results,  which  is  a  com- 
pound of  subchloride  and  subamidide  of  mercury,  Hg2Cl.-f  Hg2Ad.  This  body, 
which  I  have  termed  Black  Precipitate,  is  formed  by  a  similar  reaction  to  that  by 
which  alpha-white  precipitate  is  produced,  2Hg2Cl.  and  2H.Ad.  giving  Hg2Cl.-f- 
Hg2Ad.  and  H.Cl.-f-H.Ad.  By  several  chemists,  the  action  of  water  of  ammonia 
on  calomel  is  given  as  a  means  of  preparing  black  oxide  of  mercury,  which  is  quite 
incorrect.     The  compound  formed  contains  no  oxygen. 

The  action  of  the  bromides  of  mercury  with  ammonia  has  not  been  s&  minutely 
studied  as  that  of  the  chlorides ;  it  is  known,  however,  that  bromide  of  mercury  gives 
with  water  of  ammonia  a  white  precipitate,  consisting  of  bromide  and  amadide,  Hg, 
Br.+Hg.Ad.,  and  analogous  to  the  alpha- white  precipitate.  The  subbromide  of 
mercury  produces  with  water  of  ammonia  a  black  powder,  consisting  of  Hg2Br.-|- 
Hg2Ad. 

Iodide  of  mercury  dissolves  plentifully  in  hot  water  of  ammonia,  and  the  solution 
deposites,  on  cooling,  long  prisms  of  a  snow-white  colour,  which,  however,  rapidly 
exhale  ammonia  when  exposed  to  the  air,  and  leave  red  iodide  of  mercury  in  pseu- 
domorphous  crystals.    This  white  body  has  the  formula  SHg.I.-f-H.Ad. 

There  is  no  iodine  compound  analogous  to  alpha-white  precipitate ;  but  when  that 
substance  is  warmed  in  a  solution  of  iodide  of  potassium,  ammonia  is  evolved  and  a 
brown  powder  is  formed,  having  the  formula  Hg.I.-|-2Hg.0.-|- Hg.Ad. 

B.  Action  of  Ammonia  on  the  Oxygen  Salts  of  Mercury, 

Wlien  sulphate  of  mercury  is  digested  in  water  of  ammonia,  it  is  converted  into  a 
white  substance,  to  which  I  have  given  the  name  of  ammonia-turpeth.  It  is  not  act- 
ed on  by  water  nor  by  alkalies.  Its  formula  is  SHg.O.+S.Oa-l-Hg.Ad.  It  is  there- 
fore ordinary  turpeth  mineral  combined  with  amadide  of  mercury. 

When  water  of  ammonia  is  added  to  a  solution  of  nitrate  of  mercury,  being  cold 
and  not  in  excess,  a  white  precipitate  is  formed,  a  basic  ammonia-nitrate,  which  is 
found  to  consist  of  H.Ad.  .  N.05-4-3Hg.O.  It  is  therefore  a  basic  nitrate  of  mercu- 
ry, analogous  to  the  ordinary  basic  nitrate,  H.O.  .  N.05+3Hg.O.,  except  that  ant 

Sss 


506  AMMONIA-SALTS     OF     PLATINUM. 

monia  (amidide  of  hydrogen)  is  substituted  for  water  (oxide  of  hydrogen).  If  an  ex- 
cess of  ammonia  be  added,  and  the  mixture  boiled,  the  white  precipitate  becomes 
heavier  and  granular,  and  is  then  found  to  consist  of  Hg.Ad.  ,  N.Os+SHg.O.  This 
substance,  the  ^  basic  ammonia-nitrate,  is  evidently  analogous  to  the  former,  the  hy- 
drogen being  replaced  by  mercury,  and  it  corresponds  accurately  in  constitution  also 
to  the  ammonia-turpeth. 

If  either  of  these  basic  ammonia-nitrates  be  boiled  in  water  containing  much 
nitrate  of  ammonia,  they  dissolve  and  form  double  salts ;  that  usually  formed  is  in 
short  opaque  white  prisms,  having  the  very  simple  composition  4Hg.O.+3(H.Ad.  . 
H.O.  .  N.O5);  but  as  it  is  decomposed  by  water  into  the  /?  basic  ammonia-nitrate, 
its  formula  must  be  (Hg.Ad.  ,  N.05+3Hg.O.)+2(H.Ad. .  N.Os+SH.O.).  The  dou- 
ble salt,  which  forms  less  frequently,  is  in  yellow  plates,  and  has  the  formula  (Hg. 
Ad.  .  N.05+3Hg.O.)+(H.Ad.  .  N.O5 .  H.O.). 

These  double  salts  may  also  be  generated  by  boiling  oxide  of  mercury  in  solution 
of  nitrate  of  ammonia.  If  the  common  basic  nitrate  of  mercury  be  boiled  in  a  solu- 
tion of  nitrdte  of  ammonia,  this  is  decomposed ;  the  ammonia  being  employed  in 
forming  amidide  of  mercury,  and  the  nitric  acid  being  set  free,  as  may  be  recog- 
nised by  litmus. 

The  subsulphate  of  mercury,  Hg20.  .  S.O3,  acted  on  by  water  of  ammonia,  pro- 
duces a  black  powder,  the  formula  of  which  is  Hg20.  .  S.03+Hg2Ad. :  it  is  easily 
decomposed. 

By  acting  on  a  solution  of  subnitrate  of  mercur}'  in  water  with  ammonia  added 
dilute,  and  in  such  quantities  as  to  leave  a  portion  of  the  mercurial  salt  undecompo- 
sed,  a  fine  velvet  black  precipitate  is  obtained,  known  in  pharmacy  as  Hahnemann's 
solvJjle  Mercury.  It  is  very  easily  decomposed  by  heat  or  by  an  excess  of  ammonia. 
In  order  to  obtain  it  pure,  the  solution  should  be  quite  free  from  red  oxide,  and  not 
more  than  three  fourths  of  the  whole  quantity  of  mercury  should  he  precipitated. 
When  quite  pure,  I  have  found  its  formula  to  be  H.Ad.  .  N.Os+SHggO.,  it  being 
perfectly  analogous  to  the  common  basic  subnitrate  H.O.  .  N.054-2Hg20,,  the  ox- 
ide of  hydrogen  being  replaced  by  the  amidide. 

The  results  with  the  other  salts,  both  of  the  red  and  black  oxide  of  mercury,  are 
similar  to  those  above  described ;  but  as  none  of  them  are  specially  important,  I  shall 
not  occupy  space  with  their  description. 

7.  Ammonia-Salts  of  Platinum. 

When  protochloride  of  platinum  is  dissolved  in  muriatic  acid,  and  an  excess  ol 
ammonia  added,  a  green  precipitate  is  produced,  composed  of  Pt.Cl.-f-H.Ad.  It 
may  be  prepared  in  larger  quantity  by  passing  a  current  of  sulphurous  acid  gas 
through  a  solution  of  bichloride  of  platinum  until  it  assumes  a  deep  brown  colour, 
and  then  adding  ammonia.  By  boiling  this  green  substance  in  strong  water  of  am- 
monia, it  forms  a  white  powder,  the  formula  of  which  is  Pt.Cl.-f2H.Ad. 

The  action  of  amm.onia  on  a  solution  of  bichloride  of  platinum  is  very  complex ; 
it  gives  origin  to  a  series  of  bodies,  composed  of  bichloride,  binoxide,  and  binami- 
dide  of  platinum,  in  proportions  which  vary  with  the  temperature  and  proportions 
used.  The  ultimate  effect  is  the  formation  of  a  colourless  solution,  when  the  ammo- 
nia is  boiling  and  in  considerable  excess,  from  which  a  white  powder  separates  by 
cooling,  or  by  the  addition  of  alcohol.  This  powder,  which  consists  of  (Pt.Ck+Pt. 
Ad2)-f 3H.Ad.-f2  Aq.,  combines  with  acids,  and  generates  a  very  remarkable  series 
of  double  salts,  discovered  by  Gros,  who  formed  them  differently,  having  obtained 
the  nitric  acid  salt  by  heating  the  green  substance  Pt.Cl.+H.Ad.  with  nitric  acid, 
and  the  other  salts  by  double  decomposition.  Liebig  proposed  to  consider,  that  in 
these  salts  there  exists  a  compound  radical,  Pt.Cl. .  N2H6,  which  combines  with  chlo- 
rine and  with  oxygen,  and  the  oxide  of  which  unites  with  acids.  Thus  the  oxa- 
late contains  Pt.Cl.  .  N2H6O.+C2O3,  &c.  But  as  the  gradual  formation  of  this  sup- 
posed oxide  can  be  traced  from  the  bichloride  of  platinum,  we  must  admit  it  to  con- 
tain a  compound  of  bichloride  and  binamidide,  similar,  in  many  respects,  to  white 
precipitate,  and  we  must  look  upon  the  salts  formed  by  Gros  as  consisting  of  that 
compound  united  to  ordinary  ammoniacal  salts,  just  as  are  the  double  ammonia-ni- 
trates of  mercury. 

The  formulas  of  Gros's  salts  are  upon  my  view  : 

fPt.Cl2+Pt.Ad2)+2(H.O.  .  HAd.),  the  base  of  the  series. 
(Pt.C]2-|-PtAd2)-|-2(H.Cl.  .  H  Ad.),  the  muriatic  salt. 
(Pt.Cl2+PtAd2)+2(H.O.  .  N.O5 .  H  Ad.),  the  nitric  salt. 
(Pt.Cl24-PtAd2)-f  2(H.O.  .  S.O3 .  H.Ad.),  the  sulphuric  salt. 
(Pt.Cl2+Pt.Ad2)-j-2(H.O.  .  C2O3  .  H.Ad.),  the  oxalic  salt. 


AMMONIACAL    SALTS.  507 

The  action  of  ammonia  on  biniodide  of  platinum  is  more  simple ;  a  deep  red  pow- 
der is  formed,  which  has  the  formula  Pt.l2+Pt.Ad2+4  Aq. 

Our  knowledge  of  the  action  of  ammonia  on  the  oxygen  salts  of  platinum  is  yet 
too  inexact  to  justify  me  in  bringing  forward  here  the  statements  that  have  been 
made  concerning  the  results. 

By  the  action  of  ammonia  on  perchloride  of  gold,  an  olive-brown  powder  is  pro- 
duced, which  fulminates  when  rubbed.  It  is  decomposed  by  water,  and  its  real  for- 
mula has  not  yet  been  established. 

Products  of  the  Action  of  Jlmmonia  on  the  Anhydrous  Acids. 

When  chloro-sulphurous  acid,  S.O2CI.,  is  exposed  to  dry  ammonia,  it  is  converted 
into  a  white  saline  mass,  which  is  a  mixture  of  sal  ammoniac  and  sidph-amide,  S. 
O2CI.  and  2Ad.H.  giving  S.02Ad.  and  H.Cl+H.Ad.  The  former,  which  consists 
of  amidogene  united  to  sulphurous  acid,  is  soluble  in  water,  and  may  be  obtained 
crystallized,  but  when  boiled  with  water  it  is  changed  into  common  sulphate  of 
ammonia,  2H.0.  and  S.02Ad.  giving  S.Oa+Ad.H.  .  H.O. 

"When  dry  sulphurous  acid  and  ammonia  gases  are  mixed,  they  combine  to  form 
a  reddish  substance,  which  is  decomposed  by  water;  there  appear  to  be  two  propor- 
tions, giving  the  bodies  S.O2 .  H.Ad.  and  2S.O2  .  H.Ad. 

Dry  sulphuric  acid  unites  with  dry  ammonia  in  two  proportions,  forming  S.O3 .  H. 
Ad.  and  2S.O3  .  H.Ad.  I  consider  these  compounds  as  corresponding  to  the  English 
and  German  hydrates  of  sulphuric  acid,  the  ammonia  playing  the  part  of  water. 
A  solution  of  these  bodies  is  not  at  first  precipitated  by  barytes,  but  gradually  be- 
comes changed  into  ordinary  sulphate  of  ammonia. 

It  was  supposed  that  the  chloro-carbonic  acid,  C.O.Cl.,  combined  directly  with 
ammonia,  but  Regnault  has  found  that  decomposition  occurs,  and  that  sal  ammo- 
niac and  amidide  of  carbonic  oxide  result.  This  body,  which  he  terms  carb-amide^ 
C.O.Ad.,  is  white,  soluble  in  water,  is  not  deliquescent,  and  resists  the  action  of  al- 
kalies and  acids,  unless  they  be  very  concentrated. 

Of  the  Common  Ammoniacal  Salts. 

From  the  great  number  of  classes  of  compounds  described  in  the 
preceding  sections,  it  is  evident  that  ammonia  enters  into  combina- 
tion with  acids  and  with  bases,  with  haloid  and  with  oxygen  salts, 
in  such  manner  as  assimilates  it  fully  to  the  oxide  and  chloride  of 
hydrogen  in  its  action,  but  removes  it  totally  from  all  analogy  with 
the  alkalies,  to  which  it,  in  other  points  of  view,  strictly  belongs. 
For  the  ordinary  salts  of  ammonia,  of  which  the  description  now 
comes,  are  isomorphous  with  the  corresponding  salts  of  potash,  and 
the  strong  basic  characters  of  the  solution  of  ammonia  had  given  to 
it,  from  the  earliest  times,  the  name  of  the  Volatile^  or  the  Animal 
Alkali.  The  characteristic  distinction  is,  that  in  all  cases  where  it 
acts  as  an  alkali,  ammonia  is  associated  with  water  :  it  is  not  x'^.d.H., 
which  is  the  alkali,  but  Ad.H.  +  H.O.,  or,  rather,  N.H4O.,  the  ele- 
ment which  replaces  potassium  in  the  isomorphous  salts  being  sub- 
amidide  of  Hydrogen,  Ad.Hg,  or  N.H4. 

At  the  time  when  Mitscherlich  showed  the  isomorphism  of  the 
potash  and  ammonia  salts,  nothing  was  known  of  the  true  constitu- 
tion of  ammonia  or  of  amidogene  ;  and,  in  order  to  explain  the  ne- 
cessity of  the  presence  of  water,  a  very  ingenious  theory  was  pro- 
posed by  Berzelius  and  Ampere.  It  was,  to  consider  that  these 
ammoniacal  salts  do  not  contain  ammonia  at  all,  but  another  com- 
pound of  nitrogen  and  hydrogen,  N.H4,  which  is  metallic,  and  re- 
sembles potassium  in  all  general  characters,  and  for  which  the  name 
Ammonium  was  proposed.  This  view  squared  accurately  with  ex- 
periment, as  in  every  oxygen  salt  of  ammonia  there  is  just  so  much 
water  as  may  form  with  the  ammonia  Oxide  of  Ammonium,  N.H4 
O.  J  and  in  every  haloid  salt,  the  electro-negative  body  is  combined 


508 


AMMONIACAL     AMALGAM. 


with  as  much  hydrogen  as  may  convert  the  ammonia  into  the  com- 
pound metal;  thus  N.Hg .  H.O.  +  S.O3  and  N.H34-H.CI.  would  give 
N.H40.-fS.03  and  N.H4CI.  Not  merely  was  this  theory  conso- 
nant to  numbers,  but  experiment  gave  very  good  reason  to  believe 
in  the  real  existence  of  this  compound  metal,  by  the  remarkable 
properties  of  the  ammoniacal  amalgam. 

When  a  globule  of  mercury,  immersed  in  water  of  ammonia,  is 
made  the  negative  pole  of  a  galvanic  battery,  it  increases  fifty  times 
in  volume,  becomes  semi-fluid  and  covered  with  warty  excrescen- 
ces, and  finally  becomes  so  light  as  to  float  on  water.  No  hydro- 
gen is  evolved  from  its  surface,  but  oxygen  is  copiously  given  off 
from  the  positive  electrode.  If  the  current  be  interrupted,  a  copi- 
ous disengagement  of  hydrogen  occurs  from  this  metallic  sponge, 
which  also  gives  off  ammonia,  and  it  soon  falls  back  to  its  original 
appearance.  By  cold,  this  decomposition  may  be  retarded  ;  the 
pasty  mass  may  be  removed  from  the  liquor,  and  is  found  to  crys- 
tallize in  cubes  at  a  cold  of  0^  ;  and  if  decomposed  when  dry  over 
mercury,  it  evolves  ammonia  and  hydrogen,  by  volume  in  the  pro- 
portion of  2  :  1.  This  indicates  that  the  mercury  is  therein  com- 
bined with  a  body  which  consists  of  N.H4,  and  as  the  mercury  re- 
tains its  lustre,  the  compound  formed  is  properly  an  alloy,  and  the 
body  N.H4  is  of  a  metallic  nature.  It  may  be  the  metal  Ammonium^ 
almost  perfectly  isolated.  All  these  phenomena  may  be  observed 
by  dissolving  one  grain  of  potassium  in  100  grains  of  mercury,  and 
dropping  the  globule  into  a  glass  containing  strong  solution  of  sal 
ammoniac.  By  the  action  of  K.Hg.  on  N.H4CI.,  there  are  pro- 
duced K.Cl.  and  Hg.N.H4 ;  the  globule  of  mercury  swells  up  rapid- 
ly, and  the  amalgam  is  sufficiently  permanent  to  be  easily  examined. 

I  have  no  doubt  there  is  thus  obtained  a  substance  possessing 
some  metallic  characters,  and  consisting  of  ammonia  and  hydrogen  ; 
in  fact,  subamidide  of  Hydrogen,  Ad.Ha ;  but  whether  the  water  which 
is  found  in  the  common  ammoniacal  salts  exists  therein  as  such,  or 
whether  these  salts  contain  true  oxide  of  ammonium,  is  not  thus 
decided.  In  fact,  among  the  metallic  compounds  of  ammonia  al- 
ready examined,  we  have  found  bodies  every  way  similar  to  the 
ordinary  salts  of  ammonia,  except  that  a  part  of  the  hydrogen  is 
replaced  by  a  metal.  Thus,  if  Ave^ compare  sal  ammoniac  with  other 
similar  bodies,  as  in  the  following  formulae, 

1.  CI.N.H4,  5.  Cl.N..H3Ni., 

2.  Cl.N. .  H3CU.,  6.  Cl.N. .  HaHg., 

3.  Cl.N. .  HaZn.,  7.  Cl.N. .  H^Hg^, 

4.  Cl.N. .  HaPd.,  8.  Cl.N. .  HaPt^, 

and  find  them  all  produced  by  the  action  of  ammonia  on  a  chloride 
of  a  metal,  just  as  sal  ammoniac  is  formed  by  the  action  of  am- 
monia on  chloride  of  hydrogen,  we  must  admit  their  similarity  of 
constitution  j  and  if  we  say  that  in  No.  1,  N.H4  forms  a  compound 
metal,  we  must  consider  all  the  others  as  chlorides  of  compound 
radicals  also.  Still  more,  the  connexion  is  so  perfect  from  these 
bodies  to  such  as  resemble  the  yellow  powder,  Hg.Cl.-f-2Hg.0.-f 
Hg.Ad.,  and  from  that  to  the  oxychloride,  Hg.Cl.  +  3Hg.O.,  that  if 
we  insist  on  assuming  the  compound  metal  ammonium  to  exist 
ready  formed  in  the  salts  of  ammonia,  we  must  lay  down  as  a  gen- 


MANUFACTURE     OF     SAL     AMMONIAC.  509 

eral  principle  that  all  basic  salts  are  salts  of  compound  metals, 
which  could  not  be  tolerated  in  an  exact  science  for  a  moment.  At 
the  same  time,  therefore,  that  I  consider  the  ammoniacal  amalgam 
to  contain  ammonium,  I  believe  it  to  be  formed  only  at  the  time, 
and  that  the  ordinary  salts  of  ammonia  contain  ammonia  and  water, 
the  latter  being  united  as  the  constitutional  water  is  in  the  magne- 
sian  sulphates,  but  more  intimately.  Thus,  sulphate  of  ammonia, 
S.Oa+Ad.H.  .H.O.,  I  consider  to  resemble  the  bihydrated  sulphuric 
acid,  S.Og+H.O. .  H.O.  In  both  cases  an  atom  of  water  may  be  re- 
placed by  an  oxide  of  the  magnesian  class. 

It  will  be  necessary  only  to  notice  the  more  important  of  the  or- 
dinary salts  of  ammonia. 

Muriate  of  Ammonia.  Sal  Ammoniac. — Cl.HaAd.  Eq.  666*8  or  53*5. 
This  salt,  formerly  derived  from  Africa,  is  now  manufactured  on 
the  large  scale  from  the  ammoniacal  liquor  obtained  in  the  destruc- 
tive distillation  of  horns,  bones,  coals,  and  such  other  organic  mat- 
ters as  contain  nitrogen.  Those  liquors  which  contain  ammonia, 
combined  principally  with  carbonic  acid  and  sulphuretted  hydrogen, 
are  decomposed  by  means  of  muriatic  acid  added  in  slight  excess. 
By  evaporation  to  a  pellicle  and  cooling,  the  sal  ammoniac  is  obtain- 
ed in  small  crystals,  deeply  coloured  with  tarry  matter.  They  are 
purified  by  re-crystallization,  and  finally  placed  in  cast  iron  pots, 
set  in  a  furnace,  lined  with  fire-tiles,  and  fitted  with  leaden  heads, 
into  which  the  sal  ammoniac  is  sublimed.  The  temperature  is  so 
managed  that  the  sublimed  salt  forms  a  coherent,  hemispherical 
mass,  often  weighing  100  lbs.,  and  when  pure  should  be  perfectly 
free  from  yellow  stains,  and  nearly  transparent.  If  muriatic  acid 
be  dear,  the  ammoniacal  liquor  may  be  neutralized  by  sulphuric 
acid  ;  sulphate  of  ammonia  is  formed,  which  is  decomposed  by  the 
addition  of  common  salt,  and  the  sulphate  of  soda  and  sal  ammo- 
niac separated  by  crystallization. 

Sal  ammoniac  is  very  soluble  in  water ;  it  crystallizes  both  by 
sublimation  and  solution,  in  cubes  and  octohedrons ;  it  is  slightly 
deliquescent,  and  is  soluble  in  alcohol ;  it  volatilizes  below  a  red 
heat.  When  heated  with  lime  or  potash,  it  yields  ammonia,  as  de- 
scribed in  p.  499.  It  consists  of  an  equivalent  of  each  element,  its 
formula  being  H.Cl.  .  H.Ad.  It  may  be  formed  by  their  direct  com- 
bination. When  equal  volumes  of  dry  muriatic  acid  gas  and  am- 
monia are  mixed  together,  the  two  gases  disappear,  and  a  snow- 
white  powder  of  sal  ammoniac  results.  Hence  arise  the  white 
fumes  when  a  rod  dipped  in  water  of  ammonia  is  brought  where 
cblorine  or  muriatic  acid  gas  is  evolved,  or  when  a  rod  dipped  in 
muriatic  acid  is  brought  to  where  ammonia  is  escaping.  It  thus 
renders  these  bodies  the  means  of  detecting  each  other. 

Sal  ammoniac  is  remarkable  for  the  number  of  double  salts  which  it  produces, 
and  of  which  some  deserve  notice. 

With  chloride  of  magnesium,  it  forms  the  anhydrous  salt  Ad.H2Cl.+Mg.Cl., 
which  is  used  in  preparing  metallic  magnesium. 

With  perchloride  of  iron,  it  crystallizes  in  fine  red  octohedrons,  Fe2Cl3+3('Ad.Ha 
CL).  When  these  are  heated,  sal  ammoniac  sublimes,  coloured  by  some  cnloride 
of  iron,  and  forms  thus  the  Flvres  Martiales. 

The  double  salts  formed  with  the  chlorides  of  copper,  zinc,  and  nickel,  crystallize 
in  cubes.  They  are  all  composed  like  that  of  copper,  which  is  Cu.Cl.-l-Ad.HaCL-f 
8Aq. 


510         HYDROSULPHURET,     ETC.,     OF     AMMONIA. 

Corrosive  sublimate  unites  in  two  proportions  with  sal  ammoniac.  The  first  salt, 
of  which  the  formula  is  Hg.Cl.+Ad.H2Cl.+Aq.,  is  very  soluble  in  water,  and  crys- 
tallizes in  flat  rhomboidal  tables,  which  effloresce  when  exposed  to  the  air.  This  is 
the  Sal  Alembroth  of  the  older  chemists.     The  second  salt  crystallizes  in  rhomboidal 

Erisms,  which  sublime  unchanged,  and  have  the  formula  2Hg.Cl.+Ad.H2Cl.  It  is 
y  the  formation  of  these  salts  that  corrosive  sublimate  becomes  so  easily  soluble  in 
a  solution  of  sal  ammoniac. 

Sal  ammoniac  and  bichloride  of  platinum  form  a  double  salt,  whose  formula  is 
Pt.Cl2+Ad.H2Cl.  It  precipitates  as  a  bright  yellow  powder  when  solutions  of  iU 
constituents  are  mixed,  and  especially  if  alcohol  be  added,  in  which  it  is  quite  in- 
soluble. It  is  but  very  sparingly  soluble  in  water,  but  more  so  in  boiling  water,  from 
which  it  crystallizes  in  orange-red  octohedrons.  When  ignited,  it  leaves  behind 
metallic  platinum  in  the  form  of  a  light  sponge.  It  is  of  use  in  preparing  spongy 
platina,  and  in  the  detection  of  ammonia. 

With  chloride  of  gold,  sal  ammoniac  forms  a  double  salt,  which  crystallines  in 
orange-red  cubes,  having  the  formula  Au.Cls-f  Ad.H2Cl.-f-2  Aq. 

The  hydrobromate  and  hydriodate  of  ammonia  do  not  require  notice.  They  re- 
semble the  sal  ammoniac  in  all  important  characters,  and  combine  with  the  metal- 
lic bromides  and  iodides  to  form  similar  double  salts. 

Hydrosulphuret  of  Ammonia. — When  sulphuretted  hydrogen  and 
ammonia  gases  are  mixed  in  equal  volumes,  in  a  vessel  cooled  by 
ice,  they  combine,  forming  colourless  needles,  which  evaporate  at 
ordina'^y  temperatures.  The  formula  of  this  compound  is  S.H.  +  H. 
Ad.,  or  S.N.H4,  analogous  to  protosulphuret  of  potassium,  S.K.  Like 
that,  it  combines  with  as  much  more  sulphuret  of  hydrogen,  forming 
a  volatile  crystalline  compound,  Ad.HgS.-f-H.S.  This  hihydrosul^ 
phuret  of  Ammonia  is  formed  also  when  sulphuretted  hydrogen  is 
passed  into  water  of  ammonia,  as  long  as  it  is  absorbed.  For  each 
atom  of  ammonia  present,  two  atoms  of  sulphuretted  hydrogen  are 
taken  up.  By  exposure  to  the  air,  this  solution  becomes  yellow, 
owing  to  the  absorption  of  oxygen  and  the  liberation  of  sulphur.  It 
is  capable  of  dissolving  a  large  quantity  of  sulphur,  forming  com- 
pounds analogous  to  the  higher  sulphurets  of  potassium.  This  hy- 
drosulphuret of  ammonia  is  of  great  importance  in  the  detection  of 
the  metals,  from  the  formation  of  metallic  sulphurets.  It  is  a  sul- 
phur base,  and  forms  salts  with  the  sulphur  acids,  analogous  to  those 
formed  by  sulphuret  of  potassium. 

Sulphate  of  Ammonia. — Ad.Hg .  O.S.Og-f  Aq.  This  salt  is  formed 
on  the  large  scale  in  the  manufacture  of  sal  ammoniac  ]  it  may  be 
prepared  pure  by  neutralizing  water  of  ammonia  by  sulphuric  acid  j  it 

t  crystallizes  in  flat  rhomboidal  prisms,  as  in  the  figure,  or  in 
macles,  isomorphous  with  the  crystals  of  sulphate  of  pot- 
ash. It  is  very  soluble  in  water,  but  insoluble  in  alcohol ; 
when  heated,  it  gives  off  water,  ammonia,  and  azote,  and 
sulphite  of  ammonia  sublimes.  It  combines  with  the  sul- 
phates of  copper,  zinc,  iron,  alumina,  &c.,  forming  double  salts  ex- 
actly analogous  to  those  formed  by  sulphate  of  potash.  With  oil 
of  vitriol  it  unites  to  form  bisulphate  of  Ammonia,  which  is  deliques- 
cent and  soluble  in  alcohol. 

Kitratt  of  Ammonia,  Ad.HaO. .  N.O5,  is  formed  by  neutralizing  ni- 
tric acid  by  ammonia.  It  crystallizes  in  striated  hexagonal  prisms, 
isomorphous  with  nitre,  of  a  bitter  saline  taste  ;  they  are  deliques- 
cent and  very  soluble  in  water.  When  heated,  they  fuse  at  230°, 
and  at  about  460^  are  rapidly  decomposed  into  nitrous  oxide  and 
water,  as  described  p.  2.72.  By  the  presence  of  a  large  excess  oi 
sulphuric  acid,  this  action  takes  place  at  much  lower  temperatures. 


PHOSPHATES     OP     AMMONIA.  511 

When  heated  with  combustible  bodies,  it  deflagrates  with  extreme 
violence. 

Phosjihates  of  Ammonia. — The  tribasic  phosphoric  acid  forms  with 
ammonia  two  salts;  the  first,  whose  formula  is  (P.O^+Ad.HaO.-f 
H.O.)-{-Aq.,  is  prepared  by  adding  the  acid  in  excess  to  water  of 
tmmonia  j  it  crystallizes  in  rhombic  prisms,  which  are  very  soluble 
'n  water.  Their  reaction  to  test-paper  is  strongly  acid.  If  the  amr 
monia  be  added  in  excess,  a  salt  crystallizes,  possessing  nearly  the 
isame  characters,  except  that  its  reaction  is  alkaline,  and  its  formula 
P.03-]-2(Ad.H20.)-l-H.O.  Both  of  these  salts  yield,  by  ignition, 
phosphoric  acid. 

AmmoniacO'Magnesian  Phosphate. — When  a  solution  of  a  salt  of 
•magnesia  is  added  to  any  soluble  phosphate,  and  the  liquor  rendered 
alkaline  by  ammonia,  a  crystalline  precipitate  is  formed,  which  is 
soluble  in  acids,  sparingly  soluble  in  water,  but  insoluble  in  alkaline 
.iquors.  Its  formula  is  P.05-|-(Ad.H,0.-|-2Mg.O.)  + 12  Aq.  Its 
formation  is  often  of  use  for  the  detection  of  magnesia,  and  it  is 
occasionally  generated  in  urine  by  the  action  of  ammonia,  produced 
oy  the  spontaneous  decomposition  of  urea  upon  the  soluble  phos- 
phates of  magnesia  which  it  contains.  It  then  constitutes  a  com- 
mon variety  of  calculus. 

Phosphate  of  Ammonia  and  Soda. — This  salt,  of  which  the  formula 
IS  P.0,+(Ad.H,0.  +  Na.0.+H.0.)-{-8  Aq.,  is  easily  produced  by 
mixing  together,  in  solution,  six  parts  of  common  phosphate  of  soda 
and  one  of  sal  ammoniac.  On  cooling,  it  crystallizes  in  large  prisms, 
which  effloresce  in  the  air.  When  heated,  it  gives  monobasic  phos- 
phate of  soda  and  free  phosphoric  acid,  as  a  source  of  which  it  is 
much  used  in  blowpipe  experiments,  under  the  name  of  Microcosmic 
Salt.     It  is  found  in  all  the  animal  fluids. 

Carbonates  of  Ammonia. — The  salt  which, under  this  name,is  used 
for  medicinal  purposes,  is  prepared  by  mixing  together  one  part  of 
sal  ammoniac  with  two  of  powdered  chalk,  and  exposing  the  mixture 
in  an  earthen  pot  to  a  heat  below  redness.  These  bodies  reacting, 
produce  chloride  of  calcium  and  carbonate  of  ammonia,  which  sub- 
limes, and  is  condensed  as  a  crystalline  semi-transparent  mass,  in  a 
dome-shaped  receiver,  which  is  fastened  on  the  subliming  pot.  By 
right,  this  should  be  a  neutral  salt,  Ad.H^Cl.  and  Ca.O. .  C.Og  giving 
Ca.Cl.  and  Ad.H^O. .  C.O^ ;  but  a  quantity  of  ammonia  and  water  is 
given  off",  and  the  sublimed  salt  was  considered  to  be  a  sesquicarbon- 
ate,  consisting  of  2(Ad.H20.)-f-3C.02,  until  Scanlan  showed  that 
it  was  a  mixture  of  two  different  salts,  which  may  be  separated  by 
water.  Rose  has  recently  thoroughly  examined  the  carbonates  of 
ammonia,  of  which  there  are  a  great  number,  but  only  four  sufficient- 
ly important  to  be  noticed  here. 

The  proper  neutral  carbonate  of  ammonia,  Ad.H20.  .  CO.,  does 
not  exist  except  in  combination,  but  its  compounds  are  very  nu 
merous  5  it  forms, 

1st.  With  carbonate  of  water,  the  ordinary  bicarbonate  of  Ammonia^ 
Ad.H.O. .  C.O.4-H.O.  .  C.O2.  This  is  prepared  by  washing  the  com- 
mercial sesquicarbonate  with  cold  water  or  alcohol,  when  it  remains 
behind  as  a  skeleton  of  crystalline  grains,  which  are  isomorphous 
with  bicarbonate  of  potash.     It  evaporates   spontaneously,  with  a 


512   CARBONATES  AND  OXALATES  OF  AMMONIA. 

weak  odour  of  ammonia.  Its  solution  reacts  feebly  alkaline.  By 
pouring  on  the  commercial  sesquicarbonate  as  much  boiling  water 
as  dissolves  it,  and  letting  the  solution  cool  in  a  close  bottle,  so  that 
no  carbonic  acid  can  escape,  this  salt  may  be  obtained  in  large  rhom- 
boidal  crystals,  which  contain  one  and  a  half  atoms  of  water. 

2d.  The  substance  which  is  dissolved  out  of  the  sublimed  mass 
of  sesquicarbonate  by  alcohol  is  identical  with  that  formed  by  the 
union  of  dry  carbonic  acid  and  ammonia.     Its  formula  is  therefore 
Ad.H.  .  C.O2,  and  the  ordinary  sesquicarbonate  is  a  mechanical  mix 
ture  of  it  with  the  bicarbonate. 

When  the  sublimed  sesquicarbonate  is  distilled  at  a  moderate 
heat  in  a  retort,  it  abandons  carbonic  acid,  and  two  salts,  differing 
in  volatility,  are  condensed  in  the  neck.  The  more  volatile  consists 
of  Ad.HaO. .  C.Oa+H.Ad. .  C.O2,  being  a  compound  of  neutral  carbo- 
nate with  dry  carbonate,  or  a  bicarbonate  in  which  the  basic  oxide  of 
hydrogen  is  replaced  by  amidide  of  hydrogen,  the  two  double  salts, 

Ad.HaO. .  C.Oa-f-H.O.  .  C.O2,  water-bicarbonate  of  ammonia, 
Ad.HaO. .  C.O^+H.Ad. .  C.O2,  ammonia-bicarbonate  of  ammonia, 

being  precisely  equivalent  in  composition.  The  less  volatile  product 
is  of  very  complex  composition  j  its  formula  is  4(Ad.H20.)-j-5C.02, 
or  it  consists  of  an  atom  of  neutral  carbonate  united  to  an  atom  of 
each  of  the  different  bicarbonates,  thus : 

Ad.H20. .  C.O2  ) 

Ad.H20. .  C.O2+H.O.  .  C.O2  >  =4(Ad.H20.)  +  5C.02. 

Ad.H20. .  C.02+H.Ad.Co2     ) 

Oxalate  of  Ammonia,  Ad.H20.  .  C2O3,  may  be  prepared  by  neutral- 
izing oxalic  acid  by  water  of  ammonia ;  it  crystallizes  in 
right  rhombic  prisms,  as  in  the  figure,  where  p,  w,  u  are 
primary,  and  i,  t  secondary  planes.  These  crystals  con- 
tain an  atom  of  water,  which  they  lose  by  efflorescence 
in  dry  air.  When  heated,  it  is  completely  decomposed, 
water  being  evolved,  and  oxamide  subliming,  Ad.H^O. .  C^ 
O3  producing  2H.0.  and  Ad. 0202-  This  neutral  oxalate  of  ammonia 
combines  with  oxalic  acid,  forming  a  binoxalate  and  a  quadroxalate 
like  those  of  potash. 

The  oxamide  may  also  be  prepared  by  acting  on  oxalic  ether  with 
water  of  ammonia,  or  by  dissolving  oxalic  acid  in  a  mixture  of  equal 
volumes  of  oil  of  vitriol  and  alcohol,  and  adding  ammonia  in  excess. 
It  is  a  light  white  powder,  tasteless  and  insoluble  in  water  ;  it  is  de- 
composed by  acids  and  by  strong  bases,  in  contact  with  water,  ox- 
alic acid  and  ammonia  being  regenerated.  Its  discovery  by  Dumas 
laid  the  foundation  of  our  present  knowledge  of  the  nature  of  am- 
monia, by  leading  him  to  the  idea  of  the  probable  existence  of  ami- 
dogene. 


PREPARATION     OF     CYANOGEN.  513 


CHAPTER  XIX. 

OF   CYANOGEN  AND   ITS  COMPOUNDS,  AND  OF  THE  BODIES  DERIVED  FROM  IT. 

There  is  no  class  of  organic  bodies  of  which  our  knowledge  is 
more  extensive  and  exact,  than  those  which  have  cj'^anogen  as  their 
basis.  The  powerful  affinities  which  this  radical  exerts,  the  simpli- 
city of  its  constitution,  and,  above  all,  our  being  able  to  prepare  it 
in  an  isolated  form,  and  to  generate  its  compounds  directly  from  it, 
as  we  could  those  of  a  truly  simple  body,  render  its  history  the  most 
advanced  portion  of  organic  chemistry,  and  that  to  which  the  anal- 
ogy of  mineral  bodies  and  the  theory  of  compound  radicals  is  most 
undeniably  applicable. 

Cyanogen  does  not  exist  in  nature  ready  formed  j  the  kernels  of 
peaches,  plums,  bitter  almonds,  &c.,  and  the  leaves  of  the  cherry- 
laurel,  yield,  by  simple  distillation,  abundance  of  prussic  acid  (cy- 
anide of  hydrogen),  but  this  is  only  then  produced  by  the  decompo- 
sition of  other  substances  containing  nitrogen. 

Cyanogen  may,  however,  be  formed  abundantly,  and  in  a  simple 
manner,  by  bringing  its  elements  together  at  a  high  temperature,  in 
contact  with  substances  with  which  it  may  unite.  Thus,  when  any 
organic  substance  containing  nitrogen  is  calcined  with  potash,  the 
nascent  carbon  and  nitrogen  unite,  and  cyanide  of  potassium  is 
formed  ;  even  with  pure  charcoal  this  occurs,  nitrogen  being  derived 
from  the  air ;  and  Mr.  Fownes  has  shown,  that  when  a  mixture  of 
pure  charcoal  and  potash  is  ignited  in  a  tube,  and  a  current  of 
pure  nitrogen  passed  through  it,  this  is  absorbed,  and  carbonic  oxide 
gas  being  given  off,  cyanide  of  potassium  is  produced,  3C.  with  K.O. 
and  N.  giving  CO.  and  C^N.K.  By  the  action  of  ammonia,  also,  on 
ignited  charcoal,  cyanogen  is  formed  in  abundance  ;  it  combines 
with  hydrogen  and  the  excess  of  ammonia,  and  produces  prussiate 
of  ammonia.  In  this  case  2C.  and  2N.H3  produce  C^H.+N.Hj,  and 
H2  become  free.  It  is  by  virtue  of  these  processes  that  cyanogen 
is  produced  for  its  various  applications  in  the  arts  j  but,  as  I  shdl  re- 
turn to  them  in  detail,  l  shall  now  only  consider  farther  the  mode 
of  obtaining  it  free  and  pure. 

Cyanide  of  silver,  or  cyanide  of  mercury,  of  which  the  prepara- 
tion will  be  described  hereafter,  is  to  be  introduced  into  a  small 
glass  retort,  and  heated  to  just  below  redness ;  a  gas  is  given  off, 
which  must  be  collected  over  the  mercurial  trough ;  the  cyanide  of 
silver  separates  simply  into  metal  and  cyanogen  ;  but  when  cyanide 
of  mercury  is  used,  a  brown  powder  appears,  the  quantity  of  which 
is  less  as  the  temperature  of  decomposition  has  been  lower.  The 
gas  which  comes  over  is,  however,  cyanogen  completely  pure. 

Its  properties  are  very  marked.  It  is  colourless,  of  a  sharp  smell, 
which  irritates  the  eyes.  Its  sp.  gr.  is  1819.  If  a  quantity  of  cya- 
nide of  silver  be  sealed  up  in  a  strong  tube,  bent  as  in  the  figure, 
and  then  heated  at  one  end,  a,  the  cyanogen  is  condensed  by  apress- 

Ttt 


514  CYANIC     ACID. 

ure  of  about  four  atmospheres,  and 
^  collects  at  the  other  end,  b,  as  a  col- 
ourless liquid.  It  is  combustible, 
burning  with  a  beautiful  rose-colour- 
ed flame,  and  producing-  two  volumes  of  carbonic  acid  and  one  of 
nitrogen.  It  is  constituted,  therefore,  of  equal  volumes  of  carbon 
vapour  and  nitrogen,  the  two  volumes  being  condensed  to  one  j 
hence  843  +  976  =  1819  is  its  sp.  gr.  It  dissolves  abundantly  in  al- 
cohol and  water,  but  these  solutions  soon  undergo  very  complex 
decompositions,  the  liquor  being  found  to  contain  carbonic  acid, 
prussic  acid,  ammonia,  urea,  and  oxalic  acid,  besides  a  brown  in- 
soluble matter.'  A  similar  decomposition  is  produced  much  more 
rapidly  by  contact  with  water  of  ammonia.  The  composition  of 
this  brown  matter  appears  to  be  C4N2 .  H.O.  It  dissolves  in  alkalies, 
and  gives  precipitates  with  the  metallic  salts ;  it  has  been  termed 
hence  Azulmic  Jicid.  When  heated,  it  gives  off  water,  and  leaves  a 
deep  brown  powder,  of  the  same  composition  as  cyanogen,  and 
which  has  been  termed  Paracyanogen.  This  may  be  also  formed  by 
heating  cyanide  of  mercury  very  strongly.  It  dissolves  in  hot  ni- 
tric acid,  and  the  solution  gives,  with  water,  a  yellow  precipitate, 
which  combines  with  bases,  and  has  been  termed  Paracyanic  Acid. 
By  strong  ignition,  paracyanogen  evolves  nitrogen,  and  a  very  dense 
carbon  remains. 

Cyanogen  combines  directly  with  hydrogen  and  with  the  metals, 
but  its  oxygen  combinations  require  to  be  indirectly  formed ;  there 
ate  three  compounds  of  cyanogen  and  oxygen,  which  are  all  acids, 
and  are  polymeric  bodies.  It  unites  also  with  sulphur,  and  its  com- 
pounds have  a  remarkable  tendency  to  form  double  and  triple  com- 
binations. 

The  formula  of  cyanogen  is  indifferently  written  CgN.  or  Cy.  Its 
equivalent  number  is  328*6  or  26-05. 

SECTION  I. 

NON-METALLIC    COMPOUNDS    OF    CYANOGEN. 

Compounds  of  Cyanogen  and  Oxygen. 

Cyanic  Acid — Cy.O. ;  Eq.  428*6  or  34*05 — is  very  easily  obtained 
in  combination,  by  calcining  the  cyanide  of  potassium  in  contact 
Avith  the  air,  at  a  temperature  below  redness,  in  which  case  oxygen 
is  directly  absorbed  ;  or  by  heating  the  cyanide  with  nitre,  or  with 
peroxide  of  manganese,  which  yield  the  oxygen  required.  For  this 
purpose  the  yellow  prussiate  of  potash  of  commerce  may  be  em- 
ployed, as  the  cyanide  of  iron  which  it  contains  is  totally  decom- 
posed, and  the  cyanide  of  potassium  then  acts  as  if  it  were  com- 
pletely pure.  The  cyanic  acid  cannot,  however,  be  isolated  from 
these  salts  by  a  stronger  acid,  as  it  then  rapidly  changes  into  bicar- 
bonate of  ammonia,  uniting  with  the  elements  of  three  atoms  of 
water  ;  thus  C.2N.O.  and  3H.0.  produce  N.H3  and  2C.0,. 

The  cyanic  acid  can  be  obtained  free  only  by  distilling  the  cyan- 
uric  acid,  CysOg+SH.O.,  which  then  transforms  itself  into  the  hy- 
drated  cyanic  acid,  Cy.O. -[-H.O. ,  and  is  to  be  collected  in  a  receiv- 
er surrounded  with  snow.     It  is  a  colourless  liquid,  of  a  very  pun- 


SALTS     OF     CYANIC     ACID,     ETC.  515 

gent  odour,  cauterizes  the  skin,  and,  when  mixed  with  water,  is 
decomposed  as  above  stated.  When  preserved  in  its  most  concen- 
trated form,  it  soon  transforms  itself  into  a  white  mass,  like  porce- 
lain, of  the  same  composition,  C^N. .  H.O2,  which  has  been  termed 
Cyanamelide.  This  body  is  insoluble  in  water,  but  by  heat  is  trans- 
formed back  again  into  hydrated  cyanic  acid,  and  by  strong  acids 
is  resolved  into  carbonate  of  ammonia. 

Cyanic  acid  does  not  exist  in  the  anhydrous  state. 

The  cyanic  acid  forms  but  one  series  of  salts,  being  monobasic  j 
those  of  the  alkalies  are  soluble  j  the  others  are  white  insoluble 
powders. 

Cyanate  of  Potash. — Cy.O. .  K.O.  The  yellow  prussiate  of  potash 
of  commerce,  being  roasted  in  an  earthen  dish,  absorbs  oxygen,  and 
the  cyanide  of  potassium  is  converted  into  cyanate  of  potash. 
When  the  mass  becomes  adhesive  from  the  fusion  of  the  product, 
it  is  to  be  digested  with  alcohol,  from  which  the  pure  cyanate  crys- 
tallizes, on  cooling,  in  rhombic  tables  like  chlorate  of  potash.  In 
contact  with  water  this  salt  is  rapidly  decomposed,  ammonia  being 
evolved,  and  carbonate  of  potash  formed.  If  dry  cyanate  of  potash 
and  dry  crystals  of  oxalic  acid  be  rubbed  together  in  a  mortar,  ox- 
alate of  potash  is  formed,  and  the  cyanic  acid  changes  into  cya- 
namelide. 

Cyanic  Acid  and  Ammonia. — If  hydrated  cyanic  acid  be  placed  in 
contact  with  dry  ammonia,  they  combine,  and  form  a  white,  woolly 
mass,  which  dissolves  in  water,  and  acts  as  an  ordinary  cyanate.  It 
appears  to  contain  Cy.O.  +  H.O.  +  2N.H3.  If  it  be  gently  heated  it 
gives  ofFanjmonia,  and  is  transformed  into  an  important  substance, 
Urea^  which,  though  thus  capable  of  being  artificially  produced,  will 
be  specially  described  as  a  product  of  the  organization,  in  another 
chapter.  Whenever  we  attempt  to  form  the  neutral  cyanate  of 
ammonia,  Cy.O.  .  N.H3 .  H.O.,  urea  is  produced  j  thus,  by  acting  on 
cyanate  of  silver  with  muriate  of  ammonia,  or  by  mixing  solutions 
of  sulphate  of  ammonia  and  cyanate  of  potash.  But  still  we  cannot 
consider  urea  to  be  merely  cyanate  of  ammonia,  to  which  it  bears 
the  same  relation  that  cyanamelide  does  to  hydrated  cyanic  acid. 

Fulminic  Acid. — Cy202+2H.O.  This  acid,  which  has  attracted 
much  attention  from  the  detonating  properties  of  its  salts,  is  pre- 
pared by  the  action  of  nitric  acid  on  alcohol,  in  presence  of  oxide 
of  mercury  or  silver.  The  reaction  is  very  complex  \  a  crowd  of 
products  of  the  oxidation  of  the  alcohol  being  evolved,  as  aldehyd, 
formic,  acetic,  and  oxalic  acid,  &c.  If  the  action  were  limited  to 
the  essential  conditions,  it  would  probably  consist  in  two  equiva 
lents  of  alcohol  and  two  of  nitric  acid,  producing  one  of  acetic  acid, 
one  of  fulminic  acid,  and  eight  of  water  j  thus  2N.O3  and  2(C4H602) 
give  C,H404  and  C^N^O^,  besides  8H.0. 

The  fulminic  acid  cannot  be  obtained  in  an  isolated  form ;  when 
we  attempt  to  separate  it  from  bases,  it  is  instantly  decomposed. 
Thus,  if  fulminate  of  silver  be  acted  on  by  dilute  muriatic  acid, 
chloride  of  silver,  and  a  peculiar  acid  containing  chlorine  and  cyan- 
ogen, are  produced.  The  fulminic  acid  is  bibasic,  and  forms  two 
series  of  salts,  of  which  the  neutral  contains  two  equivalents  of  fixed 
base,  the  acid  salts  containing  one  of  fixed  base  and  one  of  water 


516    FULMINATES     OF     SILVER     AND     MERCURY,     ETC. 

Fulminate  of  Silver. — CyaOi  +  SAg.O.  It  is  prepared  by  dissolv- 
ing silver  in  ten  parts  of  nitric  acid,  specific  gravity  1-35,  and  pour- 
ing the  solution,  when  cold,  into  twenty  parts  of  rectified  spirits  of 
wine.'  The  mixture  is  to  be  gently  heated  till  it  begins  to  boil,  and 
then  left  to  cool  slowly.  The  fulminate  of  silver  is  deposited  in 
fine  silky  crystals,  snow-white,  and  equal  in  weight  to  the  silver 
employed.  It  is  very  sparingly  soluble  in  cold  water.  It  detonates 
with  the  slightest  shock,  or  by  contact  with  sulphuric  acid.  When 
acted  on  by  a  caustic  alkali,  as  potash,  half  of  the  silver  separates 
as  oxide,  and  a  salt  is  formed,  Cy202  +  K.O. .  Ag.O.  If  it  be  dissolv 
ed  in  warm  dilute  nitric  acid,  half  of  the  silver  is  also  removed  an<5 
replaced  by  water,  and  on  cooling,  the  acid  fulminate  of  silver,  Cy< 
O^-f-H.O.  .  Ag.O.,  crystallizes  out.  This  explodes  more  readilj 
than  the  first  salt,  by  friction,  and  by  contact  with  oil  of  vitriol  or 
chlorine  gas. 

By  digesting  these  fulminates  of  silver  with  metallic  zinc  o; 
copper,  fulminates  of  these  metals  with  two  atoms  of  oxide  are  ob 
tained ;  and  by  acting  on  these  salts  with  an  alkali  or  barytes,  salt*' 
with  two  different  bases  may  be  formed.  In  no  case,  however,  caa 
a  fulminate  containing  two  atoms  of  an  alkaline  base  be  produced. 
All  these  salts  possess  detonating  properties  more  or  less  violent. 

Fulminate  of  the  Suboxide  of  Mercury. — Cy202+2Hg20.  This,  the 
most  important  salt  of  fulminic  acid,  is  prepared  by  dissolving  mer- 
cury in  nitric  acid,  and  treating  it  by  alcohol,  as  in  preparing  ful- 
minate of  silver.  As  the  solution  cools,  some  metallic  mercury 
precipitates,  and  the  fulminate  of  the  suboxide  is  deposited  in  hard, 
opaque,  white  crystals,  generally  very  minute.  It  is  to  be  washed 
and  redissolved  in  boiling  water,  and  crystallizes  then  in  fine  silky 
needles.  This  salt  detonates  violently  when  struck  between  two 
hard  bodies.  It  is  extensiv^ely  used  in  the  manufacture  of  the  per- 
cussion caps  used  for  firearms.  As  a  great  quantity  of  alcohol  is 
wasted  in  this  process,  it  was  proposed  to  carry  on  the  action  in 
close  vessels,  and  condense  the  spirit,  which,  however,  was  found 
to  be  unfit  for  any  but  the  same  use,  from  containing  a  large  quan- 
tity of  prussic  acid. 

Cyanuric  ^cid. — CyaOg-j-SH.O. 

This  acid  is  produced  under  a  variety  of  circumstances  where 
the  elements  of  cyanic  acid  become  free.  Thus,  if  the  solid  chlo- 
ride of  cyanogen  be  treated  with  water,  Cy.Cl.  and  H.O.  produce 
H.Cl.  and  Cy.O.,  but  this  transforms  itself  immediately  into  cyanu- 
ric acid.  It  is  formed  abundantly,  as  a  white  sublimate,  in  the  dry 
distillation  of  uric  acid,  and  may  be  very  simply  produced  by  heat- 
ing urea  a  little  above  its  point  of  fusion  in  a  glass  retort ;  ammo- 
nia is  given  off,  and  the  urea  changes  into  a  dry,  gray  mass,  which 
is  to  be  dissolved  in  strong  sulphuric  acid,  and  treated  with  nitric 
acid,  added  in  small  quantities,  until  it  becomes  quite  colourless. 
Being  then  diluted  with  its  own  weight  of  water,  the  liquor  yields 
crystals  of  cyanuric  acid  on  cooling.  It  is  evident  that  three  atoms 
of  urea,  3(C2H4 .  NgOJ,  contain  the  elements  of  three  atoms  of  am- 
monia and  one  of  cyanuric  acid,  CgNsOg+SH.O. 

By  means  of  a  substance  which  will  be  hereafter  noticed,  termed 


PREPARATION     OF     PRUSSIC      ACID.  517 

Melam^  cyanuric  acid  may  be  formed  simply  and  in  quantity.  The 
details  of  the  process  will  be  given  when  describing  the  properties 
of  that  body. 

Cyanuric  acid  is  colourless  and  nearly  tasteless,  possessing  a  very 
slight  acid  reaction.  It  crystallizes  in  oblique  rhombic  prisms,  which 
have  the  formula  Cy3034-3H.O.+4  Aq.  By  a  moderate  heat,  the  4 
Aq.  are  expelled,  and  when  more  strongly  heated,  the  dry  acid  chan- 
ges into  hydrated  cyanic  acid.  This  acid,  being  tribasic,  forms 
three  distinct  classes  of  salts,  which  differ  as  the  quantity  of  fixed 
base  is  one,  or  two,  or  three  atoms.  If  any  of  these  salts  be  acted 
on  by  a  stronger  acid,  the  cyanuric  acid  is  completely  liberated. 

Cyanide  of  Hydrogen.     Hydrocyanic  Acid.     Prussia  Acid. 

This  remarkable  substance  may  be  formed  by  the  direct  combina- 
tion of  hydrogen  and  cyanogen.  It  exists  in  the  water  distilled 
from  bitter  almonds,  or  from  the  leaves  of  the  cherry-laurel,  being 
produced  by  the  decomposition  of  a  peculiar  substance,  Amygdaline, 
which  those  plants  contain.  For  the  purposes  of  medicine  and 
chemistry,  it  is  prepared  by  indirect  processes  of  many  kinds. 
Thus,  if  forraiate  of  ammonia  (C2H.O3+N.H4O.)  be  passed  in  va- 
pour through  a  red-hot  porcelain  tube,  it  is  totally  converted  into 
prussic  acid  and  water,  C2N.H.  and  4H.0.  Also,  by  passing  ammo- 
nia over  red-hot  charcoal,  hydrocyanate  of  ammonia  is  formed  in 
such  quantity  that  prussic  acid  may  be  economically  pTepared  from 
it.  If  cyanide  of  silver  be  decomposed  by  muriatic  acid,  chloride 
of  silver  and  cyanide  of  hydrogen  are  produced  (Ag.Cy.  and  H.CI. 
giving  Ag.Cl.  and  H.Cy.)  j  and  by  sulphuret  of  hydrogen,  cyanide 
of  mercury  gives  sulphuret  of  mercury  and  prussic  acid.  For  its 
preparation  on  the  large  scale,  however,  the  substance  used  is  the 
yellow  prussiate  of  potash  of  commerce. 

This  salt,  the  preparation  of  which  will  be  hereafter  described, 
consists  of  cyanide  of  iron  united  to  cyanide  of  potassium ;  by  the 
action  of  sulphuric  acid,  three  fourths  of  the  latter  are  decomposed, 
bisulphate  of  potash  being  formed,  and  prussic  acid  liberated,  2(S. 
O3+H  0.)  and  Cy.K.  giving  (K.O.  .  S.^+HO.  .  S.O3)  and  Cy.H. 
The  cyanide  of  iron  remains  still  combined  with  the  other  fourth 
of  the  cyanide  of  potassium,  forming  a  compound  first  described  by 
Mr.  Everitt.  The  prussic  acid  thus  produced  contains,  therefore, 
one  half  of  the  cyanogen  which  existed  in  the  salt  employed.  The 
precise  decomposition  is,  that  two  equivalents  of  the  yellow  ferro- 
prussiate  of  potash,  2(Fe.Cy.  +  2K.Cy.),  acted  on  by  six  atoms  of  oil 
of  vitriol,  6(S.0;iH-H  O.),  produce  three  atoms  of  bisulphate  of  pot- 
ash, 3(H.O. .  S.O3+K.O.  .  S.O3),  and  three  atoms  of  prussic  acid,  3H. 
Cy. ;  there  remains  then  an  atom  of  Everitt's  salt,  2(Fe.Cy.  +  K.Cy.), 
which,  when  first  formed,  is  yellow,  but  by  rapidly  absorbing  oxygen 
it  becomes  greenish,  and,  abandoning  its  cyanide  of  potassium,  is 
finally  converted  into  basic  Prussian  blue. 

The  mode  of  conducting  the  process  depends  on  the  degree  of 
strength  at  which  the  prussic  acid  is  required.  To  obtain  the  an- 
hydrous acid,  three  parts  of  yellow  prussiate  of  potash,  in  fine  pow- 
der, are  to  be  decomposed  by  a  mixture  of  two  parts  of  oil  of  vit- 
riol and  two  of  water,  in  a  small  retort,  at  a  very  gentle  heat,  and 


518  TROPERTIES     OF     PRUSSIC     ACID. 

the  product  collected  in  a  receiver,  surrounded  by  ice,  and  contain- 
ing some  fragments  of  recently-fused  chloride  of  calcium,  by  which 
any  traces  of  water  which  come  over  are  absorbed.  The  process 
originally  employed  by  Gay  Lussac  consists  in  decomposing  cyan- 
ide of  mercury  by  strong  muriatic  acid,  and  passing  the  vapour 
through  a  long  tube,  of  which  the  half  next  the  retort  contains  small 
fragments  of  marble,  and  the  other  half  fragments  of  recently-fused 
chloride  of  calcium  ;  any  muriatic  acid  vapour  is  arrested  by  the 
former,  and  the  prussic  acid  is  rendered  anhydrous  by  the  latter  j 
the  vapour  is  then  condensed  in  a  receiver,  surrounded  by  ice. 

Pure  prussic  acid  is  a  colourless  liquid  ;  its  specific  gravity  at 
67^  is  0*6969  ;  at  5'^  Fah.  it  congeals  into  a  mass  of  fibrous  crystals, 
and  at  80'  boils.  In  consequence  of  this  great  volatility,  if  a  drop 
of  it  be  suspended  from  a  glass  rod,  one  part  of  it  will  be  solidified 
by  the  cold,  produced  by  the  rapid  evaporation  of  another  portion. 
The  density  of  its  vapour  is  943-9,  consisting  of  equal  volumes  of 
cyanogen  and  hydrogen,  united  without  condensation,  as  (1819'0-{- 
68'8)-i-2=943'9.  It  reddens  litmus  paper  feebly,  and  the  tint  dis- 
appears by  heat.  Its  odour  is  extremely  suffocating  and  pungent, 
and  resembles  that  of  bitter  almonds.  Its  taste  is  bitter  and  acrid. 
It  is  combustible,  burning  with  a  bright  white  flame.  Being  a  poi- 
son of  intense  activity,  the  greatest  care  should  be  used  in  manipu- 
lating with  it  in  this  concentrated  form. 

Anhydrous  prussic  acid  decomposes  rapidly,  especially  if  exposed 
to  light.  It  forms  ammonia,  and^a  brown  substance,  probably  the 
.same  as  that  produced  from  a  solution  of  cyanogen  in  water,  and 
termed  Azulmic  Acid^  as  noticed  p.  514,  but  of  which  the  composi- 
tion is  not  well  known.  By  contact  with  a  strong  acid,  prussic  acid 
assimilates  the  elements  of  three  atoms  of  water,  and  produces  for- 
mic acid  and  ammonia  (C2N.H.  and  3H.0.  giving  C2H.O3  and  N. 
H3).  Hence,  in  the  preparation  of  prussic  acid,  an  excess  of  any 
mineral  acid  should  be  avoided.  With  chlorine,  prussic  acid  forms 
muriatic  acid  and  chloride  of  cyanogen,  and  with  iodine  it  acts 
similarly. 

For  medicinal  use,  the  prussic  acid  is  prepared  in  a  very  dilute 
condition.  The  directions  sometimes  given  in  pharmacoposias  to 
distil  over  an  acid  of  a  specific  strength,  are,  in  practice,  very  dif- 
ficult to  execute,  and  might  give  rise  to  serious  errors.  The  prop- 
er method  is  to  prepare  an  acid  stronger  than  that  required ;  then, 
to  ascertain  by  accurate  analysis  its  strength,  and  dilute  it  with  dis- 
tilled water  until  it  be  brought  exactly  to  the  degree  required. 
This  process  is  carried  on  in  the  manufacturing  laboratory  of  the 
Apothecaries'  Hall  of  Ireland  as  follows :  1  lb.  of  crystallized  yellow 
prussiate  of  potash,  in  fine  powder,  is  placed  in  a  capacious  retort, 
and  2  lbs.  of  water  poured  on  it ;  to  this  is  added  a  mixture  of  12 
ozs.  of  oil'of  vitriol  and  2  lbs.  of  water,  previously  suffered  to  cool.. 
These  materials  are  well  agitated,  and  allowed  to  digest  for  three 
or  four  hours,  and  then  between  2  and  3  lbs.  of  dilute  acid  are  dis- 
tilled over  into  a  receiver  containing  already  1  lb.  of  distilled  water  j 
there  are  obtained  thus  3  or  4  lbs.  of  an  acid  containing  from  6  to 
8  per  cent,  of  real  acid.  200  grs.  of  this  are  weighed  and  decom- 
posed by  an  excess  of  nitrate  of  silver  j  the  cyanide  of  silver  pre* 


DETECTION     OF     PRUSSIC     ACID.  519 

cipitated  is  carefully  collected,  washed,  and  dried.  Being  then 
weighed,  the  exact  per  centage  of  acid  present  is  found  by  calcu- 
lation, and  the  necessary  quantity  of  water  is  added,  so  as  to  bring 
it  to  the  standard  strength  of  the  Dublin  pharmacopoeia,  which  is 
that  of  1-6  per  cent,  of  real  acid,  and  specific  gravity  of  0-998. 

As  an  example  of  this  process,  let  us  suppose  that  the  200  grs.  of  distilled  acid  gave, 
with  nitrate  of  silver,  74  grs.  of  cyanide ;  as  this  contains  1495  of  cyanogen,  the  200 
grs.  contained  15-53  of  real  acid,  or  7-76  per  cent. ;  now,  to  reduce  this  to  the  Dublin 
standard,  divide  7-76  by  1-6,  which  gives  485;  indicating  that  by  adding  3-85  lbs. 
of  distilled  water  to  each  pound  of  acid,  the  mixture  will  have  accurately  the  strength 
directed  by  the  pharmacopoeia.  Some  of  this  calculation  may  be  spared  by  consid- 
ering the  cyanide  of  silver  to  be  equivalent  to  one  fifth  of  its  weight  of  real  prussic 
acid ;  the  quantity  per  cent,  in  the  supposed  example  should  then  be  one  tenth  of 
the  weight  of  cyanide  of  silver  obtained!^  from  the  200  grs.,  that  is,  7-4  per  cent.;  and 
the  water  necessary  to  bring  it  to  the  Dublin  standard  should  be  3-63  times  its 
weight.  The  error  introduced  by  this  simplification  is  not  sensible,  being  but  0*002 
per  cent. 

The  strength  of  the  prussic  acid  directed  by  the  British  pharma- 
copoeias differs  very  much :  that  prescribed  by  the  London  College 
contains  about  2  per  cent,  of  real  acid  ;  that  of  the  Edinburgh  Col- 
lege contains  about  4>  per  cent.  ;  while  the  Dublin  strength  is  but 
1-5  or  1-6  of  real  acid  per  cent.  This  should  be  carefully  attended 
to  in  practice. 

A  method  has  been  proposed  for  determining  the  value  of  prassic  acid,  by  digest- 
ing it  on  a  known  quantity  of  red  oxide  of  mercury ;  when  the  prussic  acid  has  sat- 
urated itself  with  the  oxide,  what  remains  is  to  be  washed,  dried,  and  weighed. 
Now,  as  116-4  of  oxide  of  mercury  is  converted  into  cyanide  by  27-1  of  prussic  acid, 
which  proportion  is  nearly  4  to  1,  the  quantity  of  prussic  acid  is  pretty  correctly  one 
fourth  of  the  weight  of  the  oxide  of  mercury  dissolved.  But  as  cyanide  of  mercury- 
may  combine  with  an  excess  of  oxide,  and  as  the  quantity  thus  liable  to  be  taken 
up  is  not  constant,  it  is  dangerous  to  rely  on  this  method  for  medicinal  or  analyti- 
cal purposes. 

The  detection  of  prussic  acid  is  very  simple.  1st.  Its  solution 
gives,  with  nitrate  of  silver,  a  white  precipitate,  cyanide  of  silver, 
insoluble  in  strong  nitric  acid  when  cold,  but  dissolved  by  boiling ; 
it  is  insoluble  in  ammonia.  If  a  liquor  containing  even  a  very  small 
trace  of  prussic  acid  be  boiled,  the  vapour  produces  a  white  cloud 
on  a  piece  of  glass  moistened  with  solution  of  nitrate  of  silver.  2d. 
If  a  solution  of  sulphate  of  iron  be  added  to  prussic  acid,  there  is 
no  change ;  but  on  adding  some  potash  liquor,  a  dirty  greenish  pre- 
cipitate is  produced,  from  which  muriatic  acid  dissolves  out  the  ex- 
cess of  oxide  of  iron,  and  leaves  Prussian  blue  (cyanide  of  iron)  of 
a  very  rich  colour :  it  is  essential  to  the  proper  action  of  this  test, 
that  both  protoxide  and  peroxide  of  iron  be  present  in  the  solution. 
3d.  If  a  solution  of  sulphate  of  copper  be  added  to  the  liquor  con- 
taining prussic  acid,  and  then  treated  successively  with  potash  and 
muriatic  acid,  as  above,  a  white  precipitate  remains  undissolved, 
which  is  cyanide  of  copper.  The  theory  of  these  last  actions  is, 
that  the  prussic  acid  is  too  weak  to  decompose,  by  itself,  either 
metallic  sulphates,  but,  on  the  addition  of  potash,  double  decompo- 
sition occurs,  sulphate  of  potash  and  a  metallic  cyanide  being  form- 
ed. As  the  potash  is  always  added  in  excess,  a  quantity  of  metal- 
lic oxide  is  at  the  same  time  precipitated,  which  masks  the  colour 
of  the  result,  but  is  removed  by  the  addition  of  the  muriatic  acid. 
4th.  These  insoluble  cyanides  may  be  recognised  very  elegantly  by 
heating  them  with  a  little  potash  and  sulphur,  and  dissolving  the 


520  CYANIDE     OF     POTASSIUM.    ETC. 

fused  mass  in  water.  The  solution  gives,  with  a  persalt  of  iron,  a 
fine  blood-red  colour.  5th.  The  cyanide  of  silver,  also,  is  known 
by  giving  off  cyanogen  when  heated. 

There  are  two  ddarides  of  Cyanogen  of  the  same  composition,  and  bearing  to  each 
other  the  same  relation  as  the  cyanic  and  cyanuric  acids.  One  is  gaseous,  the  other 
solid ;  the  first  is  prepared  by  acting  on  moist  cyanide  of  mercury  by  chlorine,  or  by 
passing  chlorine  into  weak  prussic  acid,  and  warming  the  mixture  in  which  the 
chloride  of  cyanogen  dissolves.  This  gas,  which  is  very  irritating  and  poisonous, 
may  be  obtained  crystallized  in  needles  by  exposure  to  a  very  low  temperature.  II 
combines  with  ammonia,  forming  a  crystalline  substance. 

The  solid  chloride  may  be  prepared  by  acting  on  anhydrous  prussic  acid  with 
chlorine,  or  by  heating  sulphocyanide  of  potassium  in  a  current  of  chlorine.  It  sub- 
limes in  white  transparent  needles.  It  dissolves  unaltered  in  alcohol  and  ether,  and 
is  decomposed  by  hot  water  into  hydrochloric  and  cyanuric  acids. 

Iodide  of  Cyanogen  is  prepared  by  distilling,  in  a  retort,  a  mixture  of  iodine,  cyan- 
ide of  mercury,  and  water.  At  a  moderate  heat,  the  iodide  of  cyanogen  passes  over, 
and  condenses  in  the  neck  of  the  retort  as  a  flocculent  mass  of  snow-white  needles. 
These  crystals  irritate  the  eyes :  they  dissolve  in  water  unaltered,  and  volatilize  at 
113°. 

SECTION  II. 

OF    THE    METALLIC    CYANIDES. 

Cyanide  of  Potassium^  K.Cy.,  may  be  formed  by  the  direct  union 
of  its  elements,  or  by  adding  an  excess  of  prussic  acid  to  a  solution 
of  potash,  and  evaporating  rapidly  without  the  access  of  air.  It  is 
produced  also  whenever  carbonaceous  matter  is  calcined  in  contact 
with  potash,  provided  nitrogen  be  present.  The  best  mode  of  ob- 
taining it,  however,  is  to  expose  the  yellow  prussiate  of  potash  to  a 
full  red  heat,  in  a  close  iron  crucible.  The  cyanide  of  iron  is  de- 
composed, nitrogen  being  given  off,  and  carburet  of  iron  remaining 
with  the  unaltered  cyanide  of  potassium.  The  half-melted  mass  is 
to  be  coarsely  powdered,  and  digested  in  boiling,  weak  spirit  of 
wine,  from  which  the  salt  crystallizes  in  cubes  on  cooling.  Spirit 
of  specific  gravity  0900  at  60^,  is  remarkable  for  dissolving  a  large 
quantity  of  cyanide  of  potassium  when  boiling,  but  depositing  it 
nearly  totally  when  it  cools. 

This  salt  in  solution  reacts  alkaline,  and  smells  of  bitter  almonds, 
and  hence  probably  decomposes  water  when  dissolved.  Its  crystals 
deliquesce  and  are  decomposed,  even  in  close  vessels,  after  a  short 
time,  by  contact  with  water,  into  ammonia  and  formiate  of  potash. 

The  properties  of  the  cyanide  of  sodium  and  of  the  hydrocyanate 
of  ammonia  are  quite  similar. 

The  Cyanides  of  Barium,  strontium,  calcium,  and  magnesium  are  soluble  in  wa- 
ter, and  crystallizable. 

Cyanide  of  Zinc  is  prepared  by  adding  prussic  acid  to  a  solution  of  acetate  of 
zinc,  when  it  precipitates  as  a  white  powder.  Chloride  of  zinc  is  not  decomposed 
by  prussic  acid.    With  cyanide  of  potassium  it  forms  a  double  salt. 

Cyanide  of  Copper  is  formed  as  a  whitish  precipitate  when  prussic  acid  and  potash 
are  added  to  a  solution  of  sulphate  of  copper.  When  boiled  it  becomes  yellow,  and 
combines  with  the  oxide  ©f  copper  to  form  an  oxycyanide  of  a  lively  green  colour. 
It  forais  double  salts  with  the  alkaline  cyanides. 

Cyanide  of  Mercury — Hg.Cy. ;"  Eq.  1594-4  or  127-45 — may  be  pre- 
pared by  boiling  two  parts  of  Prussian  blue  with  one  of  red  oxide 
of  mercury  and  eight  of  water,  until  the  residue  becomes  red-brown. 
The  filtered  liquor  yields  cyanide  of  mercury  in  crystals,  which, 
however,  are  not  quite  free  from  iron,  and  require  to  be  digested 
with  a  little  more  oxide  of  mercury  and  recrystallized.     The  best 


f 


CYANIDE     OF     MERCURY,    ETC.  521 

mode  of  preparing  it  is  to  distil  fifteen  parts  of  yellow  prussiate  of 
potash,  with  thirteen  of  oil  of  vitriol  and  100  of  water,  nearly  to  dry- 
ness, and  to  digest  the  prussic  acid  so  obtained  with  twelve  parts 
of  finely-powdered  oxide  of  mercury,  until  this  is  completely  dis- 
solved. The  solution  yields,  by  evaporation  and  cooling,  fourteen 
parts  of  pure  crystallized  cyanide  of  mercury.  By  washing  out  the 
residue  in  the  retort  with  water,  five  parts  of  pure  Prus-  ^,.<-;55^^v. 
sian  blue  may  be  obtained.  0^^^\ 

Cyanide  of  mercury  crystallizes  in  colourless  rectan- 
gular prisms,  as  q  q,  in  the  figure,  terminated  by  numer- 
ous secondary  faces,  as  e  e.  These  crystals  are  anhy- 
drous, and  occasionally  opaque.  When  heated,  it  is  re- 
solved into  mercury  and  cyanogen,  of  which  a  portion  is  resolved 
into  the  brown  powder  (paracyanogen).  It  is  sparingly  soluble  in 
alcohol.  It  tastes  as  the  other  mercurial  salts.  So  great  is  the 
affinity  of  mercury  to  cyanogen,  that  cyanide  of  potassium,  when 
boiled  with  oxide  of -mercury,  is  decomposed,  and  caustic  potash 
liberated.  In  a  solution  of  cyanide  of  mercury,  no  test  indicates 
the  presence  of  the  metal  except  sulphuretted  hydrogen.  It  is  not 
decomposed  by  oxygen  acids,  but  muriatic  acid  forms  prussic  acid 
and  chloride  of  mercury. 

Cyanide  of  mercury,  when  digested  with  an  excess  of  oxide  of  mercury,  combines 
with  it  in  two  proportions,  forming  the  oxycyanixles  of  Mercury,  Hg.Cy.+Hg.O.  and 
Hg.Cy.+3Hg.O.  These  bodies  are  soluble  in  water,  and  crystallize  in  prismatic 
needles. 

With  iodide  of  potassium,  cyanide  of  mercury  combines,  forming  a  substance,  2 
Hg.Cy.-fK.L,  which  is  very  soluble  in  boiling  water,  and  crystallizes  in  brilliant 
white  micaceous  plates  on  cooling.  This  salt  is  instantly  reddened  by  any  mineral 
acid  which  liberates  iodide  of  mercury.  With  sulphocyanide  of  potassium  a  simi- 
lar compound  is  formed,  •2Hg.Cy.4-K.Cy.S2. 

Cyanide  of  mercury  combines  with  the  alkaline  cyanides,  and  with  the  alka- 
line chlorides  and' bromides,  forming  double  salts  possessing  no  special  interest.  It 
combines  with  many  oxygen  salts  also,  as  the  chromate  and  formiate  of  potash. 

As  prussic  acid  is  now  no  longer  prepared  from  cyanide  of  mercury,  this  body  is 
not  so  important  as  formerly.  It  is  poisonous,  and  is  occasionally  employed  in 
medicine. 

Cyanide  of  Silver,  Ag.Cy.,  is  a  white  powder  insoluble  in  water,  which  combines 
with  other  cyanides  to  form  double  salts.  It  is  soluble  in  water  of  ammonia,  but 
insoluble  in  nitric  acid,  except  it  be  strong  and  boiling.  Heated,  it  gives  cyanogen 
and  metallic  silver. 

Cyanide  of  Palladium. — In  its  affinity  for  cyanogen,  palladium  resembles  mercury. 
Every  soluble  salt  of  palladium  is  decomposed  by  prussic  acid,  a  pale  yellow  precip- 
itate being  formed.  This  cyanide  of  palladium  is  insoluble  in  water,  but  soluble  in 
acids  and  in  ammonia.  Heated,  it  gives  cyanogen  and  leaves  the  metal.  It  forms 
a  very  extensive  class  of  double  salts. 

Cyanide  of  Gold,  Au.Cya,  is  a  pale  yellow  powder,  forming  double  salts  with  the 
alkaline  cyanides. 

Protocyanide  of  Iron,  Fe.Cy.,  is  not  known  in  an  isolated  fou"  lat  it  enters  into 
combination  with  the  other  metallic  cyanides,  forming  double  salts,  which  are  some 
of  the  most  interesting  of  the  cyanogen  compounds.  The  iron  in  these  salts  cannot 
be  separated  by  an  alkali,  and  hence  may  be  looked  upon  as  an  element  of  the  neg- 
ative constituent ;  they  are  hence  often  termed  ferrocyanides,  or  ferroprussiates  of 
whatever  other  metal  they  may  contain. 

Ferrocyanide  of  Hydrogen.  Ferrocyanic  Jlcid. — Fe.Cy. -f-2H.Cy 
When  the  ferrocyanide  of  lead  is  decomposed  by  sulphuret  of  hy 
drogen,  a  solution  is  obtained,  which  yields,  on  evaporation  in  vacuo, 
small  granular  crystals,  which  have  a  well-marked  acid  reaction, 
and  produce,  by  acting  on  metallic  oxides,  all  the  ordinary  ferrocy- 
anides.    If  the  solution  be  boiled,  it  is  resolved  into  prussic  acid, 

Uuu 


522  FERROCYANIDE     OF     POTASSIUM. 

and  a  white  precipitate,  which  becomes  blue  in  the  air.  The  crys- 
tals undergo  the  same  change  spontaneously  after  some  time. 

Ferrocyanide  of  Potassium. — Fe.Cy.  +  2K.Cy.  +  3  Aq.  Eq.  2656*9 
or  212*5.  This  compound,  of  which  I  have  often  spoken  as  Yellow 
Prussiate  of  Potash,  is  prepared  on  the  large  scale  for  the  purposes 
of  the  arts  and  of  pharmacy,  by  calcining  together  some  animal 
matters,  as  blood,  hoofs,  horns,  &c.,  with  pearl  ashes  and  iron 
filings.  It  may  be  formed  even  if  the  organic  matter  do  not  contain 
nitrogen,  as  that  element  may  be  supplied  from  the  air.  The  oper- 
ation is  conducted  in  large  iron  pots  arranged  in  a  furnace,  so  that 
the  mass  can  be  heated  to  dull  redness,  and  continually  agitated  as 
it  forms  a  tenacious  paste,  the  calcining  of  which  is  continued  as 
long  as  it  burns  with  a  white  flame  j  it  is  then  taken  out  of  the  pot, 
and  when  cold,  boiled  in  water,  which,  by  evaporation,  yields  the 
salt  in  crystals.  If  it  has  not  dissolved  iron  enough,  some  copperas 
is  added  as  long  as  the  Prussian  blue,  which  at  first  forms,  is  found 
to  redissolve.  After  what  has  been  said  of  the  formation  of  cyan* 
ogen  (p.  513),  the  theory  of  this  process  may  easily  be  understood. 

The  ferrocyanide  of  potassium  crystallizes  in  truncated  octohe- 

A/^Z ~f~~^    73  drons  with  a  rectangular  base,  e  e   e', 

/K     e     \ ''V  /$^~7^^^^^c'''^)  ^®  ^^  ^^^  figure,  of  which  A  represents 

l^  \ .XJ   \>^^^^^^=^~^  the  usual  simple,  and  B  a  more  com- 

^^/  ^ "  -/^  ^^ — - — <C^  plicated  form  ;  the  secondary  plane  n 
often  being  so  large  as  to  render  the  crystal  merely  tabular.  Its 
colour  is  fine  citron-yellow,  but  when  dried  it  becomes  white.  By 
a  farther  heat  in  close  vessels  it  fuses,  and  when  ignited  gives  off 
nitrogen,  and  leaves  cyanide  of  potassium  and  carburet  of  iron. 
Heated  in  open  vessels,  it  absorbs  oxygen,  and  forms  cyanate  of 
potash.  Its  use  in  the  preparation  of  these  bodies  and  of  prussic 
acid  has  been  already  detailed.  If  it  be  digested  with  oxide  of  mer- 
cury, cyanide  of  mercury  is  formed,  and  oxide  of  iron  and  caustic 
potash  set  free.  With  sulphate  of  mercury  it  gives  sulphate  of  pot- 
ash, cyanide  of  mercury,  and  Everitt's  yellow  salt. 

With  cyanide  of  mercury,  ferrocyanide  of  potassium  forms  a 
double  salt,  whose  formula  I  found  to  be  SHg.Cy.  +  (Fe.Cy. -f2K 
CyO  +  '^  Aq.     It  crystallizes  in  pale  yellow  rhombic  tables. 

In  the  arts,  the  ferrocyanide  of  potassium  is  of  importance  for 
dyeing  various  shades  of  blue  j  to  the  chemist  it  is  specially  of  in- 
terest, as  from  it  all  the  cyanogen  compounds  are  most  economi- 
cally formed,  and  from  the  peculiar  precipitates  it  gives  with  solu- 
tions of  most  metals,  it  is  of  eminent  service  in  their  detection. 
Thus,  with  solutions  of  silver,  mercury,  bismuth,  tin,  lead,  nickel,  zinc, 
manganese,  and  cerium,  it  gives  white  precipitates;  that  with  mercu- 
ry gradually  becomes  blueish,  and  that  of  manganese  reddish.  With 
copper,  the  precipitate  is  of  a  rich  chocolate  colour ;  with  cobalt, 
greenish,  changing  to  red  ;  with  uranium  and  molybdenum,  brown ; 
and  with  chrome,  grayish-green.  All  these  precipitates  contain  cy- 
anide of  iron,  united  to  two  atoms  of  cyanide  of  the  other  metal, 
being  true  ferrocyanides. 

It  is  on  solutions  of  iron  that  the  action  of  this  reagent  is  the  most 
remarkable.  With  solution  of  protosulphate  of  iron,  a  whitish  pre- 
cipitate is  obtained,  which  consists  of  the  cyanides  of  iron  and  po- 


PREPVRATION     OF     PRUSSIAN     BLUE,    ETC.         523 

tassium,  united  in  proportions  which  are  not  well  known.  Exposed 
to  the  air,  this  body  absorbs  oxygen  and  becomes  blue.  With  a  so- 
lution of  sulphate  of  iron  pure  Prussian  Blue  is  precipitated.  This 
substance  is  insoluble  in  water  and  in  muriatic  acid,  and  gives  with 
caustic  alkalies  oxide  of  iron  and  ferrocyanide  of  potassium ;  its 
formula  is  Fe7Cy9,  or  it  consists  of  3Fe.Cy.4-2Fe2Cy3.  Its  forma- 
tion involves  3(Fe.Cy.  +  2K.Cy.)  and  2(FeA  +  3S.03),  and  there  re- 
main dissolved  six  atoms  of  sulphate  of  potash.  For  the  manufac- 
ture of  Prussian  blue  for  the  purposes  of  the  arts,  the  impure  liquor 
obtained  by  digesting  in  water  the  calcined  mass  of  animal  matter, 
potash  and  iron,  described  p.  522,  is  decomposed  by  an  excess  of 
sulphate  of  iron,  and  the  resulting  precipitate  digested  in  muriatic 
acid,  and  exposed  to  the  air  until  it  assumes  its  proper  colour.  It 
is  then  dried  carefully  at  a  moderate  heat. 

Another  kind  of  Prussian  blue  is  produced  when  Everitt's  salt, 
or  the  white  precipitate  produced  by  protosulphate  of  iron  with  yel- 
low prussiate  of  potash,  is  exposed  moist  to  the  air.  It  is  termed 
basic  Prussian  Blue.  As  Everitt's  salt  consists  of  2Fe.Cy.4-K.Cy., 
and  this  last  dissolves  out,  there  is  the  same  number  of  atoms  of 
cyanogen  and  iron,  and  the  excess  of  iron  above  that  necessary  to 
form  true  Prussian  blue  combines  with  the  oxygen  of  the  air,  the 
oxide  so  formed  remaining  united  with  the  Prussian  blue.  From  9 
Fe.Cy.  and  30.  there  is  thus  formed  3(Fe.Cy.4-2Fe2Cy3H-Fe203),  the 
basic  compound. 

The  ferrocyanides  of  Sodium,  Barium,  &c.,  possess  all  the  essential  characters  of 
the  potassium  salt,  and  need  not  be  farther  noticed. 

The  ferrocyanides  in  many  cases  combine  with  each  other,  forming  salts,  which 
contain  three  different  metals  combined  with  cyanogen. 

Sesqtiicyanide  of  Iron,  FeaCy^,  is  not  known  in  an  isolated  form,  but,  like  the  pro- 
tocyanide,  enters  into  a  number  of  combinations  with  the  other  metallic  cyanides, 
which  may  be  called  either  pe7 ferrocyanides  or  ferridcyanides,  as  proposed  by  Lie  big. 

Ferridcyanide  of  Potassium — Red  Prussiate  of  Potash^  Fe2Cy3-f-3K. 
Cy.,  is  formed  by  passing  chlorine  through  a  solution  of  yellow  prus- 
siate of  potash  until  it  ceases  to  give  Prussian  blue  with  solution 
of  persulphate  of  iron.  The  liquor  becomes  of  a  deep  green  colour, 
but  on  evaporation  yields  anhydrous  fine  ruby-red  prismatic  crys- 
tals, which  are  generally  macles.  The  products  of  its  decomposi- 
tion by  heat  are  the  same  as  those  of  the  yellow  salt.  It  dissolves 
in  thirty-eight  parts  of  cold  water  j  its  solution,  if  pure,  is  yellow, 
but  more  commonly  is  green. 

This  salt  rivals  that  already  described  in  its  utility  as  a  reagent 
for  the  proper  metals.  The  precipitates  it  gives  with  their  solutions 
are,  tin,  white;  mercury,  silver,  and  zinc,  yellow;  titanium,  nickel, 
copper,  and  bismuth,  yellowish  brown ;  and  cobalt,  uranium,  and  man- 
ganese, brown.  It  is,  however,  with  the  salts  of  iron  that  its  reac- 
tion is  most  remarkable.  With  a  persalt  of  iron  it  merely  colours 
the  liquor  green,  but  with  a  solution  of  a  protosalt  it  gives  a  blue 
precipitate,  even  richer  in  colour  than  the  proper  Prussian  blue,  and 
consisting  of  Fe.Cyg,  or  of  Fe^Cyg  +  SFe.Cy. ;  thus  containing  the 
same  protocyanide  with  half  as  much  sesquicyanide  as  exists  in 
common  Prussian  blue.  This  ferridcyanide  of  Iron  is  made  for 
commerce,  and  sold  as  TurnbulVs  Prussian  Blue. 

Ferridcyanide  of  Hydrogen. — If  we   digest  ferridcyanide   of  lead 


524     THEORY  OF  THE   COMPLEX  CYANIDES. 

with  dilute  sulphuric  acid,  a  red  liquor  is  obtained,  which  yields  on 
evaporation  a  mass  of  minute  brownish-yellow  needles,  the  formula 
of  which  is  FeaCya-f-SCy.H.  This  body  reddens  litmus,  and  has  a 
sour  astringent  taste  ;  upon  another  theory  it  is  considered  to  be  a 
compound  of  hydrogen  with  a  compound  radical,  (FcaCye),  and  is 
termed  Ferridcyanic  Acid. 

In  the  history  of  these  complex  cyanides  we  meet  three  facts,  on  which  the  the- 
ories of  their  constitution  must  be  founded.  1st.  The  extraordinary  tendency  to 
double  combination^  which  no  other  body  possesses  in  the  same  degree.  2d.  In 
almost  all  cases,  the  cyanogen  enters  into  the  compound  in  the  proportion  of  three, 
six,  or  nine  atoms ;  and,  3d.  One  metallic  element,  as  iron,  in  each  compound,  is 
retained  with  extraordinary  force,  not  being  detected  therein  by  its  ordinary  re- 
agents. The  original  view  proposed  by  Berzelius,  of  considering  these  compounds 
as  mere  double  salts,  and  upon  which  the  formulae  given  hitherto  have  been  con- 
structed, does  not  account  sufficiently  for  these  facts,  and  I  hence  consider  it  as 
less  applicable  to  them  than  the  theories  suggested  by  Graham  and  by  Liebig. 

The  latter  chemist  founds  his  view  upon  the  third  fact,  and  supposes  that  there 
exists  a  series  of  compound  radicals,  consisting  of  cyanogen  united  with  a  metal. 
Thus,  Ferrocyanogen,  {Fe.Cy^)  or  Cfy.,  and  Ferridcyanogen,  (FejCye)  or  Cfya,  these 
two  being  isomeric  ;  Cohaltocyanogen,  (CozCye)  or  Cky.,  and  many  others  ;  and  these 
radicals  combine  with  hydrogen  to  form  polybasic  hydracids,  from  which,  the  hy- 
drogen being  replaced  by  a  metal,  result  the  ordinary  complex  cyanides.  Thus, 
the  ferrocyanogen  being  bibasic,  its  acid  is  Cfy.-|-2H.  ;  its  potash  salt,  Cfy.-}-2K. ; 
its  copper  salt,  Cfy.-|-2Cu. ;  and  if  each  atom  of  hydrogen  be  replaced  by  a  different 
metal,  then  the  triple  salts  formed  by  Mosander  are  produced  :  thus,  the  salt  writ- 
ten on  Berzelius's  view  as  (Fe.Cy.4-2K.Cy.)-f  (Fe.Cy.-i-2Ca.Cy.)  becomes  Cfy.-{- 
Ca.K.,  and  similarly  there  is  Cfy.-f  Ca.K.,  &c. 

The  red  prussiate  of  potash  Liebig  supposes  to  contain  a  radical,  (FcoCye)  or 
Cfy 2,  isomeric  with,  but  of  double  tlie  atomic  weight  of  ferrocyanogen  ;  this  fer- 
ridcyanogen forms  with  hydrogen  a  tribasic  acid,  Cfya+Hs,  by  replacement  of  the 
hydrogen,  in  which,  by  three  atoms  of  the  same  or  of  different  metals,  the  various 
ferridcyanides  are  produced,  as  Cfya-j-Ks,  Cfy2-f-3Cu.,  &c. 

The  Prussian  blues,  on  this  theory,  are  considered  to  be  compounds  of  ferro- 
cyanide  with  ferridcyanide  of  iron  ;  thus, 

SCfy.Fca+CfyaFea  expresses  common  Prussian  blue. 
CfyaFcg  "         Turnbull's  Prussian  blue. 

SCfy.Fea-hCfyjFea-l-FezOa  "  basic  Prussian  blue. 

This  theory  accounts  very  strictly  for  the  first  and  third  of  the  fundamental 
facts  which  I  have  described  as  characterizing  the  cyanogen  compounds.  The 
theory  of  Graham  is  specially  based  upon  the  tendency  of  three  atoms  of  cyanogen 
to  enter  together  into  combination  with  other  bodies,  as  is  shown  not  only  in  its  re- 
lation to  metals,  but  to  oxygen,  as  in  cyanuric  acid,  and  hence  we  may  assume 
that  cyanogen,  as  Cyg,  with  three  times  its  ordinary  atomic  weight,  forms  a  dis- 
tinct radical  {paracyan  ?),  which  forms  with  oxygen  and  with  hydrogen  tribasic 
acids,  CygOg  and  CygHg.  From  the  replacement  of  more  or  less  of  this  hydrogen 
in  the  latter  by  equivalents  of  one  or  more  metal,  the  various  cyanides  may  be 
formed.    Thus,  for  example, 

Cyg-|-Fe.2K.  .  .  .  yellow  prussiate  of  potash. 
Cys-j-Fe.K.Ca. .  .  ferroprussiate  of  lime  and  potash. 
Cy3-\-Fe.2Il.  .  .  .  ferroprussic  acid. 

The  basis  of  the  red  prussiate  of  potash  should  be,  then,  another  polymeric  cyano- 
gen, Cye,  which  would  form,  with  hydrogen,  a  pentabasic  acid,  Cye-j-Hs,  in  which 
more  or  less  of  replacement  by  metals  should  give  the  various  ferridcyanides. 
Thus  ferridprussic  acid  should  be  Cys+FesHa,  and  red  prussiate  of  potash  Cye-f 
FejKs,  and  so  on  ;  Turnbull's  Prussian  blue  becomes,  on  this  theory,  simply  Cye-f 
Fcg ;  the  common  Prussian  blue  is  (Cy3-4-Fe2)4-Cy6Fe5 ;  and,  by  the  addition  of 
Fe203  to  that,  the  basic  Prussian  blue  is  formed. 

I  am  rather  inclined  to  adopt  Graham's  view,  although,  in  the  present  state  of 
our  knowledge,  we  have  not  grounds  for  positive  decision.  He  proposes  to  term 
the  radical  Cy^  Prussine,  but  has  not  given  any  name  to  that  whose  formula  is  Cyg. 


METALLIC      S  U  L  P  11  O  C  y  A  X  I  D  E  S.  525 

Of  Sulpho cyanogen^  and  the  Products  of  its  Decomposition. 

If  yellow  prussiate  of  potash,  well  dried,  and  mixed  carefully  with 
half  its  weight  of  sulphur,  in  fine  powder,  be  heated  in  an  iron  ves- 
sel to  perfect  fusion,  which  takes  place  at  a  dull  red  heat,  the  sul- 
phur combines  with  all  the  cyanogen,  forming  sulphocyanogen, 
which  unites  with  the  potassium,  while  the  iron  is  converted  into 
sulphuret.  By  digesting  the  fused  mass  in  water,  the  former  dis- 
solves, and  is  obtained,  by  evaporation  and  cooling,  in  long  striated 
prisms,  similar  to  those  of  nitre.  If  the  temperature  be  not  raised 
too  high,  the  iron  forms  also  sulphocyanide,  which  dissolves,  and 
may  be  decomposed  by  the  addition  of  a  slight  excess  of  carbonate 
of  potash ;  by  this  means  one  half  more  product  may  be  obtained 
than  is  yielded  if  the  sulphocyanide  of  iron  be  too  violently  heated, 
and  thereby  converted  into  sulphuret. 

Sulphocyanogen  is  prepared  by  passing  a  current  of  chlorine  gas 
into  a  solution  of  the  salt  thus  formed,  or  by  heating  it  in  dilute 
nitric  acid ;  chloride,  or  nitrate  of  potassium  is  formed,  and  a  deep 
yellow  precipitate  produced,  which  contains  all  the  sulphui*  and  cy- 
anogen of  the  salt,  its  formula  being  Cy.So.  It  is  very  light,  and 
insoluble  in  water.  It  combines  with  all  the  metals  and  with  hy- 
drogen, forming  well-defined  salts. 

Hydrosulphocyanic  Acid,  Cy.Sa  +  H.,  is  formed  by  decomposing 
sulphocyanide  of  lead  by  dilute  sulphuric  acid,  or  by  sulphuret  of 
hydrogen.  It  is  a  colourless  liquid,  which  reacts,  and  tastes  acid. 
By  distillation  it  is  decomposed. 

Sulphocyanide  of  Potassium. — Cy.S^+K.  This  salt,  of  which  the 
mode  of  preparation  has  been  just  described,  forms  anhydrous 
prisms,  cool  and  pungent  in  taste  ;  it  is  abundantly  soluble  in  water 
and  alcohol,  and  slightly  deliquescent.  It  is  employed  in  the  labor- 
atory as  a  test  for  peroxide  of  iron. 

Sulphocyanide  of  Lead  is  a  crystalline  powder,  prepared  by  mix- 
ing solutions  of  a  salt  of  lead  and  of  sulphocyanide  of  potassium. 

Of  the  sulphocyanides  of  Iron,  the  protosalt,  Fe.  +  Cy.S^,  forms  a 
colourless  solution,  which  becomes  red  on  exposure  to  the  air.  The 
sesquisalt,  Fe2+3Cy.S2,  forms  a  deep  blood-red  liquor,  when  a  sol- 
uble sulphocyanide  is  mixed  with  any  salt  of  the  peroxide  of  iron. 
It  serves  thus  as  a  very  delicate  test  of  the  presence  of  iron,  and 
also  for  that  of  cyanogen  ;  it  is  so  applied  to  the  detection  of  prus- 
sic  acid,  as  noticed  p.  520. 

These  sulphocyanides  may  be  considered  either  as  double  sul- 
phurets  of  cyanogen  and  of  a  metal,  as  Cy.S.+S.K.,  &c.,  or  as  salts 
of  the  compound  radical  sulphocyanogen,  Cy.S2+K.,  &c.  The 
latter  view  has  been  almost  universally  adopted  by  chemists. 

It  appears,  however,  from  the  researches  of  Parnell,  that  al- 
though sulphocyanogen  really  exists  in  these  salts,  yet  the  yellow 
substance  extracted  from  them  by  chlorine  or  by  nitric  acid,  as  de- 
scribed just  now  under  that  name,  is  only  a  product  of  the  decom- 
position of  the  real  sulphocyanogen,  which  has  not  been  as  yet  iso- 
lated. The  formula  of  the  yellow  powder  he  finds  to  be  S.^CiaNg  . 
H3O.  When  acted  on  by  alkalies  or  by  nitric  acid,  it  produces  an 
acid  which  he  terms  the  Thiocyanic,  which  is  polybasic.     It  is  a 


526  MELLON,     M  E  L  A  M,     ETC. 

pale  yellow  powder,  sparingly  soluble  in  water,  more  so  in  alcohol. 
Its  formula  is  SjaCioNj  .  H^02.  Its  compounds  with  the  oxides  of 
lead,  silver,  mercury,  &c.,  are  insoluble.  This  new  acid  is  but  one 
of  the  bodies  produced  in  this  reaction ;  the  others  have  not  been 
examined. 

Mellon. — When  sulphocyanogen  is  heated,  it  is  decomposed, 
yielding  sulphur,  sulphuret  of  carbon,  and  a  yellow  powder  which 
remains  as  fixed  residue,  and  to  which  Liebig  has  given  the  name 
of  Mellon.  This  is  a  compound  radical,  analogous  to  cyanogen  in 
its  characters.  It  is  insoluble  in  water,  alcohol,  or  dilute  acids.  Its 
formula  is  C6N4  or  ML,  and  when  strongly  ignited  it  is  decomposed 
into  three  volumes  of  cyanogen  and  one  of  nitrogen.  Heated  with 
potassium,  they  unite  with  combustion  ;  and  if  it  be  fused  with  the 
iodide  or  bromide  of  potassium,  iodine  or  bromine  is  expelled,  and 
mellonide  of  potassium  formed. 

Hydromellonic  Acid,  H.Ml.,  is  formed  by  dissolving  mellonide  of  potassium  in 
boiling  water,  and  adding  a  strong  acid.  A  gelatinous  white  precipitate  forms, 
which  dries  into  a  yellowish  powder,  H.Ml.-j-Aq. 

Mellotiide  of  Potassium,  K.Ml.,  is  produced  by  adding  mellon  to  sulphocyanide 
of  potassium,  fused  .in  a  porcelain  capsule  ;  sulphur  and  sulphuret  of  carbon  are 
evolved.  On  dissolving  the  brown  mass  thus  formed  in  boiling  water,  the  mellon- 
ide of  potassium  crystallizes,  on  cooling,  in  fine  colourless  needles. 

If  we  take  the  formula  of  sulphocyanogen  at  C2N.S2,  the  formation  of  mellon  con- 
sists in  4(C2N.S2),  producing  2(C.S2)  with  4S.,  and  leaving  C6N4 ;  but,  on  Mr.  Par- 
nell's  view,  the  decomposition  is  by  no  means  so  simple. 

When  mellon  is  boiled  with  strong  nitric  acid,  it  dissolves,  and,  on  cooling,  the 
liquor  yields  octohedral  crystals  of  Cyanilic  Acid.  This  substance  has  the  same  for- 
mula as  cyanuric  acid,  CyaOa-f-S  Aq.,  but  its  relations  to  bases  are  not  well  under- 
stood. Nitrate  of  ammonia  is  formed ;  mellon,  C6N4,  and  three  atoms  of  water, 
giving  CeNsOa  and  N.H3. 

Melam. — C12H9N11.  Sulphocyanide  of  ammonium,  on  being  heated,  is  decom- 
posed into  ammonia,  sulphuret  of  carbon,  and  sulphuret  of  hydrogen,  which  pass  off, 
while  a  grayish-white  powder  remains,  which  is  Melam.  The  same  result  is  ob- 
tained by  heating  to  fusion  a  mixture  of  sulphocyanide  of  potassium  and  sal  am- 
moniac :  in  this  case  chloride  of  potassium  also  remains  behind,  but  may  be 
removed  by  washing.  Melam  is  insoluble  in  water  and  alcohol.  It  is  dissolved 
and  decomposed  by  boiling  acids  and  alkaline  solutions,  giving  origin  to  a  series  of 
remarkable  bodies. 

Melamine,  CeCeNe,  is  prepared  by  boiling  melam  with  a  dilute  solution  of  caustic 
potash  until  the  liquor  becomes  quite  clear ;  it  is  then  to  be  evaporated  until  it  be- 
gins to  deposite  small  crystalline  plates,  and  being  then  allowed  to  cool,  the  mel- 
lamine  crystallizes  out  in  colourless  octohedrons,  scarcely  soluble  in  cold  water. 
It  has  no  action  on  vegetable  colours,  but  it  combines  with  dilute  acids,  acting  as 
a  base,  and  forming  well-defined  salts,  which  have  an  acid  reaction,  and  may  be 
obtained  crystallized. 

Ammeline. — CeNs  .  H5O2.  After  the  alkaline  solution  has  deposited  the  melamine 
by  cooling,  it  contains  ammeline,  which  precipitates  when  acetic  acid  is  added. 
This  is  to  be  purified  by  solution  in  dilute  nitric  acid,  and  precipitation  by  carbonate 
of  ammonia.  It  then  forms  fine  silky  needles,  insoluble  in  water  and  alcohol.  It 
combines  with  the  dilute  acids,  forming  crystallizable  salts. 

The  origin  of  these  bodies  consists  in  the  melam  decomposing  two  atoms  of 
water,  and  then  C12H11  .  NnOj  producing  CeHeNs  and  CeNs  .  H5O2.  By  boiling 
melam  in  dilute  muriatic  acid,  the  same  decomposition  occurs,  and  the  muriates 
of  melamine  and  ammeline  crystallize  together  on  cooling. 

If  any  of  the  above  three  bodies  be  dissolved  in  strong  sulphuric  acid,  and  the 
solution  be  precipitated  by  alcohol,  a  white  powder  is  obtained,  insoluble  in  water 
and  alcohol,  but  soluble  in  strong  acids  and  alkalies.  It  is  nearly  indifferently  acid 
or  base,  as  it  combines  with  nitric  acid,  and  also  with  oxide  of  silver.  It  is  termed 
Ammelide.  Its  formula  is  C12H7 .  N904-|-2  Aq.  When  this  body  is  boiled  for  a  long 
time  with  dilute  sulphuric  or  nitric  acid,  it  is  resolved  into  ammonia  and  Cyanuric 
Acid,  which  last  is  the  ultimate  product  of  the  similar  treatment  of  all  the  bodies  of 
this  series. 


OP     STARCH,     ETC.  527 

The  theoretical  constitution  of  these  bodies  remains  exceedingly  obscure.  The 
bases,  melamine  and  ammeline,  are  of  great  importance,  from  their  close  analogy 
to  the  alkaloids,  which  are  found  naturally  in  many  plants ;  but  still  we  have  no 
idea  of  the  mode  of  arrangement  of  their  elements. 

Some  other  sulphur  compounds  of  cyanogen  are  known,  but  do  not  require  muck 
notice.  Cyanogen  and  sulphuretted  hydrogen  combining,  form  orange  crystals,  in- 
soluble in  water. 


CHAPTER  XX. 

OF    STARCH,    LIGNINE,    GUM,    AND    SUGAR,    WITH    THE    PRODUCTS    OF    THEIR 
DECOMPOSITION    BY   ACIDS    AND    ALKALIES. 

The  substances  now  to  be  described  form  a  very  remarkable  class 
of  organic  bodies.  They  are  found  abundantly  in  most  plants,  but 
varying  somewhat  in  characters,  according  to  their  immediate 
source,  and  are  subservient  to  the  most  important  offices  of  the 
vegetable  organization,  being  the  materials  from  whence  the  tissues 
and  secretions  of  the  plant  are  elaborated.  In  a  chemical  point  of 
view,  they  are  distinguished  by  a  remarkable  similarity  of  compo- 
sition, all  containing  the  same  quantity  of  carbon  (twelve  atoms)  in 
the  equivalent,  united  to  oxygen  and  hydrogen,  which  are  always 
present  in  the  proportions  to  form  water.  In  this  may  be  found  the 
cause  of  the  extraordinary  transmutations  of  these  bodies  from  one 
to  another,  by  the  mere  fixation  of  the  elements  of  water,  effected 
by  the  influence  of  reagents,  or  by  the  organic  power  -of  the  plant. 
In  these  bodies,  also,  we  find  an  example  of  the  difficulty  of  distin- 
guishing between  a  constitution  derived  from  physical,  and  that  re- 
sulting from  vital  force.  In  the  different  kinds  of  sugar,  the  crys- 
talline condition,  solubility,  &c.,  indicate  that  the  elements  are 
combined  by  forces  merely  chemical ;  but  in  the  different  varieties 
of  starch,  and  especially  in  lignine,  traces  of  organized  structure 
are  found,  and  properties  manifested,  which  attach  their  history  as 
closely  to  the  physiology  as  to  the  chemistry  of  plants.  Under  this 
point  of  view  they  shall  be  hereafter  reconsidered. 

Of  Starch,  its  Varieties  and  Products. 

The  most  important  variety  of  this  principle  is  that  known  as 
Common  Starch.  It  exists  in  most  plants,  and  in  all  parts  of  them. 
It  is  extracted  from  the  seeds  of  wheat  and  barley  ;  from  the  tubers 
of  the  potato  ;  from  the  root  of  the  jatropha  manihot,  as  Tapioca  or 
Cassava,  and  of  the  maranta  arundinacea,  as  j^rrow-root ;  and  from 
the  stems  of  palms,  as  the  sagus  rumphii,  which  furnishes  the  Sago 
of  commerce.  The  starch  is  imbedded  in  the  cellular  tissue  of  the 
plant  as  small  white  grains,  totally  destitute  of  any  crystalline  struc- 
ture. They  differ  in  size  in  almost  every  plant.  Those  of  the  po- 
tato, which  are  the  largest,  do  not  exceed  in  diameter  o  j^^^  of  an 
inch  ;  those  of  arrow-root,  which  are  some  of  the  smallest,  do  not 
exceed  ^  ^o^^*    ^^  form,  these  grains  vary  also,  some  being  globular, 


528  PRE  PAR  AT  I  O'N     OF     STARCH,     ETC. 

Others  ovoidal,,  and  often,  eve^^.  in  the  same  plant,  irregular.  Each 
grain  is  formed  by  a  number  of  concentric  layers,  which  increase  in 
density  and  consistence  from  the  centre ;  the  most  external  being 
so  hard  as  to  resemble  a  membranous  envelope  filled  by  a  softer 
material. 

The  grains  of  starch  are  quite  insoluble  in  cold  water;  in  boiling 
water  they  dissolve,  except  the  outer  layers,  which,  floating  in  the 
liquor,  give  it  a  peculiar  opalescent  aspect.  On  cooling,  the  solu- 
tion gelatinizes.  If  the  solution  of  starch  be  dried  at  a  gentle  heat, 
and  then  digested  with  cold  water,  the  outer  layers  of  the  grains 
may  be  separated  by  filtration,  and  a  colourless  transparent  solution 
of  starch  thus  obtained. 

The  preparation  of  starch  rests  on  its  insolubility  in  cold  water. 
The  texture  of  the  plant  is  first  broken  up  by  rasping  or  coarse 
grinding,  and  being  then  mashed  up  with  water,  the  starch  grains 
fall  out  from  the  ruptured  cells,  and  are  carried  off  by  the  current, 
from  which  they  deposite  themselves  when  the  liquors  are  left  at 
rest.  In  obtaining  starch  from  wheat,  this  liquor  is  allowed  to  fer- 
ment and  become  sour,  by  which  a  quantity  of  gluten  that  would 
otherwise  attach  itself  to  the  starch  is  removed.  If  the  moist  starch 
grains  be  dried  at  a  temperature  of  about  140^,  they  gelatinize  to  a 
semitransparent  mass,  which  remains  so  when  dried,  and  is  not 
granular  or  mealy.  It  is  thus  that  the  peculiar  aspect  of  tapioca 
and  sago  is  produced. 

By  the  vital  action  of  the  seed  in  germination,  the  transformation 
of  starch  into  sugar  is  effected,  and  constitutes  the  saccharine  fer- 
mentation. It  is  artificially  induced  by  malting  the  grain,  for  the 
preparation  of  alcoholic  liquors  by  brewers  and  distillers.  The  cir- 
cumstances .of  this  change  will  be  specially  noticed  when  describing 
the  mode  of  nutrition  and  of  the  growth  of  plants. 

If  starch  be  heated  beyond  240\  it  softens  and  becomes  brown. 
If  the  heat  be  increased  until  the  mass  smokes,  it  is  found  to  be 
changed  into  a  substance  totally  soluble  in  cold  water,  and  known 
as  British  Gum. 

The  action  of  reagents  on  starch  is  very  remarkable.  By  boiling 
with  dilute  sulphuric  or  muriatic  acids,  a  kind  of  saccharine  ferment- 
ation is  induced,  it  being  changed  successively  into  gum,  sugar, 
and  sacchulmine.  By  boiling  with  nitric  acid,  it  gives  saccharic 
and  oxalic  acids.  These  reactions  will  be  hereafter  studied  in  de- 
tail. A  solution  of  it  is  precipitated  by  basic  acetate  of  lead  and  by 
infusion  of  galls.  With  bromine  it  gives  a  yellow  precipitate,  which 
is  decomposed  by  heat,  the  bromine  being  expelled.  With  iodine 
it  produces  a  compound  of  an  intense  blue  colour,  which  is  its  most 
remarkable  property. 

Iodide  of  Starch  is  produced  when  a  solution  of  free  iodine  is  add- 
ed to  a  solution  of  starch.  Its  colour  is  violet  blue  or  nearly  black, 
according  to  the  proportion  of  starch.  It  is  very  soluble  in  water, 
but  insoluble  in  alcohol,  and  may  be  obtained  solid  by  adding  alco- 
hol to  a  very  strong  aqueous  solution,  and  collecting  the  precipi- 
tate on  a  filter.  It  is  decomposed  by  alkalies  and  hy  chlorine  ,•  in- 
deed, by  all  bodies  which  combine  with  iodine  ;  and  its  formation 
serves,  therefore,  as  a  test  only  for  free  iodine,  as  described  in  p. 


I 


INULIN,    LICHENINE,    AND     LIGNINE.  529 

313.  When  a  solution  of  iodide  of  starch  is  heated,  it  becomes 
quite  colourless  below  200°,  and,  if  it  be  not  boiled,  regains  its  col- 
our perfectly  as  it  cools.  When  the  liquor  remains  colourless  after 
cooling,  the  blue  may  be  restored  by  oxalic  acid  or  by  chlorine, 
which  expels  the  iodine  from  the  combination  it  had  formed. 

The  composition  of  starch,  no  matter  what  plant  it  may  be  deri- 
ved from,  is  C,2H,oO,o,  as  confirmed  by  a  variety  of  reactions.  Its 
combination  with  oxide  of  lead,  Amylate  of  Lead,  is  Cj2HioOjo4-2 
Pb.O. 

Jnulin. — This  kind  of  starch  is  found  in  the  roots  of  the  inula,  dahlia,  angelica, 
leontodon,  and  many  other  plants.  It  may  be  prepared  in  the  same  way  as  common 
starch.  It  is  a  white  and  very  fine  powder,  almost  insoluble  in  cold  water,  but  easi- 
ly dissolved  by  boiling  water ;  forming  a  liquor  which  becomes  thick,  but  not  gelati- 
nous, when  it  cools,  and  deposites  the  greater  part  of  the  inulin  unchanged.  It  is 
transformed  by  acids,  like  common  starch,  but  more  easily.  It  is  precipitated,  like  it, 
by  solutions  of  borax  and  subacetate  of  lead,  and  by  infusion  of  galls.  It  is  pecu- 
liarly distinguished  from  it  by  not  giving  with  iodine  any  blue  colour,  being  merely 
tinged  yellow.  The  structure  of  the  grains  of  inulin  has  not  been  accurately  ex- 
amined. Its  formula  is  C12H10O10,  like  that  of  common  starch,  but  in  combining 
with  oxide  of  lead  it  appears  to  lose  one  atom  of  water,  and  to  become  C12H9O9,  as 
remarked  by  Parnell. 

Licheniyie. — This  variety  of  starch,  which  is  found  in  many  lichens,  especially  the 
Iceland  moss  and  the  carrigeen  (sphcero coccus  crispus),  is  not  contained  in  the 
plant  in  grains,  but  in  a  soluble  condition.  To  obtain  it,  the  lichen  is  first  digested 
in  a  cold  dilute  solution  of  carbonate  of  soda,  to  dissolve  the  bitter  resinous  princi- 
f)le,  and  this  being  completely  washed  away,  the  lichen  is  boiled  for  a  long  time 
in  water;  a  liquor  is  obtained,  from  which,  on  cooling,  the  lichenine  separates  as  an 
opaque  gray  jelly,  which,  when  dried,  is  black,  hard,  and  glassy.  Its  properties  are 
very  similar  to  those  of  inuline.  It  gives  with  iodine  a  greenish-brown  colour.  Its 
composition  is  expressed  by  the  same  fonnula  as  the  others,  C12H10O10. 

Of  Lignine.     Principle  of  Woody  Fibre, 

When  any  kind  of  wood  is  treated  successively  and  repeatedly 
by  dilute  acids  and  alkalies,  by  water  and  by  alcohol,  so  that  every 
soluble  material  is  removed  from  it,  we  find  that  the  substance 
which  remains  is  of  very  constant  composition,  being  expressed  by 
the  formula  CjaH^Oj;.  Of  this  substance,  Lignine,  the  proper  wood 
of  the  plant  is  constituted  ;  its  molecules  being  arranged  so  as  to 
form  the  tubes  and  cells  of  the  vegetable  tissues,  and  cohering  so 
firmly  as  to  produce  the  fibres  of  flax,  cotton,  and  hemp,  which  con- 
stitute the  materials  of  our  most  important  woven  textures,  of  pa- 
per, &-C.  Although  the  lignine  is  thus  rather  the  remains  of  an  or- 
ganized body  than  a  mere  chemical  substance,  it  forms  some  com- 
binations which  are  of  great  importance  in  the  arts.  Thus,  if  linen 
or  cotton  cloth  be  dipped  in  dilute  solution  of  acetate  of  alumina, 
the  earth  abandons  the  acid  to  combine  with  the  lignine,  and  thus 
serves  as  the  means  of  fixing  on  the  cloth  the  various  colouring 
matters  used  in  the  processes  of  dyeing.  The  same  occurs  with 
oxide  of  iron ;  and  other  metallic  o-xides  have  a  similar,  though 
weaker  affinity  for  lignine,  and  thus  serve  as  mordants  for  various 
colours. 

Lignine,  when  quite  pure,  is  white ;  the  bleaching  of  linen,  cot- 
ton, paper,  &c.,  being  eflfected  by  destroying,  by  means  of  the  air 
or  of  chlorine,  the  resinous  and  other  matters  which  are  associated 
with  the  lignine  in  the  fibres  or  cells  of  the  plants  j  the  lignine  it- 
self resists  these  agents,  unless  applied  in  a  very  concentrated  form 

X  X  X 


530  ARABINE     AND     TRAGACANTHINE. 

With  cold  nitric  acid  lignine  combines  directly,  forming  a  very  re- 
markable substance,  Xylo'idine,  which  may  be  produced  by  immer- 
sing for  a  moment  a  piece  of  paper  in  strong  nitric  acid,  and  then 
washing  it  well  in  pure  water.  It  assumes  the  feel  and  toughness 
of  parchment,  and  is  so  combustible  as  to  serve  for  tinder.  Hot 
nitric  acid  converts  lignine  into  oxalic  acid  ;  with  sulphuric  acid  it 
is  changed  into  gum,  and  ultimately  into  sugar,  as  will  be  detailed 
farther  on. 

If  sawdust  be  heated  with  a  warm  solution  of  potash  for  some 
hours,  the  liquor  will  be  found  to  contain  a  considerable  quantity 
of  common  starch,  capable  of  striking  a  blue  colour  with  iodine ; 
but  by  this  means  the  ligneous  fibre  is  dissected,  and  not  decom- 
posed. The  starch  may  be  extracted  also  by  mechanical  means, 
and  pure  lignine  does  not  yield  any.  If  lignine  be  strongly  heated 
with  hydrate  of  potash,  hydrogen  is  evolved,  and  a  mixture  of  ace- 
tate and  oxalate  of  potash  results  5  C,2Hs08  and  4H.0.  giving  6H., 
with  2(C,03)  and  2(0^03). 

In  dry  air,  or  immersed  under  water  free  from  air,  lignine  remains 
for  an  indefinite  length  of  time  unaltered  ;  but  if  both  air  and  water 
have  access,  oxygen  is  absorbed,  and  carbonic  acid  and  water  given 
out,  and  a  series  of  products  of  decomposition  result,  which  form 
the  basis  of  vegetable  soil^  and  thus  serve  as  the  materials  for  a  new, 
generation  of  plants.  By  the  conjoint  action  of  heat  and  water,  lig- 
nine produces  another  class  of  products,  and  a  third  series  arises 
from  the  destructive  distillation  of  dry  wood.  These  subjects  will 
be  examined  specially  in  their  proper  place. 

Of  the  different  Varieties  of  Gum. 

It  is  necessary  to  distinguish  three  varieties  of  gum,  to  which 
the  names  of  Arahine^  Cerasine^  and  Dextrine  may  be  given.  The 
first  two  are  natural,  the  last  is  a  product  of  the  transmutation  of 
starch. 

Arahine  is  found  in  the  juices  of  many  species  of  acacia  and  pru- 
nusj  it  exudes  from  crevices  in  the  bark,  and  forms  lumps,  in  which 
state  it  is  found  in  commerce  (^Gum  Arabic  and  Gum  Senegal).  The 
roots  of  mallow,  comfrey,  and  many  other  plants  contain  a  great 
deal  of  arabine.  It  is  never  crystalline,  and  is  colourless  and  trans- 
parent, with  a  vitreous  fracture.  It  is  dissolved  by  water  in  all 
proportions,  forming  a  thick,  adhesive  liquid  (mucilage).  It  is  not 
dissolved  by  alcohol,  which  precipitates  its  watery  solution.  It 
combines  with  bases,  forming  well-defined,  insoluble  compounds, 
and  is  not  in  any  way  acted  on  by  iodine.  A  solution  of  arabine 
exercises  sinistral  rotatory  power  on  a  ray  of  polarized  light  (p.  41). 
By  contact  with  sulphuric  acid,  arabine  is  gradually  converted  into 
dextrine,  and,  if  the  digestion  be  continued,  this  then  changes  into 
sugar.  With  nitric  acid  arabine  gives  mucic  acid,  and  afterward 
oxalic  acid  ;  another  characteristic  property  of  it  is,  that  of  giving 
a  precipitate  with  solution  of  silicate  of  potash  (soluble  glass,  p. 
437).     Its  composition  is  expressed  by  the  formula  Ci^HnO,,. 

Tragacanthine^  or  Vegetable  Mucus,  exists  in  cherry-tree  gum  mix- 
ed with  arabine,  but  is  purer  in  gum  tragacanth,  in  flaxseed,  and  in 
quince- seed.     It  is  extracted  by  digestion  in  water,  when  it  gradu- 


DEXTRINE. CANE-SUGAR.  531 

ally  swells  up  and  appears  rather  to  imbibe  the  water  than  to  dis- 
solve ;  a  thick  tenacious  liquor  is  obtained,  which  is  precipitated  by 
alcohol  and  by  solution  of  basic  acetate  of  lead,  but  not  by  silicate 
of  potash.  With  sulphuric  and  nitric  acid,  the  same  products  are 
formed  as  from  arabine. 

The  Salep  of  commerce  is  the  tragacanthine  extracted  from  the 
roots  of  various  species  of  orchis,  and  dried. 

Dextrine. — This  variety  of  gum  is  formed  from  the  starch  of  the 
seed,  in  germination,  and  may  be  obtained  by  digesting  starch  in 
dilute  sulphuric  acid.  If  five  parts  of  starch,  with  one  of  oil  of  vit- 
riol and  fifteen  of  water,  be  kept  at  200*^  for  some  time,  the  starch 
completely  disappears,  the  solution  loses  its  power  of  gelatinizing; 
it  acquires  the  characteristic  rotatory  power  of  Dextrine^  and  colours 
iodine  of  a  port-wine  red,  without  any  tinge  of  blue.  If  the  liquor 
be  neutralized  by  carbonate  of  barytes,  the  whole  quantity  of  sul- 
phuric acid  separates,  and  by  evaporation,  the  dextrine  is  obtained 
as  a  pale  yellow  mass  of  a  vitreous  fracture ;  it  is  not  adhesive  like 
common  gum,  nor  does  it  yield  any  mucic  acid  when  acted  on  by 
nitric  acid. 

Dextrine  precipitates  a  solution  of  basic  acetate  of  lead,  but  is  not 
aftected  by  silicate  of  potash.  If  dextrine  be  boiled  too  lo«ng  with 
the  sulphuric  acid,  it  passes  into  a  substance  more  analogous  to 
tragacanthine,  which  is  also  formed  when  arabine  or  lignine  is  so 
treated.  In  this  state  its  rotatory  power  is  feeble,  and  it  is  not  at 
all  coloured  by  iodine.  In  both  these  forms  the  composition  of 
dextrine  is  CiaHjoOio. 

Of  the  different  Varieties  of  Sugar. 

The  species  of  sugar  are  much  better  distinguished  from  each 
other,  both  by  properties  and  composition,  than  the  various  kinds 
of  starch,  or  of  gum,  have  been  found  to  be.  They  are  all  charac- 
terized by  being  capable  of  undergoing  the  alcoholic  fermentation. 

Cane-sugar. — C,2HioO,o+Aq.  when  crystallized.  This  species  of 
sugar  is  found  abundantly  in  the  juices  of  many  plants.  It  is  ex- 
tracted for  use  from  the  sugar-cane,  the  maple,  and  the  beet-root. 
The  juice,  when  fresh,  runs  into  fermentation  with  great  quick- 
ness, and  is  therefore  clarified  by  being  warmed  to  150^,  with  a  lit- 
tle lime,  by  which  the  vegetable  albumen  is  coagulated,  and  the  fer- 
mentation checked.  The  juice  is  then  evaporated  with  as  little 
heat  as  possible,  and  allowed  to  cool  in  vessels,  at  the  bottom  of 
which  a  number  of  small  apertures,  stopped  with  plugs,  are  situated. 
The  sirup  congeals  into  a  granular  mass,  and  when  it  is  quite  cold, 
the  apertures  below  are  opened,  and  the  liquid  portion  allowed  to 
run  out.  The  sugar  thus  obtained  in  fine  crystalline  grains  is 
brownish-coloured,  and  is  termed  Muscovado,  or  Raw  Sugar.  The  li- 
quid uncrystallizable  portion  constitutes  Molasses,  or  Treacle.  To  ob- 
tain the  sugar  pure,  it  is  redissolved,  and  the  liquor  having  been 
cautiously  evaporated  (in  some  establishments,  in  vacuo,  see  p.  85) 
to  the  necessary  degree,  is  poured  into  cones  of  unglazed  earthen- 
ware, which  are  placed  on  their  summits,  the  orifice  in  which  is 
stopped  by  a  plug.  When,  by  cooling,  the  sirup  has  crystallized, 
during  which  the  mass  is  continually  stirred  about  to  render  the 


532  SACCHULMINE. SACCHARIC      ACID. 

crystals  very  minute  and  close,  the  plug  below  is  removed,  and  tha 
coloured  liquor  drains  out ;  the  last  portions  of  it  being  removed  by 
laying  a  sponge,  moistened  with  some  spirit  or  with  a  clear  sirup, 
on  the  sugar  at  the  base  of  the  cone,  and  allowing  the  pure  liquid 
to  filter  throuo-h.  Thus  is  obtained  refined^  or  Loaf-sugar.  If  a  strong 
sirup  be  laid  aside  in  a  warm  place,  it  crystallizes  in  very  beautiful 
oblique  rhombs,  which  constitute  the  Sugar-candy  of  commerce. 

Cane-sugar  is  perfectly  colourless.  Its  sp.  gr.  is  1*6  ;  when  heat- 
ed, it  fuses  at  350^  into  a  clear  yellow  liquid,  and  congeals,  on  cool- 
inor,  into  a  hard  brittle  mass  (barley-sugar),  which,  after  some  weeks, 
becomes  opaque,  white,  and  crystalline.  If  the  temperature  rises  to 
630°,  water  is  given  off,  and  the  sugar  becomes  dark  brown,  being 
changed  into  Caramel ;  more  strongly  heated,  it  is  totally  decom- 
posed. Sugar  dissolves  in  one  third  of  its  weight  of  cold,  and  in  all 
proportions  in  boiling  water.  A  saturated  solution  becomes  quite 
solid  when  it  cools.  If  a  strong  solution  of  sugar  be  kept  for  some 
time  near  its  boiling  point,  it  is  gradually  changed  into  uncrystalli- 
zable  sugar;  hence  arises  the  most  important  source  of  loss  in  the 
manufacture  and  refining  of  sugar.  It  is  sparingly  soluble  in  abso- 
lute alcohol,  and  but  moderately  in  weak  spirit. 

Suga?  combines  with  some  bases  and  salts,  acting  as  a  feeble  acid  j 
the  compound  with  oxide  of  lead  is  insoluble,  and  has  the  formula 
C,2H,oO,o4-2Pb.O. ;  that  with  barytes  is  crystalline:  its  formula  is 
C,2H,oO,o+Ba.O.  With  common  salt  sugar  combines,  forming  crys- 
tals, easily  soluble  in  water,  and  consisting  of  Ci^HioOio  +  Na.Cl. 

The  action  of  acids  on  cane-sugar  is  very  remarkable.  When  di- 
gested with  very  dilute  sulphuric  or  muriatic  acid,  it  is  converted 
into  grape-sugar  ;  but  with  stronger  acids,  it  is  changed  into  two 
brown  substances,  insoluble  in  water,  one  of  them  soluble,  the  other 
insoluble  in  alkaline  liquors.  The  former  is  termed  Sacchulmine^ 
the  latter,  Sacchulmic  Acid.  These  bodies  are  formed  even  with 
very  dilute  acids  if  the  digestion  be  continued  for  a  long  time.  Ac- 
cording as  the  reaction  proceeds,  the  sacchulmine  separates  in  mi- 
nute brilliant  brown  crystalline  plates,  mixed  with  a  dull  brown 
powder,  which  is  sacchulmic  acid.  They  are  separated  by  water 
of  ammonia,  which  dissolves  the  latter.  The  composition  of  these 
bodies  is  not  quite  definitely  established,  as  it  appears  to  be  influ- 
enced by  the  strength  of  the  acid  used  and  other  circumstances. 
The  best-grounded  idea  is,  that  they  have  both  the  same  composi- 
tion, CaoH,50|5,  being  isomeric  with  ulmine.  If  in  this  reaction  the 
atmospheric  air  have  access,  oxygen  is  absorbed,  and  a  large  quan- 
tity of  formic  acid  generated.  • 

The  preparation  of  oxalic  acid  by  means  of  nitric  acid  and  sugar 
has  been  already  described  (p.  493).  If  dilute  acid  be  used,  so  that 
the  oxidation  may  not  be  forced  so  far,  a  liquor  is  obtained  which 
gives  with  carbonate  of  lime  a  neutral  solution.  When  this  is  de- 
composed by  acetate  of  lead,  a  white  precipitate  is  thrown  down, 
which  being  acted  on  by  sulphuretted  hydrogen,  the  acid  is  set  free, 
and  may  be  obtained  crystallized  by  evaporating  and  cooling  its  so- 
lution. This  is  termed  the  Saccharic  Acid.  It  gives  an  extensive 
series  of  salts,  being  a  pentabasic  acid.  Its  formula  is  Q^JlfS^u-\-^ 
H.O.  when  crystallized.     Its  potash  salt  is  CjzHiOa-fK.O.  .  4H.0. 


GRAPE-SUGAR.  533 

Its  lead  salt  CizHsOn+SPb.O.  The  saccharate  of  lime  is  sparingly 
soluble  in  water,  but  dissolves  in  a  very  slight  excess  of  acid,  which 
distinguishes  it  from  an  oxalate.  An  ammoniacal  solution  of  sac- 
charate of  silver  is  decomposed  by  heat ;  metallic  silver  being  de- 
posited, and  forming  a  mirror-surface  on  the  interior  of  the  vessel. 

The  Caramel  formed  by  heating  sugar  to  650^  appears  as  a  porous, 
shining,  jet  black  mass.  It  is  completely  soluble  in  water,  and  free 
from  any  empyreumatic  taste.  It  is  insoluble  in  alcohol ;  it  com- 
bines with  bases  j  its  formula  is  CiaHgOg.  The  sugar,  in  forming  it, 
therefore,  loses  the  elements  of  an  atom  of  water,  besides  its  water 
of  crystallization.  By  heating  sugar  with  lime,  a  volatile  liquid  is 
obtained,  which  has  the  formula  CeHjO.,  and  is  termed  Metacetone. 

Grape'SVgar.  Glucose. — C12H,, 0,1+3  Aq.  when  crystallized.  This 
kind  of  sugar  is  still  more  extensively  distributed  in  nature  than 
the  former.  It  gives  the  sweet  taste  to  fruits,  and  forms  the  solid 
part  of  honey.  It  is  produced  in  the  animal  body  in  certain  forms 
of  disease,  as  diabetes,  and  by  the  transformation  of  starch  in  ger- 
mination, and  by  artificial  processes.  In  consequence  of  this  vari- 
ety of  sources,  it  is  better  to  term  it  glucose,  as  suggested  by  Du- 
mas, than  to  use  a  name  indicating  any  one  special  origin. 

Glucose  may  be  obtained  from  raisins  or  honey  by  digestion, 
first  with  cold,  strong  alcohol,  to  remove  the  uncrystallizable  sugar, 
and  then  expressing  the  residue,  which  is  to  be  dissolved  in  water, 
and  neutralized  by  chalk.  The  liquor  so  obtained  may  be  clarified 
by  white  of  Qgg^  and  evaporated  to  crystallization. 

From  starch,  gum,  or  cane-sugar,  it  may  be  prepared  by  the  ac- 
tion of  sulphuric  acid  as  follows :  one  part  of  potato-starch  is  to  be 
boiled  with  four  parts  of  water  and  -V^^  ^^  ^i^  ^^  vitriol  during  36 
or  40  hours,  the  water  which  evaporates  being  replaced.  The  jelly 
does  not  assume  any  consistence ;  the  liquor  remains  clear,  and  the 
material  used  is  found  completely  converted  into  sugar.  By  means 
of  chalk,  the  acid  is  removed,  and  the  solution  being  evaporated, 
the  sugar  crystallizes. 

If  starch  paste  be  moistened  with  an  infusion  of  pale  malt,  it  is 
rapidly  converted  into  dextrine,  and  thence  into  grape-sugar.  This 
occurs  from  the  catalytic  influence  of  a  principle  termed  Diastase, 
which  exists  in  the  malt,  and  the  formation  of  which  will  be  de- 
tailed under  the  head  of  germination. 

To  convert  lignine  into  sugar,  bits  of  paper  or  linen  are  to  be  im- 
bibed with  their  own  weight  of  oil  of  vitriol,  until  they  are  convert- 
ed into  a  uniform  viscid  mass,  taking  care  that  it  shall  not  become 
hot ;  this  is  then  to  be  diluted,  and  the  liquor  boiled  for  some  time. 
The  acid  being  then  removed  by  chalk,  the  sugar  is  obtained  pure, 
by  crystallization,  as  in  the  former  case. 

Sugar  of  grapes  crystallizes  in  hard  colourless  tables  or  in  hemi- 
spherical grains,  consisting  of  minute  needles  closely  aggregated 
together ;  its  specific  gravity  is  1-38 ;  it  is  much  sweeter  than  cane- 
sugar,  and  less,  soluble  in  water.  When  heated  to  212°,  it  gives  off 
two  atoms  of  water,  which  it  recovers  when  redissolved  3  but  by  a 
stronger  heat  it  is  changed  into  caramel.  It  is  soluble  in  twenty 
parts  of  boiling  absolute  alcohol,  and  separates  almost  totally  on 
cooling,  ia  granular  crystals,  which  contain  alcohol  combined.     It 


534  CONSTITUTION     OF     GRAPE-SUGAR. 

combines  with  bases,  forming  compounds  analogous  to  those  given 
by  cane-sugar. 

The  composition  of  crystallized  grape-sugar  is  C,2H,40i4,  or  CigHn 
Oh  +  3  Aq.  When  fused  at  212°,  it  becomes  C,2H,^0,2,  or  C,2H„0h 
+Aq.  Its  compound  with  chloride  of  sodium,  which  crystallizes 
in  fine  double  six-sided  pyramids,  consist  of  2(C|2H,20i2)4-Na.Cl.+ 
2  Aq.  With  a  solution  of  basic  acetate  of  lead  it  gives  a  white 
precipitate,  the  formula  of  which  is  C,2Hi,Oi,  +  3Pb.O.,  correspond- 
ing to  the  crystallized  sugar.  The  dry  grape-sugar  has  evidently 
the  same  composition  as  the  crystallized  cane-sugar. 

The  kinds  of  sugar  (glucose)  derived  from  these  different  sources 
are  not  so  really  identical  as  has  been  generally  supposed,  since 
they  are  found  to  act  differently  upon  polarized  light.  Grape-sugar, 
as  contained  in  the  grape-juice  or  in  the  juice  of  the  flowering 
grasses,  rotates  the  plane  of  polarization  to  the  left ;  but  if  the  juice 
be  evaporated  and  the  sugar  crystallized,  its  molecular  constitution 
is  so  totally  altered,  as  that,  when  redissolved,  it  gives  a  rotation  to 
the  right.  The  starch-sugar,  as  well  as  cane-sugar,  rotates  also  to 
the  right,  but  in  a  much  inferior  degree  to  the  starch-gum,  which, 
as  already  mentioned,  receives  its  name  of  dextrine  from  that 
quality. 

As  lignine,  starch,  gum,  and  cane-sugar  all  contain  the  same  quan- 
tity of  carbon  (C,2),  their  transformation  into  grape-sugar  consists 
evidently  in  the  fixation  of  the  elements  of  water  j  thus  lignine, 
Ci^HgOs  takes  4H.0.,  and  100  parts  of  sawdust  have  been  found  to 
give  115  of  sugar;  starch  (C|2H,oOio)  takes  2H.0.,  and  100  parts  of 
it  usually  yield  106.  It  has  been  remarked,  that  a  certain  quantity 
of  Mannite  is  at  the  same  time  produced,  besides  sacchulmine. 

Grape-sugar  yields,  when  treated  with  dilute  sulphuric  acid,  the 
same  brown  substances  as  cane-sugar ;  but  if  the  sulphuric  acid  be 
concentrated,  it  forms  with  the  elements  of  the  sugar  a  peculiar 
acid  termed  the  Sulphosaccharic.  Sugar  of  starch  or  grapes  is  to  be 
fused  at  a  low  heat,  and  1|  parts  of  oil  of  vitriol  then  well  mixed 
with  it.  If  the  sugar  be  pure  and  the  temperature  be  kept  low,  the 
product  is  not  coloured.  Its  constitution  is  not  rigidly  determined, 
but  its  lead  salt  consists  of  2(C,2HHO„)  +  S.03+4^Pb.O. 

In  acting  on  grape-sugar,  nitric  acid  gives  rise  to  the  same  pro- 
ducts, oxalic  and  saccharic  acids,  as  cane-sugar ;  indeed,  it  appears 
probable,  that,  like  the  other  strong  acids,  this  also  first  changes  the 
cane-sugar  into  glucose,  and  that  the  saccharic  acid  is  really  de- 
rived from  the  latter.  On  this  view  its  formation  is  more  easily 
explained  ;  for  as  the  dry  glucose  is  C,2H,|0|„  and  the  saccharic  acid 
is  C,2H^0,,,  the  oxygen  of  the  nitric  acid  simply  removes  six  atoms 
of  the  hydrogen  of  the  grape-sugar,  and  the  elements  of  the  acid  re- 
main. 

By  contact  even  with  the  strongest  bases,  cane-sugar  is  but  slowly 
altered,  and  hence  lime  may  be  employed  to  clarify  the  vegetable  jui- 
ces which  contain  it ;  but,  under  the  same  circumstances,  grape-su- 
gar is  rapidly  decomposed  and  an  acid  formed,  which  is  termed  Glu- 
cic  Acid.  It  is  very  soluble  in  water,  and  does  not  crystallize  ;  with 
lime,  barytes,  and  lead,  it  forms  neutral  soluble  salts,  but  it  precip- 
itates a  solution  of  basic  acetate  of  lead.     Its  taste  is  purely  acid. 


L  A  C  T  I  N  E. M  A  N  N  I  T  E.  535 

and  it  reddens  litmus.  Its  composition  is  CiaHgOg,  and  it  is  isomeric, 
therefore,  in  its  dry  state,  with  lignine.  When  a  strong  solution  of 
caustic  potash  is  added  to  fused  grape-sugar  boiled,  the  glucic  acid 
which  at  first  forms  is  decomposed.  The  liquor  becomes  deep 
brown,  and  yields,  on  the  addition  of  muriatic  acid,  a  black  fioccu- 
lent  precipitate  of  Melassic  Acid.  The  formula  Ca^HiaOjo  has  been 
assigned  to  it,  but  its  nature  is  not  well  know^n. 

Lacfine,  or  Sugar  of  Milk. — This  remarkable  substance,  which  is  found  only  in 
the  milk  of  the  mammalia,  is  obtained  by  evaporating  whey  to  a  pellicle  and  setting 
it  aside  to  cool,  when  the  sugar  crystallizes  in  small  square  prisms,  white,  semi- 
transparent,  hard,  and  gritty  under  the  teeth.  The  taste  of  the  crystals  is  but 
slightly  sweet,  but  that  of  a  strong  solution  is  much  more  so.  It  dissolves  very 
slowly  in  water,  and  is  insoluble  in  alcohol. 

When  the  crystals  of  lactine  are  gradually  heated  to  270°,  they  give  off  two 
atoms  of  water ;  at  about  300*^  they  fuse,  and  give  off  three  atoms  of  water  more. 
The  composition  of  the  dry  sugar  thus  obtained  is  C24H19O19,  and  of  the  crystals 
C24H19O194-5  Aq.  By  mixing  solutions  of  sugar  of  milk  and  of  basic  acetate  of 
lead,  a  wliite  precipitate  is  produced,  the  formula  of  which  is  C24Hi90i9-f-5Pb.O. 

By  digestion  with  dilute  sulphuric  acid,  sugar  of  milk  is  changed  into  grape-sugar, 
and  then  produce  the  other  reactions  already  described.  With  alkalies  the  decom- 
position is  also  the  same  as  that  of  glucose,  but  the  action  of  nitric  acid  on  lactine 
differs  from  that  on  any  other  sugai,  as  the  acid  formed  is  not  the  saccharic,  but 
that  already  noticed  as  obtained  from  native  gum,  the  Mucic  Acid. 

To  obtain  mucic  acid,  one  part  of  gum  or  lactine  is  to  be  dissolved  in  four  parts 
of  nitric  acid,  specific  gravity  1-42,  mixed  with  one  part  of  water.  Heat  is  to  be 
applied  until  all  effervescence  has  ceased,  and  the  mucic  acid  is  deposited  on  cool- 
ing. It  is  a  crystalline  powder,  gritty  under  the  teeth,  and  feebly  acid.  It  dissolves 
in  six  parts  of  boiling  water,  but  is  insoluble  in  alcohol.  Its  crystals  have  the  form- 
ula C)2HioOi6,  being  formed  from  gum  by  the  simple  addition  of  six  equivalents  of 
oxygen.  This  formula  contains,  however,  2  Aq.,  as  it  is  a  bibasic  acid,  and  its  salts 
consist  of  C2iH80i4-|*2M.O.  The  alkaline  mucates  are  soluble,  the  earthy  and  me- 
tallic salts  are  insoluble  in  water. 

When  mucic  acid  is  long  boiled  with  water,  its  acid  properties  become  much 
stronger,  and  it  becomes  more  soluble  in  water  and  soluble  in  alcohol ;  it  gradually 
returns  from  this  state  to  its  ordinary  condition,  even  when  combined  with  bases. 
If  mucic  acid  be  distilled  at  a  high  temperature,  water  and  carbonic  acid  are  evolv- 
ed, and  a  sublimate  forms  in  brilliant  white  plates,  which  are  soluble  in  alcohol  and 
water  ;  CuHioOie  giv^  20. O2  and  6H.0.,  besides  C10H4O6,  which  is  the  formula  of 
the  hydrated  Pyromucic  Acid.  This  substance  fuses  at  270°,  and  is  volatile  at  290° 
without  decomposition.  Its  salts  contain  one  equivalent  of  base  ;  those  of  lead, 
barytes,  and  silver  are  insoluble  ;  those  of  the  alkalies  are  very  soluble  in  water. 

With  this  acid  a  certain  quantity  of  chlorine  may  be  combined,  forming  Chloro- 
pijromucic  Acid,  C10H3 .  CI4O5,  which  is  prepared  by  acting  with  chlorine  on  Pyro- 
mucic Ether. 

Sugar  of  Mushrooms  is  deposited  in  rhombic  prisms  from  the  watery  solution  of 
the  alcoholic  extract  of  ergot  of  rye.  They  are  insoluble  in  ether  ;  they  give  oxalic 
acid  by  nitric  acid,  and  undergo  the  alcoholic  fermentation.  Their  composition 
was  found  to  give  the  formula  C12H13O13,  but  little  is  known  accurately  of  this  va- 
riety of  sugar. 

Of  Mannite  and  Glycyrrhizine. 

These  bodies  are  connected  so  closely  with  the  true  sugars,  that,  although  want- 
ing in  the  characteristic  of  forming  alcohol  by  fermentation,  they  may  be  best  de- 
scribed here. 

Mannite,  CeHvOs,  is  found  in  manna,  of  which  it  constitutes  the  sweet  principle. 
It  exudes  also  from  the  bark  of  other  trees,  and  exists  in  most  mushrooms.  It  is 
produced  by  the  decomposition  of  cane-sugar  in  certain  cases.  To  obtain  it,  manna 
is  digested  in  boiling  alcohol,  and  the  liquor  filtered  while  very  hot ;  on  cooling,  the 
mannite  is  deposited  almost  totally,  and  may  be  purified  by  repeated  crystalliza- 
tions. Its  taste  is  slightly  sweet ;  it  is  very  soluble  in  water,  and  it  crystallizes  in 
brilliant  white  prisms  of  silky  lustre.    When  heated  gently,  it  fuses  without  losing 


536  LACTIC     ACID. GLYC  YRRHIZINE. 

weight.     With  nitric  acid  it  gives  oxaUc  and  saccharic  acids.     It  does  not  appeal 
to  combine  with  bases. 

If  the  unclarified  juice  of  the  beet  or  carrot  root  be  kept  at  a  temperature  of  100^ 
for  some  time,  a  tumultuous  decomposition  sets  in,  which  is  termed  the  mucous  fer- 
mentation. Ail  the  sugar  disappears,  and  the  liquor  is  found  to  contain  a  large 
quantity  of  gum  and  of  mannite,  with  a  peculiar  acid,  which  exists  naturally  in  aU 
the  animal  fluids,  but  especially  in  milk,  and  is  termed  the  Lactic  Acid.  At  the 
same  time,  carbonic  acid  gas  is  evolved,  and  the  liquor  contains  ammonia.  This 
reaction  is  too  complex  to  be  expressed  in  formulae,  but  it  may  be  noticed  that  one 
equivalent  of  dry  cane-sugar  contains  the  elements  of  two  equivalents  of  lactic  acid ; 
while,  by  abstracting  two  atoms  of  oxygen  from  an  equivalent  of  crystallized  grape- 
sugar,  the  constituents  of  two  atoms  of  mannite  remain. 

Lactic  acid  is  most  easily  prepared  by  means  of  this  mucous  fermentation,  but 
may  be  also  obtained  abundantly  from  sour  whey,  or  the  sour  waters  obtained  in 
making  wheaten  starch.  The  acid  liquor  is  to  be  neutralized  by  carbonate  of  lead, 
and  the  solution  of  lactate  of  lead  evaporated  until  it  is  tolerably  concentrated.  It 
is  then  to  be  decomposed  by  sulphate  of  zinc,  and  the  precipitated  sulphate  of  lead 
being  removed  by  the  filter,  the  lactate  of  zinc  may  be  obtained  in  large  crystals, 
easily  rendered  quite  pure  by  re-solution  and  crystallization.  A  solution  of  pure 
lactate  of  zinc  being  decomposed  by  water  of  barytes,  lactate  of  barytes  is  obtained, 
which,  with  sulphuric  acid,  gives  sulphate  of  barytes,  and  the  pure  lactic  acid  dis- 
solves. The  solution  is  to  be  placed  in  vacuo  over  sulphuric  acid  ;  it  gives  a  sirup- 
thick  liquor,  which  has  the  formula  CeHsOe  or  CeHsOa-^Aq.,  as  it  contains  an  atom 
of  basic  water  ;  it  tastes  strongly  acid.  When  heated  to  480°  it  gives  off  water, 
and  a  white  smblimate  forms  in  brilliant  white  rhomboidal  plates,  which  is  Paralac 
tic  Acid.  It  is  purified  by  solution  in  boiling  alcohol,  from  which  it  crystallizes. 
The  composition  of  this  body  is  C6H4O4 ;  it  fuses  at  225°,  and  sublimes  at  450°  ;  it 
tastes  very  slightly  acid,  and  dissolves  but  very  slowly  in  water ;  the  solution  gives, 
when  evaporated,  only  the  sirupy  liquid  of  the  hydrated  acid,  and  does  not  crys 
tallize. 

The  lactic  acid  coagulates  albumen  ;  it  mixes  with  milk  when  cold,  but  coagu- 
lates it  when  boiled.  It  forms  monobasic  salts,  in  which  its  formula  is  CeHsOs, 
They  are  all  soluble  in  water,  and  crystallize  but  imperfectly,  except  that  of  zinc, 
which  forms  brilliant  white  four-sided  prisms,  containing  three  atoms  of  crystal- 
water.  The  Protolactate  of  Iron,  C6H505-i-Fe.O.-f3  Aq.,  may  be  obtained  crystal- 
lized in  small  prisms  of  a  greenish-yellow  colour.  The  Perlactate  of  Iron  dries  into 
a  reddish  transparent  mass  like  shell-lac.     These  last  are  used  in  medicine. 

The  lactic  acid  will  be  again  noticed  as  a  constituent  of  the  animal  system. 

Glycyrrhizine. — This  substance,  which  is  found  in  the  liquorice-root,  and  in  some 
other  sweet  woods,  is  obtained  by  boiling  the  root  or  liquorice  in  water,  and,  after 
concentrating  the  liquor,  adding  thereto  sulphuric  acid.  A  white  precipitate,  con- 
taining the  glycyrrhizine  combined  with  sulphuric  acid  and  albumen,  is  formed. 
This  is  to  be  washed  with  acid  water,  and  then  with  pure  water, -and  to  be  dissolv- 
ed in  alcohol,  which  leaves  the  albumen.  The  alcoholic  solution  is  to  be  decom- 
posed by  carbonate  of  potash,  which  throws  down  ths  sulphuric  acid,  and  by  evap- 
orating the  filtered  liquor,  the  sweet  principle  remains  pure  as  a  yellow  transparent 


Its  most  remarkable  property  is  that  of  combining  very  definitely  with  acids  and 
bases,  and  with  several  neutral  salts.  Almost  every  acid  precipitates  a  compound 
from  a  solution  of  glycyrrhizine.  It  expels  the  carbonic  acid  from  the  carbonates 
of  potash,  soda,  and  barytes,  combining  with  the  base,  and  it  precipitates  the  solu- 
tions of  most  of  the  ordinary  metallic  salts.  Neither  the  pure  substance  nor  any 
of  its  compounds  have  been  accurately  analyzed. 


GLUTEN,    MUCIN,    AND     ALBUMEN.  537 


CHAPTER  XXI. 

OF  THE  ALCOHOLIC  AND  ACETIC  FERMENTATIONS — OF  ALCOHOL,  THE  ETHERS, 
ALDEHYD,  ACETIC  ACID,  AND  OTHER  BODIES  DERIVED  FROM  IT. 

An  aqueous  solution  of  pure  sugar  may  remain  perfectly  unaltered  for 
any  length  of  time,  if  carefully  excluded  from  the  air.  If  the  air  have 
access,  it  is  gradually  decomposed,  becoming  brown  and  sour,  but  no  al- 
cohol is  generated.  If,  however,  the  solution  of  sugar  be  brought  in  con- 
tact  with  any  organic  substance  which  is  itself  in  the  act  of  slow  decom- 
position, then  the  particles  of  sugar  participate  in  the  change  which  is 
going  forward,  and  carbonic  acid  and  alcohol  result. 

The  substance  which  is  specially  active  in  inducing  this  kind  of  fer 
mentation  is  an  azotized  body  termed  yeast ;  but  a  number  of  animal 
and  vegetable  substances  can  also  effect  it.  Blood,  white  of  egg,  glue, 
flesh,  if  they  have  begun  to  putrefy,  are  capable  of  exciting  it;  but  the 
bodies  of  most  practical  importance  in  that  respect  are  vegetable  albu- 
men and  gluten.  These  bodies  exist  in  all  fruits  and  seeds,  in  greater 
or  less  proportion,  but  they  differ  in  character,  according  to  the  plants 
they  are  derived  from,  nearly  in  the  same  way  as  the  varieties  of  starch. 
I  shall  here  only  notice  them  as  derived  from  wheat  and  from  beans,  as 
I  shall  have  occasion  to  describe  some  other  forms  hereafter.  If  wheaten 
flour  be  washed  with  water  in  a  linen  bag,  the  starch  passes  off,  and  a 
tenacious  paste  remains,  which  consists  of  albumen  and  gluten  mixed. 
They  may  be  separated  by  boiling  in  alcohol,  which  dissolves  the  latter, 
and  leaves  the  former  behind.  On  mixing  the  alcoholic  liquor  with 
water,  the  gluten  is  precipitated,  and  may  be  collected  and  dried. 

Vegetable  Gluten  so  obtained  is  pale  yellow,  and  forms,  when  soft,  an 
adhesive  mass,  very  extensive  and  elastic.  Its  solution  in  alcohol  ia 
thick-fluid  when  concentrated  ;  insoluble  in  ether ;  it  dissolves  in  acetic 
acid,  and  in  alkaline  solutions.  It  combines  with  the  mineral  acids, 
forming  bodies  very  sparingly  soluble  in  water,  which  are  precipitated 
by  adding  the  acid  to  the  solution  of  gluten  in  acetic  acid  or  in  potash. 
If  these  solutions  be  mixed  with  solutions  of  earthy  or  metallic  salts, 
precipitates  are  formed,  which  are  compounds  of  the  gluten  with  the 
metallic  oxide. 

In  all  these  reactions,  the  gluten  is  accompanied  by  a  slimy  material, 
termed  Mucin,  which  it  is  difficult  to  remove  perfectly  from  the  gluten ; 
it  is  best  effected  by  boiling  with  water,  when  the  mucin  remains  dissolv- 
ed. Its  solution  is  precipitated  by  sulphate  of  iron  and  infusion  of  galls, 
but  not  by  acetate  of  lead  or  corrosive  sublimate. 

Vegetable  Albumen  remains  behind  after  the  rough  gluten  has  been 
boiled  in  alcohol.  It  is  destitute  of  elasticity  when  softened,  and  dries  to 
a  hard  white  mass ;  it  is  moderately  soluble  in  water,  and  its  solution  is 
coagulated  by  heat ;  it  dissolves  in  alkaline  liquors.  Its  solutions  are 
precipitated  by  acids,  except  the  phosphoric  and  acetic,  and  by  all  earths 
and  metallic  salts  ;  these  precipitates  are  white  or  coloured,  according  to 
the  nature  of  the  metallic  oxide  ;  with  ferro-prussiate  of  potash  and  with 

Y  T  Y 


538  L  E  G  U  M  I  N. N  ATURE     OF     YEAST. 

infusion  of  galls,  the  solution  of  vegetable  albumen  in  acetic  acid  gives 
white  precipitates. 

Legumin. — This  substance,  which  exists  in  pease  and  beans,  possesses 
properties  intermediate  to  those  of  the  gluten  and  albumen  of  wheat. 
When  powdered  pease  are  diffused  through  water,  the  starch  settles  to 
the  bottom,  but  the  legumin  is  dissolved,  and  separates  by  evaporation, 
on  the  surface  of  the  liquor,  in  mucous  transparent  pellicles.  Its  solution 
is  not  coagulated  by  heat ;  it  is  insoluble  in  alcohol.  It  dissolves  in  so- 
lutions of  the  vegetable  acids,  and  is  precipitated  on  the  addition  of  a 
mineral  acid.  It  dissolves  in  alkalies,  and  gives,  with  the  earthy  and 
metallic  salts,  compounds  insoluble  in  water. 

All  these  substances  differ  from  most  vegetable  bodies,  in  containing 
a  large  quantity  of  nitrogen,  and,  in  the  latter  case,  sulphur,  as  a  con- 
stituent. They  leave  behind,  when  burned,  an  ash  consisting  of  phos- 
phates of  lime,  magnesia,  and  iron,  similar  to  the  ash  of  animal  sub- 
stances. Indeed,  an  almost  perfect  similarity  of  properties  exists  be- 
tween these  bodies,  and  fibrine,  albumen,  and  casein  among  animal  prod- 
ucts ;  in  the  case  of  casein  and  lupuline  probably  amounting  to  identity. 
In  contact  with  air  and  water,  these  bodies  enter  spontaneously  into 
decomposition,  evolving  carbonic  acid  and  ammonia,  and  forming  new 
products ;  and  in  this  state  of  decomposition  they  superinduce  the  alco- 
holic fermentation  on  those  particles  of  sugar  which  lie  in  contact  with 
them.  Hence,  in  fruits,  the  sugar  may  lie  in  contact  with  these  vegeto- 
animal  substances  without  any  change  occurring,  as  long  as  the  investing 
membrane  of  the  fruit-cells  remains  perfect ;  but  if  the  fruit  be  crushed, 
so  that  the  air  have  access,  then  oxygen  is  absorbed,  the  vegeto-animal 
body  begins  to  putrefy,  and  the  sugar  is  soon  engaged  in  the  decomposi- 
tion. It  is  remarkable,  that  the  necessity  for  oxygen  is  at  the  com- 
mencement  of  the  decomposition  :  when  the  putrefaction  of  the  albu- 
men or  gluten  has  once  begun,  it  extends  itself  throughout  its  whole 
mass  without  requiring  any  farther  action  of  the  air. 

The  principles  of  the  conservation  of  vegetable  juices,  by  enclosure  in 
vessels  from  which  the  air  is  excluded,  can  easily  be  understood  from 
this,  as  well  as  the  utility  of  such  agents  as  sulphurous  acid  or  sulphite 
of  potash,  which  absorb  any  traces  of  oxygen  that  may  be  present,  and 
prevent  it  from  acting  on  the  organic  substance. 

The  general  characters  of  these  natural  ferments  being  thus  sketched, 
it  is  necessary  to  add  the  important  facts  of  the  history  of  artificial  fer- 
ment^ or  yeast.  This  is  nothing  more  than  the  decomposing  mass  of 
vegetable  gluten  or  albumen  produced  in  a  previous  fermentation.  If 
the  yeast  be  too  old,  that  is,  if  all  the  vegeto-animal  matters  be  already 
decomposed,  its  power  of  exciting  action  is  destroyed  ;  it  is  also  destroyed 
by  boiling,  by  alcohol,  by  many  salts  and  acids,  and,  generally,  by  all 
those  means  which  give  to  the  albumen  and  gluten  an  insoluble  form,  and 
prevent  their  farther  putrefaction. 

When  a  solution  of  pure  sugar  is  fermented  by  contact  with  a  certain 
quantity  of  yeast,  this  last  is  found  to  be  very  much  diminished  in  quan- 
tity, and  to  have  totally  lost  its  activity.  On  the  contrary,  if,  in  place  of 
pure  sugar,  grape  or  currant  juice,  or  an  infusion  of  malt,  be  used,  the 
quantity  of  ferment  is  found  to  be  much  increased,  and  to  preserve  all 
its  power.  In  this  case  the  albumen  and  gluten  of  the  vegetable  juices 
are  themselves  brought  into  the  same  train  of  decomposition  as  the  added 


ALCOHOLIC     FERMENTATION.  539 

portion  of  yeast,  and  thus  form  a  new  and  larger  quantity  of  active  fer- 
menting material.  Thus,  in  a  brewery,  the  quantity  of  yeast  continu- 
ally  increases.  If  yeast  be  examined  with  the  microscope,  it  is  found  to 
contain  a  vast  number  of  minute  globular  bodies,  possibly  animalcules, 
which  derive  their  nutriment  from  it ;  but  recently  some  very  unfounded 
attempts  have  been  made  to  connect  these  globules  essentially  with  the 
process  of  fermentation,  by  the  idea  that,  in  the  process  of  nutrition,  they 
absorbed  the  sugar,  and  that  the  products  of  fermentation  were  excreted 
subsequently  by  them.  But  this  is  shown  to  be  absurd  by  the  simple 
fact  that  the  weight  of  the  alcohol  and  carbonic  acid  is  greater  than  the 
weight  of  the  sugar. 

The  phenomena  of  the  alcoholic  fermentation  are  best  observed  on  the 
clear-expressed  grape-juice,  kept  at  a  temperature  between  70°  and  80°, 
in  a  lightly  covered  vessel.  Alter  a  few  hours  a  slight  effervescence  is 
observed,  and  the  liquor  becomes  turbid,  as  if  pipeclay  were  diffused 
through  it.  As  the  effervescence  increases,  the  liquor  becomes  warmer, 
and  the  precipitate  forms  flocculi,  on  which  the  gas-bubbles  are  evolved, 
being  thereby  carried  to  the  surface  of  the  liquor,  and  falling  down  again 
when  the  gas- bubbles  have  broken.  This  circulation  continues  until  the 
fermentation  has  ceased,  when  the  precipitate  collects  at  the  bottom. 
The  liquor  no  longer  tastes  sweet ;  it  contains  no  sugar,  but  in  place  of 
it  an  equivalent  quantity  of  alcohol.  An  infusion  of  malt  does  not  so 
readily  ferment  as  the  grape  juice,  unless  some  yeast  be  first  added.  Id 
its  spontaneous  fermentation,  most  of  the  gum  and  sugar  which  it  con 
lains  passes  into  the  mucous  fermentation,  while  but  little  alcohol  is 
formed.  In  the  practical  manufacture  of  malt-drinks  and  spirits,  there- 
fore, the  worts  are  always  set  to  ferment  by  the  addition  of  a  suitable 
quantity  of  the  yeast  formed  in  a  preceding  operation. 

Although  the  essential  character  of  sugar  is  to  be  capable  of  alcoholic 
fermentation,  yet  the  different  kinds  of  sugar  enter  on  that  process  with 
unequal  facility.  The  sugar  of  milk  requires  the  presence  of  a  very 
active  ferment,  and  of  an  acid,  by  the  influence  of  which  it  is  changed 
into  sugar  of  grapes.  Thus  milk  does  not  ferment  until  it  has  become 
clotted  and  sour  ;  the  casein  then  acts  as  yeast,  in  superinducing  the  al- 
coholic fermentation.  Indeed,  no  matter  what  kind  of  sugar  is  employed 
in  this  process,  it  is  changed  into  grape-sugar  before  fermenting,  as  is 
shown  by  the  action  of  the  liquor  upon  polarized  light.  The  grape-sugar, 
as  dried  at  212°,  contains  exactly  the  elements  of  two  atoms  of  alcohol 
and  four  of  carbonic  acid,  as  2(C4H602)  and  4C.O2  arise  from  CiaHigOu. 
As  cane-sugar  takes  an  atom  of  water  to  form  grape-sugar,  it  follows  that 
cane-sugar,  in  fermenting,  should  yield  more  than  its  own  weight  of  car- 
bonic  acid  and  alcohol ;  and  it  has  been  ascertained  by  experiment  that 
100  pans  actually  give  104,  while  by  theory  105  should  be  produced, 
consisting  of  51*3  of  carbonic  acid  and  53*7  of  alcohol.  This  coinci- 
dence of  numbers  proves  that  these  bodies  are  the  only  products.  The 
influence  of  the  yeast  is,  therefore,  strictly  what  Berzelius  terms  cata- 
lytic, but  its  action  becomes  much  more  definitely  intelligible  by  consid- 
ering it  as  a  case  of  the  general  principle  expressed  by  Liebig,  that  mo- 
tion (decomposition)  may  be  communicated  from  the  particles  of  one 
body  (yeast)  to  those  of  another  (sugar)  by  virtue  of  proximity,  as  de- 
scribed more  fully  in  p.  235-237. 

As  farther  details  of  the  circumstances  of  the  alcoholic  fermentatioa 


540  CONSTITUTION     OF     ALCOHOL. 

would  vary  with  the  nature  of  the  liquor  to  be  produced,  whether  it  be 
for  immediate  drinking,  as  wine,  ale,  or  porter,  or  for  distillation,  and 
as  these  lead  to  purely  technical  descriptions  of  the  arts  of  brewing, 
&c.,  I  shall  not  enter  on  them. 

Of  Alcohol  and  the  Ethers  derived  from  it. 

When  any  saccharine  liquor,  which  has  undergone  the  alcoholic  fer- 
mentation, is  distilled  at  a  gentle  heat,  a  very  volatile  liquid  passes  over, 
which,  by  successive  rectifications,  may  be  deprived  of  most  of  the  water 
which  had  been  mixed  with  it.  In  various  degrees  of  strength,  and  con- 
taminated by  minute  traces  of  essential  oils,  characteristic  of  the  plants 
from  which  the  saccharine  liquor  has  been  obtained,  it  constitutes  the 
potato-spirit,  brandy,  malt-whiskey,  arrack,  rum,  &c.,  of  commerce.  In 
a  still  stronger  form  it  constitutes  the  sjpirit  of  wine,  or  rectified  spirit, 
the  term  alcohol  being  applied  to  it  only  when  it  is  chemically  pure. 
By  mere  distillation  alcohol  cannot  be  freed  from  all  the  admixed  water, 
for  which  it  exerts  a  strong  affinity.  When  its  specific  gravity  is  redu- 
ced to  0*813  at  60°,  in  which  state  it  still  contains  8*2  per  cent,  of 
water,  or  exactly  half  an  equivalent,  its  boiling  point  remains  constantly 
at  172°,  and  it  distils  over  unchanged.  In  the  form  of  proof  spirit  of 
commerce,  its  sp.  gr.  is  about  0'920,  and  it  contains  48  per  cent,  of  ab 
solute  alcohol ;  the  rectified  spirit  containing  about  83  per  cent.,  and 
having  the  specific  gravity  0*839  at  60°  F. 

To  obtain  real  alcohol,  or  absolute  alcohol,  as  it  is  generally  termed, 
rectified  spirit  is  to  be  distilled  at  a  moderate  heat  from  some  substance 
having  a  stronger  affinity  for  water ;  as  lime,  caustic  potash,  carbonate 
of  potash,  or  chloride  of  calcium.  Of  these  the  last  named  should  be 
preferred.  The  water  of  the  spirit  combines  with  the  body  used,  and, 
forming  a  hydrate,  the  real  alcohol  distils  over.  The  rectification 
should  be  conducted  in  a  water- bath. 

A  singular  mode  of  concentrating  alcohol  is  founded  on  the  fact  that 
a-lcohol  does  not  moisten  the  animal  tissues,  but  corrugates,  and  rather 
abstracts  water  from  them.  Hence,  if  a  bladder  be  filled  with  spirit  of 
sp.  gr.  0*820,  containing  90  per  cent,  of  alcohol,  and  if  it  be  left  for  a 
few  days  in  a  warm  room,  the  spirit  will  be  found  to  have  its  sp.  gr. 
reduced  to  0-800,  containing  97  per  cent,  of  real  alcohol.  The  water 
permeates  the  bladder,  and  evaporates  from  the  outer  side ;  but,  as  the 
alcohol  does  not  moisten  the  bladder,  it  cannot  get  through,  and  conse- 
quently remains  behind,  freed  from  water. 

The  very  ingenious  way  of  obtaining  alcohol,  devised  by  Graham,  by 
evaporation  in  vacuo  with  quicklime,  has  been  described  in  p.  87. 

Alcohol  thus  obtained  anhydrous  has  a  sp.  gr.  of  0*7947  at  60°  ;  it 
boils  at  168° ;  tne  specific  gravity  of  its  vapour  is  1601 ;  it  does  not 
become  solid  even  in  the  most  intense  cold ;  its  taste  is  burning  and  dry 
upon  the  tongue,  owing  to  its  abstracting  water  from  its  tissue.  It  is 
highly  inflammaole,  and  burns  with  little  light.  From  its  volatility,  if 
some  drops  of  it  are  poured  into  a  jar  of  oxygen  gas,  its  vapour  forms  a 
powerfully  explosive  mixture.  It  does  not  conduct  electricity.  It  mix- 
es with  water  in  every  proportion,  contracts  in  volume,  and  evolves  heat. 
The  sp.  gr.  of  spirituous  liquors  is  therefore  always  above  the  mean  sp. 
gr.  of  the  alcohol  and  water  they  contain.  The  greatest  condensation 
occurs  with  54  volumes  of  alcohol  and  50  of  water ;  the  mixture  occu- 


USES     OF     ALCOHOL.  541 

pies  only  100  volumes,  and  its  sp.  gr.  is  0;927,  being  a  little  denser 
than  proof  spirit. 
The  formula  of  alcohol  is  C^HeOz,  and  its  composition  is, 

4  equivalents  of  carbon,      =24-2  .  .  .  5266 

6      "        "         hydrogen,  =  60  .  .  .  12  90 

2      "        "          oxygen,     =160  .  .  .  34-44 

The  equivalent  of  alcohol,  =462  .  .  .  10000 

This  is  cwfifirmed  by  the  products  of  its  decomposition,  and  by  the  specific  giavit? 
©fits  vapouf;  for, 

4  volumes  of  carbon  vapour    .    (843x4)=3372  0 
12       "  hydrogen  .     .      (688x12)=  825-6 

2         «  oxygen      .     .    (1102-6 x2)=22052 

Give  four  volumes  of  alcohol  vapour    .       64028 
Of  which  one  volume  weighs  .     .    .     .       1600  7 

It  will  be  fcuown,  however,  that  alcohol  consists  of  ether  united  to  water,  and  that 
Its  formula  is  C4H50.-|-Aq.     Its  vapour  is  then  formed  by  the  union  of 

i  volume  of  vapour  of  ether,  =12906  )  iqqq.j 
^  volume  of  vapour  of  water,  =  310- 1  J 

The  uses  of  alcohol  in  chemistry  and  pharmacy  are  numerous  and 
important.  It  dissolves  the  caustic  alkalies  and  most  deliquescent  salts, 
combining  with  them  to  form  alcoatesy  which  resemble  very  remarkably 
the  hydrates.  Thus,  if  dry  chloride  of  calcium  be  dissolved  in  alcohol, 
the  alcoate  crystallizes  by  cooling  in  large  transparent  plates.  By  heat, 
these  are  decomposed,  and  also  by  contact  with  water,  which  expels  the 
alcohol,  and  takes  its  place.  The  permanent  and  efflorescent  salts  are 
generally  insoluble  in  alcohol,  and  may  be  even  precipitated  by  it  from 
their  solution  in  water,  the  alcohol  seizing  on  the  water. 

An  important  pharmaceutic  use  of  alcohol  is  for  the  solution  of  the 
resinous  principles  of  plants,  in  the  preparation  of  tinctures  and  alcoholic 
extracts.  The  strength  of  the  alcohol  must  in  these  cases  be  regulated 
by  the  nature  of  the  substances  to  be  dissolved.  Sometimes  rectified 
spirit,  at  other  times  proof  spirit  being  more  effectual. 

The  manufacture  of  alcohol  is  itself  one  of  the  most  important  arts ; 
it  is  the  basis,  also,  of  the  manufacture  of  vinegar,  of  the  making  of  res- 
inous varnishes,  and  various  other  processes.  To  the  chemist  it  is 
specially  of  interest  as  the  type  of  a  very  interesting  group  of  organic 
bodies,  and  yielding  by  its  decomposition  a  very  numerous  series  of 
products,  which  are  of  great  importance  in  science,  in  pharmacy,  and 
in  the  arts. 

When  alcohol  is  exposed  to  the  air  it  gradually  absorbs  oxygen, 
aldehyd  and  acetic  acid  being  formed.  It  is  then  said  to  undergo  the 
acetous  fermentation.  Under  the  influence  of  acids  it  loses  an  atom  of 
water,  compounds  being  formed  which  are  termed  ethers^  into  the  com- 
position of  which  the  acid  employed  generally  enters. 

Of  Sulphuric  Ether,     Ether,     Oxide  of  Ethyle, 

This  substance  may  be  prepared  by  any  process  which  deprives  alco- 
hol of  the  equivalent  of  water  which  it  contains.  Thus,  if  potassium  be 
placed  in  contact  with  absolute  alcohol,  hydrogen  gas  is  evolved,  and  a 
compound  of  ether  and  potash  crystallizes,  041150. -j-H.O.  ahd  K.  giving 
C4H6O.+K.O.  and  free  H.     If  a  current  of  gaseous  fluoride  of  boron 


542 


PREPARATION     OF      ETHER. 


(p.  326)  be  passed  into  alcohol,  it  is  absorbed,  and  boracic  acid  separates 
in  crystals,  while  the  liquor  contains  ether ;  here,  also,  the  water  of"  the 
alcohol  is  decomposed,  fluoric  and  boracic  acids  being  produced,  and 
ether  liberated.  By  distillation  with  chloride  of  zinc,  also,  the  water 
may  be  abstracted  from  alcohol,  and  ether  obtained ;  but  the  affinity  of 
the  other  deliquescent  salts  is  not  sufficiently  intense  to  decompose  it. 

It  is  by  the  action  of  sulphuric  acid  upon  alcohol  that  ether  is,  for 
practical  purposes,  always  obtained.  Equal  weights  of  rectified  spirit 
and  of  oil  of  vitriol  being  well  mixed,  and  avoiding  any  considerable  rise 
of  temperature,  are  to  be  introduced  into  a  glass  globe,  to  which  heat 
may  be  applied  by  a  sand-bath,  as  represented  in  the  figure.  To  this, 
may  be  attached  the  form  of  condenser  devised  by  Liebig  for  the 
distillation  of  very  volatile  liquids.     It  consists  of  a  glass  tube  three 


fourths  or  one  inch  wide,  and  twenty-four  or  thirty  inches  long,  d  d,  to 
which  is  attached  at  one  end  by  a  good  cork  a  narrower  tube,  passing 
to  the  globe,  and  to  the  other  end  is  soldered  a  smaller  tube,  bent  at  an 
obtuse  angle,  and  conducting  to  the  receiver  e.  The  tube  d  d  fits  water- 
tight by  corks  into  a  tinned  cylinder  c,  the  proportions  of  which  may  be 
judged  from  the  figure  ;  this  is  kept  full  of  cold  water.  When  the  distil- 
lation commences,  the  hot  vapours  entering  the  condensing  tube  at  d, 
give  out  their  latent  heat  to  the  surrounding  water,  and  that  part  of  the 
condenser  would  soon  get  hot,  were  not  the  water  constantly  changed  ; 
by  the  funnel/,  a  stream  of  cold  water  flows  from  the  reservoir  i  into  the 
lower  part  of  the  tube  c,  and  presses  up  before  it  the  warm  and  lighter 
water,  until  this  is  expelled  by  the  tube  h,  when  it  is  collected  at  h. 
The  supply  of  cold  water  should  be  so  proportioned  to  the  supply  of  va- 
pour, thai,  flowing  away  at  h,  it  should  not  be  sensibly  warm  to  the 
hand.  With  this  precaution,  most  volatile  liquids  may  be  perfectly  con- 
densed even  in  the  midst  of  summer.  The  mixture  of  acid  and  spirit  in 
the  globe  being  brought  to  a  temperature  of  about  260°  as  rapidly  as 
possible,  it  begins  to  boil,  and  the  ether  distilling  over,  accompanied  by 
some  water  and  unaltered  alcohol,  collects  in  the  receiver. 

Since  th^  quantity  of  sulphuric  acid  continually  increases  in  the  globe 
as  the  distillation  proceeds,  its  action  on  the  remaining  alcohol  changes, 


CONTINUOUS     FORMATION    OF     ETHER.  543 

the  mixture  becomes  dark  coloured,  an  oily  substance  distils  over  (oil  of 
wine),  and  the  quantity  of  ether  formed  diminishes  rapidly.  Sulphurous 
acid  and  defiant  gases  are  then  evolved,  and  finally  the  mixture  becomes 
thick  and  black,  and  froths  up  very  much.  When  the  object  is  only  the 
preparation  of  ether,  these  reactions  may  be  prevented,  and  a  much  lar- 
ger product  obtained,  by  admitting  to  the  globe,  by  means  of  the  bent 
funnel,  a  continual  but  minute  stream  of  rectified  spirit.  The  action  of 
the  sulphuric  acid  is  thus  exercised  upon  successive  quantities  of  spirit, 
and  the  liberation  of  the  ether  continues  until  the  acid  becomes  so  weak 
as  to  be  no  longer  able  to  decompose  the  alcohol,  which  occurs  when  the 
whole  quantity  of  rectified  spirit  used  is  about  twice  the  weight  of  the  oil 
of  vitriol,  which  is  then  reduced  to  the  strength  of  S.03-f4  Aq. 

Although  we  may  represent  the  results  of  this  reaction  by  considering 
the  sulphuric  acid  to  take  water  directly  from  the  alcohol,  and  set  the 
ether  free,  such  is  by  no  means  really  the  case ;  on  the  contrary,  when 
the  alcohol  acts  on  the  oil  of  vitriol,  the  water  of  both  is  disengaged, 
and  the  sulphuric  acid  and  ether  unite  to  form  Sulphate  of  Ether,  (C4H5 
O.  +  Aq.)  and  S.Oa+Aq.  giving  C4H5O.  +  S.O3  and  2  Aq.  This  body, 
which  resembles  very  much  sulphate  of  ammonia  in  its  tendency  to  com- 
bination, unites  with  an  atom  of  oil  of  vitriol  to  form  Bisulphate  of  Ether , 
^  or,  as  it  is  generally  termed,  Sulphovinic  Acid.  The  two  atoms  of  sul- 
phuric acid  thus  engaged  change  very  much  in  properties,  forming  salts 
with  barytes  and  oxide  of  lead,  which  are  very  soluble  in  water.  The 
two  equivalents  of  water,  which,  as  above  described,  are  set  free,  dilute 
the  remaining  sulphuric  acid  to  such  a  degree  as  that  it  cannot  decom- 
pose more  alcohol ;  hence,  if  absolute  alcohol  be  used,  3(C4H50.-{-Aq.) 
with  8(S.03  .  H.O.)  produce  3(C4H50.  .  S.O3+H.O.  .  S.O3)  and  2(S. 
O3-I-4  Aq.),  one  fourth  of  the  sulphuric  acid  remaining  over  ;  if  a  weak- 
er alcohol  be  used,  the  quantity  of  dilute  sulphuric  acid  formed  becomes 
proportionally  greater.  An  acid  which  already  contains  four  atoms  of 
water,  forms  no  sulphate  of  ether  when  put  in  contact  even  with  absolute 
alcohol,  except  the  temperature  be  very  high. 

The  ether  obtained  by  distilling  a  mixture  of  alcohol  and  oil  of  vi^iol 
results,  therefore,  not  from  the  water  being  seized  on  by  the  oil  of  vimol, 
but  from  the  decomposition  of  its  compound  with  sulphuric  acid,  the  sul- 
phate of  ether;  the  ether  being  a  base  not  much  superior  in  energy  to 
water,  is  expelled  by  it  in  turn  under  favourable  circumstances,  especially 
when  the  water  is  present  in  excess.  In  this  respect  it  resembles,  as 
Rose  has  remarked,  the  sesquioxides  of  iron,  antimony,  and  bismuth, 
which  form  salts  with  sulphuric  acid  that  are  totally  decomposed  by  a 
large  quantity  of  water,  especially  if  their  solutions  be  boiled ;  the  acid 
then  combines  with  the  water,  and  the  metallic  oxide  precipitates.  Be- 
fore deciding  on  this  view  of  the  production  of  ether,  it  is  necessary  to 
describe  some  collateral  phenomena. 

If  absolute  alcohol  and  strong  oil  of  vitriol  be  employed  in  the  prepara- 
tion  of  ether,  it  is  found  that  the  distilled  product  consists  of  ether  and* 
water,  forming  two  distinct  layers  in  virtue  of  their  different  specific 
gravities,  but  in  quantity  identical  with  those  which  constitute  alcohol ; 
100  parts  of  the  mixed  liquids  consisting  of  19-5  water  and  79*5  ether, 
when  separated  from  a  quantity  of  alcohol  which  had  escaped  decompo- 
sition.  The  oil  of  vitriol  remains  in  the  retort  in  its  original  state  of 
concentration,  and  hence  might  be  applied  to  etherify  an  infinite  quantity 


544    THEORY  OF  THE  FORMATION  OF  ETHER. 

of  absolute  alcohol,  introduced  in  a  continuous  stream.  To  explain  this 
very  remarkable  result,  Mitscherlich  advanced  that  the  action  of  the 
sulphuric  acid  on  the  alcohol  is  merely  catalytic ;  that  it  splits  it,  as  it 
were,  into  ether  and  water,  and  these  pieces  not  being  able  to  reunite, 
come  over  in  vapour,  merely  mixed  with  each  other  ;  this  idea  is,  how- 
ever, quite  inadmissible,  as  the  whole  quantity  of  ether  is  proved  to  be 
united  with  the  sulphuric  acid  in  the  first  place,  and  to  distil  over  only- 
after  the  decomposition  of  the  compound  that  had  been  so  formed.  The 
observations  of  Liebig  and  Rose  have  removed  the  difficulty  which  this 
simultaneous  evolution  of  water  and  ether  presented  to  the  adoption  of 
the  theory  which  supposes  the  ether  to  be  expelled  from  its  combination 
with  the  sulphuric  acid  by  the  water.  In  fact,  it  is  only  at  a  particular 
temperature  that  the  ether  and  water  come  over  in  atomic  proportions, 
and  this  then  results  from  the  identity  of  the  boiling  points  of  the  solution 
of  sulphovinic  acid  and  of  the  dilute  sulphuric  acid.  Thus,  when  we 
heat  together  sulphate  of  ether,  (C4H5O. -I-S.O3),  and  the  dilute  sulphuric 
acid,  S.O34-4  Aq.,  the  former  is  decomposed,  bihydrate  of  sulphuric 
acid,  S.O3+2  Aq.,  being  formed,  and  ether  set  free ;  but  at  this  temper- 
ature the  sulphuric  acid  begins  to  abandon  its  second  atom  of  water, 
which  then  distils  over  with  the  ether.  If  we  conduct  the  distillation 
very  slowly,  and  retain  the  temperature  below  212°,  the  ether  comes 
over,  almost  perfectly  free  from  water;  but  at  a  higher  temperature,* 
the  ether,  when  liberated,  is  immediately  converted  into  elastic  vapour, 
which  bubbles  through  the  liquid  lil^e  a  gas,  and  the  water  evaporates  in 
the  space  thus  afforded,  as  it  should  evaporate  in  a  current  of  air  forced 
to  bubble  through  the  liquid  in  the  same  way. 

The  production  of  ether  depends,  therefore,  upon  the  facts,  that  when 
alcohol  and  oil  of  vitriol  are  mixed,  sulphate  of  ether  is  formed  and  wa- 
ter is  set  free  ;  but  on  the  application  of  heat,  this  action  is  inverted,  and 
the  ether  is  expelled  from  the  acid,  with  which  the  water  recombines.  If 
the  distillation  be  conducted  so  that  the  mixture  boils,  the  dilute  sulphuric 
acid  concentrates  itself,  at  the  same  time,  by  giving  off  an  atom  of  water, 
which  condenses  mixed  with  the  ether,  but  had  its  origin  in  a  perfectly 
in*pendent  action. 

If  we  heat  alcohol  in  contact  with  glacial  phosphoric  or  arsenic  acids, 
it  is  similarly  acted  on,  and  the  ether  forms  a  phosphovinic  or  arseniovi- 
flic  acid,  which  is  decomposed  by  boiling,  the  ether  being  set  free.  These 
acids  would  be  too  costly  to  admit  of  their  employment  in  the  prepara- 
tion of  ether  on  the  great  scale,  and,  besides,  they  do  not  act  as  power- 
fully as  oil  of  vitriol.  Although  this  ether  does  not  contain  any  sulphuric 
acid,  it  is  very  generally  called  Sulphuric  Ether,  and  I  shall  often  use  that 
name,  but  the  distinction  between  it  and  the  compound  ethers  formed  by 
its  union  with  acids  must  be  carefully  kept  in  mind. 

The  ether  formed  by  the  process  now  described  is  rendered  impure  by 
admixture  with  alcohol  and  water,  and  sometimes  oil  of  wine  and  sul- 
phurous acid.  It  is  freed  from  these  by  rectification,  from  a  water- 
bath,  over  some  dry  carbonate  of  potash.  It  is  then  a  colourless  liquid, 
of  an  agreeable  penetrating  odour,  and  a  pungent  taste.  Its  sp.  gr.  is 
0*720  at  60°  ;  it  does  not  conduct  electricity  ;  at  — 47°  F.  it  freezes 
into  a  crystalline  mass  ;  it  boils  at  96° ;  the  sp.  gr.  of  its  vapour  is 
2581 'S.  In  evaporating  it  produces  great  cold,  of  which  numerous  ap- 
plications have  been  noticed  under  the  head  of  vaporization.  (Sec.  IV., 
Chap.  III.) 


CONSTITUTION     OF     ETHER. 


545 


Ether  is  very  combustible  ;  its  vapour,  diffused  through  air  or  oxygen, 
forms  powerfully  explosive  mixtures.  Exposed  to  the  air,  it  gradually 
absorbs  oxygen,  forming  acetic  acid.  Its  flame  is  brighter  than  that  of 
alcohol,  but  it  gives  no  smoke ;  it  dissolves  sulphur  and  phosphorus  in 
small  quantity  ;  iodine  and  bromine  are  abundantly  dissolved,  but  they 
soon  act  on  the  ether  ;  most  bodies  that  are  soluble  in  alcohol  are  dis- 
solved by  ether,  except  salts,  of  which  only  very  few,  as  the  perchlorides 
of  gold,  of  platina,  and  of  iron,  are  taken  up  by  it.  Ether  combines  with 
almost  all  acids,  forming  well-defined  neutral  salts,  the  compound  ethers, 
which  have  a  remarkable  similarity  to  the  ammoniacal  salts.  It  is,  there- 
fore, an  organic  base ;  its  composition  is  expressed  in  the  formula  C4H5O 
giving  the  numbers  by  weight :  • 


4  equivalents  of  carbon    . 

5  "        "      hydrogen 
1        "        "      oxygen    . 


24-20 
500 
800 

37-20 


65-31 

1333 

21-36 

10000 


and  by  volume, 


4  volumes  of  carbon  vapour,      (843x4)=:38720 
10         "  hydrogen  "        (68-8x10)=:  6880 

1         "  oxygen     "     .     .     .     .     =1102-6  • 

Produce  two  volumes  of  vapour  of  ether    .  5162-6 
Of  which  one  weighs,  therefore     .     .    .    .25813 

In  chemistry  and  pharmacy  ether  is  of  importance  as  a  vehicle  for  the 
solution  of  many  resinous  and  other  bodies,  and  from  its  action  on  the 
animal  economy.  By  the  action  of  reagents  it  yields  a  great  number 
of  derived  compounds,  of  which  the  most  important  will  be  described  in 
their  proper  place. 

The  question  of  the  intimate  constitution  of  ether  has  been  very  much 
discussed,  and  opinions  have  followed  precisely  the  same  course,  with 
regard  to  the  theory  of  its  compounds,  as  for  that  of  the  combinations 
of  ammonia ;  thus  it  has  been  looked  upon  as  an  oxide  of  a  compound 
(metallic  ?)  radical,  Ethereum  or  Ethyle,  as  the  salts  of  ammonia  were  sup- 
posed to  contain  a  compound  metal.  Ammonium.  The  formula  of  ethyie 
should  be  C4H5,  and  its  symbol  Ae.  On  the  other  hand,  it  may  be  con- 
sidered to  consist  of  olefiant  gas,  C4H4,  united  to  water,  and  the  latter 
then  takes  the  place  of  the  ammoniacal  gas  in  the  theory  of  ammonia. 
I  shall  frequently  employ  for  ether  the  symbol  Ae.O.,  and  speak  of  it  and 
other  bodies  as  compounds  of  ethyie,  as  oxide,  chloride,  &c.,  but  without 
any  other  present  object  than  convenience  of  language,  for  it  would  be 
impossible  to  discuss  the  comparative  merits  of  these  theories,  without 
knowing  the  properties  of  the  compound  ethers,  of  olefiant  gas,  of  al- 
dehyd,  acetic  acid,  and  many  other  bodies,  which  are  involved  in  the  re- 
actions by  which  we  may  endeavour  to  test  their  value,  and  hence  I  shall 
postpone  all  details  of  the  principles  of  the  ether-theories  until  the  end  of 
the  present  chapter. 

Compounds  of  Ether  with  Sulphuric  Acid, 

Sulphovime  Acid.  Bisulphate  of  Ether,  C4H5O. .  S.O3-J-H.O. .  S.O3,  is  produced  by 
Miixing  alcohol  with  oil  of  vitriol,  as  described  for  the  preparation  of  ether,  or  by 
passing  vapour  of  ether  into  oil  of  vitriol  as  long  as  it  is  absorbed.  By  heat  this 
splution  is  decomposed.  The  sulphovinic  acid  cannot  be  obtained  in  a  sohd  form^ 
if  a  eolation  of  sulphovinate  of  leaid  be  decomposed  by  sulphuret  of  hydrogen,  a  col  • 

Zzz 


546  SULPHOVINATE     OF     POTASH,     ETC. 

ourless  and  very  acid  liquor  is  obtained,  which,  when  concentrated,  evolves  ether, 
blackens,  and  is  totally  decomposed.  Its  salts  are  all  soluble,  and  generally  deli- 
quescent ;  when  boiled  with  muriatic  acid,  alcohol  is  evolved,  and  sulphuric  acid 
set  free.  By  a  high  temperature  they  are  decomposed,  oil  of  wine,  ether,  olefiant 
gas,  and  sulphurous  acid  being  given  off,  while  a  metallic  sulphate  or  sulphuret  re- 
mains behind,  mixed  with  some  charcoal.  By  distilling  a  sulphovinate  with  a  pot- 
ash salt  of  any  volatile  acid,  a  compound  of  ether  with  that  acid  distils  over,  and 
sulphate  of  potash  remains.  By  fusing  a  sulphovinate  with  a  caustic  alkali,  water 
and  olefiant  gas  are  expelled,  and  all  the  sulphuric  acid  remains  combined  with  the 
alkali. 

Sulphovinate  of  Potash,  Ae.O. .  S.Og-j-K-O. .  S.O3,  crystallizes  in  colourless  rhom- 
boidal  plates,  which  are  anhydrous  ;  it  is  very  soluble  in  water,  but  sparingly  solu- 
ble in  alcohol.  Sulphovinate  of  Barytes,  Ae.O.  .  S.Og-j-Ba.O. .  S.O3-4-2  Aq.,  crystal- 
lizes in  obligue  rhomboidal  prisms  unalterable  in  the  air  ;  it  tastes  strongly  acid  ; 
in  vacuo  it  abandons  its  water,  and  is  then  not  altered  by  a  heat  of  212°,  but  if  the 
hydrated  salt  be  heated  to  212°,  alcohol  is  given  off,  and  sulphuric  acid  set  free. 
Sulphovinate  of  Lime  crystallizes  in  thin  hexagonal  plates,  which  are  very  deliques- 
cent ;  it  is  soluble  in  less  than  its  own  weight  of  cold  water.  Sulphovinate  of  Lead 
forms  large  rhombic  crystals,  dehquescent ;  very  soluble  in  water  and  in  alcohol ; 
it  is  gradually  decomposed  at  ordinary  temperatures.  Sulphovinate  of  Copper, 
Ae.O. .  S.O3-I-CU.O. .  S.O3-I-4  Aq.,  forms  large  blue  octagonal  plates,  permanent 
in  the  air,  and  very  soluble  in  alcohol  and  water ;  heated  to  212°  it  is  totally  de- 
composed. 

^thionic  and  Isethionic  Acids. — These  substances  are  formed  by  acting  on  alco- 
hol or  ether  with  the  vapours  of  anhydrous  sulphuric  acid  ;  the  liquor,  neutralized 
by  barytes,  gives  the  insoluble  sulphate  and  the  soluble  ethionate  of  barytes,  which 
last  separates  from  the  concentrated  liquor  as  a  crystalline  precipitate  on  the  addi- 
tion of  alcohol.  A  solution  of  this  salt,  when  decomposed  by  sulphuric  acid,  gives 
free  Ethionic  ^.a^Z,  which,  by  boiling,  is  decomposed  into  sulphovinic  acid  and  isethi- 
onic acid,  of  which,  indeed,  Liebig  considers  it  to  be,  in  reality,  only  a  mixture. 
The  isethionic  acid  is  formed  more  characteristically  by  the  direct  union  of  anhy- 
drous sulphuric  acid  and  olefiant  gas,  and  will  be  described  as  a  compound  of  that 
body. 

Althionic  and  Methionic  Acids. — When  the  mixture  of  alcohol  and  oil  of  vitriol, 
for  making  ether,  has  been  distilled  so  far  as  that  it  has  become  black  and  begun  to 
froth,  it  produces,  when  neutralized  with  bases,  a  series  of  salts,  which,  though 
having  the  same  per  cent,  composition  as  the  sulphovinates,  differ  very  much  from 
them  in  properties  ;  thus  the  Althionate  of  Lime  does  not  crystallize  ;  the  Althionate 
of  Barytes  crystallizes  in  fine  needles,  in  place  of  the  large  plates  of  the  sulphovi- 
nate ;  the  Althionate  of  Copper  is  still  more  distinct,  as  its  crystals  are  thin,  acute 
rhombs,  of  a  pale  green  colour. 

If  the  ether,  into  which  the  vapours  of  sulphuric  acid  are  passed,  Be  allowed  to 
grow  hot,  it  becomes  black,  sulphurous  acid  is  evolved,  and  an  acid  is  formed  dif- 
ferent from  any  of  the  preceding  ;  it  is  called  the  Methionic  Acid,  and  is  character- 
ized by  its  barytes  salt  being  totally  insoluble  in  alcohol,  and  but  sparingly  soluble 
in  water.  When  its  salts  are  fused  with  caustic  potash,  merely  sulphite  of  potash 
remains  ;  the  formula  of  the  acid  contained  in  the  barytes  salt  is  C2H3  .  S2O7.  It 
evidently  does  not  contain  any  simple  combination  of  alcohol  or  ether. 

Heavy  Oil  of  Wine.  Sulphate  of  Ether  and  Etherol. — CsH9O.-l-2S.O3,  or  Ae.O. . 
S.03-)-C4H4  .  S.O3.  When  one  part  of  rectified  spirit  is  distilled  with  two  and  a 
half  parts  of  oil  of  vitriol,  a  little  ether  passes  over,  followed  by  an  oily  yellow  liquid 
and  water,  with  much  sulphurous  acid.  The  oil  is  to  be  washed  with  a  little  water, 
and  then  dried  in  vacuo  under  a  bell-glass,  beside  two  cups,  one  of  oil  of  vitriol  and 
the  other  of  caustic  potash  ;  the  first  absorbs  the  water  and  ether,  and  the  last  the 
sulphurous  acid.  This  substance  is  then  a  thin  oil,  sometimes  green  and  sometimes 
yellow  ;  its  odour  aromatic  and  pungent ;  its  specific  gravity  1-133  ;  when  heated 
it  begins  to  boil,  but  is  rapidly  decomposed,  blackening  and  evolving  sulphurous 
acid,  and  but  little  distilling  over.  It  is  scarcely  soluble  in  water,  but  abundantly 
so  in  alcohol  and  ether.  When  boiled  with  water,  or  with  an  alkaline  solution, 
sulphovinic  acid  is  formed,  and  Etherol  {light  oil  of  wine)  set  free,  which  floats  upon 
the  surface. 

The  composition  of  this  body  is  not  absolutely  constant.  I  consider  it  to  be  a 
mixture,  in  variable  proportions,  of  true  Sulphate  of  Ether,  Ae.O. .  S.O3,  with  Sulphate 
of  Etherol,  C4H4  .  S.O3.    I  have  found  that  when  distilled  with  oxalate  or  acetate 


COMPOUNDS    OP     ETHER.  547 

nt  potash,  with  chloride  or  sulphuret  of  potassium,  oxalic  and  acetic  ethers,  muriat- 
ic ether,  &c.,  are  generated,  and,  at  the  same  time,  etherol  remains  indifferent  to 
these  re-agents. 

Another  process  for  obtaining  this  heavy  oil  of  wine  consists  in  mixing  dry  sul 
phovinate  of  lime  with  its  own  weight  of  quicklime,  and  distilling  at  a  heat  not  ex- 
ceeding 520'^.  The  oil  which  comes  over  mixed  with  alcohol  is  to  be  purified  as 
already  noticed. 

Etherol  and  Etherine. — C4H4.  The  oil  which  is  separated  from  the  foregoing 
substance  by  hot  water  or  by  alkalies,  divides  itself  generally,  after  some  time,  into 
a  liquid  and  a  sohd  portion  ;  the  first  constitutes  the  light  oil  of  wine,  Etherol.  It  is 
pale  yello\Y,  and  thick,  like  olive  oil ;  its  odour  is  aromatic  ;  its  specific  gravity 
=0  921 ;  it  boils  at  500°  ;  at  —35°  it  freezes.  The  Etherine  forms  hard,  brittle,  col- 
ourless prisms  ;  it  is  tasteless  ;  its  specific  gravity  0-980 ;  it  melts  at  230°,  and 
boils  at  464°  ;  it  is  soluble  in  alcohol  and  ether.  The  composition  of  both  these 
bodies  is  the  same,  consisting  of  equal  numbers  of  atoms  of  carbon  and  hydrogen, 
but  their  atomic  weights  are  not  known.  It  is  very  probable  that  the  etherol  is  re- 
ally a  mixture  of  two  other  bodies ;  for  when  a  saturated  solution  of  chloride  of  zinc 
in  alcohol  is  distilled,  an  oily  liquor  is  obtained,  which,  by  rectification,  may  be  sep- 
arated into  two  fluids,  of  which  one,  boiling  at  212°,  has  the  formula  CgH?,  and  the 
other,  which  boils  only  at  570°,  has  the  formula  CsHg.  A  mixture  of  equal  quanti- 
ties of  the  two  should  have  the  composition  assigned  to  etherol. 

Liebig  and  Regnault  have  found  the  etherol  obtained  by  alcohol  and  sulphuric 
acid  to  have  the  'formula  C4H3,  so  that  it  must  be  looked  upon  as  an  irregular  mix- 
lure  of  several  oils,  which  have  not  yet  been  obtained  pure.  The  etherol,  or  Ethe- 
real Oil,  is  employed  to  prepare  Hoffman'' s  Anodyne  Liquor,  being  dissolved  in  a  mix- 
ture of  one  part  of  ether  and  two  of  spirit  of  wine. 

Compounds  of  Ether  icith  the  Phosphoric  and  Arsenic  Acids. 

Phosphovinic  Acid. — Ae.O.  .  P.O5+2H.O.  When  concentrated  tribasic  phos- 
phoric acid  is  dissolved  in  alcohol,  great  heat  is  evolved,  and  one  atom  of  water  re- 
placed by  an  atom  of  ether.  The  acid  salt  thus  formed  may  be  obtained  crystal- 
lized, but  when  its  solution  is  heated  strongly  it  is  decomposed.  It  combines  with 
two  atoms  of  base  to  form  the  Phosphovinates,  of  which  few  are  as  yet  well  known. 
The  barytes  salt,  P.Os-j-Ae.O.  .  2Ba.O.-|-12  Aq.,  crystallizes  in  brilliant  colourless 
plates,  and  is  remarkable  for  being  equally  soluble  in  water  at  32°  and  212°,  but 
three  times  more  soluble  in  water  at  104°. 

Arseniovinic  Acid,  As.05-|-Ae.O.-j-2H.O.,  is  formed  with  arsenic  acid  and  alcohol, 
like  the  body  last  described.     Its  salts  have  been  but  very  slightly  examined. 

Compounds  of  Ether  with  the  other  Mineral  Acids. 

Muriatic  Ether.  Chloride  of  Ethyle,  C4H5CI.,  is  prepared  by  distilling 
a  mixture  of  three  parts  of  oil  of  vitriol,  four  of  fused  common  salt,  and 
two  of  absolute  alcohol.  The  retort  should  be  connected  with  two  two- 
necked  bottles,  of  which  the  first  should  be  immersed  in  a  vessel  of  water 
at  60°,  and  the  second  be  surrounded  by  ice,  or  a  freezing  mixture. 
Some  alcohol  and  common  ether,  which  pass  over,  are  condensed  in  the 
first  bottle,  while  the  muriatic  ether  is  reduced  to  the  liquid  state  only 
in  the  second.  By  digestion  with  some  chloride  of  calcium  it  is  rendered 
quite  pure. 

It  is  a  colourless  liquid,  of  a  pungent  garlic  odour  ;  its  specific  gravity 
=0*874  ;  it  boils  at  52°  ;  is  neutral ;  sparingly  soluble  in  water  ;  it 
burns  with  a  bright  flame,  green  at  the  edges,  and  gives  off*  muriatic  acid 
gas.  By  passing  through  a  red-hot  tube,  it  affords  equal  volumes  of 
olefiant  and  muriatic  acid  gases,  or  by  heating  with  potash,  it  gives  ole- 
fiant  s^as  and  chloride  of  potassium.  Heated  with  alkaline  salts,  it  yields 
compound  ethers  and  alkaline  chlorides.  When  muriatic  ether  is  heated 
with  potassium,  Lovvig  states  that  chloride  of  potassium  is  formed  and  a 
light  oily  substance  separates,  which  has  the  formula  C4H5.  It  should  be 
EthylCf  but  so  important  an  observation  has  need  of  verification.     This 


548 


HYDROBROMIC     ETHER,    ETC. 


body  is  often  called  ligTit  Muriatic  Ethers  to  distinguish  it  from  heavy 
Muriatic  Ether,  which  resuhs  from  the  action  of  chlorine  on  weak  alco- 
hoi. 

Hydrobromic  Ether,  Bromide  of  Ethyle,  C4H5Br.,  is  obtained  by  dis. 
tilling  together  two  parts  of  bromine,  one  of  phosphorus,  and  six  of  alco- 
hoi.  There  is  first  formed  bromide  of  phosphorus,  which  instantly  de- 
composes the  water  of  the  alcohol,  and  the  nascent  hydrobromic  acid 
acting  on  the  ether  forms  the  hydrobromic  ether.  In  properties  it  per- 
fectly resembles  the  following  body  : 

Bydriodic  Ether.  Iodide  of  Ethyle,  C4H5I.,  is  formed  by  distilling 
iodine,  alcohol,  and  phosphorus.  It  is  a  colourless  liquid,  of  a  pungent 
ethereal  smell ;  its  specific  gravity  =1*92  ;  it  boils  at  161°  ;  it  is  abun- 
dantly soluble  in  alcohol.  Heated  with  potash,  it  gives  pure  olefiant  gas 
and  iodide  of  potassium.  The  theory  of  its  formation  is  the  same  as  in 
the  former  case. 

Hydrosulphuric  Ether.  Sulphur et  of  Ethyle,  C4H5S.,  may  be  formed 
by  acting  on  muriatic  ether  with  an  alcoholic  solution  of  sulphuret  of 
potassium.  It  boils  at  187°^  it  combines  with  sulphuret  of  hydrogen  to 
form  the  following  very  remarkable  substance : 

Sulphur-alcohol,  or  Mercaptan,  04^1^29  or  Ae.S.  +  H.S.,  which  is  obtain- 
ed directly  by  distilling  in  awater-bath  concentrated  solutions  of  sulpho- 
vinate  "of  lime  and  of  potash  saturated  with  sulphuret  of  hydrogen,  K.S.-f 
H.S.  and  Ae.O.  .  S.O3+K.O.  .  S.O3  producing  2K.0. .  S.O3  and  Ae.S. 
-j-H.S. ;  the  mercaptan  distils  over,  and  sulphate  of  potash  remains  in 
the  retort ;  it  is  a  colourless,  thin  liquid,  of  an  insupportable  smell  of 
onions;  it  boils  at  96°  ;  its  specific  gravity  is  0*84  ;  it  dissolves  in  al- 
cohol ;  is  perfectly  neutral  ;  burns  with  a  bright  blue  flame  ;  and  by  cold, 
freezes  into  a  crystalline  mass.  In  constitution,  it  is  perfectly  analogous 
to  alcohol,  the  oxygen  being  replaced  by  sulphur.  When  placed  in  con- 
tact with  metallic  oxides,  water  is  formed,  and  a  double  sulphuret  of  ethyle 
■  and  the  metal  produced.  This  occurs  remarkably  with  oxide  of  mercury, 
whence  the  barbarous  name  given  to  this  body  by  Zeize,  from  Mercurium 
Captans,  and  to  its  compounds  of  Mercapiides.  That  of  mercury  is  a 
crystalline  solid,  fusible  at  110^,  and  soluble  in  alcohol. 

The  properties  of  this  body  induced  its  discoverer,  Zeize,  to  look  upon 
it  as  a  compound  of  hydrogen  with  a  compound  radical,  which  he  called 
Mercaptum,  which  should  be  really  the  following  compound.  Its  formula 
then  became  0411582-1- H.  He  extended  this  view  also  to  common  alco- 
hol, which  he  considers  as  C4H502-hH.  ;  but  his  theory  has  met  with 
very  few  supporters. 

Thialbl.  Bisulphuret  of  Ethyle,  Ae.Sj,  is  formed  by  distilling  a  mix- 
ture  of  sulphovinate  of  lime  and  persulphuret  of  potassium.  It  is  a  lim- 
pid,  oily  fluid,  with  a  strong  garlic  smell ;  it  boils  at  124°.  Its  solution 
in  alcohol  precipitates  the  salts  of  lead  and  mercury.  By  the  action  of 
nitric  acid  on  these  sulphurets  of  ethyle,  acids  are  produced  analogous  to 
the  sulphovinic,  but  which  are  not,  as  yet,  accurately  known. 

The  Seleniuret  and  Telluret  of  Ethyle  have  been  formed,  but  do  not  re- 
quii'e  description. 

Nitrous  Ether.  Hyponitrite  of  Ethyle. — Ae.O.  .  N.Oa-  When  alco- 
hol and  nitric  acid  are  directly  mixed,  the  action  is  very  violent ;  heat 
is  evolved,  red  fumes  are  copiously  given  off*,  and  acetic,  oxalic,  and  car- 
i>onic  acids  formed.     Even  when  the  acid  is  dilute,  its  action  is  very 


NITROUS     ETHER,     ETC.  549 

complex ;  giving  up  two  atoms  of  oxygen  to  one  portion  of  the  alcohol, 
it  produces  aldehyd,  and  acetic  and  oxalic  acids,  and  it  is  only  the  hypo- 
nitrous  acid  thus  produced  that  acts  on  the  remaining  alcohol,  and,  com- 
bining with  the  ether  of  it,  forms  the  proper  nitrous  ether.  To  avoid 
these  oxidized  products,  the  best  plan  is  to  generate  red  fumes  of  hypo- 
nitrous  acid,  by  acting  on  starch  by  nitric  acid  in  a  retort,  and  to  conduct 
these  fumes  by  a  bent  tube  to  the  bottom  of  a  two-necked  bottle  contain- 
ing alcohol.  They  are  copiously  absorbed,  and  combine  directly  with 
the  ether.  From  the  second  neck  of  the  bottle  a  tube  should  pass  to  a 
condensing  apparatus  and  receiver  ;  enough  of  heat  is  evolved  by  the  ab- 
sorption of  the  red  fumes  to  distil  over  the  nitrous  ether  formed,  which 
may  be  thus  obtained  quite  pure. 

Another  process,  which  may  now  be  considered  as  obsolete,  consisted 
in  distilling  a  mixture  of  oil  of  vitriol,  nitrate  of  potash,  and  rectified 
spirit,  by  the  heat  of  a  water-bath,  into  a  receiver  cooled  by  snow.  The 
nitric  ucid  acted  very  violently  on  the  alcohol,  and  the  product  was  im- 
pure, and  small  in  quantity. 

Nitrous  ether  is  a  liquid,  colourless  or  pale  yellow,  of  a  pungent  odour 
of  apples  ;  it  usually  reacts  acid  from  slight  decomposition,  but  is  neutral 
if  quite  pure;  its  specific  gravity  is  0*947  ;  it  boils  at  61^  Fah.  Exposed 
to  the  air,  it  absorbs  oxygen  rapidly,  and  forms  aldehyd,  acetic  and  formic 
acids  ;  at  the  same  time,  nitric  oxide  is  given  off.  By  contact  with  any 
strong  base,  it  is  decomposed,  alcohol  being  set  free,  and  a  hyponitrite 
formed.  A  solution  of  this  nitrous  ether  in  spirit  (spiritus  nitri  dulcis) 
is  employed  in  pharmacy.  It  is  prepared  by  distilling  a  mixture  of  one 
part  of  nitric  acid  and  ten  of  rectified  spirit,  collecting  the  first  seven 
parts  which  come  over,  and  digesting  them  on  a  little  dry  carbonate  of 
potash,  to  remove  any  traces  of  free  acid.  Its  specific  gravity  should  be 
0*850.  It  may  be  prepared  directly  by  dissolving  one  part  of  real  nitrous 
ether  in  eight  parts  of  spirits  of  wine. 

Cyanogen  Compounds  of  Ether, 

Hydrocyanic  Ether.  Cyanide  of  Ethyle,  Ae.Cy.,  is  prepared  by  distil- 
ling a  mixture  of  sulphovinate  of  potash  and  cyanide  of  potassium  at  a 
moderate  heat.  It  is  a  colourless  liquid,  of  a  strong  garlic  odour  ;  it 
boils  at  179^,  and  is  lighter  than  water  ;  it  is  very  poisonous. 

Cyanuric  Ether,  SAe.O.+SCysOs+B  Aq.,is  formed  when  the  vapours  of  hydrated 
cyanic  acid  are  passed  into  ether,  as  long  as  they  are  absorbed.  After  some  time, 
xHiQ  new  compomid  separates  in  crystals,  which  are  colourless  prisms,  destitute  of 
taste  and  smell,  soluble  in  water,  and  but  sparingly  soluble  in  ether, 

Hydrostdphocyanic  Ether  appears  to  be  formed  by  distilling  sulphocyanide  of  potas- 
sium with  sulphovinate  of  potash.     It  is  a  liquid  heavier  than  water. 

Compounds  of  Ether  with  the  Acids  of  Carbon, 

Carbonic  Ether.  Carbonate  of  Ethyle. — Ae.O. ,  C.O2.  This  ether  can  only  be  pro- 
duced by  an  indirect  process,  the  theory  of  which  is  not  well  understood.  Metallic 
potassium  or  sodium  is  added,  in  small  pieces,  to  oxalic  ether,  as  long  as  a  disen- 
•gagement  of  carbonic  oxide  gas  occurs ;  a  thick  brown  mass  is  formed,  which  is  to 
be  distilled,  the  excess  of  metal  being  first  destroyed  by  the  addition  of  water;  the 
carbonic  acid  distils  over.  It  is  a  colourless  liquid,  of  an  aromatic  smell,  lighter 
than  water.  It  boils  at  2G0°  ;  it  is  insoluble  in  water,  but  dissolves  in  alcohol ;  its 
alcoholic  solution  is  decomposed  by  potash,  alcohol  and  carbonate  of  potash  being 
formed. 

Carbonate  of  Ether  and  Water.  Carbovinic  Acid. — Ae.O.  .C.O24-H.O.  .C.O2.  At 
one  time  it  was  considered  that  anhydrous  sugar  was  actually  bicarbonate  of  ether, 
C6H503=C4H50.+2C.02,  and  that  the  alcoholic  fermentation  consisted  in  the  sep. 


550  OXALIC     ETHER,     ETC. 

aration  of  these  bodies,  the  nascent  ether  combining  with  water  to  form  alcohol ; 
but  that  idea  is  now  inadmissible.  The  true  carbovinic  acid  is  prepared  by  dissolv- 
ing caustic  potash  in  absolute  alcohol,  and  passing  dry  carbonic  acid  gas  through 
the  liquor  as  long  as  it  is  absorbed.  A  crystalline  mass  is  formed  of  carbonate  and 
Carbovinate  of  Potash,  which  last  is  dissolved  out  by  cold  alcohol ;  and  this  solution, 
being  mixed  with  ether,  deposites  the  salt,  whose  formula  is  Ae.O. .  C.O2+K.O. .  Q. 
O2,  in  pearly  plates,  which  are  immediately  decomposed  by  water  into  alcohol  and 
bicarbonate  of  potash.     The  carbovinic  acid  is  not  known  in  an  isolated  form. 

Oxalic  Ether.  Oxalate  of  Ethyle,  Ae.O. .  C2O3,  is  prepared  by  distilling  one  part 
of  alcohol  with  one  of  binoxalate  of  potash  and  two  of  oil  of  vitriol.  At  first  alcohol 
and  common  ether  come  over,  but  then  a  heavy  fluid,  which  sinks  to  the  bottom  of 
the  receiver.  The  portions  last  distilled  are  richest  in  product.  It  is  rectified  by 
another  distillation  from  off  a  little  litharge.  It  is  a  colourless  oily  liquid,  denser 
than  water,  of  a  heavv  but  aromatic  smell;  it  boils  at  370°.  In  contact  with  water 
or  bases,  it  is  gradually  decomposed  into  alcohol  and  oxalic  acid.  The  sp.  gr.  of  its 
vapour  is  5077. 

Oxalovinic  Acid. — ^Ae.O. .  C2O3+H.O. .  C2O3.  This  acid  is  not  known  except  in 
combination.  It  is  produced  by  adding  to  a  solution  of  oxalic  ether  in  alcohol  half 
as  much  potash  as  would  suffice  to  decompose  it.  The  Oxalovinate  of  Potash  sep- 
arates as  a  crystalline  powder,  being  insoluble  in  alcohol.  By  an  excess  of  base  it 
is  decomposed  into  alcohol  and  an  oxalate.  Its  other  salts  do  not  require  special 
notice. 

Oxaniethan. — Ae.O. .  C203+C202Ad.  When  oxalic  ether  is  acted  on  by  water 
of  ammonia,  it  is  totally  decomposed,  alcohol  and  oxamide  being  formed,  as  already 
noticed.  If  a  solution  of  ammonia  in  alcohol  be  used,  but  one  half  of  the  oxalic 
ether  is  decomposed,  and  the  oxamide  produced  unites  with  the  other  half,  forming 
a  substance  soluble  in  alcohol  and  water,  and  crystallizing  in  brilliant  prisms  and 
plates.  It  melts  at  212°,  and  sublimes  unchanged,  at  430°.  Its  solution  in  cold  wa- 
ter does  not  precipitate  lime-water,  but  if  it  be  boiled  alcohol  is  expelled,  and  the 
solution  contains  binoxalate  of  ammonia.  By  water  of  ammonia  it  is  totally  chan- 
ged into  oxamide, 

Chloroxycarbonic  Ether. — Ae.O. .  C.O2+C.O.CI.  This  substance  is  formed  by  the 
action  of  chlorocarbonic  acid  gas  on  absolute  alcohol.  It  is  a  colourless  liquid, 
perfectly  neutral,  heavier  than  water,  and  boiling  at  201° ;  sparingly  soluble  in  wa- 
ter. It  consists,  or,  at  least,  contains  the  elements,  of  an  atom  of  carbonic  ether  and 
an  atom  of  phosgene  gas.  When  put  in  contact  with  water  of  ammonia,  it  is  dis- 
,  solved  violently,  and  heat  evolved,  sal  ammoniac  and  a  peculiar  substance  termed 
Urethan  being  formed.  The  liquor  is  to  be  dried  down,  and  the  residue  distilled  in  a 
dry  retort  with  an  oil-bath.  The  urethan  passes  over,  and  solidifies  in  the  receiver 
to  a  crystalline  mass  resembling  spermaceti.  In  it  the  chlorine  of  the  preceding 
substance  is  replaced  by  amidogene,  its  formula  being  Ae.O..  C.Oa+C.O.Ad. ;  it 
consists  thus  of  carbonic  ether  and  carbamide  in  the  proportion  of  one  atom  of  each. 

Sulphocarhonic  Ether.  Hydroxanthic  Acid,  Ae.O.  .C.S24-H.O.  .C.S2,  is  prepared 
by  decomposing  the  xanthate  of  potash  by  dilute  sulphuric  acid.  A  milky  liquor  is 
obtained,  from  which,  after  some  time,  a  heavy  oil  separates ;  it  is  to  be  rapidly 
washed  with  water,  and  dried  by  chloride  of  calcium.  It  is  then  pale  yellow,  slight- 
ly acid,  inflammable,  and  burns  with  a  blue  sulphurous  flame ;  it  is  decomposed  by 
warm  water  into  alcohol  and  sulphuret  of  carbon ;  it  decomposes  the  alkaline  car- 
bonates, expelling  the  carbonic  acid.  Of  its  salts,  that  of  potash  is  obtained  direct- 
ly, and  from  it  the  others.  Xanthate  of  Potash,  Ae.O. .  C.Sa+K.O. .  C.S2,  is  formed 
by  adding  sulphuret  of  carbon  to  a  warm  solution  of  caustic  potash  in  alcohol.  On 
cooling  the  liquor,  it  deposites  the  salts  in  crystals,  which  are  to  be  collected  on  a  fil- 
ter, washed  with  ether,  and  dried  between  folds  of  bibulous  paper.  The  salts  of 
lead,  copper,  &c.,  may  be  prepared  by  double  decomposition;  they  are  all  yellow, 
whence  tne  ordinary  name  of  the  acid. 

Mucate  of  Ether  is  solid  and  crystalline.  It  is  formed  by  dissolving  mucic  acid  in 
cil  of  vitriol,  and  gradually  adding  an  equal  weight  of  alcohol.  The  liquor  3-ields, 
after  some  time,  the  mucic  ether  in  crystals,  which  are  to  be  dried  on  a  porous  stone, 
and  recrystallized  from  alcohol. 

The  remaining  compounds  of  ether  with  acids  will  be  described  along  with  the 
other  salts  of  those  acids. 

Of  Olefiant  Gas  and  its  Compounds. 

This  gas  has  been  frequently  mentioned  as  one  of  the  products  of  the  ac- 
tion of  sulphuric  acid  on  alcohol.    The  usual  process  to  obtain  it  consists 


PREPARATION     OF     OLEFIANT     GAS. 


551 


in  heating  one  part  of  alcohol  with  six  of  oil  of  vitriol  in  a  flask,  J,  from 
which  a  tube  passes  to  the  water  pneumatic  trough,  as  in  the  figure  ;  the 
mass  becomes  dark  ; 
ether,  water,  and  oil 
of  wine  collect  in  the 
interposed  globe,  a, 
and  olefiant  gas  is  co- 
piously evolved,  mix. 
ed  with  an  equal  vol- 
ume of  sulphurous 
acid,  which,  however, 
being  absorbed  by  the 
water,  the  other  gas 
remains  pure.  To- 
wards the  end  of  the 
process  the  materials 
in  the  flask  swell  up  very  much,  and  might  boil  over  if  not  carefully  at- 
tended to.  The  theory  of  this  action  appears,  at  first  sight,  very  simple ; 
the  alcohol  losing  an  atom  of  water,  is  first  converted  into  ether,  which, 
by  the  influence  of  the  excess  of  sulphuric  acid,  is  deprived  of  the  ele- 
ments of  another  equivalent  of  water,  and  olefiant  gas  remains,  C4H5O. 
giving  C4H4  and  H.O. ;  but  we  cannot  by  this  process  generate  the  ole- 
fiant gas,  without,  at  the  same  time,  more  complex  products  appearing, 
as  etherol,  sulphurous  acid,  and  the  black  matter  which  remains  in  the 
retort.  This  last,  which  had  been  considered  formerly  as  charcoal,  ap- 
pears to  consist  of  C27H804-f-S.03;  it  combines  with  bases,  and  is  termed 
the  Thiomelanic  Acid  ;  it  evidently  results  from  the  sulphuric  acid,  giving 
up  oxygen  to  the  hydrogen  of  a  portion  of  the  alcohol. 

Olefiant  gas  is  generated  on  the  large  scale  by  the  decomposition  of 
coal,  pitch,  oil,  &c.,  at  a  red  heat,  and  is  employed  for  the  purpose  of  il- 
lumination, being  the  most  valuable  constituent  of  the  gas  which  is  burn- 
ed in  our  streets  and  shops.  To  this  source  of  it  I  shall  have  occasion 
to  return. 

We  may  obtain  this  gas,  however,  by  much  more  definite  and  simple 
processes.  Thus,  if  vapour  of  muriatic  ether  be  passed  through  a  red- 
hot  porcelain  tube,  it  is  resolved  into  equal  volumes  of  olefiant  and  muri- 
atic acid  gases ;  also,  if  muriatic  ether  be  heated  with  ammoniacal  gas, 
sal  ammoniac  is  formed,  and  olefiant  gas  evolved ;  the  same  decomposi- 
tion is  caused  by  caustic  potash.  If  vapour  of  alcohol  be  passed  into  oil 
of  vitriol  so  far  diluted  as  to  boil  at  320°,  and  heated  to  that  degree,  it  is 
totally  resolved  into  water  and  olefiant  gas.  In  a  theoretical  point  of 
view,  these  sources  of  olefiant  gas  are  peculiarly  of  interest. 

Olefiant  gas,  when  pure,  is  colourless  ;  its  odour  is  very  slightly  ethe- 
real ;  it  is  sparingly  absorbed  by  water ;  it  burns  with  a  brilliant  white 
flame,  producing  much  smoke.  When  mixed  with  twice  its  volume  of 
chlorine,  and  set  on  fire  in  a  tall  narrow  jar,  a  brilliant  flame  descends 
rapidly,  muriatic  acid  being  formed,  and  charcoal,  smelling  strongly  of 
napthaline,  separating  in  dense  flocculi.  Its  specific  gravity  is  980*8,  as 
one  volume  of  it  contains  a  volume  of  carbon  vapour  and  two  volumes  of 
hydrogen  (843'0  +  137*6  =  980'6).  It  consists  of  an  equal  number  of 
equivalents  of  hydrogen  and  carbon,  but  chemists  are  not  unanimous  as 
to  its  real  atomic  weight.     Berzelius,  who  looks  upon  it  as  an  organic 


552  COMPOUNDS     OF     ETilERENE. 

radical,  and  the  basis  of  a  scries  of  compounds  with  oxygen,  chlorine, 
&c.,  has  proposed  for  it  the  name  Elayl,  and  the  formula  CgHj.  The  name 
Olejiant  Gas  being  very  inconvenient,  I  shall,  in  speaking  of  its  com- 
pounds, term  it,  for  the  present,  Etherene.  The  principal  support  of  the 
theory,  which  considers  this  gas  to  be  the  radical  of  the  ethers  and  of  al- 
cohol, is  derived  from  the  great  simplicity  of  their  constitution  by  volume, 
in  the  state  of  vapour,  on  that  view.  Thus,  two  volumes  of  defiant  gas 
combine  with  two  of  vapour  of  water  to  form  alcohol ;  with  one  of  vapour 
of  water  to  form  ether  ;  with  two  of  muriatic  or  hydriodic  acid  gases  to 
form  the  hydriodic  or  muriatic  ethers,  and  so  in  similar  simple  propor- 
tions of  volume  in  other  cases.  But  this  evidence  is  very  insecure,  as 
we  might  show  nearly  as  simple  gaseous  relations  upon  other  and  very 
improbable  points  of  view.  Its  combinations  are  generally  formed  indi- 
rectly, as  from  alcohol  or  ether,  but  it  combines  immediately  with  iodine, 
chlorine,  and  sulphuric  acid. 

Anhydrous  sulphuric  acid  absorbs  etherene  in  large  quantity,  form- 
ing white  crystals,  which,  when  dissolved  in  water,  constitute  Iselhionic 
Acid,  identical  in  every  respect  with  that  formed  as  described  p.  546. 
When  dry,  its  composition  is  8206+0404;  but  when  in  contact  with 
water,  it  combines  with  two  atoms  thereof,  and  becomes  isomeric  with 
sulphovinic  acid.  That  it  differs  from  it  essentially  in  constitution  is 
shown  by  its  salts  giving  a  mixture  of  sulphate  and  sulphite  when  fused 
with  potash  ;  the  sulphurous  element  is  therefore  as  hyposulphuric,  and 
not  sulphuric  acid,  and  its  rational  formula  is  S20g+C4H40.  This  ise- 
thionic  acid  is  much  more  energetic  than  the  sulphovinic  ;  it  decomposes 
all  salts  of  organic  acids  ;  its  own  salts  are  all  soluble  and  crystallizable, 
and  sustain  a  heat  of  450°  without  decomposition. 

If  a  jar  of  defiant  gas,  c,  be  inverted  in  the  pneumatic  trough,  over  a 
capsule,  h,  as  in  the  figure,  and  bubbles  of  chlorine  be  passed  up  into  it, 
•  both  gases  disappear,  and  a  heavy  oily  liquid  collects 
in  the  capsule,  the  formation  of  which  gave  to  the  gas 
its  common  name  of  Olejiant  Gas.  In  this  process 
a  quantity  of  gas  is  totally  decomposed,  and  muriatic 
acid  is  evolved  in  great  quantity,  but  the  oil  results 
from  the  direct  union  of  the  chlorine  and  etherene, 
its  formula  being  C4H4CI2.  I  will  name  it  Chlor- 
etherene,  but  it  is  called  the  Oil  of  the  Dutch  Chemists^ 
as  it  was  first  formed  by  the  members  of  a  scientific 
association  in  Holland.  When  quite  pure  it  is  col- 
ourless, of  a  sweet  ethereal  odour.  Its  specific  gravity  =1*25  ;  it  boils 
at  180°  ;  it  burns  with  a  greenish  flame,  giving  off  muriatic  acid ;  the 
specific  gravity  of  its  vapour  is  3421.  Exposed  to  an  excess  of  chlorine, 
it  is  decomposed,  hydrogen  being  removed,  and  replaced  by  chlorine  ;  a 
volatile  oily  liquid,  C4H2CI4,  and  ultimately  sesquichloride  of  Carbon,  C4 
Clg,  are  produced. 

The  chlor-etherene  is  not  decomposed  by  a  watery  solution  of  potash  ; 
but  if  it  be  dissolved  in  an  alcoholic  solution  of  that  alkah,  and  gently 
warmed,  chloride  of  potassium  is  formed,  and  a  peculiar  body  produced, 
whose  composition  is  expressed  by  the  formula  C4H3CI.  This  substance 
is  gaseous ;  of  a  garlic  odour,  burning  with  difficulty  with  a  smoky  red 
flame  ;  its  specific  gravity  is  2166.  It  is  evident  that  the  chlor-etherene 
may  be  considered  as  a  compound  of  this  gas  with  muriatic  acid,  C4H 


PREPARATION     OF     ALDEHYD.  553 

Cl.  +  H.Cl.,  in  which  case  the  action  of  the  potash  is  easily  explained. 
This  gas  itself  is  supposed  to  be  a  chloride  of  the  same  carbohydrogen 
as  is  the  basis  of  acetic  acid  and  aldehyd,  (C4H3),  or  Acetyl ;  and  the  ole- 
fiant  gas,  on  this  view,  is  Hydruret  of  Acetyl,  G4H3-I-H.,  or  Ac.H.  The 
farther  discussion  of  this  opinion  will  be  reserved  for  another  place.  If 
the  gas,  C4H3CI.,  be  passed  over  perchloride  of  antimony,  it  combines 
with  more  chlorine  and  forms  a  liquid,  which  boils  at  240°,  and  consists 
of  C4H3CI3 ;  by  an  alcoholic  solution  of  potash  this  is  decomposed  into 
muriatic  acid,  and  another  body,  also  liquid,  but  boiUng  at  86°,  and  hav- 
ing the  formula  C4H2CI2.  By  contact  with  chlorine,  this  produces  the 
liquid  C4H2CI4,  noticed  in  the  preceding  paragraph,  as  obtained  directly 
from  chlor-etherene,  and,  as  the  next  stage,  the  sesquichloride  of  carbon. 

If  a  mixture  of  olefiant  gas  and  vapour  of  ether  be  acted  on  by  chlorine,  an  oily 
liquid  is  obtained,  which  boils  at  350'^,  and  consists  of  C4H4  .  Cl.O. ;  it  is  called  Chlor- 
etheral,  but  is  properly  a  compound  of  aldehyd  and  the  chlor-etherene,  C4H4CI24- 
C4H4O2. 

Bromine  combines  with  olefiant  gas,  with  the  same  phenomena  as  chlorine,  and 
gives  rise  to  a  similar  series  of  compounds,  which  it  is  consequently  unnecessary 
to  detail. 

Iodine  absorbs  olefiant  gas  abundantly,  and  forms  a  white  crystalline  substance, 
which  melts  at  180°,  and  may  be  sublimed  if  air  be  not  present.  It  is  soluble  in 
alcohol,  insoluble  in  water ;  its  formula  is  C4H4I2,  but  the  products  of  its  decompo- 
sition are  not  similar  to  those  of  the  chlorine  compound. 

When  bichloride  of  platinum  is  dissolved  in  alcohol,  a  very  complex  reaction  oc- 
curs, and  a  substance  is  produced  consisting  of  Pt.Cl.-|-C2H2.  This  body  combines 
with  the  chlorides  of  the  alkaline  metals  to  form  double  salts.  On  Berzelius's  view, 
the  C2H2  being  a  compound  radical  (Elayl),  may  be  supposed  simply  to  replace  the 
second  atom  of  chlorine,  and  thus  form  an  Elayl-chloride  of  platinum,  which  has 
the  same  power  of  forming  double  salts  as  the  ordinary  bichloride.  They  are  thus 
(Pt.+El.Cl.)+K.Cl.  and  (Pt.+El.Cl.)-|-Na.Cl.,  &c. 

Of  the  Products  of  the  Oxidation  of  Alcohol,  Aldehyd,  Hypoacetous 
Acid.—Eq.  555-6  or  44*2. 

It  has  been  mentioned,  in  speaking  of  nitrous  ether,  that  by  the  ox- 
idation of  alcohol  we  obtain  a  crowd  of  products,  as  aldehyd  and  acetic 
acid,  formic,  malic,  and  oxalic  acids  ;  these  last  are  secondary  products 
of  the  too  violent  reaction,  and  the  result  of  the  true  oxidation  of  alco. 
hoi  is  found  to  be  aldehyd  or  acetic  acid,  according  to  the  point  at  which 
the  process  stops.  The  formation  of  acetic  acid  thus  directly  from  al- 
cohol  constitutes  the  acetic  fermentation^ 

Although  aldehyd  is  formed  when  nitric  acid  acts  on  alcohol,  yet,  from 
the  other  products  being  difficult  to  separate,  it  is  not  so  prepared  ;  a 
large  quantity  of  it  is  generated  in  the  destructive  distillation  of  wood, 
and  it  may  be  obtained  in  the  rectification  of  the  pyroxylic  spirit.  The 
most  ordinary  process  is  that  given  by  Liebig  ;  six  parts  of  oil  of  vitriol 
with  four  of  water,  four  of  spirit  of  wine,  and  six  of  black  oxide  of  man- 
ganese, are  to  be  distilled  with  a  very  gentle  heat,  and  the  product  col- 
lected in  a  receiver  surrounded  with  melting  ice.  The  apparatus  de- 
scribed for  preparing  ether  (p.  542)  should  be  employed.  The  process 
is  completed  as  soon  as  the  materials  in  the  retort  cease  to  froth  up.  I 
have  found  a  purer  product  to  be  obtained  by  distilling,  at  a  very  gentle 
heat,  two  parts  of  spirit  of  wine  with  three  of  bichromate  of  potash,  three 
of  oil  of  vitriol,  and  six  of  water  ;  the  last  two  being  previously  mixed 
and  allowed  to  cool.  To  obtain  the  aldehyd  absolutely  pure,  it  is  to  be 
combined  with  ammonia,  and  the  crystallized  aldehyd-ammonia  decom- 

4  A 


554 


PROPERTIES    OF    ALDEHY  D. A  C  E  T  A  L. 


posed  by  dilute  sulphuric  acid,  distilled  in  a  water-bath  at  120°  with  the 
greatest  care,  and  rectified  over  fused  chloride  of  calcium. 

Aldehyd  is  a  colourless  liquid,  of  an  agreeable  but  suffocating  odour ; 
it  boils  at  71°  ;  it  is  lighter  than  water ;  it  mixes  with  water,  alcohol, 
and  ether ;  it  is  neutral  and  inflammable,  burning  with  a  blue  flame  ;  in 
contact  with  oxidizing  agents,  it  is  changed  into  acetic  acid,  passing 
through  an  intermediate  state  of  Aldeliydic  Acid.  On  this  fact  is  found- 
ed its  most  characteristic  property  ;  if  any  liquor  containing  aldehyd  be 
added  to  a  solution  of  the  ammoniacal  nitrate  of  silver,  and  gently  heat- 
ed, the  silver  is  deposited  as  a  brilliant  metallic  film,  hning  the  sides  of 
the  vessel  like  a  mirror,  and  in  the  liquor  is  found  aldehydate  of  silver  ; 
if  to  this  potash  be  added,  oxide  of  silver  precipitates,  and  on  boiling  for 
a  moment,  it  is  reduced  to  the  state  of  metallic  silver,  and  acetate  of 
potash  is  formed.  From  the  composition  of  aldehyd,  these  changes  are 
at  once  explained.  It  is  formed  by  the  abstraction  of  two  atoms  of  by. 
drogun  from  alcohol,  which  are  carried  away,  as  water,  by  the  oxygen 
supplied ;  its  formula  is  hence  C4H4O2 :  now,  in  contact  with  Ag.O.,  it 
forms,  first,  aldehydic  acid,  C4H4O3,  and  metallic  silver,  and  then  C4H4O3 
with  Ag.O.  gives  hydrated  acetic  acid,  C4H4O4,  and  another  quantity  of 
silver.  The  formation  of  acetic  acid  from  alcohol  consists,  therefore,  in 
two  stages  ;  first,  the  abstraction  of  hydrogen,  by  which  aldehyd  is  form- 
ed, and,  second,  the  addition  of  oxygen,  by  which  acetic  acid  is  produced. 
When  aldehyd  is  heated  in  a  solution  of  potash,  this  becomes  brown, 
and  by  an  acid  a  solid  brown  substance  separates,  which  is  fusible,  and 
possesses  many  properties  of  a  resin.  This  also  is  a  very  distinctive 
character  of  aldehyd. 

When  long  kept,  aldehyd  undergoes  an  isomeric  change  into  two 
bodies,  one  liquid,  Elaldehydy  the  other  solid,  Metaldehyd ;  they  have  the 
same  formula  as  aldehyd,  C4H4O2,  but  difler  in  all  their  properties. 

The  general  characters  of  aldehyd  show  that  it  contains  the  same  rad- 
ical  as  acetic  acid,  Acetyl,  C4H3  or  Ac,  combined  with  oxygen;  it  is, 
therefore,  Hydrated  Oxide  of  Acetyl,  Ac.O.  +  Aq.  =0411402;  it  has  been 
called,  also,  Hypoacetous  Acid,  for  it  is  capable  of  perfectly  neutralizing 
ammonia.  Its  compound  with  ammonia  is,  indeed,  very  remarkable  ; 
it  is  best  prepared  by  dissolving  aldehyd  in  ether,  and  passing  ammo- 
niacal gas  into  the  liquor ;  the  aldehyd-ammonia,  being  very  sparingly 
soluble  in  ether,  crystallizes  as  it  forms  in  large  hexagonal  plates,  which 
are  very  brilliant  and  colourless.  Their  solution  in  water  soon  decom- 
poses, becoming  brown,  and  exhaling  an  animal  smell.  The  dry  crystals 
may  be  fused  and  sublimed  without  alteration  ;  their 
formula  is  C4H3O.4-H.O.  .  N.H3. 

Aldehyd  is  formed  also  by  the  direct  action  of  the 
air  on  alcohol ;  this  may  be  facilitated  very  much  by 
means  of  spongy  platina,  which  contains  much  oxy- 
gen condensed  in  its  pores,  but  the  process  is  of  more 
interest  in  consequence  of  another  body  which  then 
forms,  and  which  cannot  be  otherwise  generated  ;  it 
is  Acetal.  To  prepare  it,  a  large  bell-glass  is  ta- 
ken, open  above,  and  standing  in  a  basin,  so  sup- 
ported as  to  allow  the  air  inside  to  be  frequently  re- 
newed, as  in  the  figure  ;  through  the  top  passes  the 
tube  of  a  small  funnel,  a,  under  which  is  a  watch- 


^ 


FORMATION     OF    ACETIC     ACID.  555 

glass,  b,  with  a  layer  of  platina  black  (p.  407).  Into  the  funnel  strong 
alcohol  is  poured,  so  that  from  time  to  time  a  drop  falls  into  the  watch- 
glass  ;  being  thus  presented  to  oxygen  in  a  favourable  condition,  it  is 
decomposed,  and  aldehyd,  acetic  acid,  and  acetal  are  formed.  These 
liquids  are  vaporized  by  the  heat  evolved,  but  condense  on  the  sides 
of  the  bell-glass,  and,  flowing  down,  collect  in  the  basin  underneath. 
By  processes  detailed  in  the  systematic  works,  the  acetal  is  purified. 
It  is  a  colourless  hquid,  boiUng  at  200°  ;  its  odour  is  agreeable  ;  its  for- 
mula is  CgHgOg,  and  it  appears  to  be  a  compound  of  aldehyd  and  ether, 
C^HA+aH^O. 

The  Aldeliydic  Acid — Acetous  Acid — as  already  noticed,  is  formed  by 
the  partial  oxidation  of  aldehyd  ;  but  it  appears  to  be  produced  also  under 
the  circumstances  of  slow  combustion,  described  in  p.  179,  along  with 
acetic  and  formic  acids.  It  is  obtained  pure  by  decomposing  its  silver 
salt  by  sulphuret  of  hydrogen,  forming  a  liquor  of  an  agreeably  acid 
taste. 

Of  Acetic  Acid,  Vinegar, — Eq.  755-6  or  51*2. 
As  all  alcoholic  liquors  are  liable  to  undergo  spontaneous  decomposi- 
tion, and  form  vinegar,  this  acid  has  been  known  from  the  earliest  ages 
as  produced  by  the  acetous  fermentation ;  its  origin  was,  however,  long 
wrapped  in  obscurity,  for  the  complex  constitution  of  the  fermented 
liquors,  in  which  it  was  ordinarily  produced,  prevented  the  simple  na- 
ture of  the  change  from  being  understood.  It  is  now  fully  established, 
that  the  change  from  alcohol  to  acetic  acid  consists  simply  in  the  remo- 
val of  two  atoms  of  the  hydrogen  of  the  alcohol,  and  addition  of  two 
atoms  of  oxygen ;  these  actions  not  being  simultaneous,  but  successive, 
and  aldehyd  being  the  intermediate  product,  thus  : 

A.lcohol,  C4H6O2,  and  Aldehyd,  C4H4O2, 

gives  by  — H2,  gives  by  -J-Oz, 

Aldehyd,  "cIhIo^  Hydrated  Acetic  Acid,  C4H4O4. 

By  means  of  chromic  and  nitric  acids,  but  especially  by  the  platinum 

black  as  described  just  now,  this  reaction  may  be  carried  on  with  perfect 

accuracy  and  distinctness. 

But  if  we  place  ourselves  in  the  actual  condition  oi  practice,  the  the- 
ory of  the  acetous  fermentation  becomes  much  more  difficult ;  for  exactly 
as  a  pure  solution  of  grape-sugar  will  not  break  up  into  alcohol  and  car- 
bonic acid,  and  a  cause  of  disturbance  is  necessary  in  order  to  enable 
the  new  arrangement  of  its  particles  to  occur,  so  do  we  find  it  to  be  in 
changing  alcohol  into  acetic  acid.  Pure  alcohol,  whether  weak  or 
strong,  absorbs  no  oxygen  by  mere  exposure  to  the  air,  and  hence  forms 
no  vinegar  •,  it  is  necessary  there  should  be  another  body  more  liable  to 
decomposition  (ferment),  which,  abstracting  oxygen  from  the  air  for  the 
purpose  of  its  own  decomposition,  may  confer  upon  the  molecules  of  al- 
cohol such  instability  of  structure  as  will  admit  of,  and  cause  the  similar 
absorption  of  oxygen  by  them.  The  ferment,  in  decomposing,  evolves 
water  and  carbonic  acid ;  the  alcohol  evolves  water  only,  but  absorbs 
the  oxygen  from  the  air.  The  platinum  black,  in  the  process  that  has 
been  described,  supplies  the  place  of  the  ferment.  In  making  vinegar 
from  malt  liquors  or  from  wine,  they  are  placed  in  hogsheads  partially 
full,  and  left  more  or  less  exposed  to  the  air,  according  to  circumstances. 
To  supply  oxygen,  the  air  must  have  access ;  but  if  the  air  were  very 


556  MANUFACTURE    OF     VINEGAR. 

rapidly  renewed,  a  large  quantity  of  the  volatile  aldehyd  would  be  car. 
ried  off.  These  solutions  contain  abundance  of  organic  matter,  proper 
for  acting  as  ferment ;  and  when  the  fermentation  is  complete,  the  prod, 
ucts  of  their  decomposition  collect  upon  the  bottom  and  sides  of  the 
vats,  in  a  gelatinous  mass,  termed  mothers. 

The  manufacture  of  wine  or  malt  vinegar  by  the  old  process  of  mere  partial  ex- 
posure to  the  air  in  vats  consumed  much  time,  and  is  almost  superseded  by  the 
German  method,  by  which  excellent  vinegar  may  be  made  in  thirty-six  hours.  A 
cask  is  to  be  filled,  as  in  the  figure,  with  wood  shavings,  and 
closed  at  the  top  by  a  pan,  b,  the  bottom  of  which  is  perforated 
with  a  number  of  small  holes,  through  which  short  threads  are 
passed,  to  bring  down  the  liquid  more  rapidly.  The  shavings, 
before  being  used,  are  well  steeped  in  vinegar,  which  is  itself 
one  of  the  most  active  ferments.  Below,  at  c  c,  is  a  circle  of 
holes  about  half  an  inch  in  diameter,  by  which  the  air  may  enter, 
which  then  escapes  above  by  a  number  of  tubes,  which  pass 
through  the  pan,  and  are  left  white  in  the  figure.  If  now  we  take 
a  spirit  containing  about  one  part  of  proof  spirit  to  four  of  water, 
and,  having  mixed  with  it  joVo^h  of  honey  or  yeast,  pour  it 
into  the  pan  above,  it  trickles  down  the  orifices  by  the  threads, 
and,  spreading  over  the  shavings,  has  its  surface  enormously  extended.  It  absorbs 
oxygen  veiy  rapidly,  and,  having  been  warmed  to  about  75°  before  being  poured  in, 
its  temperature  soon  rises  to  100°  ;  the  interior  being  so  hot,  a  current  of  air  is  es- 
tablished through  the  vessels,  by  which  a  constant  supply  of  oxygen  is  kept  up. 
According  as  the  liquid  passes  down,  it  escapes  through  the  pipe  at  the  bottom,  and 
is  collected  in  the  vessel  a ;  when  it  has  passed  through  three  or  four  times,  it  is 
found  to  be  converted  into  excellent  vinegar,  and  the  whole  time  occupied  is  only 
between  twenty- four  and  thirty-six  hours. 

The  manufacture  of  vinegar  by  the  distillation  of  wood  will  be  described  in  an- 
other place. 

The  vinegar  of  commerce  has  frequently  its  pungency  and  acidity  in- 
creased by  the  addition  of  acrid  herbs,  as  capsicum,  and  by  sulphuric 
acid.  To  obtain  it  free  from  these  impurities,  it  is  redistilled.  As,  how- 
ever, its  volatility  is  about  the  same  as  that  of  water,  it  cannot  be  con- 
centrated in  that  way,  and  hence  the  strong  acetic  acid  must  be  obtained 
by  the  decomposition  of  its  salts  by  a  stronger  acid.  For  this  purpose, 
one  part  of  acetate  of  soda,  which  has  been  dried  at  a  gentle  heat,  is  to 
be  distilled  with  two  parts  of  oil  of  vitriol ;  so  much  heat  is  evolved  by 
the  mixture,  that  a  quantity  of  the  acetic  acid  distils  over  spontaneously, 
and  to  complete  the  decomposition  only  a  very  moderate  heat  need  be  ap- 
plied. In  this  process,  S.Os-j-Aq.  and  Na.O.-j-C4H303  give  S.Og+Na.O. 
and  C4H303-|-Aq.  The  acid  which  passes  over  generally  contains  some 
sulphurous  acid,  arising  from  its  secondary  action  on  the  oil  of  vitriol ; 
in  order  to  separate  this,  it  is  rectified  over  some  peroxide  of  lead,  with 
which  the  sulphurous  acid  forms  sulphate  of  lead.  The  liquid  acetic 
acid  which  distils  is  then  to  be  exposed  to  a  cold  of  about  23°,  and  the 
crystals  which  form  are  to  be  separated  from  the  liquid  portion ;  these 
crystals  are  the  Prolohydrate  of  Acetic  Acid,  and  in  its  most  concentrated 
form. 

Acetic  acid  may  be  prepared  also  by  distilling  acetate  of  lead  with  oil 
of  vitriol,  or  by  the  destructive  distillation  of  acetate  of  copper  :  by  this 
last  method  an  acid  is  obtained  (radical  vinegar)  of  an  agreeable  aromat- 
ic odour,  from  an  admixture  of  Acetone,  The  acetate  of  potash  is  pre- 
scribed by  the  Dublin  Pharmacopoeia ;  but,  as  acetate  of  soda  is  found 
abundant  and  cheap  in  commerce,  it  is  now  exclusively  employed. 
The  Hydrated  Acetic  Acid,  when  free  from  any  excess  of  water,  crvs- 


PROPERTIES     OF     ACETIC     ACID,     ETC.  557 

tallizes  at  50°  in  large  white  plates,  which  do  not  again  become  liquid 
until  heated  above  60° ;  it  is  hence  called  Glacial  Acetic  Acid;  its  odour 
is  very  characteristic  and  pungent ;  its  taste  caustic  ;  it  blisters  the  skin  ; 
it  mixes  with  water,  alcohol,  and  ether,  and  dissolves  camphor  and  essen- 
tial  oils,  which  solution  constitutes  the  aromatic  vinegar  of  the  shops. 
When  liquid,  its  sp.  gr.  is  1*063 ;  but  its  specific  gravity  does  not  indi- 
cate  its  strength,  as  it  increases  according  as  water  is  added  until  it  be- 
comes 1*078,  which  is  that  of  an  acid  containing  34*6  per  cent.,  or  three 
atoms  of  water ;  being  a  definite  compound,  C4H3034-H.O.  + 2  Aq.  On 
farther  dilution,  the  sp.  gr.  again  diminishes,  and  an  acid  containing  64 
per  cent,  of  water  has  a  sp.  gr.  of  1*063,  the  same  as  that  of  the  most 
concentrated  acid.  The  strength  of  any  acetic  acid  may,  however,  be 
very  simply  found  by  immersing  in  it  a  weighed  piece  of  white  marble, 
and  weighing  it  again  when  the  acid  has  been  completely  neutralized ; 
the  loss  of  weight  gives  pretty  accurately  the  quantity  of  acetic  acid,  as 
the  atomic  weight  of  Ca.O.  .  C.Og  (50*5)  is  nearly  the  same  as  that  of 
C4H3O3  (51*2) ;  of  course,  if  the  acetic  acid  be  not  pure,  this  method 
cannot  be  employed. 

The  formula  of  hypothetic  dry  acetic  acid  is  C4H3O3,  and  its  equiva- 
lent  =51*2.     The  acetate  of  water,  C4H303+Aq.,  consists  of 

4  equivalents  of  carbon,      =2420    .     .    4020 
4  "  hydrogen,  =  4  00    .    .      664 

4  "  oxygen,      =3200    .    .    5316 

60-20  10000 

The  hydrated  acetic  acid  boils  at  240°.  The  specific  gravity  of  its 
vapour  is  2278,  and  is  anomalous  as  showing  that  its  equivalent  volume 
is  3,  in  place  of  4  or  2,  as  occurs  with  almost  all  other  organic  bodies. 

The  products  of  the  decomposition  of  acetic  acid  by  chlorine  and  by 
bases  will  be  hereafter  noticed ;  with  powerfully  oxidizing  bodies  it  yields 
formic,  oxalic,  and  carbonic  acids. 

Acetic  acid  is  recognised  by  its  peculiar  odour  and  its  volatility ;  it 
reddens  litmus  powerfully ;  its  solutions  are  precipitated  by  the  nitrates 
of  silver  and  of  black  oxide  of  mercury,  giving  white  crystalline  salts, 
sparingly  soluble  in  cold  water.  But  even  strong  solutions  are  not  af- 
fected by  the  salts  of  lead  or  barytes.  It  combines  with  all  bases  form- 
ing salts,  of  which  none  are  quite  insoluble  in  water,  but  generally  very 
soluble  and  easily  crystallized.  The  most  important  of  these  acetates 
will  now  be  described. 

Acetate  of  Potash^  K.O.  .  C4H3O3,  is  formed  by  neutralizing  acetic 
acid  by  means  of  pure  carbonate  of  potash.  The  solution  is  generally 
evaporated  at  once  to  dryness,  and  the  salt  fused  at  a  dull  red  l;ieat,  in 
order  to  obtain  it  quite  white.  It  forms,  on  cooling,  a  foliated  mass, 
greasy  to  the  feel.  From  its  concentrated  solution  it  may  be  obtained, 
also,  in  delicate  crystals.  It  is  very  deliquescent,  and  dissolves  copiously 
in  alcohol. 

Acetate  of  Soda^  Na.O.  .  C4H4O3+6  Aq.,  may  be  obtained  in  the 
same  way  as  acetate  of  potash,  but  is  made  on  the  large  scale  in  purify- 
ing the  rough  wood-vinegar.  The  impure  acetate  of  lime,  obtained  by 
neutralizing  the  pyroligneous  liquors  with  chalk,  is  decomposed  by  6^ 
times  its  weight  of  crystallized  sulphate  of  soda.  These  are  in  the  pro- 
portion  of  two  equivalents  of  Glauber's  salt,  as  but  one  half  of  the  quan^ 
tity  added  is  decomposed  by  the  acetate  of  lime.     It  answers  still  better 


558 


ACETATE     OF     BARYTES,     LIME,     ETC. 


to  neutralize  the  acid  liquors  by  sulphuret  of  sodium,  prepared  by  roast- 
ing Glauber's  salt  with  small  coal,  as  for  making  soda-ash  (p.  488). 

When  purified  by  successive  crystallizations,  the  acetate 
of  soda  forms  oblique  rhombic  prisms,  as  z,  u,  in  the  figure, 
with  many  secondary  planes,  as  a,  e,  o.  These  contain  six 
atoms  of  water.  It  is  permanent  in  the  air ;  soluble  in 
three  parts  of  cold  and  in  one  of  boiling  water  ;  at  a  red 
heat  it  melts.  Its  principal  use  is  in  the  preparation  of 
acetic  acid. 

Acetate  of  Barytes,  Ba.O.  .  C4H3O3,  is  formed  by  neutralizing  acetic  acid  with 
carbonate  of  barytes  or  sulphuret  of  barium.  It  crystallizes  in  oblique  rhombic 
prisms  ;  by  heat  it  is  completely  decomposed  into  carbonate  of  barytes  and  acetone 
(Ba.O.  .  C.O2  and  CgHaOA 

Acetate  of  Lime  is  made  on  the  large  scale,  but  in  a  very  impure  form,  as  one 
stage  in  the  process  of  purifying  the  wood-vinegar.  When  pure,  it  crystallizes  in 
needles,  which  do  not  deliquesce.  It  is  decomposed  by  heat  in  the  same  way  as 
the  preceding  salt. 

Acetate  of  Alumina  is  of  considerable  technical  importance,  from  its 
use  as  a  mordant  in  dyeing.  It  is  formed  by  mixing  solutions  of  alum 
and  of  acetate  of  lead  when  to  be  employed  in  the  arts.  The  solution 
then  contains  much  acetate  of  potash.  To  obtain  it  f  ure,  the  simple 
sulphate  of  alumina  should  be  decomposed  by  acetate  of  barytes.  Evap- 
orated at  a  very  gentle  heat,  it  dries  into  a  transparent  gummy  mass ; 
but  if  boiled,  acetic  acid  passes  off,  and  a  hasic  acetate  of  Alumina  is  de- 
posited as  a  white  powder.  This  effect  is  produced  also  by  contact  with 
linen  or  cotton  cloth,  the  acetic  acid  becoming  free.  A  piece  of  calico 
is  thus  mordanted  uniformly  by  immersion  in  a  bath  of  acetate  of  alumina, 
and  then  dried  at  about  80°,  or  it  is  mordanted  partially,  so  as  subse- 
quently  to  form  a  coloured  pattern,  by  being  printed  with  the  solution  of 
this  salt,  thickened  with  gum  or  starch,  in  order  that  it  may  not  spread  ; 
on  being  then  dried  by  passing  over  warm  cylinders,  the  acetic  acid 
passes  off,  and  the  alumina  fixes  itself  upon  the  tissue. 
Acetate  of  Zinc,  Zn.O.  .  C4H3O3-I-3  Aq.  Metallic  zinc  dissolves  in  acetic  acid, 
evolving  hydrogen ;  but  this  salt  is  generally  prepared  by  mixing 
solutions  of  acetate  of  lead  and  sulphate  of  zinc,  and  separating 
the  sulphate  of  lead  which  is  formed  by  filtration.  On  evapora- 
ting the  solution,  the  acetate  of  zinc  crystallizes  in  brilliant,  soft, 
hexagonal  rhombic  tables,  as  in  the  figure,  of  which  i,  u  are  pri- 
mary, and  m  a  secondary  face.  They  are  unalterable  in  the  air, 
but  very  soluble  in  water.  When  boiled  with  alcohol,  a  basic 
acetate  of  Zinc  precipitates,  3Zn.O.-l-C4H303.  A  solution  of  this 
salt  is  completely  decomposed  by  sulphuret  of  hydrogen. 

Protoacetate  oflron.—Fe.O.  .  C4H3O3.  This  salt,  which  may  be  prepared  by  dis- 
solving protosulphuret  of  iron  in  acetic  acid,  forms  a  colourless  solution,  which 
yields,  when  evaporated  in  vacuo,  pale  green  prisms,  which  attract  oxygen  with 
great  avidity.  It  cannot  be  formed  by  decomposing  protosulphate  of  iron  by  ace- 
tate of  lead,  as  only  a  portion  of  the  lead  salt  precipitates  until  the  iron  becomes 
peroxidized. 

Sesquiacetate  of  Iron,¥e203  +  S(CJisOs),  is  prepared  by  dissolving  red 
oxide  of  iron  in  acetic  acid,  or  by  decomposing  red  sulphate  of  iron  with 
acetate  of  barytes.  It  forms  a  brownish  red  solution,  which,  when  boil- 
ed, gives  off  acetic  acid,  and  oxide  of  iron  separates.  By  very  cautious 
evaporation,  a  dark  red  gummy  mass  may  be  obtained,  which  redissolves 
in  cold  water.  It  thus  resembles  closely  acetate  of  alumina,  and,  like  it, 
serves  in  dyeing  as  a  mordant,  to  fix  upon  the  cloth  oxide  of  iron,  with 
which  the  colouring  matters  may  combine ;  being  roughly  prepared  by 


ACETATES    OF     LEAD.  559 

digesting  old  iron  in  the  impure  acetic  acid  from  wood,  it  is  commonly 
termed  Pyrolignite  of  Iron. 

A  tincture  of  Acetate  of  Iron  is  employed  in  medicine,  which,  as 
directed  by  the  Dublin  Pharmacopoeia,  is  formed  by  triturating  together 
protosulphate  of  iron  and  acetate  of  potash,  and  digesting  in  alcohol ;  in 
order  that  the  solution  shall  have  the  rich  wine-red  colour  which  is  re- 
quired,  the  mixture  of  the  salts  should  be  left  for  a  little  time  pasty,  so  as 
to  absorb  oxygen,  and  there  should  be  present  an  excess  of  acetate  of 
potash.  The  iron  is  present  in  these  tinctures  as  black  oxide.  If  too 
much  sesquioxide  be  formed,  the  solution  decomposes  very  easily,  red 
oxide  of  iron  separating,  and  acetic  ether  and  aldehyd  being  produced.. 
If  the  protoxide  be  present  in  excess,  the  colour  is  a  brownish  yellow, 
and  the  preparation  is  liable  to  spoil  when  oxygen  has  subsequently  ac- 
cess to  it.  Although  the  acetate  of  potash  does  not  form  a  true  double 
salt  in  this  case,  yet  it  gives  much  greater  stability  to  the  acetates 
of  iron. 

Acetates  of  Lead. — Acetic  acid  forms,  with  oxide  of  lead,  four  well- 
characterized  salts. 

Neutral  Acetate  of  Lead.  Sugar  of  Lead,  Pb.O.  .  C4H3O34-3  Aq., 
is  prepared  by  dissolving  litharge,  or  white  lead,  in  acetic  acid,  of  which 
a  slight  excess  should  be  used.  The  liquors  yield  by  evaporation  right 
rhombic  prisms  with  dihedral  summits,  as  in  the 
i\  figure,  which  are  very  bright  and  colourless ; 
-|-J\  their  taste  is  sweet  and  astringent ;  the  solution 
j  in  water  reddens  litmus,  but  turns  sirup  of  vio* 

I       J  lets  green.      In   very  dry  air  they  effloresce ; 
'^^y^'^  when  heated  to  136°  they  undergo  aqueous  fu- 
sion, but,  having  lost   their  water  of  crystalli- 
^"^V^  zation,  become  solid  again.     The  dry  salt  thus 

obtained  fuses  again  at  a  higher  temperature,  and  without  blackening, 
is  decomposed  into  carbonic  acid,  acetone,  and  sesquibasic  acetate  of 
lead,  which  remains,  3(Pb.O.  .  C4H3O3)  giving  C.O2  with  C3H.O.  and 
3Pb.0.4-2C4H303. 

This  neutral  salt  dissolves  easily  in  alcohol ;  it  is  very  pois  .ous ;  the 
antidote  to  it  is  Glauber's  or  Epsom  salt,  which  forms  insolu  .e  sulphate 
of  lead. 

Sesquihasic  Acetate  of  Lead. — 3Pb.O.+2C4H303.  This  salt,  which 
is  formed  as  just  described,  dissolves  in  water,  and  the  sirupy  solution 
crystallizes  in  pearly  hexagonal  plates  ;  its  solution  reacts  alkaline. 

Trihasic  Acetate  of  Lead. — 3Pb.O. +04^303.  When  ammonia  is 
added  to  a  solution  of  neutral  acetate  of  lead,  so  as  to  render  it  strongly 
alkaline,  it  does  not  combine  with  it  as  with  most  other  metallic  salts, 
but  acetate  of  ammonia  and  trihasic  acetate  of  lead  are  formed ;  it  may 
also  be  prepared  by  boiling  together  six  parts  of  crystallized  acetate  of 
lead,  seven  of  litharge,  and  thirty  of  water.  This  solution,  known  in 
pharmacy  as  Extractum  Satumi,  gives,  by  evaporation,  a  mass  of  fine 
crystalline  needles;  it  reacts  powerfully  alkaline;  it  is  insoluble  in 
alcohol. 

Sexbasic  Acetate  of  Lead,  6Pb.O.-|-C4H303,  is  precipitated  when  a 
solution  of  neutral  acetate  is  added  to  a  great  excess  of  water  of  ammo- 
nia ;  it  is  formed,  also,  when  acetic  acid  acts  on  metallic  lead  with  access 
of  air,  and  is  hence  generally  present  in  the  Ceruse  of  commerce.     (See 


560    ACETATES  OF  COPPER,  MERCURY,  ETC. 

p.  491.)  It  forms  minute  feathery  crystals  when  deposited  from  boiling 
water,  in  which  it  is  shghtly  soluble. 

All  these  basic  acetates  of  lead  are  decomposed  by  carbonic  acid, 
giving  neutral  acetate  and  carbonate  of  lead. 

Acetates  of  Copper. — The  acetate  of  the  suboxide  of  copper  is  not 
important ;  there  are  four  acetates  of  the  black  oxide. 

Neutral  Acetate  of  Copper,  Distilled  Verdigris,  Cu.O. .  C4H303+Aq., 
is  prepared  by  dissolving  verdigris  in  acetic  acid.  It  forms 
/<^</^^X^  oblique  rhombic  prisms,  as  in  the  figure,  where  i,  u,  u  are 
^"^y^^  "^  primary,  and  e,  e  secondary  faces  of  a  fine  deep  green  col- 
our. It  crystallizes  in  another  form  with  five  atoms  of 
water :  these  crystals  are  blue,  like  sulphate  of  copper, 
^^^^^  and  when  heated  to  86°,  give  off  4  Aq.,  and  change  into 
^^^<^^^^^^5^   the  common  green  crystals ;  it  effloresces  gradually  in 

^ —  the  air  ;  when  heated  in  close  vessels,  it  gives  a  mixture 

of  acetic  acid  and  acetone  ;  in  the  air  it  takes  fire,  burning  with  a  bright 
green  flame. 

If  a  solution  of  this  salt  be  mixed  with  sugar  or  honey,  and  heated,  it 
deposites  a  green  powder  of  carbonate  of  copper,  which  changes  into 
minute  crystals  of  the  orange-red  suboxide :  the  liquor  contains  then 
abundance  of  formic  acid. 

Bibasic  Acetate  of  Copper.  Verdigris.  —  2CU.O.+C4H3O3+6  Aq. 
This  salt  is  manufactured  in  wine  countries  by  stratifying  plates  of 
copper  alternately  with  the  residual  stalks  and  pulp  of  the  grapes  that 
have  passed  into  acetous  fermentation  ;  oxygen  is  absorbed,  and  the  mass 
being  occasionally  turned  over  and  moistened,  to  give  access  to  air,  the 
plates  of  copper  become  covered  with  a  crystalline  crust  of  basic  acetate  ; 
this  is  scraped  off,  made  into  a  paste  with  vinegar,  and  put  into  moulds, 
where  it  is  allowed  to  dry;  the  mass  so  formed  contains  all  the  basic 
salts  mixed  together.  In  this  country  it  is  prepared  by  stratifying  cop- 
per plates  with  cloths  steeped  in  pyroligneous  acid.  When  pure,  the 
bibasic  acetate  is  of  a  fine  blue  colour ;  it  is  decomposed  by  water  into 
the  insoluble  tribasic  acetate,  and  the  soluble  sesquihasic  acetate  of  cop- 
per, which  forms  a  pale  blue  solution,  whence  it  may  be  precipitated  in 
crystalline  scales  by  alcohol. 

Tribasic  Acetate  of  Copper,  3CU.O.+C4H3O3+2  Aq.,  remains  as  an 
insoluble  residue  when  verdigris  is  treated  with  water,  or  by  digesting  a 
solution  of  neutral  acetate  with  oxide  of  copper.  It  is  a  clear  green 
powder,  which  detonates  feebly  when  heated.  For  Emerald  Green,  see 
p.  456. 

Acetate  of  Black  Oxide  of  Mercury,  Hg.02+C4H303,  may  be  formed 
by  mixing  boiling  solutions  of  acetate  of  potash  and  subnitrate  of  mer- 
cury, and  filtering  rapidly.  On  cooling,  it  is  deposited  in  brilliant  white 
crystalline  scales,  which  are  very  sparingly  soluble  in  cold  water,  and 
insoluble  in  alcohol.  The  Acetate  of  the  Red  Oxide  is  very  soluble  in  wa- 
ter, and  does  not  crystallize. 

Acetate  of  Silver,  Ag.O.  .  C4H3O3,  is  formed  by  mixing  boiling  solu- 
tions  of  nitrate  of  silver  and  acetate  of  potash,  and  filtering  the  liquor 
while  very  hot.  On  cooling,  it  crystallizes  in  pearly  white  needles, 
which  are  but  very  sparingly  soluble  in  cold  water.  These  last  salts 
serve  as  tests  for  the  acetic  acid  in  liquids. 

Acetate  of  Ammonia^  N.H4O.  .  C4B3O8,  is  prepared  by  passing  ammo- 


ACETATE  OF  ETHER. ACETONE.         561 

niacal  gas  over  the  crystalline  hydrate  of  acetic  acid,  or  by  heating 
moderately  a  mixture  of  equal  parts  of  acetate  of  potash  and  of  sal 
amnnoniac.  The  acetate  of  ammonia  sublimes  mixed  with  a  little  free 
acetic  acid  ;  it  crystallizes  in  needles,  which  are  very  soluble  in  alcohol 
and  in  water ;  by  exposure  to  the  air  it  loses  ammonia,  and  appears  to 
form  an  acid  salt ;  its  solution  in  water,  prepared  by  neutrahzing  distilled 
vinegar  with  carbonate  of  ammonia,  is  used  in  medicine  by  the  name  of 
Sjiirit  of  Mindererus ;  in  its  original  form,  when  the  carbonate  of  ammo- 
nia, obtained  by  the  distillation  of  bones  (salt  of  hartshorn),  and  which 
contained  empyreumatic  animal  oil,  was  used,  it  was  a  much  more  pow- 
erful medicinal  agent  than  when  prepared,  as  now,  with  pure  carbonate 
of  ammonia. 

Acetate  of  Ether.  Acetic  Ether,  C4H5O.+C4H3O3,  is  prepared  by 
distilling  16  parts  of  dry  sugar  of  lead,  4i  of  alcohol,  and  6  of  oil  of 
vitriol ;  the  product  should  be  rectified  over  some  lime  to  remove  free 
acetic  acid.  This  ether  is  colourless,  and  very  inflammable  ;  it  boils  at 
165°  ;  it  is  lighter  than  water ;  it  is  remarkable  for  being  isomeric  with 
aldehyd,  their  per  cent,  composition  being  the  same,  but  the  sp.  gr.  of 
the  vapour  of  acetic  ether  (3063)  is  double  that  of  aldehyd  (1531). 

Products  of  the  Detomposition  of  Acetic  Acid  by  Heat. 
A.  Of  Pyroacetic  Spirit.     Acetone. 

When  acetate  of  lime  or  barytes  is  heated  to  redness,  the  acetic  acid 
is  completely  decomposed,  an  earthy  carbonate  remaining,  and  a  volatile 
inflammable  liquid,  of  an  agreeable  aromatic  odour,  distilling  over,  C4 
H3O3  separating  itself  into  C.O^  and  C3H3O.  The  metallic  acetates  are 
similarly  decomposed,  but  the  products  are  not  so  pure.  This  liquid, 
for  which  I  shall  retain  the  name  Acetone,  is  formed  also  abundantly 
when  the  vapour  of  acetic  acid  is  passed  through  a  tube  containing 
charcoal,  at  a  temperature  just  below  redness. 

x^cetone  is  colourless,  and  lighter  than  water  ;  it  burns  with  a  lumin- 
ous flame ;  it  boils  at  132° ;  the  specific  gravity  of  its  vapour  is  2022. 
When  heated  with  hydrate  of  potash,  it  is  totally  converted  into  carbonic 
acid  and  marsh  gas,  C3H3O.  and  H.O.  producing  C2H4  and  COj.  When 
treated  by  oxidizing  agents,  as  permanganate  of  potash,  or  bichromate  of 
potash  and  sulphuric  acid,  it  is  totally  converted  into  acetic  acid. 

With  sulphuric  acid,  acetone  yields  a  series  of  products  closely  analogous  to  those 
derived  from  alcohol,  but  still  presenting  such  characteristic  differences  as  induce 
me  to  look  upon  them  as  not  simply  extracted  from  acetone,  but  derived  from  its 
total  decomposition.  Thus  it  gives  a  hydrocarbon,  Mesilijlene,  whose  formula  is 
C6H4,  and  also  an  ether,  Mcsitic  Ether,  CeHaO.  With  sulphuric  acid,  this  forms  the 
Sulphomcsitic  and  Persulphomesitic  Acids,  which  are  remarkable,  as  the  sulphuric 
acid  retains  all  its  power  of  saturating  bases.  With  phosphoric  acid,  it  produces 
Phospho mcsitic  Acid,  and  with  hypophosphorous  acid  a  very  remarkable  compound, 
whose  barytes  salt  has  the  formula  CeHsO.-j-SBa.O. .  P.O.  The  series  of  wine-alco- 
hol contains  no  similar  body.  The  mesitic  ether  combines  also  with  protochloride 
of  platinum. 

When  acetone  is  treated  with  chloride  of  phosphorus,  it  gives  phosphoric  acid 
and  ChloTomesitic  Ether,  CeHsCl. ;  with  iodide  of  phosphorus  it  produces  lodomesitic 
Ether,  CcHsI. ;  and,  when  acted  on  by  chlorine,  it  forms,  first,  the  Mesitic  Chloral,  of 
which  the  formula  is  C3H2 .  Cl.O.,  and  subsequently  another  body,  also  a  heavy, 
oily  liquid,  C3H.  .  CI2O. 

When  red  fumes  of  hyponitrous  acid  are  passed  into  acetone,  and  the  vessel  is 
kept  cool,  they  are  copiously  absorbed,  and,  on  adding  water,  a  dense  fluid  separ- 
ates, which  is  Nitrous  Mesitic  Ether,  CeHsO.-j-N.Os. 

By  acting  on  mesitylene,  C6H4,  with  nitric  acid,  a  heavy  liquid  is  produced, 

4  B 


562  BODIES     OF     THE     KACODYL     SERIES. 

which  is  termed  Mesitic  Aldehyd ;  its  formula  is  CeHaO.-f-Aq.  Its  solution  in  alka« 
line  liquors  becomes  brown  after  some  time,  and  precipitates  most  salts  of  the 
heavy  metals.  By  chlorine,  the  mesitylene  is  converted  into  a  crystalline  body, 
soluble  in  ether,  and  separating  from  it  in  brilliant  colourless  prisms.  Its  formula 
is  CeHaCl.     I  have  termed  it  Chloride  of  Pleleyl. 

In  my  original  examination  of  this  series  of  bodies,  I  looked  upon  acetone  as  an 
alcohol  {Mesitic  Alcohol),  C6H602=(C6H50.-|-Aq.),  from  which  they  were  all  derived ; 
but  I  do  not  now  consider  that  either  mesitylene  or  mesitic  ether  pre-exists  in  ace- 
tone.   The  intimate  nature  of  that  body  remains  yet  to  be  examined. 

B.  Of  the  Bodies  of  the  Kacodyl  Series. 

When  equal  weights  of  acetate  of  potash  and  arsenious  acid  are  mix- 
ed and  distilled  at  a  dull  red  heat,  a  dense  colourless  liquid  is  obtained, 
which  had  been  long  known  to  chemists  as  the  Fuming  Liquor  of  Cadet. 
The  admirable  researches  of  Bunsen  have  shown  that  it  is  an  oxide  of 
a  compound  radical,  which  he  has  succeeded  in  isolating,  and  which,  in 
the  variety  of  its  combinations,  and  the  influence  their  discovery  will 
doubtless  exercise  on  science,  ranks  with  cyanogen.  Nevertheless,  as 
they  are  not  of  practical  importance,  a  short  notice  of  them  will  suffice. 

The  Fuming  Liquor  of  Cadet,  or  Alkarsine,  when  purified  from  acetone 
and  other  accidental  products  of  the  distillation,  is  colourless  ;  much 
heavier  than  water.  It  freezes  at  — 9°,  and'boils  at  300°.  The  specific 
gravity  of  its  vapour  is  7180  ;  its  odour  is  excessively  disagreeable,  pro- 
voking weeping  and  nausea  ;  it  is  actively  poisonous  ;  in  contact  with 
the  air  it  fumes  very  much,  and  absorbs  oxygen  so  rapidly,  that  if  a  large 
surface  be  exposed,  it  takes  fire  spontaneously,  and  burns  with  a  large 
white  flame,  throwing  ofT  much  arsenious  acid.  Its  composition  is  ex- 
pressed by  the  formula  C4H6 .  As.O.,  and  in  all  the  combinations  which 
it  gives,  the  oxygen  alone  is  replaced.  Thus,  when  distilled  with  strong 
muriatic  acid,  a  dense  liquid  of  an  insupportable  odour  is  produced,  which 
gradually  changes  into  a  crystalline  mass,  consisting  of  C4H6  .  As. CI. 
By  digesting  this  liquid  with  zinc  and  water,  in  a  vessel  kept  full  of  pure 
carbonic  acid,  chloride  of  zinc  is  formed,  and  the  radical  C4H6AS.  is  set 
ire^  ;  this  is  an  oily-looking,  heavy  liquid,  insoluble  in  water,  and  taking 
fire  immediately  on  contact  with  air.  This  is  the  Kacodyl,  and  as  its 
symbol  1  shall  adopt  that  used  by  Bunsen,  Kd.=C4H6As.  The  alkar- 
sine is  therefore  oxide  of  kacodyl,  Kd.O.,  and  the  body  formed  by  mu- 
riatic acid  is  the  chloride,  Kd.Cl.  The  iodide,  bromide,  sulphuret,  and 
cyanide  of  kacodyl,  may  be  formed  by  the  simple  process  of  distilling  al. 
karsine  with  the  corresponding  hydracids,  or  the  chloride  of  kacodyl  with 
the  iodides,  &;c.,  of  potassium. 

When  alkarsine  is  distilled  with  dilute  muriatic  acid,  or  when  chloride 
of  kacodyl  is  treated  with  water,  this  is  decomposed,  and  an  oxychloride 
obtained,  the  formula  of  which  is  Kd.O.  +  SKd.Cl.  In  a  similar  man- 
ner,  a  corresponding  oxybromide,  Kd.O.  +  SKd.Br.,  may  be  produced, 
and  an  oxyiodide. 

If  alcoholic  solutions  of  oxide  of  kacodyl  and  of  corrosive  sublimate  be 
mixed,  a  brilliant  white  precipitate  is  obtained,  which  is  soluble  in  wa- 
ter,  and  crystallizes  therefrom  in  large  but  delicate  rhombic  tables,  of  a 
satiny  lustre.  It  is  a  direct  combination,  its  formula  being  Kd.O.-f 
2Hg.Cl.  A  precisely  similar  compound  is  formed  with  the  bronnide  of 
mercury. 

When  alkarsine  is  exposed  to  the  air,  so  that  it  may  absorb  oxygen, 
but  not  burst  into  flame,  it  is  changed  totally  into  a  white  crystalline 
mass  ;  at  the  same  time,  arsenious  acid  and  some  volatile  products  are 


SOURCES,    ETC.,    OF    MARSH    GAS.  563 

termed.  The  crystals  being  dissolved  in  a  small  quantity  of  water,  this 
liquor  is  evaporated  to  dryness,  and  the  residue  dried  by  blotting-paper, 
and  recrystallized  from  alcohol.  The  substance  thus  obtained  is  termed 
•dlkargene ;  it  forms  large  oblique  prisms,  which  are  inodorous  and  taste- 
less ;  it  deliquesces  in  moist  air  ;  it  combines  with  alkalies  and  metallic 
oxides,  forming  very  instable  compounds  ;  it  melts  at  390°,  and  is  de- 
composed by  a  stronger  heat.  By  deoxidizing  agents,  as  protochloride 
of  tin  or  phosphorous  acid,  it  is  reduced  to  the  state  of  alkarsine  ;  it  is 
not  poisonous.  Its  composition  is  expressed  by  the  formula  C4H7 .  As. 
O4,  or  Kd.Os+Aq.  ;  its  proper  name  is  therefore  Kacodylic  Acid. 

C.  Of  light  Carburetted  Hydrogen,     Marsh  Gas, 

This  gas  is  formed  by  the  decomposition  of  almost  every  organic  sub- 
stance at  a  high  temperature.  Thus  it  exists  always  mixed  with  defi- 
ant gas,  in  the  coal  or  oil  gas  used  for  illumination.  It  may  be  formed 
by  passing  olefiant  gas  through  a  red-hot  tube,  when  half  of  its  carbon  is 
deposited  and  its  volume  doubled.  It  is  produced,  also,  by  passing  the 
vapours  of  alcohol,  of  ether,  or  of  acetic  acid  through  bright  red-hot 
tubes  in  a  similar  manner. 

A  very  interesting  source  of  this  gas  is  the  decomposition  of  vegetable 
matter  in  contact  with  water,  but  excluded  from  the  air.  By  assimila- 
ting  the  elements  of  four  atoms  of  water,  the  lignine  breaks  up  into  car- 
bonic acid  and  this  gas,  CigHgOg  with  4H.0.  giving  6C.O2  and  GCHg. 
As  the  origin  of  the  great  deposites  of  coal  is  to  be  found  in  the  slow  de- 
composition of  submerged  forests  of  high  antiquity,  this  gas  was  then 
generated  in  large  quantity,  and,  being  subjected  to  enormous  pressure 
under  the  mineral  strata,  which  gradually  settled  on  the  vegetable  mass- 
es,  it  remained  infiltrated  through  the  coal,  probably  in  a  liquid  condi- 
tion. During  the  operations  of  mining,  when  this  great  pressure  is  re- 
moved, it  reassumes  its  gaseous  condition,  and,  mixing  with  the  air  of 
the  mine,  creates  the  danger  of  explosion,  against  which  the  genius  of 
Humphrey  Davy  provided  by  the  construction  of  his  safety-lamp  (see  p. 
183).  Under  the  name  of  Fire-damp,  this  gas  is  known  and  dreaded 
by  the  miners,  while  the  carbonic  acid,  which  results  simultaneously  from 
the  decomposition  of  the  wood,  and  is  known,  also,  from  its  fatal  eflfects 
when  breathed,  is  termed  Choke-damp, 

This  decomposition  of  wood  goes  on  in  every  muddy  ditch.  If  the 
mud  be  stirred,  numerous  gas  bubbles  will  be  seen  to  ascend,  and  when 
collected  will  be  found  to  consist  of  fire-damp  mixed  with  carbonic  acid  ; 
hence  this  gas  has  got  the  name  of  Pond  or  Marsh  Gas,  It  is  obtained, 
however,  most  pure  by  the  decomposition  of  acetic  acid  by  hydrate  of 
potash.  About  equal  parts  of  acetate  of  potash  and  caustic,  potash  are 
to  be  well  mixed,  and  heated  in  a  hard  glass  retort  nearly  to  redness. 
The  acetic  acid  and  water  are  simultaneously  decomposed,  C4H3O3  and 
H.O.  producing  2C.H2  and  2C.O2.  This  last  remains  combined  with 
the  potash,  while  the  gas  which  passes  off  may  be  collected  over  water. 

It  is  colourless  and  transparent.  It  burns  with  a  yellow  flame,  pos- 
sessing but  little  illuminating  power  ;  its  sp.  gr.  is  559  ;  its  formula  be- 
ing  C.H2,  and  consisting  of 

One  volume  of  carbon  vapour =8430 

Four  volumes  of  hydrogen =275-2 

Forming  two  volumes  of  marsh  gas      ....      11182 
Of  which  one  weighs,  therefore        559  1 


564  C  H  L  O  R  A  L. C  HLOROACETIC     ACID. 

Or  it  may  be  considered  as  containing  one  volume  of  olefiant  gas  and  two  of  hydro- 
gen, condensed  to  two,  (980-4-f-137-6)-r-2=559. 

The  real  atomic  weight  of  the  marsh  gas  is  difficult  to  determine,  as 
it  does  not  form  any  well-defined  combinations.  There  is  reason  to 
suppose  it  to  be  Cjtl^.  When  acted  on  by  chlorine,  it  gives  muriatic 
acid  gas  and  bichloride  of  carbon  (p.  498),  which  has  been  already  no- 
ticed. 

Of  the  Action  of  Chlorine  on  Alcohol.,  Aldehyde  Acetic  Acid,  and  the  va- 
rious Kinds  of  Ethers. 

When  cljlorine  gas  is  passed  into  alcohol  not  absolutely  anhydrous,  a  heavy 
oily  liquid  is  obtained,  known  as  heavy  Muriatic  Ether  or  Chlorine  Ether.  It  is  a 
mixture  of  several  substances  in  indeterminate  proportions. 

When  the  alcohol  is  anhydrous  and  the  gas  quite  dry,  the  action  is  definite,  and 
gives  rise  to  a  remarkable  result.  Five  sixths  of  the  hydrogen  of  the  alcohol  are 
removed,  and  are  replaced  by  three  of  chlorine,  and,  after  the  evolution  of  a  large 
quantity  of  muriatic  acid  gas,  a  dense  oily  liquid  is  obtained,  to  which  the  name 
of  Chloral  has  been  given  ;  its  formula  is  C4H.  .  CI3O2.  The  first  operation  of  the 
chlorine  is  to  remove  two  equivalents  of  hydrogen,  and  thus  to  reduce  the  alcohoJ 
to  the  state  of  aldehyd,  just  as  any  other  oxidizing  agent  should  have  done ;  but 
then  it  acts  on  the  hydrogen  of  the  radical,  acetyl,  and,  expelling  it,  takes  its  place, 
generating  a  new  compound  radical,  Acechloryl,  C4CI3.  This  is  combined  with  oxy- 
gen and  water  in  chloral,  as  acetyl  is  in  ordinary  aldehyd  ;  the  rational  formula  of 
chloral  is  therefore  C4Cl30.-|-Aq. 

Chloral  combines  with  water,  forming  a  crystalline  hydrate.  It  gradually  chan- 
ges into  an  isomeric  porcellaneous-looking  substance.  The  equivalent  change  of 
common  aldehyd  has  been  described  (p.  554).  When  chloral  is  acted  on  by  a 
solution  of  potash,  it  yields  formic  acid  and  chloroform,  C4H.  .  CI3O2  and  H.O.  giv- 
ing C2H.O3  and  C2H.CI3. 

By  the  action  of  chlorine  on  aldehyd,  chloral  is  directly  formed. 

When  the  crystallized  acetic  acid  is  exposed  to  the  action  of  chlorine  in  bright 
sunshine,  a  substance  is  formed  which  crystallizes  in  brilliant  rhombs,  and  pos- 
sesses strong  acid  properties ;  its  formula  is  C4H.  .  CI3O4.  It  is  formed  by  the 
replacement  of  the  hydrogen  of  the  radical  acetyl  by  chlorine,  forming  thus  the 
Chloroacctic  Acid,  C4Cl3034-Aq.  Its  salts  crystallize  with  facility,  and  have  great 
similarity  to  the  acetates.  When  the  chloroacetate  of  potash  is  heated  with  an  ex- 
cess of  potash,  it  is  decomposed  into  carbonic  acid  and  chloroform ;  C4Cl30^  and 
H.O.  giving  2C.O2  and  C2H.CI3.  This  reaction  is  exactly  similar  to  that  of  the 
common  acetate  of  potash,  the  chloroform  replacing  the  pond  gas. 

When  chlorine  acts  upon  sulphuric  ether,  a  remarkable  series  of  bodies  is  pro- 
duced ;  the  first  formed  is  a  dense  oily  liquor,  having  the  formula  C4H3  .  CI2O., 
which,  by  contact  with  water  or  an  alkali,  is  decomposed  into  hydrochloric  and 
acetic  acids,  3(C4H3  .  CI2O.)  and  6H.0.  producing  6H.C1.  and  3(C4H303).  This 
body  is  properly,  therefore,  Oxychloride  of  Acetyl ;  it  is  decomposed  by  sulphuret  of 
hydrogen,  muriatic  acid  being  given  off,  and  an  Oxysulphuret  of  Acetyl  being  formed, 
which  resembles  it  in  properties. 

In  presence  of  a  great  excess  of  chlorine,  this  oxychloride  is  totally  decomposed, 
the  chlorine  entering  into  the  place  of  the  hydrogen  in  the  acetyl,  and  forming  tht 
name  radical  as  exists  in  chloral  and  chloroacetic  acid.  The  substance  thus  pro 
duced  is  solid  and  crystalline ;  it  bears  a  very  simple  relation  to  sulphuric  ether, 
as  its  formula  is  C4CI5O.,  being  apparently  ether,  in  which  all  hydrogen  is  replaced 
by  chlorine.     It  may  be  termed  Chloryl  Ether.  » 

The  action  of  chlorine  on  the  acetic  and  oxalic  ethers  h£is  thrown  much  light  on 
the  theory  of  these  bodies. 

Acetic  ether  combines  with  two  atoms  of  chlorine  and  loses  two  atoms  of  oxy 
gen,  thus  giving  from  C4H303+C4H50.,the  Chloroacctic  Ether,  C4H3O34-C4H3.  CI2O., 
an  oxychloride  of  acetyl,  containing  twice  as  much  acetic  acid  as  that  just  now 
described,  and  its  rational  formula  being,  therefore,  Ac.Cl3-}-2Ac.03;  with  potash 
it  gives  chloride  of  potassium  and  acetate  of  potash. 

By  a  stream  of  dry  chlorine  gas  oxalic  ether  is  totally  converted  into  a  mass  of 
crystalline  plates,  which  are  tasteless  and  perfectly  neutral ;  this  body  contains  no 
hydrogen,  its  formula  being  C6Cl504=C4Cl50.-|-C203.    It  is,  therefore,  a  combina- 


ACTION     OF     CHLORINE     ON     MURIATIC     ETHER.    565 

tion  ol  oxalic  acid  with  chloryl  ether,  and  is  termed  Chloroxalic  Ether.  With  water 
of  ammonia  it  gives  oxamide  ;  by  the  action  of  dry  ammonia  it  forms  a  substance 
also  crystaUine,  which  is  soluble  in  alcohol  and  ether,  sparingly  soluble  in  water, 
and  the  formula  of  which  is  CSH2CI3 .  N.Oe ;  at  the  same  time,  chloryl  ether  and 
water  are  evolved  ;  the  rational  formula  of  this  body,  Chloroxamethan,  is  at  once 
seen  by  comparing  it  with  the  oxamethan,  formed  by  ammonia  on  oxalic  ether 
(p.  550).     Thus, 

2  atoms  of  oxalic  ether,  C12H10O8,  give  an  atom  of  oxamethan,  CsH? .  N.Oe. 
1  atom  of  ammonia,  N.H3,  gives  an  atom  of  alcohol,  C4H50.-i-Aq. 

In  like  manner, 

2  atoms  of  chloroxalic  ether,  C,2Clio08,  give  1  of  chloroxamethan,  C8CI5H2 .  N.O5. 
1  atom  of  ammonia,  N.H3,  gives  1  of  chlorine  alcohol,  C4Cl50.-|-Aq. 

The  rational  formula  of  the  chloroxamethan  is  therefore  C4CI5O. .  C203+C202Ad. 

When  chloroxamethan  is  dissolved  in  water  of  ammonia,  and  the  solution  evap- 
orated, crystals  are  obtained,  which  are  Chloroxalovinate  of  Ammonia,  their  formula 
being  CgHiCb  .  N.Og,  or,  in  its  rational  form,  C4CI5O.  .  C2O3+C2O3.  N.H4O.  , 
identical  in  constitution  with  the  ordinary  oxalovinate  of  ammonia,  except  that  it 
contains  chloryl  ether  in  place  of  common  ether;  the  C  hloroxalovinic  Aciditself  hsis 
been  isolated  ;  it  crystallizes  in  long  needles,  which  react  acid,  and  combines  with 
all  bases  to  form  well-defined  salts  ;  its  formula  is  C4CI5O.  .  C203-|-C203Aq. 

A  crystallographic  examination  has  rendered  the  isomorphism  of  the  ordinary 
oxamethan  with  the  chloroxamethan  exceedingly  probable. 

The  results  of  the  action  of  chlorine  on  the  light  muriatic  ether  have  led  to  re- 
markable results.  Regnault  considered  this  body  as  affording  a  test  experiment 
for  the  actual  presence  of  defiant  gas  in  ether;  for  if  defiant  gas  be  Ac.H.,  and 
muriatic  ether  be  Ac.H.  .  H.Cl.,  the  result  of  the  action  of  chlorine  should  be  the 
same  on  both  bodies,  as  the  muriatic  acid  in  the  latter  could  not  influence  such  a 
reaction  Now,  by  acting  on  muriatic  ether  with  chlorine,  a  series  of  bodies  is 
obtained,  isomeric  with  those  arising  from  defiant  gas,  but  quite  different  in  prop- 
erties. Thus  there  is  first  formed  a  liquid,  C4H4CI2 ;  this  has  the  composition  of 
Dutch  oil ;  next,  a  liquid  forms  whose  formula  is  C4H3CI3 ;  afterward,  bodies  con- 
sisting of  C4H2CI4  and  C4H  CI5,  and  ultimately  C4CI6,  Sesquichloride  of  Carbon.  Now 
the  bodies  C4H4CI2  and  C4H3CI3,  as  derived  from  defiant  gas,  are  separated  by  pot- 
ash into  C4H3CI.  with  H.Cl,  and  into  C4H2CI2  with  H.Cl. ;  but  the  bodies  C4H4Cla 
and  C4H3CI3,  from  muriatic  ether,  are  not  decomposed  by  that  alkali.  I  do  not> 
however,  believe  in  the  indefinite  replacement  of  hydrogen  by  chlorine,  which 
Regnault  assumes,  and  look  upon  the  relation  of  these  series  of  bodies  as  being  the 
following : 

From  defiant  Gas.  From  Muriatic  Ether. 

C4H4Cl2=C4H3Cl.-fH.Cl.  C4H4Cl2=C4H3CI.+C4H5Cl. 

C4H3Cl3:=2(C2H.Cl.)  and  H.Cl.  C4H3CI3. 

C4H2Cl4=2(C2H.Cl2).  C4H2Cl4=C4Cl5Cl.-i-2(C4H3Cl3). 

C4H.Cl5=C4H3Cl3-|-2(Cl4Cl5Cl.). 

Both  these  give,  finally,  sesquichloride  of  carbon,  C4CI6CI.  The  bodies  from 
olefiant  gas,  which  contain  chloride  of  hydrogen,  are  decomposed  by  an  alcoholic 
solution  of  potash,  but  thof5«^  in  which  the  chlorine  is  combined  with  an  organic 
radical  are  not  affected  by  that  reagent. 

By  the  action  of  chlorine  on  mercaptan,  a  similar  series  of  products  is  obtained, 
of  which  the  terminal  body  is  C4H.  .  CUS.,  consisting  of  C4H3S34-2(C4Cl5Cl.). 

On  the  Theoretical  Constitution  of  Alcohol,  and  the  Bodies  derived  from  it. 

The  theory  of  alcohol  and  the  ethereal  combinations  is  of  the  more 
impoitance,  as  the  principles  of  it  regulate  our  ideas,  not  merely  concern- 
ing  the  bodies  that  have  been  now  described,  but  a  vast  number  of  others  ; 
for  the  ordinary,  or  wine-alcohol,  is  but  one  example  of  a  numerous  family 
of  bodies,  which  resemble  it  in  all  its  general  laws  of  reaction,  with,  of 
course,  peculiarities  characteristic  of  each ;  thus  wood-spirit,  oil  of  po- 
tato-spirit,  and  ethal  are  alcohols. 

The  generic  properties  of  an  alcohol  are,  that  its  composition  may  be 


I 


666  THEORY  OF  THE  ETHERS. 

represented  by  a  hydrocarbon  isomeric  with  olefiant  gas,  united  with 
two  atoms  of  water ;  that  it  gives  an  ether,  which  contains  an  atom  of 
water  less,  and  acts  as  a  base  ;  and  that,  by  combining  the  hydrocarbon 
with  four  atoms  of  oxygen,  an  acid  is  formed.     Thus  we  have, 

Wine-Alcohol.  Wood-Alcohol,  Oil  of  Potato-Spirit.  Ethal. 

Alcohol,     C4H44-2H.O.        C2H24-2H.O.        C,oH,o-j-2H.O.        C32H32-I-2H.O. 
Ether,        C4H4+H.O.  C2H2+H.O.  C.oH.o+H.O.  C32H32H-H.O. 

Acid,         C4H4O.  C2H2O4  CioH,o04  C32H32O4. 

Such  being  the  connexion  of  the  bodies  of  this  class,  the  propositions 
in  which  I  shall  now  proceed  to  imbody  the  principles  of  the  constitution 
of  the  substances  derived  from  wine-alcohol,  may  be  hereafter  immedi- 
ately  applied  to  illustrate  the  history  of  the  other  alcohols. 

1.  From  the  action  of  sulphuric  acid,  of  chloride  of  zinc,  of  fluoride  of 
boron,  of  potassium,  and  of  chlorine  on  alcohol,  it  results  that  it  contains 
an  atom  of  water  ready  formed,  united  with  sulphuric  ether ;  its  formula 
is  therefore  C4H50.  +  Aq. 

2.  The  sulphuric  ether  is  a  base,  neutralizing  the  strongest  acids,  and 
producing  both  oxy-salts  and  haloid  salts,  perfectly  resembling  those  of 
an  alkali.  The  oxygen  in  ether  may  be  replaced  by  all  other  electro- 
negative bodies,  while  the  carbohydrogen,  C4Hg,  remains  constant.  By 
the  conditions  laid  down  in  p.  467,  this,  therefore,  is  a  compound  radical ; 
it  is  called  Ethyl,  and  its  symbol  is  written  Ae.  Ether  is  oxide  of  ethyl, 
and  its  symbol  is  Ae.O. 

3.  By  the  action  of  oxidizing  agents,  hydrogen  may  be  removed  from 
ethyl,  and  a  new  radical,  C4H3,  produced,  which,  by  combining  with  oxy- 
gen, forms  aldehyd  and  acetic  acid,  its  symbol  being  Ac.  Aldehyd  is 
protoxide,  Ac.O.,  and  acetic  acid,  peroxide  of  acetyl,  AcOg,  both  being 
considered  free  from  water. 

4.  From  olefiant  gas,  by  the  action  of  oxidizing  agents,  we  cannot,  in 
any  case,  pass  to  the  series  of  bodies  containing  acetyl ;  nor  can  we, 
by  bringing  olefiant  gas  in  contact  with  water  or  acids,  produce  any 
form  of  alcohol  or  ether.  On  the  contrary,  the  isethionic  acid  is  essen- 
tially distinct  from  these  acids,  which  contain  ether,  and  yields  none  by 
any  form  of  decomposition ;  olefiant  gas,  on  the  other  hand,  gives,  by 
the  action  of  chlorine,  a  series  of  bodies,  which  are  quite  different  from 
those  given  by  muriatic  ether,  but  which  indicate  that  it  is  itself  a  radi- 
cal, having  laws  of  combination  peculiar  to  itself,  and  independent,  as 
Berzelius  had  already  suggested,  both  of  the  alcohol  and  acetic  series. 
Its  formula  is  therefore  C2H2 ;  its  symbol  El. ;  and  the  Dutch  oil  is  truly 
Chloride  of  Elayl.  The  ethyl  may  change  itself  readily  into  elayl  by  loss 
of  hydrogen,  since  C4H5=2C2H2  and  H.,  and  it  is  thus  broken  up  when 
the  hydriodic  or  muriatic  ethers  are  decomposed  by  heat,  or  by  potash, 
or  ammonia ;  or  when  sulphuric  ether  is  acted  on  by  an  excess  of  sul 
phuric  acid. 

5.  Although  from  the  decomposition  of  ether  we  obtain  olefiant  gas, 
or  light  oil  of  wine,  yet  as  ether  cannot  be  in  any  way  regenerated  from 
these  bodies  by  the  influence  of  water  or  otherwise,  neither  can  the  other 
products  derived  from  ether,  as  acetic  acid,  be  produced  from  them,  we 
must  abandon  the  theory  which  considered  ether  to  be  a  hydrate  of  C4H4, 
and  consider  it  simply  as  an  organic  base,  the  oxide  of  ethyl. 

6.  By  the  action  of  chlorine  on  the  ethereal  compounds  and  on  ole- 
fiant gas,  radicals  are  generated,  which  are  precisely  equivalent  to  the 


THEORY     OF     THE     ETHERS,     ETC.  567 

Inree,  ethyl,  acetyl,  and  elayl,  but  which  contain  chlorine  in  place  of  hy- 
drogen. Their  formulae  are  C4CI3,  CI4C5,  and  C2CI2.  This  last  is  the  pro- 
tochloride  of  carbon,  already  described ;  the  first,  Acechloryl,  exists  in 
chloraldehyd  and  in  chloroacetic  acid;  the  second,  Ethchloryl,  exists 
combined  with  oxygen  in  chloryl  ether,  which  acts  as  a  base  similar  to 
common  ether  towards  the  oxalic  and  acetic  acids.  In  contact  with  an 
excess  of  chlorine,  it  breaks  up,  as  ethyl  does,  into  defiant  gas  and  hy- 
drogen,  into  the  protochloride  of  carbon  and  chlorine,  and  thus  the  ulti- 
mate  result  is  the  sesquichloride  of  carbon,  C2CI3. 

7.  The  series  of  bodies  formed  by  the  action  of  chlorine  on  elayl  and 
on  chloride  of  ethyl,  are  double  combinations  of  bodies  containing  the 
hydrogen  and  chlorine  radicals,  and  hence  results  their  isomerism.  Thus 
the  body  (C4H2CI4),  from  elayl,  consists  of  C2H2CI.4-C2CI2CI.,  while  the 
body  (C4H2CI4),  from  the  muriatic  ether,  is  really  2(C4H3Cl3)-fC4Cl3Cl3. 
The  body,  C4H3CI.,  from  elayl,  is  3(C2H2)4-C2Cl2. 

8.  The  relation  of  acetyl  to  ethyl  is  simply  that  of  internal  constitu- 
tion, described  in  p.  467.  For  as  benzoic  acid  contains  benzoyl,  C,4H502, 
while  this,  again,  contains,  as  radical,  the  carbohydrogen,  C,4H5,  so  ethyl, 
C4H5,  contains  within  it,  ready  formed,  the  radical  acetyl,  and  its  formula 
might  be  still  more  correctly  written  as  Ac.Hz.  This  is  simply  shown 
by  the  action  of  chlorine  on  ether,  where  C4H3 .  H2O.  becomes  first 
C4H3 .  CI2O.,  and  subsequently  changes  to  C4CI3 .  CI2O. ;  the  intermediate 
compound,  AcClg,  relating  itself  to  the  oxygen,  as  the  sulphurous  acid, 
S.O2,  or  the  benzoyl,  C^Hi^Oa,  in  the  sulphuric  and  benzoic  acids.  Al- 
though the  connexion  of  these  two  radicals  is  thus  analogous  to  that  of 
amidogen.  Ad.,  and  ammonium,  Ad.H2=Am.,  yet  a  broad  line  of  distinc- 
tion is  drawn  between  the  ammonia  and  ether  theories,  by  the  very  defi- 
nite character  of  ether,  oxide  of  ethyl,  as  contrasted  with  the  hypothetic 
oxide  of  ammonium ;  and,  on  the  other  hand,  there  does  not  appear  to 
be  any  acetylide  of  hydrogen  corresponding  to  ammonia,  the  amidide  of 
hydrogen,  for  the  assumption  of  olefiant  gas  as  being  that  body  is  not 
based  upon  sufficient  evidence. 

Secondary  Products  of  the  Alcoholic  Fermentation. 

I  have  already  noticed  that,  besides  the  carbonic  acid  and  alcohol  which  are  de- 
rived from  the  sugar,  other  bodies  are  evolved  in  minute  quantities,  and  by  their 
odour  and  taste  characterize  the  spirit  obtained  from  particular  vegetables.  Thus, 
in  the  fermentation  of  grape-juice,  (Enanthic  Ether  is  produced  ;  in  the  spirit  dis- 
tilled from  potatoes,  a  peculiar  oil  is  found  ;  and  in  the  fermentation  of  malted  corn, 
both  of  these  bodies  are  generated,  besides  a  third,  to  which  the  name  of  Oleum 
Siticum,  or  Corn  Oil,  has  been  given. 

The  (Enanthic  Ether  is  a  thin,  colourless  liquid,  of  an  almost  stupifying  odour  of 
wine,  as  to  it  the  peculiar  bouquet  of  wine  is  due  ;  its  specific  gravity  is  0862  ;  it 
boils  at  445°  ;  when  heated  with  caustic  soda,  it  evolves  alcohol,  and  forms  cenan- 
thate  of  soda,  from  which  the  (Enanthic  Acid  may  be  separated  by  muriatic  acid. 
This  is  a  white  crystalline  solid,  which  melts  at  88°,  and  distils  over  at  560°  un- 
changed;  its  formula  is  C14H13O2;  it  combines  with  water,  forming  a  thick  oil, 
which  solidifies  only  at  55°,  is  tasteless  and  inodorous,  but  reddens  litmus  sensibly. 
The  formula  of  the  ether  is  Ae.O.-|-Ci4Hi302 ;  it  is  remarkable  as  the  only  ether 
that  exists  as  a  natural  product,  but  it  may  also  be  formed  artificially  by  means  of 
alcohol  and  cenanthic  acid. 

The  Corn  Oil,  of  which  the  formula  is  C42H35O4,  is  lighter  than  water,  of  a  very 
penetrating  odour,  a  biting  taste,  and  cannot  be  distilled  without  partial  decompo- 
sition. 

The  Oil  of  Potato-spirit  has  become  of  much  interest,  from  the  discovery  that  it 
gives  rise  to  a  series  of  ethereal  combinations  similar  to  those  of  wine  alcohol ;  the 
name  of  A  milic  Alcohol  may  be  applied  to  it ;  it  is  colourless,  oily,  its  odour  at  first 


568  AMILIC     ETHER,     ETC. 

pleasant,  but  subsequently  nauseous  ;  its  taste  acrid  ;  it  burns  with  a  blue  flame 
its  sp.  gr.  is  08 12  ;  it  freezes  at  4°,  and  boils  at  294°  ;  it  dissolves  in  alcohol  and 
ether  ;  its  formula  is  C10H12O2.     In  this  alcohol  a  compound  radical  is  assumed  to 
exist,  termed  Anulyl,  CioHn  ;  its  symbol  is  Ayl.,  and  it  is  combined  with  oxygen 
and  water,  Ayl.0.4-Aq.,  as  ethyl  is  in  wine-alcohol. 

The  Amilic  Ether,  Ayl.O.,  is  not  known  except  in  combination  with  acids  ;  its 
bisulphate,  or  Sulph-amilic  Acid,  is  obtained  by  acting  on  amilic  alcohol  with  oil 
of  vitriol;  its  formula  is  Ayl.O.  .  S.Os-j-S.Os  .  H.O. ;  its  barytes  salt  crystallizes  in 
pearly  plates,  colourless,  very  soluble  in  water  and  alcohol.  This  salt  is  decom- 
posed when  its  solution  is  boiled.  The  salts  of  lead  and  lime  are  completely  sim- 
ilar in  properties. 

Chloride  of  Amilyl,  CioHnCl.  or  Ayl. CI.,  is  prepared  by  acting  on  amilic  alcohol 
with  chloride  of  phosphorus  ;  it  is  a  colourless  oil,  which  boils  at  217°.  By  the 
action  of  bromine  or  iodine  and  phosphorus  on  the  amilic  alcohol,  the  bromide  and 
iodide  of  Amilyl  are  prepared  ;  they  possess  properties  similar  to  those  of  the  chlo- 
ride. 

Acetate  of  Amilyl,  Ayl.O.-j-Ac.Oa,  is  easily  formed  by  distilling  acetate  of  potash, 
oil  of  vitriol,  and  amilic  alcohol ;  it  is  a  volatile,  colourless  liquid,  which  boils  at 
257°.     The  Oxalate  of  Amilyl  may  be  similarly  formed. 

By  distilling  amilic  alcohol  with  glacial  phosphoric  acid,  a  colourless  aromatic 
liquid  is  obtained,  having  the  formula  CioHio.  It  is  in  this  series  what  olefiant  gas 
is  in  that  of  the  wine-alcohol ;  it  is  termed  Amilene ;  the  sp.  gr.  of  its  vapour  is  4918. 

Valerianic  Acid. — C10H10O4.  When  the  amilic  alcohol  is  exposed  to  the  air,  it  ab- 
sorbs oxygen,  but  its  oxidation  is  more  rapidly  effected  by  heating  it  with  caustic 
potash.  By  a  loss  of  hydrogen  and  absorption  of  oxygen  precisely  similar  to  that 
by  which  wine-alcohol  forms  acetic  acid,  it  produces  a  volatile,  oily  acid,  remarkable 
as  naturally  existing  in  the  roots  of  the  Valeriana  officinalis,  and  being  extracted 
therefrom  by  distillation  ;  it  is  lighter  than  water  ;  it  boils  at  347°,  and  neutralizes 
bases,  forming  soluble  sweet-tasted  salts  ;  it  must  be  considered  as  containing  a 
radical  analogous  to  acetyl,  valeryl,  z^CioHg  or  VI.,  and  its  formula  becomes  VI.O3 
4-Aq. 

When  valerianate  of  lime  is  heated,  carbonate  of  lime  is  formed,  and  a  volatile 
liquid  like  acetone  distils  over ;  it  is  termed  Valeron,  C10H9O3  giving  C.O2  and 
C9H9O.  The  roots  of  the  valerian  contain,  besides  the  valerianic  acid,  another  oil 
destitute  of  active  properties. 

By  cautiously  treating  amilic  alcohol  with  sulphuric  acid  and  chromate  of  potash, 
an  oily  liquid  is  obtained,  which  is  Valerianic  Aldchyd,  C10H10O2  or  Al.O.-j-Aq.  By 
an  excess  of  chromate  of  potash  it  is  changed  into  valerianic  acid. 

Treated  with  chlorine,  the  amilic  alcohol,  and  the  various  amilic  ethers,  as  well 
as  the  valerianic  acid,  give  new  products,  which  contain  chlorine,  and  are  constitu- 
ted according  to  the  same  principles  as  have  been  fully  described  for  wine-alcohol 


CHAPTER  XXII. 

OF    THE   ESSENTIAL    OILS,    CAMPHORS,    AND   RESINS. 

The  bodies  now  to  be  described  constitute  three  groups,  very  closely 
allied  in  composition,  in  properties,  and  in  origin.  For  the  most  part 
they  exist  ready  formed  in  plants,  as  secreted  by  their  proper  organs,  or 
they  are  derived,  by  reactions  of  a  very  simple  kind,  from  substances  so 
circumstanced.  They  are  employed  in  medicine  for  their  aromatic  and 
stimulant  properties,  and  in  the  arts  for  the  manufacture  of  a  variety  of 
perfumes,  varnishes,  lacquers,  &c. 

A.  Of  the  Essential  or  Volatile  Oils. 
These  oils  are  so  named  from  their  solubility  in  alcohol,  such  solutions 
being  called  essences^  and  from  their  volatility.     In  virtue  of  this  last  prop. 


PREPARATION,     ETC.,     OF     AMYGDALINE.  569 

erty,  they  are  generally  obtained  by  the  distillation  of  the  plants  with  water. 
If  the  oil  were  extracted  by  the  distillation  of  the  dry  plant,  the  heat  would 
rise  so  high  as  to  destroy  its  odour  and  alter  its  composition  ;  but,  by 
using  a  large  quantity  of  water,  the  mixed  vapours  of  the  oil  and  water 
pass  over  at  a  much  lower  temperature,  as  at  212° ;  for,  although  the 
boiling  point  of  the  oil  may  be  400",  yet  it  forms  a  quantity  of  vapour  at 
212°  proportional  to  its  tension  at  that  degree.  (See  p.  78.)  To  pre- 
vent even  the  inj*urious  heat  which  might  arise  from  the  plant  touching 
the  sides  of  the  still,  when  fragrant  flowers  or  leaves  are  operated  on, 
they  are  suspended  in  a  cage  in  the  centre  of  the  still,  and  allowed  only 
U)  come  into  contact  with  the  vapours.  These  oils  are  somewhat  solu- 
*ile  in  water,  and,  giving  to  it  their  odour  and  taste,  form  the  various 
dedicated  waters.  Hence  often  the  same  quantity  of  water  must  be 
distilled  with  fresh  quantities  of  the  plant  before  the  oil  is  in  such  pro- 
portion as  to  separate. 

Most  essential  oils,  as  those  of  turpentine,  lemon,  peppermint,  &c., 
exist  actually  in  the  plant,  as  secretions  from  peculiar  glands  ;  but  oth- 
ers  are  produced  only  at  the  moment  of  distillation,  by  the  decompo- 
sition of  substances  which  did  exist  in  the  plant,  and  which  undergo 
a  kind  of  fermentation.  This  is  the  case  with  the  oils  of  bitter  al- 
monds,  of  spircea,  of  mustard,  and  these  oils  possess  much  more  active 
chemical  properties  than  those  of  the  former  class.  Another  impor- 
tant difference  among  essential  oils  is,  that  some,  by  absorbing  oxygen 
directly,  produce  well-characterized  acids,  as  occurs  in  the  oils  of  bitter 
almonds,  of  cinnamon,  and  of  cloves ;  while  others,  as  the  oils  of  tur- 
pentine, citron,  and  copaiva,  by  a  much  more  indirect  action  of  oxygen, 
give  origin  to  resins.  On  these  principles  I  will  arrange  the  oils  in  two 
classes,  for  convenience  of  description. 

1st  Class. — Oils  forming  Acids  not  pre-existing  in  the  Plant, 
Of  Amygdaline  and  Oil  of  Bitter  Almonds. 

All  plants  which  yield  prussic  acid  on  distillation  produce,  at  the  same 
time,  a  volatile  oil,  which  is  known  as  the  Oil  of  Bitter  Almonds,  it  being 
most  abundantly  obtained  from  that  fruit.  The  leaves  of  the  cherry-lau- 
rel,  peach-kernels,  &c.,  also  yield  it.  The  oil  and  the  acid  both  arise 
from  the  decomposition  of  another  substance,  Amygdaline.  This  is  pre. 
pared  by  bruising  bitter  almonds,  and  pressing  them  strongly  between 
plates  of  hot  iron,  to  force  out  the  fixed  oil ;  the  residue  is  treated  by 
alcohol  of  93  per  cent.,  and  the  solution  evaporated  in  a  water-bath  to 
the  consistence  of  a  sirup;  this  is  then  diluted  with  water,  and  a  little 
yeast  added,  which,  by  inducing  fermentation,  destroys  a  quantity  of 
sugar.  When  this  is  over,  the  liquor  is  to  be  again  evaporated  to  a 
sirupy  consistence,  from  which  the  amygdaline  is  precipitated  by  the 
addition  of  cold  strong  alcohol,  in  which  it  is  scarcely  soluble ;  being 
dissolved  in  boiling  alcohol,  it  is  finally  obtained  pure  by  crystallization. 

The  formula  of  amygdaline  is  C40H27 .  N.O22 ;  it  forms  short  silky  nee- 
dles, which  are  anhydrous,  tasteless,  and  inodorous ;  it  is  very  soluble  in 
water,  and  crystallizes  therefrom  in  large  colourless  prisms,  containing 
6  Aq.  By  contact  with  nitric  acid  it  produces  ammonia,  oil  of  bitter 
almonds,  benzoic  and  formic  acids,  and  by  caustic  alkalies  it  is  decom- 
posed into  ammonia  and  Amygdalic  Acid,  C4oH26024+Aq. 

When  bruised  bitter  almonds  are  distilled  with  water,  all  amygdaline 

4C 


570  OIL     OF     BITTER     ALMONDS. 

disappears,  and  a  number  of  products,  as  prussic  acid  and  volatile  oil, 
are  evolved.  Pure  amygdaline  may,  however,  be  boiled  in  water  with- 
out being  altered.  It  is  the  animo-vegetal  principle  which  constitutes  the 
mass  of  the  cotelydon  of  the  almond  that  induces  the  reaction ;  it  has 
been  called  Emulsine,  and  appears  very  similar  in  properties  and  con- 
stitution  to  the  vegetable  albumen  or  legumine,  described  as  the  active 
principle  in  the  alcoholic  fermentation.  (See  p.  538.)  The  emulsine 
is  soluble  in  water,  but  insoluble  in  alcohol.  If  solutions  of  ten  parts  of 
amygdaline  in  100  of  water,  and  1  of  emulsine  in  10  of  water,  be  mixed, 
immediate  decomposition  occurs ;  the  liquor  becomes  milky,  smells  of 
bitter  almonds  ;  it  contains  sugar,  prussic  acid,  formic  acid,  and  volatile 
oil,  and  the  emulsine  coagulates.  It  is  most  probable  that  the  emulsine 
is  itself  also  decomposed  in  this  reaction,  but  we  may  explain  the  origin 
of  these  bodies  from  the  amygdaline  alone  thus : 

1  equivalent  of  prussic  acid,  C2H.N.,    "\ 

2  "  Sloaoid,  gSS;    f         lentofamygdalme. 
7            "  water,  H7O7,        ) 

In  the  cotelydon  of  the  almond,  the  amygdaline  and  emulsine  are  in 
distinct  cells,  and  have  no  means  of  acting  on  each  other,  but  when  bruis- 
ed in  water  both  dissolve,  and  decomposition  immediately  occurs.  The 
preparation  of  the  oil  by  distillation  can  hence  be  fully  understood. 

The  mixture  of  amygdaline  and  emulsine  has  been  employed  as  a 
means  of  producing  a  prussic  acid  of  standard  strength  for  medicinal 
purposes. 

Oil  of  Bitter  Almonds,     Hydruret  of  Benzyl, 

Prepared  by  distilling  bruised  bitter  almonds  with  water.  In  this 
rough  state  it  contains  a  great  quantity  of  prussic  acid,  from  which 
it  is  freed  by  distillation  with  some  water,  chloride  of  iron,  and  lime. 
It  is  then  colourless,  of  a  strong  peculiar  smell,  sp.  gr.  1*043  ;  it  boils 
at  356° ;  when  exposed  to  the  air  it  absorbs  oxygen,  and  forms  crystals 
of  benzoic  acid  ;  when  heated  with  hydrate  of  potash,  hydrogen  is  evolv- 
ed, and  benzoate  of  potash  formed.  The  formula  of  this  oil  is  C14H6O2; 
but,  from  the  series  of  compounds  to  which  it  gives  rise,  it  is  believed  to 
contain  an  organic  radical,  C14H5O2,  termed  Benzyl,  and  its  rational  for- 
mula is  therefore  Bz.H.     (See  p.  471.) 

Chloride  of  Benzyl,  Bz.CI.,  is  formed  by  acting  on  the  hydruret  with 
chlorine.  It  is  a  liquid  heavier  than  water ;  it  boils  at  383°  ;  when 
heated  with  water,  it  gradually  changes  into  benzoic  and  muriatic  acids. 
By  heating  chloride  of  benzyl  with  iodide  of  potassium,  Iodide  of  Benzyl 
is  formed ;  and  by  using  the  bromide,  sulphuret,  or  cyanide  of  potassi- 
um, compounds  of  benzyl  with  these  electro-negative  bodies  may  be 
formed. 

Amidide  of  Benzyl.  Benzamide,  Bz.Ad,,  is  formed  by  acting  on 
chloride  of  benzyl  with  dry  ammonia,  2(H.Ad.)  and  Bz.CI.  give  Bz. 
Ad.  and  Ad.H.  .  H.Cl.  ;  it  forms  rhomboidal  prisms,  which  melt  at 
240°,  and  may  be  distilled  unaltered ;  heated  with  potash,  it  gives  am- 
monia and  benzoate  of  potash. 

Oxide  of  Benzyl.  Benzoic  Acid. — Bz.O.-f-Aq.  This  acid  is  found 
ready  formed  in  the  resin  of  benzoin  and  in  dragon's  blood ;  it  some 


COMPLEX  BENZOIC  COMPOUNDS.        571 

times  appears  in  the  urine  of  herbivorous  animals,  and  is  formed  by  the 
oxidation  of  oil  of  bitter  almonds  and  of  amygdaline. 

The  following  process  for  obtaining  it  pure  was  devised  at  the  same 
time  by  Mohr  and  Hennell :  1  lb.  of  benzoin  resin,  in  powder,  is  to  be 
spread  on  the  bottom  of  a  metal  dish,  eight  or  nine  inches  diameter,  and 
two  inches  deep,  which  is  to  be  covered  with  a  drum  of  blotting  paper, 
pasted  to  the  edge  of  the  dish ;  the  whole  is  to  be  covered  with  a  cylin- 
drical cap  of  stout  packing  paper.  To  render  the  heal  uniform,  the  dish 
is  to  be  placed  on  a  metal  plate,  covered  with  sand,  resting  on  a  furnace  ; 
heat  being  cautiously  applied  for  three  or  four  hours,  the  cap  is  found 
full  of  splendid  crystals  of  benzoic  acid  ;  the  empyreumatic  oil,  which 
usually  contaminates  the  sublimed  product,  being  arrested  by  the  drum 
of  blotting  paper,  through  which  the  vapour  of  the  acid  passes  freely. 

It  may  also  be  extracted  from  the  resins  by  boiling  these  with  lime ;  a 
soluble  benzoate  of  lime  is  produced,  from  which  the  benzoic  acid  is  pre- 
cipitated by  the  addition  of  muriatic  acid ;  it  is  then  to  be  dissolved  in 
boiling  water,  and  allowed  to  crystallize  by  cooling  slowly. 

Benzoic  acid  crystallizes  in  hexagonal  needles ;  when  pure,  it  is  ino- 
dorous ;  it  reddens  litmus  feebly  ;  melts  at  248°  ;  the  fused  acid  boils  first 
at  462°,  but  it  sublimes  freely  at  293°  ;  it  dissolves  in  25  parts  of  boiling 
water,  but  requires  200  parts  of  cold  water  for  its  solution  ;  it  is  soluble 
in  twice  its  weight  of  alcohol  or  ether ;  it  forms  a  very  extensive  series 
of  salts,  of  which  few  require  special  notice. 

Benzoate  of  Lime,  Ca.O. .  Bz.O.+ Aq.,  crystallizes  in  brilliant  prisms ; 
at  a  dull  red  heat  it  is  decomposed  into  carbonate  of  lime  and  Benzene, 
the  formula  of  which  is  C13H5O.  Another  liquid,  Benzin,  CizHg,  is  at  the 
same  time  formed  by  virtue  of  a  much  more  complex  process,  napthaline, 
carbonic  acid,  and  carbonic  oxide  being  evolved. 

Benzoate  of  Ammonia,  Ad.HgO.  .  Bz.O.,  crystallizes  in  brilliant  plates. 
This  salt  is  employed  in  mineral  analysis  to  separate  iron  from  manga- 
nese ;  a  solution  of  peroxide  of  iron,  not  containing  any  excess  of  acid, 
being  completely  precipitated  by  neutral  benzoate  of  ammonia,  while  the 
salts  of  manganese  are  not  affected  by  it. 

Benzoate  of  Silver,  Ag.O.  .  Bz.O.,  is  obtained  by  double  decomposi- 
tion ;  crystallizes  from  a  boiling  solution,  on  cooling,  in  brilliant  colourless 
needles. 

Formobenzoic  Acid. — H.Bz.-j-Fo.Oa.  If  water,  saturated  with  the  impure  oil  of 
bitter  almonds,  be  mixed  with  muriatic  acid  and  evaporated,  this  substance  crystal- 
lizes. The  prussic  acid  is  decomposed  into  formic  acid  and  ammonia  (p.  517),  and 
the  nascent  formic  acid  coml)ines  with  the  hydruret  of  benzyl ;  in  this  body  all  the 
saturating  power  of  the  formic  acid  is  preserved. 

If  a  current  of  chlorine  be  passed  through  a  solution  of  impure  oil  of  bitter  al 
monds  in  water,  a  similar  body  is  formed,  consisting  of  benzoic  acid  and  hydruret 
of  benzyl,  Bz.H.-l-Bz.O. 

Sulphobenzoic  Acid. — Ci4H803-l-S205-}-2  Aq.  This  body  is  formed  by  the  action 
of  dry  sulphuric  acid  on  benzoic  acid.  A  viscid  mass  results,  which,  when  neutral- 
ized by  barytes,  yields  a  salt  permanent  in  the  air,  crystallizing  in  rhomboidal 
prisms,  and  having  the  formula  Ci4H803+S205H-2Ba.0.4-3  Aq.  From  this  the 
pure  acid  may  be  obtained ;  it  is  decomposed  if  its  solution  be  boiled,  but  when 
evaporated  in  vacuo  it  crystallizes.  The  sulphobenzoate  of  copper  crystaUizes  in 
large  rhombs  of  a  rich  blue  colour. 

Bromobenzoic  Acid,  C28H9 .  Br.08-|-2  Aq.,  is  formed  when  benzoate  of  silver  is  dty 
composed  by  bromine.  It  is  a  crystalline  solid,  very  soluble  in  water,  fuses  at  212*, 
and  sublimes  at  482°  ;  its  salts  are  all  soluble,  and  contain  two  atoms  of  base. 

Of  the  liquids  produced  by  the  distillation  of  benzoate  of  lime,  Benzonc,  CwHsO.* 
does  not  form  any  compounds ;  but  Benzin,  CuHe,  produces  with  sulphuric  acid, 


57^  OIL     OF     CINNAMON. 

nitric  acid,  and  chlorine,  a  series  of  bodies,  of  which  the  formulae  alone  need  be 
here  given  ;  they  are, 

Sulpnobenzide,  Ci2l^  •  S.O2.  Chlorbenzin,  Ci2H6C]6. 

Sulphobenzidic  acid,  C12H3 .  S2O5.  Chlorbenzid,  CijHsCb. 

Nitrobenzide,  C12H5.N.O4.  Azobenzid,     C12H5N. 

I  shall  have  occasion  to  refer  to  benzin  as  a  product  of  the  distillation  of  resm 
and  coal.  It  is  colourless,  of  an  agreeable  ethereal  odour ;  it  boils  at  187°  ;  its 
specific  gravity  is  0  85  ;  that  of  its  vapour  is  2378  ;  at  32°  it  freezes  into  a  crystal- 
line mass,  which  melts  first  at  43°. 

Oil  of  Bitter  Almonds  with  Ammonia. — By  the  action  of  water  of  ammonia  on  hy- 
druret  of  benzyl,  all  oxygen  is  removed,  and  a  crystalline  body,  Hydrobenzamide, 
produced  ;  its  formula  is  C42H1SN2.  It  is  soluble  in  alcohol,  and  by  boiling  the  so- 
lution is  decomposed  into  ammonia  and  hydruret  of  benzyl.  The  nitrogen  here  en- 
ters into  the  constitution  of  the  radical,  replacing  the  oxygen,  and  the  body  is  Hy- 
druret of  Azobenzyl  (C14H5  .  fN)-|-H.  This  azobenzyl  is  itself  also  formed  in  the 
same  process  as  the  former,  and  also  the  Azohenzoilic  Acid  (C14H5 .  |N.)-j-gN.,  which, 
is  benzoic  acid,  in  which  all  oxygen  is  replaced  by  nitrogen.  The  origin  of  these 
bodies  is  explained  by  the  constitution  of  the  radical  benzyl,  as  described  in  p.  471, 

In  the  impure  oil  of  bitter  almonds  a  substance  exists,  termed  Bcnzo'ine,  which  is 
isomeric  with  the  oil,  its  formula  being  C14H6O2 ;  it  crystallizes  in  colourless  prisms. 
By  potash  it  gives  benzoic  acid  and  hydrogen  ;  by  ammonia  it  forms  a  substance 
isomeric  with  Hydrobenzamide.  By  chlorine  it  gives  muriatic  acid,  and  in  place  of 
chloride  of  benzyl,  a  crystalline  body,  which  is  isomeric  with  that  radical,  its  form- 
ula being  C14H5O2 ;  this  is  termed  Benzcril :  when  heated  with  potash  it  gives  the 
BenzoiHc  Acid,  which  has  the  formula  C24Hii054-Aq. 

By  acting  on  oil  of  bitter  almonds  with  a  solution  of  sulphuret  of  ammonium  in 
alcohol,  Laurent  has  obtained  a  series  of  bodies,  in  which  the  oxygen  of  the  radical 
benzyl  is  replaced  by  sulphur,  and  in  some  cases  partly  by  sulphur  and  partly  by 
azote ;  there  should  thus  be  Sulphobenzyl  (C14H5S2),  corresponding  to  the  azoben- 
zyl. It  is  unnecessary,  in  an  elementary  work,  to  enumerate  the  individual  sub- 
stances, but  I  look  upon  their  formation  as  corroborating  very  much  Berzelius's 
idea,  that  the  true  radical  of  the  benzoic  series  is  the  carbohydrogen,  C14H5,  and 
that  the  chloride,  &c.,  of  benzyl  are  really  oxychlorides,  &c.  (See  p.  471.)  Cer- 
tainly the  element  which  remains  truly  constant  in  those  reactions  (and  hence  sat- 
isfies the  definition  of  a  radical,  p.  467)  is  C14H5,  and  not  C14H5O2. 

Oil  of  Cinnamon  and  the  derived  Compounds. 
This  oil  is  found  in  the  bark  and  flower-buds  of  the  laurus  cinnamomum  and  lau- 
rus  cassia.  It  is  heavier  than  water,  and  possesses  the  odour  of  the  plant  in  the 
highest  degree.  It  boils  at  428°  ;  its  formula  is  C2oHn02,  and  for  distinction  I  shall 
term  it  the  a  oil.  When  exposed  to  the  air  it  absorbs  oxygen,  and  forms  another 
oil,  which  is  that  generally  found  in  the  shops,  the  (3  oil,  the  formula  of  which  is 
C18H8O2.     Two  resins,  a  and  /?,  are  at  the  same  time  produced. 

o     *  ^         ■^         r>    XT    n.  f  (^   rCSiu,  =C3oH|504, 

3  atoms  of  a  oil,  ^CeoHaaOe,  )  U  ..g^^  =.c  2H  O. 

The  j8  oil  of  cinnamon,  although  thus  only  a  product  of  the  decomposition  of  the 
true  oil,  is  very  important,  from  the  variety  of  compounds  it  gives  rise  to.  It  is 
heavier  than  water  ;  it  dissolves  in  water  of  potash  or  of  barytes,  a  cinnamate  of  the 
base  being  formed,  and  an  oil  lighter  than  water  separating,  2(C]8H802)  and  H.O. 
giving  C)8Hio02  and  C18H7O3.  The  properties  of  this  oil  indicate  that  it  contains 
an  organic  radical,  Cinnamyl,  CigHvOz,  united  to  hydrogen.  It  is  Hydruret  of  Cin 
namyl,  Ci.H.,  and  the  oil  lighter  than  water  is  Ci.Ha. 

Cinnamic  Acid,  Ci.O.-f-Aq.,  is  formed  by  exposing  the  hydruret  of  cinnamyl  to 
the  air ;  it  absorbs  two  atoms  of  oxygen,  and  forms  crystallized  cinnamic  acid.  It 
forms  colourless  groups  of  plates  of  an  acid  taste  ;  it  is  almost  insoluble  in  water, 
but  easily  soluble  in  alcohol  and  ether.  It  melts  at  264°,  distils  over  at  554°  un 
changed.     Its  salts  are  exceedingly  similar  to  the  benzoates. 

Hydruret  of  cinnamyl  combines  directly  with  muriatic  acid,  with  nitric  acid,  and 
with  ammonia,  forming  compounds  which  are  solid  and  crystalline.  Their  formulae 
are  Ci.H.  .  H.Cl.,  Ci.H.  .  H.Ad.,  and  Ci.H.  .  H.O.+N.Os.  By  chlorine  one  half 
of  the  hydrogen  of  this  /3  oil  is  removed,  and  a  white  crystalline  body  formed,  Cis 
H4 .  CI4O2.     The  chlorine  here  enters  into  the  constitution  of  the  radical. 


OIL     OF     CLOVFS     AND     SPIRiEA.  573 

Oil  of  cinnamon  combines  with  iodidn  of  potassium  and  iodine  to  form  a  sub- 
stance which  crystallizes  in  large  needles  of  a  brilliant  bronze  colour,  like  perman- 
ganate of  potash.  Its  formula  is  Ci.H.la-j-K.I.  Once  formed,  it  is  decomposed  by 
water.     It  was  discovered  by  Moore,  of  Dublin,  and  analyzed  by  Apjohn. 

The  origin  of  the  Balsams  of  Peru  and  Tolu  is  closely  related  to  the  oil  of  cinna- 
mon. They  consist  of  resinous  substances  (the  a  and (3  cinnamic  resins'?),  and  of 
an  oil  which  may  be  obtained  pure  by  distillation.  It  is  called  Cinnameine ;  its  for- 
mula is  CigHsOz,  being  isomeric  with  the  8  oil  of  cinnamon.  It  is  neutral ;  but 
when  its  alcoholic  solution  is  boiled  with  potash,  it  forms  cinnamate  of  potash ;  or, 
by  simple  boiling  of  its  alcoholic  solution,  Cinnamic  Ether  is  produced,  and  another 
oil,  Peruvine,  is  separated,  the  formula  of  which  is  CigHuO;.  In  these  cases  three 
atoms  of  cinnameine  and  two  of  water  produce  two  atoms  of  dry  cinnamic  acid 
and  one  of  peruvine. 

These  researches  on  the  nature  of  the  balsams  are  due  to  Fremy ;  but  Richter 
has  advanced  that  the  balsam  of  Peru  contains  two  oils,  which  he  terms  Myrio- 
spermine  and  Myroxyline,  the  relation  of  which  to  peruvine  and  cinnameine  is  not 
yet  established. 

By  the  action  of  an  excess  of  nitric  acid,  both  oil  of  cinnamon  and  cinnamic  acid 
are  converted  into  oil  of  bitter  almonds  and  benzoic  acid. 

Oil  of  Cloves,  Eugenic  Acid,  SfC. 

The  oil  obtained  by  distillation  from  the  undeveloped  flower-buds  of  the  eugenia 
caryophyllata  is  a  mixture  of  several  bodies.  By  the  action  of  potash,  it  is  separa- 
ted into  a  volatile  oil  which  does  not  possess  active  properties,  is  hghter  than 
water,  and  consists  of  CioHs,  while  a  eugenate  of  potash  dissolves.  From  this 
solution  the  Eugenic  Acid  is  precipitated  by  any  strong  acid. 

Eugenic  Acid.  Heavy  Oil  of  Cloves,  C24H15O5,  is  a  colourless  oil,  sp.  gr.  1079;  it 
boils  at  4700  ;  its  taste  and  smell  are  those  of  cloves.  It  forms,  with  the  metallic 
oxides,  well-defined  salts,  most  of  which  are  soluble  and  crystallizable. 

When  the  common  oil  of  cloves  is  kept  for  some  time,  it  deposites  a  crystalline 
substance,  Caryophylline,  C20H16O2 ;  it  is  soluble  in  alcohol,  insoluble  in  water.  It 
is  volatile.  From  water  distilled  with  cloves  a  different  body  separates  in  pearly 
scales,  having  the  formula  C20H12O4.     It  is  called  Eugcnine. 

The  eugenic  acid  and  eugenine  are  rendered  blood-red  by  contact  with  nitric  acid. 

The  Light  Oil  of  Cloves  has  sp.  gr.  =0918 ;  it  boils  at  287°. 

Oil  of  Spirma  Ulmaria.     Salicide  of  Hydrogen, 

The  oil  distilled  from  the  flowers  of  the  meadow-sweet  is  a  mixture  of  a  light 
and  of  a  heavy  oil,  with  a  solid  body  Hke  camphor.  The  heavy  oil  is  of  much  in- 
terest, from  the  number  of  compounds  which  it  forms,  and  from  our  being  able  to 
form  it  at  will,  although  from  a  body,  salicine,  which  has  not  been  found  to  exist  in 
the  spiraea.  The  impure  oil  of  spiraea  is  purified  by  adding  potash,  by  which  the 
light  oil  is  separated,  and  Salicide  of  Potassium  formed,  which,  when  acted  on  by 
sulphuric  acid,  yields  the  Salicide  of  Hydrogen  pure. 

To  form  it  artificially,  equal  parts  of  salicine  and  bichromate  of  potash  are  to  be 
distilled  with  2^  parts  of  oil  of  vitriol  and  20  of  water.  There  is  heat  evolved  and 
much  gas  disengaged ;  on  then  distilling,  the  heavy  oil  passes  over.  Two  atoms 
of  dry  salicine  (C42H21O18),  without  any  oxygen,  might  yield  three  atoms  of  oil, 
3(Ci4H604),  and  six  of  water;  but  the  reaction  is  far  more  complicated  in  reality, 
as  four  parts  of  salicine  yield  but  one  of  oil. 

The  properties  of  this  oil  show  it  to  be  a  compound  of  a  radical  (C14H5O4),  Sali- 
cyle,  Syl.,  with  hydrogen  ;  it  acts  as  a  hydracid  in  combining  with  metallic  oxides  ; 
its  specific  gravity  is  1173 ;  it  boils  at  380°.  The  specific  gravity  of  its  vapour  is 
4260.  In  this  and  in  composition  it  agrees  with  crystallized  benzoic  acid,  with 
which  it  is  isomeric.  The  alkaline  Salicides  are  soluble  and  crystallizable ;  those 
of  lead,  zinc,  and  mercury  are  insoluble.  If  a  solution  of  any  salicide  be  mixed 
with  a  solution  of  a  sesqui-salt  of  iron,  the  liquor  assumes  a  fine  purple  colour,  by 
which  the  oil  is  well  characterized. 

When  salicide  of  hydrogen  is  heated  with  caustic  potash,  hydrogen  is  evolved, 
and  Salicylic  Acid,  Syl.O.,  formed ;  the  potash  salt  being  dissolved  in  water,  and 
muriatic  acid  added,  the  new  acid  is  precipitated,  and  is  purified  by  recrystalliza- 
tion ;  it  dissolves  in  boiling  water ;  it  may  be  sublimed,  and  condenses  in  long 
needles,  like  benzoic  acid ;  it  possesses  the  usual  acid  properties ;  its  salts  are 
generally  soluble,  and  resemble  closely  the  benzoates. 


574  OIL     OP    MUSTARD,     ETC. 

By  the  action  of  chlorine  on  salicide  of  hydrogen,  Chloride  of  Salicyle  is  formed, 
Syl.Cl. ;  it  crystalUzes  in  rhomboidal  tables,  which  melt  and  sublime  undecom- 
posed  ;  bromine  and  iodine  give  similar  compounds  ;  with  nitric  acid  it  produces 
Nitrosalicylic  Acid,  Syl.N.04,  which  crystallizes  in  long  prisms,  and  unites  with 
bases  forming  salts. 

The  connexion  of  salicyl  with  benzyl  is  very  remarkable ;  they  contain  the  same 
hydrogen  and  carbon,  C14H5,  but  it  is  combined  in  salicyl  with  4,  and  in  benzyl  with 
but  2  atoms  of  oxygen.  By  the  action  of  ammonia  on  the  chloride  of  salicyl  and  on 
the  oil,  this  relation  is  more  clearly  shown,  for  the  oxygen  in  the  radical  may  be 
brought  to  the  composition  of  benzyl.  Thus  the  ChlorosaUcamide  is  C42H15CIS  . 
O6N2,  or,  properly,  SCCnHsOa .  |N.)CL  ;  that  is,  (Bz.f  N.)C1.  By  the  direct  action 
of  ammonia  on  the  salicide  of  hydrogen,  the  corresponding  (C14H5O2 .  |N.)-{-H. 
may  be  formed.  To  this  new  radical,  which  is  evidently  Nitruret  of  Benzyl,  the 
name  Azosdicyl  might  be  given  (see  p.  572). 

Essential  Oil  of  Mustard. 

The  oil  obtained  by  distilling  the  seeds  of  the  sinapis  nigra  with  water  is  remark- 
able for  an  unusually  complex  constitution,  as  it  contains  five  elements ;  its  for- 
mula being  C32H20N4  .  S5O5.  When  pure,  it  is  colourless ;  it  boils  at  289°  ;  ita 
specific  gravity  is  1015 ;  that  of  its  vapour  is  3370  ;  when  acted  on  by  nitric  acid, 
it  yields  sulphuric  acid  and  an  organic  product ;  with  caustic  potash  it  forms  sul- 
phuret  and  sulphocyanuret  of  potassium,  and  organic  products  which  have  not  been 
examined.  With  ammonia  it  forms  a  substance  in  large  white  crystals,  the  for- 
mula of  which  is  C32H20N4  .  S5O5+4N.H3.  Our  knowledge  of  the  chemical  nature 
of  this  oil  is  yet  imperfect.  It  has  been  only  established  that  it  does  not  exist  in 
the  seeds,  being,  like  oil  of  bitter  almonds,  formed  at  the  moment  of  distillation. 

The  seeds  of  mustard  contain  two  crystalline  substances.  Of  these,  Sulphosin- 
apisine  is  obtained  by  a  process  similar  to  that  used  for  preparing  amygdaline.  It 
is,  when  pure,  white ;  soluble  in  alcohol  and  water  ;  it  contains  the  same  five  ele- 
ments as  the  oil,  which  is  probably  formed  from  it  by  the  action  of  the  emulsin  of 
the  seed,  as  is  the  case  with  amygdaline.  The  principle  of  the  mustard  seed  to 
which  it  appears  to  owe  most  of  its  pungency  has  been  termed  Sinapisine ;  its 
preparation  is  complex ;  it  does  not  contain  any  sulphur,  and  hence  can  act  but 
indirectly  in  the  formation  of  the  essential  oil.  Fremy  considers  the  essential  oil 
to  be  formed  by  the  action  of  the  albumen  of  the  seed  on  a  peculiar  acid  body, 
which  he  terms  Myronic  Acid ;  but  this  has  not  been  analyzed,  and  we  do  not  know 
its  relations  to  sinapisine,  with  which  it  may  possibly  be  identical.  The  formula 
given  above  for  the  oil  is  that  of  Dumas  ;  Lowig  has  since  analyzed  it,  and  denies 
that  it  contains  oxygen,  assigning  to  it  the  formula  N.Cg .  H5S2.  Accurate  re- 
searches on  the  constitution  of  these  bodies  are  very  much  to  be  desired. 

2d  Class. — Oils  pre-existing  in  the  Plant,     Properties  not  Acid, 

These  oils  are  very  numerous,  and  so  similar  in  properties  that  a  spe- 
cial description  is  quite  unnecessary  for  each.  They  are  characterized 
by  not  dissolving  in  solution  of  potash,  by  being  lighter  than  water,  and 
by  a  less  energetic  action  on  the  animal  system  than  the  oils  of  the  first 
class.  They  combine  with  muriatic  acid  to  form  heavy  oily  substances, 
in  some  cases  crystalline.  When  put  in  contact  with  iodine,  they  fre- 
quently combine  with  it  so  energetically  as  to  produce  a  feeble  explosion. 
By  chlorine,  hydrogen  is  removed,  and  an  oily  liquid,  heavier  than  water, 
is  produced.  The  oil,  as  yielded  by  the  plant,  consists  of  two  substan- 
ces, one  solid  (Slearopten),  the  other  liquid  (Elaopten) ;  the  former  gener- 
ally crystallizes  when  the  oil  is  long  kept.  I  prefer  to  term  the  liquid 
simply  the  oi7,  and  the  solid  portion  the  camphor  of  the  plant.  We  some- 
times observe  these  oils  forming  the  camphor  artificially,  by  contact  with 
water. 

These  oils  may  be  very  naturally  divided  into  two  groups,  according 
as  they  contain  oxygen  or  not.  The  following  table  includes  all  the  im- 
portant facts  of  the  history  of  the  oils  (elaoptens)  containing  oxygen  r 


NEUTRAL     ESSENTIAL     OILS,    ETC. 


575 


Plant  yielding  the  oil. 


Cajeput  .     . 
Lavender    . 
Rosemary   . 
Pennyroyal 
Camphor-tree 
Valerian 
Spearmint  . 
Marjoram    . 
Asarura  .     . 
Fennel    .    . 
xlnise      .     . 
Peppermint 
Rue    .     .    . 
Olibanum    . 
Cumin     .     . 


Sp.gr. 
as   Liquid. 


0-927 
0-896 
0-897 
0-925 
0-910 


0-914 
0-867 


0-997 


0-902 
0-837 
0-866 
0-860 


Boiling 


347° 
397° 
365° 
395° 

518° 

354° 


446^ 
323^ 

418= 


Sp.gr. 
of  Vapour. 


C10H9O. 
C15H14O2 
C45H38O2 

CoHsO. 
C20H16O, 

C20H,2O. 

C3.5H280. 

C50H40O. 
C16H902 

C2oHi20^ 

C20H12O2 
C21H20O2 
C28H2803 
C35H280. 
C20H12O2 


7690 


5094 


From  the  recent  experiments  of  Gerhardt  and  Cahours,  it  appears  that, 
by  the  action  of  fused  hydrate  of  potash,  most  essential  oils  containing 
oxygen  may  be  separated  into  an  acid,  and  an  oil  destitute  of  oxygen. 
Some  of  the  results  obtained  by  those  chemists  are  of  great  interest ; 
thus,  from  the  oil  of  valerian,  C2oH,20.,  valerianic  acid  is  obtained,  and 
an  oil  which  absorbs  oxygen  with  great  rapidity  and  generates  common 
camphor.     The  oil  of  chamomile  also  yields  valerianic  acid. 

The  oil  of  cumin  (cuminum  cyminum),  of  which  the  characters  have 
been  given  in  the  table,  yields,  when  treated  with  hydrate  of  potash,  a  pe- 
culiar acid,  Cumenic  Acid,  whose  formula  is  CaoHjiOa+Aq.  ;  it  is  per- 
fectly white,  crystallizes  in  fine  prismatic  tables,  tastes  sour,  fuses  at 
197°,  and  may  be  distilled  unchanged.  If  cumenate  of  barytes  be  dis- 
tilled at  a  dull  red  heat,  a  colourless  liquid  oil  is  obtained,  which  boils  at 
292°  ;  it  is  termed  Cymen ;  its  formula  is  CigHig,  being  isomeric  with 
mesitylene  ;  with  sulphuric  acid  cymen  unites,  forming  Cymensulphuric 
Acid,  Ci8H,2 .  S2O6,  which  forms  well-characterized  soluble  salts.  By  the 
action  of  chlorine  and  of  bromine  on  the  oil  of  cumin,  heavy  oily  com- 
pounds are  obtained,  whose  formulae  are  C20H,, .  O2CI.,  and  CaoHn  .  OgBr. 

It  is  evident  that  in  these  compounds  a  radical  (Cumyl),  C2oH,i02,  ex- 
actly analogous  to  benzyl,  may  be  assumed,  and  the  cymen  has  the  place 
of  benzin.  The  carbohydrogen  of  the  oil  of  cumin  is  termed  by  Ca- 
hours Cumen ;  its  formula  isCaoH^;  its  specific  gravity  0'860;  it  boils 
at  330°  ;  it  may  be  prepared  artificially  also  from  common  camphor  ; 
with  sulphuric  acid  it  forms  Cumensulphuric  Acid,  which  resembles  com- 
pletely the  other  acids  of  that  class. 

The  stearoptens,  or  camphors  containing  oxygen,  will  be  described  by- 
and-by. 

The  following  table  contains  a  similar  view  of  the  most  important  oils 
not  containing  oxygen : 


Plants  yielding  the  Oil. 


Citron  .     .  . 

Copaiva    .  . 

Parsley     .  . 

Juniper      .  . 

Savine .     .  . 

Cubebs      .  . 
Black  Pepper 

Bergamotte  . 

Turpentine  . 


0-847 
0-878 


0-839 
0929 


0-864 


343° 
4730 
410O 
311° 
315° 


315^ 


Formula 

Sp.  gr.  as 
Vapour. 

Circular  Polarizing 
Power. 

al 

4-80°  9',  right. 

>  >> 

4-34°  3',  left. 

fi 

—3°  5'',  left. 

^^^ 

>% 

°.2o 

*  460  V,  left. 

III 

If 

+29°  3',  light. 

-8a 

< 

—43°  3',  Ir.fl. 

576  ISOMERIC     OILS     OF     TURPENTINE. 

Although  these  oils  have  all  the  same  per  cent,  composition,  they  dif- 
fer in  the  formula  of  their  atom,  that  of  turpentine  being  CaoHje,  that 
of  cubebs,  C,5Hi2,  and  all  the  others  being  CioHg.  Although,  even  as  giv- 
en in  the  table,  they  constitute  a  remarkable  group  of  isomeric  bodies, 
yet  each  one  is  capable  of  changmg  its  molecular  condition  in  various 
ways,  and  thus  generating  other  bodies,  still  more  closely  isomeric,  as 
they  differ  only  in  their  action  on  polarized  light.  Of  these  changes 
J  shall  describe  only  those  of  oil  of  turpentine,  which  will  serve  as  an 
example. 

By  contact  with  oil  of  vitriol,  oil  of  turpentine  changes  into  another 
liquid,  which  has  the  same  specific  gravity  both  in  the  state  of  liquid  and 
of  vapour,  the  same  boiling  point,  and  the  same  atomic  weight,  but  is  to- 
tally without  action  on  polarized  light.  This  new  liquid  is  called  Tere- 
bene.  If  the  oil  of  turpentine  be  acted  on  by  muriatic  acid  gas,  it  com- 
bines therewith,  forming  a  dense  liquid,  which  is  muriate  of  terebene,  and 
which  has  no  action  on  light ;  but  another  portion  of  the  turpentine  unites 
with  the  muriatic  acid  unchanged,  and  forms  a  solid,  which  crystallizes 
in  fine  white  prisms,  and,  from  its  remarkable  odour,  is  called  artificial 
Camphor.  In  this  solid  the  oil  of  turpentine  preserves  all  its  action  upon 
light,  and,  for  convenience,  it  may  obtain  the  name  Camphene,  and  the 
solid  is  then  Muriate  of  Camphene.  Now  if  this  solid  be  distilled  with 
lime,  the  muriatic  acid  is  removed  and  an  oil  obtained,  which  differs 
from  camphene  only  in  having  no  action  on  light,  while  it  differs  from 
terebene  in  forming  with  muriatic  acid  a  solid  product.  This  oil  is 
termed  Camphilene,  and  the  Muriate  of  Camphilene  is  distinguished  from 
the  muriate  of  camphene  in  being  quite  destitute  of  rotatory  power. 
From  none  of  these  products  can  the  true  oil  of  turpentine,  or  camphene, 
be  regenerated.  There  are  thus  three  forms  of  oil  of  turpentine,  of 
which  two  give  solid  compounds,  and  the  third  a  liquid,  with  muriatic 
acid  ;  two  are  without  action  on  light,  but  the  camphene  rotates  power- 
fully  to  the  left :  with  chlorine  they  all  give  heavy  liquids,  all  of  which 
have  the  formula  C2oH,2Cl4,  but  are  distinguished  from  each  other  by  their 
action  upon  polarized  light;  the  Chlorcamphene  presenting  the  anom- 
alous  character  of  a  rotatory  power  to  the  right. 

When  oil  of  turpentine  is  mixed  with  nitric  acid  and  gently  heated,  a 
thick  and  heavy  oily  substance  is  produced,  apparently  by  their  direct 
union,  and  may  be  separated  by  the  addition  of  cold  water.  If,  however, 
the  materials  be  left  to  themselves,  after  some  time,  violent,  almost  ex- 
plosive action  sets  in,  copious  red  fumes  are  given  off,  and  a  resinous  ma- 
terial  formed,  which,  by  boiling  with  more  nitric  acid,  dissolves,  and  the 
solution,  on  cooling,  yields  crystals  of  Turpentinic  Acid.  Its  composition 
was  found  by  Bromeis  to  be  CHHeOy-f-Aq.  The  exact  theory  of  its  for- 
mation has  not  been  as  yet  ascertained. 

The  other  oils  of  this  class  are  capable  of  similar  metamorphoses, 
which  need  not  be  specially  detailed. 

The  type  C5H4  exists  probably  in  all  essential  oils,  for  it  will  be  seen, 
by  reference  to  the  former  table  of  oils  containing  oxygen,  that  their  for- 
mulse  consist  in  multiples  of  C5H4,  combined  with  oxygen,  or  with  the 
elements  of  water. 

B.   Of  the  Camphors  or  Stearoptens  of  the  Oils. 
The  most  remarkable  substance  of  this  class  is  the  common  camphor. 


CAMPHOR. CAMPHORIC     ACID. 


577 


whicli  is  extracted  from  the  wood  of  the  laurus  and  dryabalanops  cam- 
phora  by  distillation  with  water.  In  the  plant  it  is  mixed  with  the  cam- 
phor-oil  (CasHifiO.),  from  the  gradual  oxidation  of  which  it  appears  to  be 
produced. 

Camphor  forms  a  white  semitransparent  mass,  crystallized  in  irregu- 
lar octohedrons.  It  is  very  tough  and  difficult  to  powder ;  its  specific 
gravity  is  0*986  ;  its  taste  is  bitter  ;  its  odour  is  well  known  ;  it  melts  at 
347°,  and  boils  at  390°,  subliming  unaltered ;  it  is  sparingly  soluble  in 
water,  but  easily  so  in  alcohol  and  ether ;  its  formula  is  CaoHigOg.  The 
specific  gravity  of  its  vapour  is  5317,  which  might  be  considered  as  form- 
ed  by  one  volume  of  vapour  of  camphene  and  half  a  volume  of  oxygen 
(4776+ 551 'S).  Hence  camphor  and  camphor-oil  may  be  looked  upon 
as  oxides  of  an  oil  of  the  turpentine  family. 

When  camphor  is  heated  with  lime,  water,  and  an  oil,  Camphron 
(C30H22O.),  are  produced.  With  muriatic  acid  it  unites,  forming  a  col- 
ourless liquid,  whose  formula  is  CaoH,,  .  O2CI.  By  boiling  with  strong 
nitric  acid,  it  is  completely  converted  into  Camphoric  Acid, 

This  acid  crystallizes  in  small  rhomboidal  tables,  which  taste  sour  and 
bitter  ;  it  melts  at  145°,  gives  off  water,  and  leaves  the  anhydrous  acid, 
which  melts  at  423°,  and  distils  over  at  518°  without  alteration.  The 
formula  of  the  anhydrous  acid  is  C10H7O3 ;  the  crystals  contain  an  atom 
of  water.  The  salts  of  camphoric  acid  are  not  important,  and  appear  to 
differ  in  properties  according  as  the  dry  or  hydrated  acid  was  employed 
to  form  them.  The  Camphorate  of  Ether  is  a  dense  liquid,  which,  with 
camphoric  acid,  forms  the  Camphovinic  Acid,  a  thick,  heavy  liquid,  which 
is  decomposed  by  heat,  and  forms  unimportant  salts. 

When  camphor  is  distilled  with  glacial  phosphoric  acid,  water  is  form- 
ed, and  a  volatile  oil  passes  over,  having  the  formula  C2oH,4,  and  identical 
in  every  respect  with  the  Cymen  obtained  from  oil  of  cumin,  as  descri- 
bed in  p.  575. 

When  camphor  in  vapour  is  passed  over  hydrate  of  potash,  heated  to 
about  700°,  an  acid  is  formed,  which  has  the  formula  CgoHi-Oa+Aq. 
This  Camphoric  Acid  fuses  at  176°,  and  boils  at  482°  ;  it  may  be  distil- 
led  unchanged.  It  is  insoluble  in  water,  but  dissolves  abundantly  in  al- 
cohol and  ether,  and  crystaUizes  from  these  solutions  on  cooling.  When 
it  is  heated  with  phosphoric  acid,  a  volatile  oil  is  produced,  Campholen, 
having  the  formula  CigHig.  When  campholeate  of  lime  is  distilled,  an- 
other oily  fluid  is  formed,  whose  formula  is  CigH^O. 

Of  the  camphors  of  the  other  volatile  oils,  only  a  few  require  any  de. 
tailed  notice.  The  characters  of  most  of  them  are  given  in  the  follow, 
ing  table  : 


Plant  giving  the  Camphor. 


Sp.  Gr. 
as   Liquid, 


Melting 
Point. 


Boiling 
Point. 


Sp.  Gr. 

of  Vapour. 


Rose  (Otto)  . 
Parsley  .  . 
Iris  Florentina 
Elicampane  . 
Asarum  .  . 
Fennel  .  . 
Anise  .  •  . 
Peppermint  . 
Cubebs  .  . 
Turpentine  . 


77° 
70° 


550° 
552° 


1014 


108° 

104° 

68° 

64° 

91° 


530° 

428  3 
430° 
406° 


1057 
4D 


311' 


5680 
5455 


C.H. 

C]2H704 
C4H4O. 
C7H6O. 
Ci6H,i04 

C20HI2O2 

C20H;2O2 
C21H20O2 
C16H14O. 

CaoH2o04 


578  RESINS     OF     TURPENTINE.      '' 

On  comparing  these  formulae  with  those  of  the  corresponding  oils 
(p.  575).  it  is  seen  that  the  camphors  arise  from  various  causes  ;  in  some 
cases  they  are  isomeric  with  the  oils,  in  others  oxides  of  them,  and  in 
others  hydrates  ;  thus  the  camphor  of  turpentine  may  be  formed  at  will, 
by  agitating  the  oil  with  water,  and  then  exposing  it  to  cold  ;  the  hydrate 
crystallizes  out  in  colourless  prisms,  sometimes  of  great  size. 

The  peppermint-camphor  has  been  found  to  yield,  by  the  action  of  re- 
agents, a  series  of  compounds.  Thus,  by  the  action  of  glacial  phosphoric 
acid  or  of  oil  of  vitriol,  a  light  oil  was  obtained,  having  the  formula  Cg, 
Ills,  which  is  termed  Menthen.  By  the  action  of  chlorine,  a  thick,  heavy 
liquid  is  produced,  C21H14 .  ClgOa.  By  nitric  acid,  menthen  yields  a  heavy 
oily  liquid,  CaiHjgOg,  which  possesses  acid  properties  ;  and  with  chlorine, 
menthen  yields  a  sirupy  yellow  liquid,  having  the  formula  C21H13CI5. 

The  anise-camphor  yields  with  bromine  a  crystalline  substance,  C20H9 . 
BrjOg,  and  with  sulphuric  acid  an  oily  substance,  Aniso'ine,  isomeric  with 
itself.  By  nitric  acid  it  is  converted  into  a  body  which  crystallizes  in 
long  needles,  Anisic  Acid,  CieHgOs+Aq.,  which  forms  salts  with  metal- 
lic oxides,  and  gives  by  farther  action  the  Nitranisic  Acid,  Ci^s  •  N.O3+ 
Aq.,  and  Nitranisid,  C20H10 .  N2O10. 

C.  Of  the  Resins. 

The  bodies  of  this  class  approach  closely  to  the  camphors  in  compo- 
sition and  properties,  but  are  distinguished  by  not  being  volatile  without 
decomposition,  and  being  generally  capable  of  acting  as  acids.  The  most 
important  will  be  first  specially  noticed,  and  the  properties  and  formulae 
of  the  remaining  expressed  in  a  table. 

Resins  of  Turpentine. — The  ordinary  white  resin  coexists,  in  the  dif- 
ferent species  of  pine,  with  oil  of  turpentine,  and  is  obtained  by  making 
incisions  through  the  bark,  when  the  thick,  tenacious  turpentine  flows 
out.  This,  when  distilled  with  water,  gives  off  the  oil,  while  the  resin 
remains,  and  is  called  Colophony.  It  is  a  mixture  of  two  resins,  which, 
though  having  the  same  composition,  differ  in  properties,  and  are  termed 
the  pinic  and  sylvic  acids. 

The  Pinic  Acid  is  obtained  by  digesting  colophony  reduced  to  fine 
powder,  in  cold  spirit  of  sp.  gr.  0*865,  which  does  not  dissolve  sylvic 
acid.  The  solution  is  to  be  mixed  with  a  spirituous  solution  of  acetate 
of  copper  as  long  as  a  precipitate  forms.  This  Pinate  of  Copper  is 
to  be  dissolved  in  strong  boiling  spirit,  decomposed  by  a  little  muriatic 
acid,  and  then  mixed  with  water ;  the  pinic  acid  precipitates  as  a  resin- 
ous powder,  which  may  be  dried  at  a  moderate  heat. 

When  quite  pure,  pinic  acid  is  colourless  ;  it  melts  at  257°,  but  be- 
comes  soft  at  149°  :  its  solution  in  alcohol  reacts  acid.  It  expels  car- 
bonic acid  from  bases  ;  its  alkaline  salts  are  soluble  ;  its  earthy  and  me- 
tallic salts  insoluble  in  water,  but  many  of  them  soluble  in  spirit ;  its  for- 
mula is  C40H30O4. 

When  a  solution  of  pinic  acid  in  alcohol  is  long  exposed  to  the  air,  it 
absorbs  oxygen  and  forms  Oxypinic  Acid,i\\Q  formula  of  which  is  C40H3B 
Og ;  it  is  a  stronger  acid  than  the  pinic.  When  heated  with  lime,  pinic 
acid  is  decomposed,  and  three  different  volatile  oils  obtained,  which  need 
not  be  specially  noticed. 

The  Sylvic  Acid  remains  when  the  pinic  acid  is  dissolved  by  weak  al- 
cohol.     As  it  is  not  pure,  the  residue  is  to  be  dissolved  in  two  parts  of 


COMPOSITION     OP     RESINS. 


579 


boiling  spirit  of  0*865  ;  on  cooling,  the  sylvic  acid  separates.  By  a  sec- 
ond solution,  all  the  traces  of  pinic  acid  may  be  removed.  The  pure  syl- 
vic acid  crystallizes  from  its  alcoholic  solution  in  colourless  rhombic 
prisms ;  it  melts  at  212°  ;  it  is  easily  soluble  in  strong  alcohol  and  in 
ether,  but  insoluble  in  water  ;  its  formula  is  C40H30O4.  Its  salts  are  ex- 
actly similar  to  those  of  pinic  acid. 

When  either  pinic  or  sylvic  acids  are  kept  melted  for  some  time,  they 
become  brown,  and  change  into  a  resin  very  sparingly  soluble  in  alcohol, 
and  possessed  of  stronger  acid  properties  than  either  ;  it  is  termed  Colo- 
phonic  Acid ;  it  exists  in  small  quantity  in  common  resin. 

The  resin  of  the  spruce  fir  has  been  found  by  Johnstone  to  be  a  mix- 
ture of  two  resins,  which  are  separated  by  means  of  alcohol.  The  more 
soluble,  or  A  resin,  has  the  formula  C40H31O6;  the  less  soluble,  or  B  res- 
in, that  of  C40H39O5 ;  they  both  possess  acid  characters. 

For  the  manufacture  of  tar  and  pitch,  the  pine  wood  containing  tur- 
pentine is  exposed  to  a  kind  of  destructive  distillation,  in  kilns  hollowed 
out  in  the  ground.  Although  a  large  quantity  of  the  resin  flows  out  un- 
decomposed  (as  colopholic  acid),  yet  the  important  components  of  the 
tar  are  bodies  belonging  to  a  different  series,  which  will  be  described 
hereafter. 

A  great  variety  of  resins,  of  important  use  in  medicine  and  in  the  arts, 
exude  from  trees,  either  pure,  or  mixed  with  oils,  or  with  gums  (Gum 
Resins),  sometimes  with  benzoic  or  cinnamic  acids,  constituting  Balsams. 
Frequently  there  are  many  kinds  of  resins  mixed  together,  but  they  all 
possess  the  characters  of  fusibility,  insolubility  in  water,  and  of  being 
dissolved  by  alcohol,  ether,  essential  oils,  and  alkaline  solutions.  Their 
composition  is  given  in  the  following  table  : 

Anime  Resin    .    .    .    .  ?  /-•   TT._r\  B.  Sandarach 

Elemi  Resin     .    . 

Fossil  Copal     .    . 

B,  Mastic  Resin    . 

Antiar  Resin    .    . 

B.  Copal  Resin     . 

Birch  Resin ,    .    . 

A.  Mastic  Resin   . 

Copaiva  Resin 

A.  Elemi  Resin     . 

B.  Olibanum  Resin 

C.  Sandarach  .  . 
Ammoniac  Resin  . 
B.  AssafoBtida  .  . 
Guiacuin .... 
Bdellium  Resin  . 
A.  Sandarach   .    . 


C40HS3O. 

C40H32O. 
.  C49H31O2 

C40tl3oC2 
.  C40H31O3 
.      C40H33O3 

'  ]•  C40H31O4 

•;;C4oH320i 

.      C)4oH3o06 

.      C40H25O9 

C40H26O9 

.       C45H23O10 


C40H31O5 


A.Euphorbium      .    \    '.  |  C40H31O6 

Asphaltene }  C40H32O6 

A.  Olibanum     ....  5 

Labdanura C48H33O7 

Pasto  Resin C40H32O8 

Sagapenum C4oH2909 

Scammony C4oH330ao 

Jalap  Resin C4oH340a) 

•Galbanum C40H27O7 

Dragon's  Blood  .  .  .  C4oH2i08 
Gamboge C40H23O8 

A.  Assafcetida  ....  C4oH260i9 
Acaroid  Resin  ....  C40H20O12 
Opoponax C40H25OU 

B.  Benzoin  Resin  .  .  .  C40H22O9 
A.  Benzoin  Resin  .    .    .    C40H26O7 

In  all  this  series  of  resins,  it  is  evident  that  the  carbon  remains  unal- 
tered, and  Johnstone  has  shown  that  they  may  all  be  considered  as  deri- 
ved from  oils  having  the  turpentine  constitution  =C4oH32. 

A  substance  which  is  connected  with  the  preceding  in  many  ways  is 
Amber.  This  body  is  found  in  rounded  pieces,  mixed  with  or  attached 
to  fragments  of  decomposing  wood,  in  the  lignite  beds  of  the  north  of  Eu- 
rope. It  is  also  found,  cast  on  shore  by  the  waves,  along  the  coast  of 
the  Baltic.  It  is  yellow,  transparent,  and  often  contains  imbedded  in  it 
insects  and  parts  of  plants,  so  as  to  prove  it  to  have  been  perfectly  liquid 
when  first  formed.  It  is,  in  fact,  the  turpentine  of  unknown  trees,  be- 
longing to  a  former  geological  epoch;    its  specific  gravity  is  1*067; 


580 


AMBER,     SUCCINIC     ACID,     ETC. 


when  heated  it  melts,  and  is  then  totally  decomposed ;  its  relations  to 
electricity  have  been  fully  noticed,  p.  108.  Amber  is  found  to  be  a  mix. 
ture  of  two  resins,  which  are  soluble  in  alcohol  and  ether,  a  bitumen  in- 
soluble in  those  liquids,  a  volatile  oil,  and  a  peculiar  acid,  the  Succinic 
Acid.  It  is  used  very  extensively  in  the  arts  as  a  material  for  varnish- 
es, but  to  chemists  its  principal  interest  is  its  electrical  properties,  and 
as  a  source  of  its  acid. 

Succinic  Acid  is  obtained  by  the  destructive  distillation  of  amber ;  it 
partly  sublimes  into  the  neck  of  the  retort,  in  discoloured  crystals,  and 
partly  dissolves  in  the  water  which  comes  over ;  by  solution  in  nitric 
acid  it  may  be  freed  from  the  resinous  colouring  matters.  It  may  also 
be  obtained  from  the  amber  by  digestion  with  alcohol  or  solution  of 
potash ;  it  hence  pre-exists  in  the  amber,  and  is  not  produced  by  the 
heat.  It  is  found  in  small  quantity  also  in  colophony,  and  is  abundantly 
produced  by  the  action  of  nitric  acid  on  the  fatty  acids,  as  the  stearic  or 
margaric. 

Succinic  acid  crystallizes,  from  its  solution  in  water,  in 
colourless  right  rhombic  prisms,  as  tw,  t,  a  in  the  figure,  which 
have  the  formula  C4H2O34- Aq. ;  when  heated  to  350°  it  melts, 
abandoning  half  its  water,  and  at  450°  sublimes  in  an  anhy- 
drous state ;  its  solution  in  water  is  markedly  acid ;  when 
heated  with  lime,  a  volatile  hquid  is  produced,  Succinone,  the 
exact  formula  of  which  is  not  established. 
The  salts  of  succinic  acid  are  mostly  soluble  and  crystalU- 
zable. 

The  Succinate  of  Soda,  prepared  by  neutralizing  the  acid  by  carbon- 
ate of  soda,  crystallizes  in  doubly  oblique  rhombic  prisms,  of  which  i,  u,  v 
are  primary,  and  z,  n  secondary  faces  in  the  figure  ;  it  is  per- 
manent in  the  air,  and  very  soluble  in  water.  The  Succinate 
of  Ammonia,  which  is  much  used  in  mineral  analysis  for  the 
separation  of  iron  from  manganese,  crystallizes  in  nearly  the 
same  form  as  the  soda-salt  figured  above.  The  succinates 
of  barytes,  lime,  and  lead  are  white  powders,  insoluble  in 
water.  The  Succinate  of  Manganese  forms  rose-red,  four-sided  pris- 
matic crystals,  permanent  in  the  air,  and  soluble  in  ten  parts  of  cold 
water.  The  Succinate  of  the  Peroxide  of  Iron  is  precipitated  when  an 
alkaline  succinate  is  added  to  any  salt  of  iron  not  containing  an  excess 
of  acid  ;  it  forms  a  pale  brownish-red  powder,  insoluble  in  cold  water, 
but  decomposed  by  boiling  water,  which  dissolves  out  the  acid  with  a 
small  quantity  of  the  iron  ;  it  dissolves  readily  in  acid  liquors. 

The  Bisuccinate  of  Ammonia  gives  off  water  when  heated,  and  a  white 
crystalline  solid  sublimes,  which  is  termed  Succinamid.     Its  formula  is 

QHg  .    O4N. 

The  rare  mineral,  Mellite  (see  p.  498),  is  only  found  accompanying 
amber  in  the  deposites  of  lignite. 

Caoutchouc.  Indian  Rubber. — This  substance,  now  so  much  used  in 
the  laboratory  for  connecting  pieces  of  apparatus,  and  so  extensively  em- 
ployed in  the  arts,  possesses  much  similarity  to  the  resins.  It  dissolves 
but  imperfectly  even  in  ether,  its  proper  solvent  being  the  volatile  oils, 
into  which  it  is  converted  by  distillation.  One  of  these  is  the  lightest 
liquid  known,  its  specific  gravity  being  but  0.654  ;  it  boils  at  92°  ;  it  has 
been  termed  Faradyn.     Another,  known  as  Caouichene,  has  a  specific 


CONSTITUTION    OF    FATTY     BODIES.  581 

gravity  of  0.842  ;  it  boils  at  340°.  The  composition  of  these  liquids, 
or  of  caoutchouc  itself,  is  not  well  known,  as  they  have  not  been,  as  yet, 
obtained  absolutely  pure ;  but,  so  far  as  I  can  judge,  they  appear  all  to 
have  the  same  composition  as  oil  of  turpentine. 


CHAPTER  XXIII. 

OF  THE  SAPONIFIABLE  FATS  AND  OILS. 

The  substances  of  this  class  are  found  both  in  the  animal  and  vegeta- 
ble kingdoms  very  extensively  distributed.  In  animals,  the  various  fats 
are  deposited  in  the  cavities  of  the  cellular  tissue,  but  often  also  diffused 
through  the  mass  of  the  glandular  organs.  In  plants,  the  oils  or  fats  are 
generally  found  in  the  investing  membranes  of  the  seed,  or  in  the  cellu- 
lar  texture  of  the  fruit.  The  leaves  or  roots  seldom  contain  any  fatty 
matter.  The  /ats  and  oils,  as  they  exist  in  nature,  are  mixtures  of  a 
few  simple  fatty  and  oily  bodies  in  variable  proportions,  their  degree  of 
consistence  depending  on  the  relative  preponderance  of  the  solid  or  li- 
quid constituent.  The  greater  number  of  fats  consist  of  two  simple  fats, 
Stearine  and  Margarine,  and  a  simple  oil,  Olein ;  but  these  three  bodies, 
which  may  be  considered  as  the  bases  of  all  fats  and  oils,  are  accompa- 
nied generally  by  smaller  quantities  of  solid  or  liquid  fats,  which  are 
often  peculiar  to  a  particular  animal  or  plant.  These  fatty  bodies  are 
all  faced ;  that  is,  they  cannot  be  distilled  without  decomposition  ;  but 
they  are  totally  converted  by  heat  into  volatile  bodies,  undergoing,  in 
some  cases,  singular  metamorphoses,  which  will  be  described  in  the  his- 
tory of  the  individual  fats. 

Exposed  to  the  air,  the  fatty  bodies  gradually  absorb  oxygen,  and 
evolve  carbonic  acid  ;  they  at  the  same  time  obtain  an  acid  reaction,  and 
a  smell  well  known  as  rancid.  Most  of  this  change  appears  to  result 
from  minute  quantities  of  azotized  organic  tissues,  which  remain  inter- 
spersed through  the  fats.  A  great  number  of  oils,  however,  absorb  ox- 
ygen very  rapidly,  and,  evolving  carbonic  acid,  change  into  a  soft  resin- 
ous body  ;  they  are  hence  termed  Drying  Oils,  and  are  used  so  in  paint- 
ing. This  drying  quality  is  increased  by  combining  the  oil  with  a  small 
quantity  of  a  base,  as  oxide  of  lead. 

The  most  important  fact  in  the  history  of  the  fixed  oils  and  fats  is, 
that,  by  the  action  of  alkalies,  they  are  converted  into  soaps ;  whence 
the  name  o^  saponijiahle  given  to  the  class.  By  means  of  the  alkali,  the 
fat  or  oil  is  decomposed  into  an  acid,  which  combines  with  the  base,  form- 
ing a  true  salt,  which  is  the  Soap,  and  a  substance  soluble  in  water,  of 
a  sweet  taste,  which  is  the  same,  no  matter  what  kind  of  fat  had  been 
employed.  This  substance,  the  swee't  principle  of  the  oils,  or  Glycerine, 
is  united  in  each  fat  with  a  different  acid,  and  hence,  as  the  fats  are  best 
described  as  salts  of  glycerine,  I  shall  first  notice  the  composition  and 
properties  of  the  base  itself. 

Of  Glycerine. — CgllA+Aq.  Eq.  1157-4  or  92-3.  To  obtain  gly- 
cerine, any  fatty  matter  is  to  be  saponified  by  a  caustic  alkali.  The 
solution  being  decomposed  by  tartaric  acid,  which  precipitates  the  fatt}- 


f'JSS       GLYCERINE,    STEARIN  E,    AND     STEARIC     ACID. 

acid,  is  to  be  evaporated,  and  the  glycerine  dissolved  out  by  strong  alco- 
hol. It  may  also  be  obtained  by  saponifying  the  fat  by  oxide  of  lead, 
and  treating  the  watery  solution  with  sulphuretted  hydrogen  to  precipi. 
tate  some  oxide  of  lead,  which  dissolves  ;  the  glycerine  may  then  be  ob- 
tained by  evaporation. 

Glycerine  cannot  be  obtained  solid.  When  brought  to  its  greatest 
degree  of  consistence  by  evaporation  in  vacuo  over  sulphuric  acid,  it  is 
a  colourless  sirup,  sp.  gr.  =1*26  ;  it  dissolves  in  water  and  alcohol,  but 
is  insoluble  in  ether ;  it  is  decomposed  by  heat.  With  nitric  acid  it 
produces  oxalic  and  formic  acids.  Boiled  with  solutions  of  copper,  it 
precipitates  metallic  copper.  With  chlorine  it  forms  a  white  flocculent 
solid,  having  the  formula  CjaH,,  .  O10CI3,  and  with  bromine  it  gives  a 
dense  oily  liquid,  whose  formula  is  CigHu  .  OjoBrg. 

When  glycerine  is  mixed  with  oil  of  vitriol,  they  unite  without  black- 
ening, and  form  an  acid  compound,  Sulphoglyceric  Acid,  the  formula  of 
which  is  CfiHyOs  .  2S.O3 .  H.O.  With  bases  this  acid  forms  soluble 
salts,  having  considerable  analogy  to  the  sulphovinates.  The  Sulpho- 
glycerate  of  Lime  crystallizes  in  long  delicate  needles,  whose  formula  is 
C6H7O5  .  S.O3+S.O3  .  Ca.O.  The  compounds  of  glycerine  with  the 
fatty  acids  constitute  the  various  kinds  of  fats  and  oils. 

Of  Stearine  and  Stearic  Acid, 

Stearine  is  the  essential  constituent  of  all  solid  fats,  and  preponder- 
ates  in  proportion  to  their  consistence.  It  is  best  obtained  from  mutton- 
suet,  either  by  washing  it  with  ether,  as  long  as  anything  is  dissolved, 
or  by  mixing  up  melted  suet  with  six  times  its  volume  of  ether,  and  sub- 
jecting the  mass,  when  cold,  to  strong  pressure.  In  both  cases  the  stea- 
rine remains  behind ;  it  is  generally  crystalline  like  spermaceti,  not  at 
all  greasy  between  the  fingers,  and  is  easily  powdered  ;  it  melts  at  143°  ; 
it  is  insoluble  in  water  and  in  cold  ether ;  it  dissolves  in  boiling  alcohol 
or  ether,  and  crystallizes  out  as  it  cools.  The  formula  of  stearine  is 
Ci42Hi4iOi7,  consisting  of 

1  atom  of  glycerine,        =C6H705,        ^ 

2  atoms  of  stearic  acid,  =rCi36Hi320io,  >  =Ci42Hi4iOi7. 
2  atoms  of  water,  =H202,  J 

By  the  action  of  strong  bases  or  of  strong  acids,  it  is  separated  into 
these  constituents.     A  similar  decomposition  is  effected  by  heat. 

Stearic  Acid  is  obtained  pure  by  saponifying  stearine  by  potash,  and 
decomposing  the  solution  by  means  of  warm  dilute  muriatic  acid.  The 
stearic  acid  which  precipitates  is  to  be  washed  with  water  and  dissolved 
in  boiling  alcohol,  whence  the  pure  acid  crystallizes,  on  cooling,  in  brill- 
iant  white  plates. 

When  mutton-suet  is  directly  saponified,  very  troublesome  operations 
are  necessary  to  free  the  stearic  acid  from  the  other  fatty  acids  which 
accompany  it. 

Pure  stearic  acid  is  tasteless  and  inodorous.  It  does  not  melt  below 
158°  ;  the  melted  acid  forms  a  crystalline  mass  on  cooling ;  it  is  appa- 
rently volatile,  and  may  be  distilled  unaltered  in  close  vessels ;  it  is  in- 
soluble in  water,  but  dissolves  in  hot  alcohol ;  the  solution  reddens  lit- 
mus ;  its  composition,  when  crystallized,  is  CgsHeeOs+S  Aq.  When  heat- 
ed in  contact  with  lime,  carbonic  acid  is  formed,  dnd  a  volatile  liquid, 
Stearon,  whose  formula  is  CegHeeO. 


MARGARINE     AND    MARGARIC     ACID.  583 

Stearic  acid  is  but  feeble  in  its  action :  it  expels  the  carbonic  acid 
from  the  alkalies  only  when  the  solution  is  boiling.  It  is  bibasic,  form- 
ing  two  classes  of  salts,  the  Bistearates,  which  contain  one  atom  of  water 
and  one  of  fixed  base,  and  the  Neutral  Stearaies,  which  contain  two  atoms 
of  fixed  base.  The  alkaline  stearates  are  the  only  salts  soluble  in  water ; 
they  dissolve  also  in  alcohol.  If  neutral  stearate  of  potash  be  mixed 
with  a  large  quantity  of  boiling  water,  it  is  decomposed,  one  half  of  the 
potash  becoming  free,  and  tlie  Bistearate  of  Potash  precipitating  in  minute 
crystalline  scales.  A.  solution  of  soap  precipitates  all  earthy  and  metal- 
lic salts,  producing  insoluble  stearates. 

The  Stearic  Ether  is  exceedingly  remarkable,  as  it  corresponds  exactly 
to  stearine  in  composition,  the  glycerine  being  replaced  by  ether.  Thus 
its  formula  is 

1  atom  of  ether,  =C4H50.,       \ 

2  atoms  of  stearic  acid,  =Ci36Hi320io,  >  Ci4oHi390i3=l  atom  of  stearic  ethei. 
2  atoms  of  water,  =H202,  ) 

Stearic  acid  is  now  very  extensively  used  for  making  candles.  The 
tallow  is  saponified  by  boiling  with  a  thin  paste  of  lime.  The  glycerine 
is  washed  out,  and  the  soap  being  decomposed  by  muriatic  acid,  the  oleic 
acid  is  removed  from  the  stearic  acid  by  violent  pressure  between  folds 
of  cloth.  The  pure  stearic  acid,  when  solidifying,  assumes  a  crystalline 
structure,  which  would  spoil  the  appearance  of  the  candle,  and  this  ten- 
dency is  removed  by  the  very  improper  addition  of  one  part  of  arsenious 
acid  to  about  2000  of  stearic  acid. 

Of  Margarine  and  Margaric  Acid, 

Margarine  exists  along  with  stearine  in  most  fats,  but  is  most  char- 
acteristic of  human  fat.  It  is  prepared  from  the  ethereal  solution,  which 
has  left  the  stearine  undissolved.  This  liquor  is  to  be  evaporated,  and 
the  residue  dissolved  in  boiling  alcohol,  from  which  the  margarine  crys- 
tallizes as  the  solution  cools;  it  melts  at  118°.  In  all  other  properties 
it  resembles  stearine,  but  is  much  more  soluble  in  ether  and  alcohol;  it 
consists  of  C74H74OJ2. 

1  atom  of  glycerine,  =C6H705,    i 

2  atoms  of  margaric  acid,  ^CesHeeOs,  >  =C74H740i2,  1  atom  of  margarine. 
1  atom  of  water,  =H.O.,        ) 

By  the  action  of  bases  it  is  separated  into  glycerme  and  margaric  acid. 

The  preparation  of  Margaric  Acid  is  precisely  similar  to  that  of  the 
stearic  acid,  which  it  resembles  very  closely,  being  most  different  in  its 
melting  point,  which  is  140°.  On  solidifying,  it  crystallizes  in  white 
needles.  When  carefully  heated,  it  volatilizes  without  alteration.  The 
formula  of  margaric  acid  is  C34H33O3+ Aq.  If  it  be  mixed  with  lime  and 
distilled,  carbonic  acid  is  produced,  which  combines  with  the  lime,  and 
a  volatile  substance  is  obtained,  which  is  termed  Margaron.  Its  formula 
is  C33H33O.  It  is  a  white  solid,  of  a  pearly  lustre,  which  melts  at  170°, 
and  forms,  on  cooling,  a  crystalline  mass  like  spermaceti.  By  repeated 
distillation  with  lime,  all  oxygen  is  removed  as  carbonic  acid,  and  a  vol- 
atile oily  substance  obtained,  having  the  composition  of  defiant  gas. 

The  experiments  of  Redtenbacher  have  indicated  a  remarkable  source 
of  margaric  acid  in  the  distillation  of  stearic  acid.  The  distilled  product, 
though  in  appearance  unchanged  stearic  acid,  yet  does  not  in  reality 


584  OLEIN     AND     OLEIC     ACID. 

contain  any  trace  of  it,  being  a  mixture  of  margaric  acid,  of  margarone, 
and  of  the  volatile  oily  carbohydrogen.     The  reaction  being  that 

(6  atoms  of  margaric  acid,  C204H204O24, 
1  atom  of  water,  H.O., 

1       "       margarone,         CasEUaO., 
1       "       carbonic  acid,     C.O2, 
The  oily  carbohydrogen,    C34H34. 

Redtenbacher  doubts  the  real  existence  of  slearone,  as  none  of  it  is 
produced  in  this  reaction. 

The  salts  of  margaric  acid  resemble  perfectly  the  stearates  in  their 
properties,  but  the  acid  being  monobasic,  there  is  but  one  class  of  marga- 
rates.  The  pearly  lustre  of  the  crystalline  scales  of  the  margarate  of 
potash  gave  occasion  to  the  name  of  this  acid,  from  the  word  fiapyapi' 
TTjg,  a  pearL 

If  we  compare  the  formulae  of  the  bodies  now  described,  we  find  them 
capable  of  being  expressed  by  a  very  simple  theory :  thus,  indicating  an 
hypothetic  carbohydrogen,  C34H33,  by  R.,  the  stearic  acid  becomes  R2  + 
O5,  and  the  margaric  acid,  R.  +  O3,  being  related  as  hyposulphuric  and 
sulphuric  acids.  Also,  as  Redtenbacher  has  remarked,  all  the  results 
obtained  might  be  accounted  for  by  ascribing  to  margarone  the  formula 
C34H33O.,  in  which  case  it  becomes  R.  +  O.,  and  the  volatile  oil  may  be 
R.+H.  Farther  researches  are,  however,  wanted  to  give  experimental 
evidence  on  these  points. 

Of  Olein  and  Oleic  Acid. 

Ole'in  exists  in  small  quantity  in  the  various  solid  fats,  but  constitutes 
the  great  mass  of  the  liquid  fixed  oils  which  are  not  drying  oils.  It 
holds  dissolved,  more  or  less,  stearine  and  margarine,  of  which  the  great- 
est part  may  be  separated  by  exposure  to  cold,  when  they  crystallize. 
Olive  oil  contains  a  large  quantity  of  margarine,  and  hence  freezes  very 
readily.  The  expressed  oil  of  sweet  almonds  is  the  purest  native  olein  ; 
next  to  it  is  rape  oil. 

To  obtain  pure  olein,  almond  oil  is  dissolved  in  hot  ether,  and  the  so. 
lution  exposed  to  great  cold ;  the  traces  of  margarine  crystallize  out 
completely,  and  by  evaporation  the  ether  is  removed.  Olein  remains 
liquid  at  0°  Fah.  In  constitution  it  resembles  the  solid  fats,  containing 
a  peculiar  acid,  Oleic  Acid,  combined  with  glycerine  and  water. 


1  atom  of  glycerine,     CgHyOs, 

2  atoms  of  oleic  acid,  CssHtsOs,  \  produce  1  atom  olein,  C94H87O15. 
2  atoms  of  water,        H2O2, 


H7O5,  i 
bHtsOs,  > 
O2,         ) 


Oleic  Acid  is  obtained  by  saponifying  olein  with  a  strong  solution  of 
potash,  then  decomposing  the  oleate  of  potash  by  muriatic  acid,  washing 
the  oil  which  separates,  and  drying  it  with  chloride  of  calcium  ;  when 
cooled  below  20°  F.,  it  congeals  as  a  mass  of  needly  crystals.  Its  spe- 
cific gravity  at  60°  is  0*898 ;  it  is  tasteless  and  inodorous  when  pure ; 
it  is  insoluble  in  water,  but  abundantly  soluble  in  alcohol  and  ether; 
these  solutions  react  strongly  acid  ;  its  composition  has  been  determin- 
ed by  Varrentrapp  to  be  C44H3904-f-Aq. ;  its  alkaline  salts  are  soluble, 
and  form  soft  masses,  destitute  of  tendency  to  crystallize  ;  they  are  still 
more  soluble  in  alcohol.  The  earthy  and  metallic  salts  are  white,  plas- 
tery  substances,  insoluble  in  water.  The  Oleate  of  Lead  is  soluble  in 
ether,  by  which  it  may  be  perfectly  separated  from  the  stearate  or  mar- 


SEBACIC    ACID,    ETC.  >  585 

garate  of  lead.  The  Oleic  Ether  was  formed  by  Varrentrapp  by  passing 
muriatic  acid  gas  into  a  solution  of  oleic  acid  in  alcohol.  It  is  a  colour- 
less liquid,  sparingly  soluble  in  alcohol,  lighter  than  water,  but  heavier 
than  alcohol,  from  which  it  is  deposited  as  it  forms;  its  formula  is 
C«H39044-Ae.O. 

When  oleic  acid  is  distilled,  a  portion  of  it  passes  over  unaltered,  "but 
the  greater  part  is  decomposed,  and  some  charcoal  remains  in  the  retort. 
The  distilled  products  are  Sebacic  Acid  and  a  liquid  carbohydrogen, 
isomeric  with  defiant  gas  ;  sebacic  acid  is  not  produced  by  the  distilla- 
tion of  any  other  fatty  substance  than  oleic  acid,  and  hence  may  be  con- 
sidered as  characteristic  of  it.     The  decomposition  consists  in  that 

r  1  atom  of  sebacic  acid,      C10H9O4, 

2  atoms  of  hydrated  oleic  acid,  )  „-^j„„_J  3  atoms  of  carbonic  acid,  C3O6, 
CggHgoOio,  $  proauce<  carbohydrogen,  C71H71, 

V  residual  charcoal,  C4. 

Sehacic  Acid  had  been  considered  as  a  product  of  the  destructive  dis- 
tillation of  all  fatty  bodies  ;  but  it  has  been  shown  by  Redtenbacher  to 
arise  only  from  oleic  acid  ;  the  distilled  product  is  to  be  washed  with 
boiling  water,  which  dissolves  the  sebacic  acid  ;  on  the  addition  of  ace- 
tate of  lead,  a  white  precipitate  is  obtained,  which,  being  decomposed  by 
sulphuretted  hydrogen,  gives  sulphuret  of  lead,  while  the  pure  sebacic 
acid  dissolves,  and  may  be  obtained  crystallized  by  the  evaporation  and 
cooling  of  its  solution. 

The  crystallized  sebacic  acid  closely  resembles  the  benzoic  acid  in 
properties  and  appearance ;  its  solution  reddens  litmus ;  its  alkaline 
salts  are  very  soluble  ;  its  lead,  silver,  and  mercury  salts  are  insoluble 
in  water  ;  from  a  strong  solution  of  an  alkaline  sebacate,  the  acid  is  pre- 
cipitated in  voluminous  crystalline  flocks  on  the  addition  of  a  stronger 
acid.  When  completely  pure,  the  sebacic  acid  is  totally  without  odour, 
the  strong  smell  of  heated  oil  being  due  to  the  formation  of  a  totally  dif- 
ferent substance,  Acroleon,  The  dry  sebacic  acid  has  the  formula 
CjoH  O3 ;  when  crystallized  it  becomes  CioHgOa+Aq. 

Of  the  Action  of  Nitric  Acid  on  Stearic,  Margaric,  and  Oleic  Acids, 

By  the  gradual  oxidation  of  those  fatty  acids,  a  series  of  bodies  result,  which 
have  so  much  connexion  with  each  other  as  to  be  most  conveniently  studied  in  re- 
lation to  their  origin. 

A.  If  stearic  acid  be  digested  with  two  or  three  times  its  weight  of  common 
aquafortis  at  a  moderate  heat,  a  very  lively  action  commences  after  some  time,  and 
copious  red  fumes  are  given  off.  When  the  mixture  has  ceased  to  froth  up,  and 
the  action  of  the  acid  ceases,  the  only  product  forms  a  colourless  layer  on  the  sur- 
face of  the  acid  liquor,  and  is  found  to  be  pure  Margaric  Acid.  The  change  here  is 
evidently  a  simple  oxidation,  as  R2-I-O5  and  0.  give  2(R.-{-03),  as  described  in  p.  584 

If  the  fatty  acid  be  acted  on  by  successive  quantities  of  the  nitric  acid  until  it 
disappears,  the  watery  liquor  deposites,  on  cooling,  abundance  of  crystallized  Suc- 
cinic Acid,  and  the  mother  liquor  of  these  crystals  being  evaporated  to  one  half, 
forms,  on  cooling,  a  thick  mass  of  crystals,  which  may  be  washed  with  cold  water, 
and  being  purified  by  recrystallization,  are  found  to  be  identical  with  the  acid  form- 
ed by  the  action  of  nitric  acid  on  the  peculiar  woody  tissue  which  exists  in  cork, 
Suberine,  and  which  will  be  hereafter  described.  This  acid  is  termed  the  Suberic 
Acid ;  it  is  white,  inodorous,  and  of  a  feebly  acid  taste ;  easily  soluble  in  alcohol 
and  water  ;  the  crystals  melt  at  248°,  and  when  heated  more  strongly,  are  decom- 
posed in  great  part ;  it  precipitates  solution  of  acetate  of  lead  ;  its  alkaline  salts  are 
soluble  and  crystaUizable  ;  when  crystallized,  the  formula  of  the  acid  is  CsHeOg-j- 
Aq.  The  Suberic  Ether  was  prepared  as  described  above  for  the  oleic  ether ;  it 
is  liquid,  and  its  formula  is  C8H603-|-Ae.O.  By  the  distillation  of  the  suberate  of 
lime,  a  volatile  liquid,  Suberone,  is  obtained,  whose  formula  is  C7H6O. 

4E 


586  HMELIC,     ADIPIC,     LIPIC     ACIDS,     ETC. 

The  artificial  formation  of  the  succinic  and  suberic  acids  in  this  way  is  exceed- 
ingly curious  ;  but  Bromeis  and  Laurent,  to  whom  the  observation  is  due,  have  not 
been  able  to  trace  the  precise  reaction  in  which  they  originate. 

B.  The  action  of  nitric  acid  on  oleic  acid  is  much  more  violent  than  on  the  stearic 
acid.  Among  the  products  of  the  reaction  are  found  the  succinic  and  suberic  acids, 
but  in  addition,  four  other  acid  bodies,  of  which,  however,  a  very  slight  notice  will 
suffice. 

The  Pimelic  Acid  forms  white  crystalline  grains,  which  melt  at  273°,  and  sublime 
easily  in  brilliant  needles  ;  its  alkaline  salts  are  soluble,  but  its  earthy  and  metallic 
salts  insoluble  in  water  ;  the  formula  of  the  acid  is  C-jHeOs-^-Aq. 

Adipic  Acid  resembles  closely  the  former ;  it  dissolves  in  water,  alcohol,  and 
ether ;  melts  at  223°  ;  it  sublimes  in  very  beautiful  crystals  ;  its  formula  is  ChH* 
Or-j-a  Aq.,  it  being  a  bibasic  acid. 

The  Lipic  and  Azoleic  acids  are  still  less  important,  and  our  knowledge  of  their 
constitution  very  imperfect.  All  these  bodies  are  obtained  from  the  mother  liquors, 
from  which  the  succinic  and  suberic  acids  have  crystallized. 

The  most  important  products  of  the  action  of  nitric  acid  on  oleic  acid,  or  on  olein, 
are  Eldidine  and  the  Eididic  Acid ;  these  bodies  are  of  pharmaceutic  interest,  from 
their  constituting  the  Citrine  Ointment,  or  Unguentum  Nitratis  Hydrargyri  of  the 
Dublin  and  London  pharmacopoeias. 

Eldidine  is  prepared  by  the  action  of  nitric  acid,  or,  still  better,  of  the  red  fumes 
of  the  nitrous  acid  on  olein  ;  the  oil  gradually  becomes  thick,  and  finally  congeals 
into  a  butyraceous  mass  of  a  deep  yellow  colour.  By  digestion  with  warm  alcohol, 
a  deep  orange-red  oil  is  dissolved  out,  and  the  pure  elaidine  is  obtained  perfectly 
white ;  it  melts  at  97°,  is  insoluble  in  water,  and  but  sparingly  so  in  alcohol ;  it 
dissolves  readily  in  ether  ;  with  caustic  alkalies,  it  saponifies  completely,  glycerine 
being  set  free.  The  whole  action  of  the  nitric  acid  in  this  reaction  is  exerted  on 
the  oleic  acid,  and  the  elaidine  is  a  true  fat,  consisting  of  elaidic  acid  united  to 
glycerine. 

Elaidic  acid  may  be  prepared  by  saponifying  elaidine,  and  decomposing  the  alka- 
line elaidate  by  a  stronger  acid,  but  it  is  obtained  in  a  much  purer  form  by  passing 
nitrous  acid  fumes,  generated  by  heating  nitrate  of  lead  (p.  276)  into  pure  oleic  acid, 
prepared  from  oil  of  sweet  almonds  ;  after  some  time,  the  liquid  becomes  a  nearly 
solid  mass  of  crystalline  plates,  of  a  fine  yellow  colour  ;  this  mass  is  to  be  boiled  in 
water  to  remove  adhering  nitric  acid  ;  then  dissolved  in  boiling  alcohol,  and  allowed 
to  cool.  The  orange-red  oil  remains  in  solution,  while  the  elaidic  acid  crystallizes 
in  large,  briUiant,  white  rhombic  tables.  This  body,  when  pure,  fuses  at  113°  ;  it 
dissolves  readily  in  alcohol  and  in  ether  ;  these  solutions  redden  litmus  ;  when 
boiled  with  a  solution  of  carbonate  of  potash,  carbonic  acid  is  expelled,  and  elaidate 
of  potash  formed ;  its  earthy  and  metallic  salts  are  insoluble  in  water.  The  crys- 
tallized elaidic  acid  has  the  formula  C72H6605-|-2  Aq.  ;  it  is  a  bibasic  acid.  The 
Elaidate  of  Silver  is  hence  C72H6605+2Ag.O. ;  and  the  Elaidic  Ether,  which  is  a 
colourless  fluid  lighter  than  water,  consists  of  CvaHeeOs-j-H.O.  .  Ae.O. 

The  orange-red  oil,  which  is  formed  simultaneously  with  the  elaidic  acid,  has  not 
been,  as  yet,  accurately  examined,  and  hence  we  cannot  explain  by  precise  formulae 
the  mode  in  which  these  bodies  are  generated.  It  is  this  oil  which  gives  to  the 
Citrine  Ointment  its  characteristic  colour  and  smell ;  it  is  lighter  than  water,  and 
dissolves  in  alkaline  liquors,  but  does  not  form  true  soaps. 

In  the  formation  of  citrine  ointment,  the  conversion  of  the  olein  into  elaidine  is 
effected  by  the  nitrous  acid  which  the  solution  of  the  mercurial  salt  always  con- 
tains, it  being  formed  by  the  deoxidation  of  the  nitric  acid,  and  there  being  no  heat 
used  to  expel  it.  The  subnitrate  of  mercury  is  then  mechanically  mixed  with  the 
elaidine  and  with  the  yellow  oil.  Some  of  the  mercurial  salt  is  often  decomposed, 
however,  as  metallic  mercury  may  usually  be  detected  interspersed  through  tha 
ointment. 

Both  oleic  and  elaidic  acids  give  origin,  when  heated  with  fused  hydrate  of  pot- 
ash, to  a  peculiar  fatty  acjd,  discovered  by  Varrentrapp  ;  it  is  white,  solid,  and  crys- 
talline ;  melts  at  144°,  and  has  the  formula  C32H3o03-j-Aq.  There  is  formed,  at  the 
game  time,  a  large  quantity  of  acetic  acid.  Another  point  of  connexion  between 
the  oleic  and  elaidic  acids  is,  that  by  distillation  both  furnish  sebacic  acid. 

The  Acroleon,  to  which  is  due  the  exceedingly  sharp  and  disagreeable  smell  of 
highly  heated  oil  or  fat,  is  generated  by  the  decomposition  of  the  glycerine,  and  in 
Buch  exceedingly  small  quantity,  that  its  isolation  has  not  yet  been  successfully  at- 
tempted.   According  to  the  observation  of  Brandes,  it  is  a  colourless  oil,  of  sp.  gr 


ACTION    OF    SULPHURIC    ACID    ON    MARGARINE,   ETC.    587 

0  578,  which,  when  distilled  with  caustic  soda,  becomes  inodorous,  while  the  soda 
combines  with  a  fatty  acid  ;  no  analytical  investigation  of  it  has  been  as  yet  made. 

Action  of  Sulphuric  Acid  on  Margarine  and  Ole'ine. 

When  olein  is  mixed  with  oil  of  vitriol,  the  sulphuric  acid  combines  with  both 
the  glycerine  and  the  oleic  acid,  forming  sulphoglyceric  and  sulphole'ic  acids.  This 
last  is  soluble  in  water,  but  insoluble  in  dilute  sulphuric  acid  ;  and  hence,  by  adding 
water  gradually  to  the  mixture  of  oil  of  vitriol  and  oleine,  it  separates,  floating  as  a 
thick  sirup  on  the  surface,  while  the  sulphoglyceric  acid  and  the  excess  of  sulphuric 
acid  dissolve.  The  sulphole'ic  acid  thus  obtained  forms,  with  lime  and  barytes, 
soluble  salts,  which  are  analogous  to  the  sulphovinates  ;  when  its  solution  in  water 
is  heated,  it  is  decomposed,  sulphuric  acid  becoming  free,  and  the  oleic  acid  being 
converted  into  two  acids,  which  have  been  named  the  Metaole'ic  and  the  Hydroleic 
Acids. 

These  acids  are  both  liquid  like  oleic  acid  ;  they  are  principally  distinguished,  as 
to  properties,  by  the  sparing  solubihty  of  the  former  in  alcohol,  and  are  thus  separa- 
ted. The  constitution  of  these  bodies  had  been  examined  by  Fremy  at  a  time 
when  the  true  constitution  of  the  oleic  acid  had  not  been  established,  and  the  formu- 
lae he  assigned  to  them  are  not  now  admissible.  They  are  isomeric  with  each  other ; 
when  distilled,  they  produce  carbonic  acid,  and  two  volatile  liquids,  Olein  and  Elaen, 
which  are  isomeric  with  olefiant  gas.  From  the  circumstances  of  the  formation  of 
these  acids,  the  change  must  consist  in  the  fixation  of  the  elements  of  water,  as  no 
other  body  containing  carbon  is  produced  ;  but,  from  his  analysis,  the  anhydrous 
metaoleic  acid  has  evidently  the  same  composition  as  the  hydrated  oleic  acid,  and 
its  formula  is  therefore  C44H40O5  when  in  combination,  and  C44H41O6  when  free.  Its 
decomposition  by  heat  consists  in  the  separation  of  3C.O2,  and  C41H41  remaining, 
which  contains  the  elements  of  the  two  volatile  oily  liquids. 

With  margarine,  oil  of  vitriol  does  not  combine  directly ;  but  if  margarine  and 
olein  together,  as  they  are  in  olive  oil,  be  mixed  with  oil  of  vitriol,  union  occurs, 
and  a  sulphomargaric  acid  is  produced,  which,  being  treated  similarly  to  the  sulph- 
ole'ic acid,  gives  two  other  acids,  the  Metamargaric  and  Hydromargaric.  These 
are  soluble  in  alcohol,  from  which  they  crystallize  by  cold,  so  combined  as  to  pro- 
duce distinct  salts,  and  to  affect  all  the  characters  of  an  independent  acid,  called  by 
Fremy  the  Hydro  mar  gar  itic. 

If  the  mixed  solutions  of  sulphomargaric  and  sulphole'ic  acids  be  left  to  decom- 
pose without  heat,  in  place  of  being  boiled,  the  metamargaric  and  metaoleic  acids 
separate  and  float  on  the  top,  but  the  hydromargaric  and  hydroleic  acids  remain 
dissolved,  and  separate  only  by  bringing  the  solution  to  boil.  Each  of  the  products 
thus  obtained  is  to  be  dissolved  in  alcohol,  and  the  modified  margaric  acids  crystal- 
lize on  cooling,  while  the  modified  oleic  acids  remain  dissolved.  The  metamarga- 
ric acid  is  polymeric  with  the  margaric  acid  ;  its  formula  is  C68H6606-[-2  Aq.,  but 
the  hydromargaric  acid  contains  the  elements  of  four  atoms  of  water  more,  its 
formula  being  CesHvoOio-}-^  Aq. 

Olein  of  the  Drying  Oils, 

The  oils  which  possess  the  property  of  rapidly  absorbing  oxygen  and  evolving 
carbonic  acid,  thereby  being  changed  into  a  kind  of  transparent  resinous  varnish, 
consist  of  glycerine  united  to  a  liquid  acid,  quite  distinct  from  the  ordinary  oleic 
acid ;  treated  with  nitric  acid,  it  yields  first  a  resinous  substance,  and  then  oxalic 
acid.  The  drying  properties  of  these  oils  is  known  to  be  much  increased  by  boiling 
on  litharge,  of  which  a  quantity  dissolves  ;  in  this  case,  however,  Liebig  has  shown 
that  no  saponification  occurs  ;  the  litharge  serving  only  to  combine  with,  and  coag- 
ulate a  quantity  of  vegetable  mucus,  which,  being  diffused  through  the  oil,  prevented 
its  acting  as  rapidly  on  the  air  as  it  does  when  pure. 

Of  Cocoa-tallow  and  Cocoa.stearic  Acid. 

The  albumen  of  the  cocoa-nut  contains  a  solid  fat,  which  is  extracted  from  it, 
and  imported  largely  into  these  countries,  to  be  used  in  the  manufacture  of  candles. 
It  is  a  mixture  of  ordinary  olein  with  a  stearine,  which  contains  a  peculiar  acid. 
The  olein  and  stearine  are  separated  by  pressure  or  by  ether,  or  by  solution  in  boil- 
ing alcohol,  from  which  the  stearine  crystallizes  on  cooling,  exactly  as  described  for 
ordinary  stearine. 

The  cocoa-stearine  is  white  and  crystalline  ;  its  specific  gravity  is  0925  ;  insolu- 


588  PALMITINE,    PALMITIC     ACID,    ETC. 

ble  in  water ;  it  dissolves  but  sparingly  in  alcohol,  except  when  boiling  ;  it  is  moro 
soluble  in  ether  ;  it  melts  at  77°.  The  products  of  its  decomposition  by  heat  have 
not  been  well  examined.  With  caustic  alkalies  it  forms  soaps,  from  which,  by  a 
stronger  acid,  the  cocoa-stearic  acid  is  separated. 

This  acid,  purified  by  repeated  crystallizations  from  alcohol,  is  brilliant  white  ;  it 
fuses  at  95°,  and  cannot  be  distilled  without  total  decomposition.  Its  formula  was 
found  by  Bromeis  to  be  C27H2603-[-Aq. ;  its  alkaline  salts  are  soluble,  but  the  earthy 
and  metallic  salts  are  insoluble  in  water.  By  the  process  described  for  oleic  ether, 
the  cocoa-stearic  ether  was  prepared  by  Bromeis  ;  it  is  a  clear  oil,  lighter  than  wa 
ter ;  its  formula  is  C27H2603-j-Ae.O. 

Palm  Oil  and  Palmitic  Acid, 

This  solid  oil,  which  is  now  extensively  employed  in  the  manufacture  of  yellovr 
soap,  is  prepared  in  Africa,  by  pressing  and  boiling  the  fruits  of  the  cocos  butyracea 
or  of  the  avoira  elais ;  it  is  of  the  consistence  of  butter,  reddish-yellow  colour,  and 
an  aromatic  odour.  When  kept,  it  acquires  a  rancid  smell,  and  becomes  white ; 
the  colour  results  from  a  small  quantity  of  a  substance  which  may  be  decomposed, 
and  the  palm  oil  bleached  by  chlorine  or  any  oxidizing  agents.  Besides  ordinary 
oleine,  this  oil  contains  a  peculiar  stearine,  Palmitine,  which  has  been  accurately 
examined  by  Fremy  and  Stenhouse. 

Pure  Palmitine  melts  at  118°,  and  is  crystalline.  It  is  insoluble  in  water,  very 
sparingly  soluble  even  in  boiling  absolute  alcohol,  but  abundantly  soluble  in  ether. 
It  is  quite  neutral ;  when  saponified  by  potash,  and  the  soap  decomposed  by  an 
acid,  palmitic  acid  is  set  free.  The  palm  oil  of  commerce  usually  contains  a  large 
quantity  of  free  palmitic  acid,  and  hence  is  more  easily  saponified  than  any  other 
fat ;  it  also  contains  free  glycerine,  so  that  the  palmitine  would  appear  to  undergo 
a  spontaneous  decomposition. 

Palmitic  Acid  melts  at  140° ;  it  dissolves  in  hot  alcohol,  and  crystallizes  therefrom 
by  cooling.  Its  formula  in  crystals  is  C64H6206-t-2H.O. ;  it  is  a  bibasic  acid ;  its 
silver  salt  is  C64H6206-|-2Ag.O.  The  Palmitic  Ether,  which  may  be  prepared  by 
heating  palmitic  acid  with  alcohol  and  oil  of  vitriol,  is  solid,  and  crystallizes  in  fine 
prisms,  which  melt  at  70°,  and  have  the  formula  C64H6206-|-2Ae.O.  By  distilla- 
tion, the  palmitic  acid  is  not  altered ;  by  the  action  of  chlorine,  hydrogen  is  removed 
from  it,  and  an  acid  containing  chlorine  produced,  the  formula  of  which  appears  to 
be  C64H54  .  ClgOe. 

The  constitution  of  palmitine  was  found  by  Stenhouse  to  be  expressed  by  the 
formula  C^oHeeOg,  from  which  should  follow,  that  the  substance  united  with  the  pal- 
mitic acid  is  formed  of  C6H4O2,  and  hence  diflfers  from  common  glycerine,  CeHrOs, 
in  having  lost  the  elements  of  three  atoms  of  water.  This  would  be  a  very  impor- 
tant fact  to  reinvestigate. 

Nutmeg  Butter.     Myristic  Acid. 

This  substance  is  a  mixture  of  an  aromatic  volatile  oil,  with  three  fats,  of  which 
two  are  easily  soluble  in  alcohol,  and  are  thus  simply  separated  from  the  third, 
which  has  been  termed  by  Playfair  Myristicine.  Of  the  fats  soluble  in  alcohol,  one 
is  liquid  and  the  other  solid  ;  but  we  do  not  know  whether  they  are  peculiar,  as  the 
analyses  of  Playfair  have  been  confined  to  the  third. 

Pure  myristicine  is  obtained  by  crystaUization  from  its  ethereal  solution ;  it  has 
a  silky  lustre,  and  melts  at  88°.  When  saponified,  it  yields  glycerine  and  Myristi* 
Acid.  This  substance  is  snow-white  and  crystalline,  easily  soluble  in  hot  alcohol 
and  then  reddening  litmus ;  it  melts  at  120°  ;  its  composition  is  expressed  by  the 
formula  C28H2703-|-Aq. ;  its  salts  are  very  well  characterized  and  crystallizable. 
The  Myristic  Ether  is  analogous  in  constitution  to  the  stearic  ether  (583),  consist' 
ing  of 

Two  atoms  of  myristic  acid,  =C56H5406,  i 

One  atom  of  ether,  =C4H50.,    >  One  atom  of  myristic  ether,  CeoHeoOg. 

One  atom  of  water,  =H.O.,        ) 

The  myristicine  was  found  by  Playfair  to  have  the  formula  CusHnsOis,  consis^ 
ing  of 

Four  atoms  of  myristic  acid,  =Ci,2Hio80i2, ) 

One  atom  of  dry  glycerine,    =C6H402,       >  CnsHnsOjs. 

One  atom  of  water,  =H.O.,  J 

Bv  distilling  myristicine,  much  acroleon  is  generated,  but  no  sebacic  acid. 


BUTYRINE,     CAPROINE,     ETC.  589 

r)rdinary  Butter.     Butyric,  Capro'ic,  and  Capric  Acids, 

iiutief  is  a  mixture  of  six  different  fats,  viz.,  common  stearine,  margarine,  and 
wleine,  with  butyrine,  caproine,  and  caprine ;  by  melting  the  butter,  and  keeping  it  for 
some  days  at  a  temperature  of  68°,  the  stearine  and  margarine  crystaUize,  while 
the  others  remain  liquid.  By  means  of  alcohol,  the  oleine  is  then  separated  from 
the  other  fats,  which  are  more  easily  soluble  in  that  menstruum  ;  their  farther  pu- 
rification depends  on  successive  solutions  in  alcohol,  but  none  of  them  can  be  con- 
sidered as  having  been  obtained  completely  pure. 

Butyrine  is  a  colourless  oil,  with  the  odour  of  heated  butter.  It  solidifies  at  32°  ; 
with  alkalies,  it  gives  a  soap,  and  sets  glycerine  free.  Its  elementary  composition 
is  not  known. 

Caproine  and  Caprine  cannot  be  obtained  sufficiently  free  from  butyrine,  or  from 
each  other,  to  be  described. 

When  butter  is  saponified,  and  the  soap  decomposed  by  tartaric  acid,  stearic, 
margaric,  and  oleic  acids  separate,  while  the  other  acids  remain  dissolved.  On  dis- 
tilling this  liquor,  the  butyric,  capric,  and  caproic  acids  pass  over  along  with  the 
^ater,  and,  being  neutralized  by  barytes,  the  three  barytic  salts  are  separated  by 
repeated  crystallizations.  Of  these  acids,  the  history  of  the  Butyric  Acid  is  most 
complete.  It  is  a  clear,  oily  liquid,  of  a  penetrating,  sour  smell  of  rancid  butter ; 
tastes  pungent  and  acid,  and  leaves  a  white  mark  on  the  tongue.  Its  specific 
gravity  is  0976 ;  its  boiling  point  is  above  212°  ;  it  burns  with  a  brilliant  white 
flame,  and  is  abundantly  soluble  in  water,  alcohol,  and  ether.  Its  formula  is 
CTHeOs-j-Aq.  ;  when  distilled  with  lime,  it  gives  a  neutral  volatile  liquid,  Butyrone, 
whose  formula  is  CeHeO.  The  Caproic  Acid  agrees  in  properties  closely  with  the 
butyric  acid,  but  has  a  characteristic  odour  of  sweat ;  its  formula  is  Ci2H903=:Aq. 
The  Capric  Acid  crystallizes  in  fine  needles,  which  melt  at  66°,  and  have  the  for- 
mula CisHuOa-j-Aq. 

Of  Fish  Oils,  Delphinine,  and  Delphinic  Acid. 

These  oils  are  generally  composed  of  ordinary  margarine,  stearine,  and  oleine ; 
but  some,  as  whale  oil  and  dolphin  oil,  contain  a  peculiar  fat,  Delphinine,  which 
yields  Delphinic  Acid.  From  the  fish  oil  the  delphinine  is  extracted  by  cold  alcohol, 
which  dissolves  it  more  readily  than  the  other  oilg;  it  is  liquid,  of  specific  gravity 
0954 ;  it  is  not  acid,  but  becomes  so  by  exposure  to  the  air  ;  it  saponifies  readily. 
From  the  soap,  the  delphinic  acid  is  separated  by  tartaric  acid,  and  may  be  obtained 
pure  by  distillation.  It  is  a  thin  oil,  of  specific  gravity  0-932 ;  it  boils  above  212^*, 
and  distils  unchanged ;  it  has  a  peculiar  aromatic  smell ;  tastes  acid,  and  reddens 
litmus  strongly ;  it  dissolves  in  twenty  parts  of  water ;  its  formula  is  CioHgOs-j-Aq., 
and  when  distilled  with  lime,  it  gives  a  volatile  neutral  liquid,  Delphinon,  C9H9O. 

The  delphinic  acid  has  been  found  in  the  berries  of  the  viburnum  opulus,  and  its 
composition  being  the  same,  and  its  properties  very  closely  resembling  those  of  the 
valerianic  acid,  I  think  it  very  likely  that  a  re-examination  of  it  would  demonstrate 
its  identity  with  that  remarkable  vegetable  acid. 

Of  Castor  Oil  and  its  Products. 

The  oil  of  the  ricinus  communis  (castor  oil)  is,  according  to  Lecanu  and  Bussy, 
a  mixture  of  three  fats,  ricino-stearine,  ricino-oleine,  and  ricine,  which  are  all  easily 
soluble  in  alcohol.  Like  the  fats  of  butter,  they  can  be  but  imperfectly  separated  ; 
but,  when  saponified,  they  yield  acids,  which  can  be  more  accurately  examined : 
the  soap,  being  decomposed  by  muriatic  acid,  yields  an  oil,  from  which,  by  cooling, 
the  Ricino-stearic  Acid  crystallizes,  and  the  remaining  oil,  when  distilled,  separates 
into  the  Ricinic  Acid,  which  passes  over,  and  the  Ricin-oleic  Acid,  which  is  not  vol- 
atile. 

Purified  by  recrystallization  from  alcohol,  the  ricino-stearic  acid  forms  pearly 
scales,  which  are  easily  soluble  in  alcohol,  redden  litmus,  and  do  not  melt  below 
266°.  The  ricin-oleic  acid  freezes  a  few  degrees  below  32°.  The  ricinic  acid  is 
solid  and  crystalline,  melts  at  71°,  and  distils  unchanged  at  a  temperature  but  little 
higher. 

When  castor  oil  is  acted  on  by  nitrous  acid,  it  is  converted  into  a  solid  sub- 
stance, termed  by  Boudet  Palmine ;  it  is  white,  of  a  waxy  appearance,  and  melts  at 
1510 ;  it  is  easily  soluble  in  alcohol  and  ether ;  with  alkalies,  it  yields  glycerine 
and  Palmic  Acid.  We  do  not  possess  any  knowledge  of  the  elementary  composi- 
tion of  these  bodies. 


590  MANUFACTURE     OP     SOAP. 

The  products  of  the  complete  oxidation  ot  castor  oil  by  nitric  acid  have  been  ac- 
curately examined  by  Mr.  Tilly.  The  action  is  violent,  and  much  nitrous  acid 
fumes  are  given  off.  Besides  suberic  and  lipinic  acids,  a  peculiar  fatty  acid  is 
formed,  which  is  colourless,  of  an  agreeable  smell,  and  a  sweet,  stimulating  taste  ; 
it  boils  at  300°,  but  cannot  be  distilled  without  being  in  great  part  decomposed. 
Its  formula  was  found  to  be  CuHiaOa-l-M- ;  he  formed  the  ether  of  this  acid  in  the 
way  described  for  oleYc  ether,  and  ascertained  its  formula  to  be  CuHiaOa-j-Ae.  0.  This 
body  is  termed  the  Peroenanthic  Acid,  as  it  contains  the  same  carbon  and  hydrogen 
as  the  oenanthic  acid  which  exists  in  wine,  as  described  in  page  567,  but  combined 
with  an  atom  more  of  oxygen*. 

Oil  of  Tiglium,     Crotonine.     Crotonic  Acid. 
The  experiments  that  have  been  made  on  this  oil  have  not  given  very  satisfac- 
tory results :  by  saponification,  it  yields  an  acid  which  is  exceedingly  volatile  ;  but 
whether  the  active  properties  of  the  oil  reside  in  this  crotonic  acid  is  not  estab- 
lished, nor  have  any  analytical  results  been  obtained  as  to  its  constitution. 

Of  the  Manufacture  of  Soaps  and  Plasters, 

Although  the  general  principles  of  the  constitution  of  soaps  have  been 
frequently  alluded  to  in  the  description  of  individual  fatty  substances,  and 
a  detailed  account  of  their  manufacture  would  be  out  of  place  in  the  pres- 
ent work,  yet  it  may  not  be  uninteresting  to  notice  briefly  some  cir- 
cumstances  of  the  processes  employed,  which  could  not  be  deduced  from 
the  mere  theory  of  their  nature,  and  yet  are  essential  to  practical  success. 

There  are  found  in  commerce  three  varieties  of  soap  :  1st,  hard  white 
soap,  which  is  made  from  tallow  and  caustic  soda  ;  2ol,  hard  yellow  soap, 
which  is  made  from  soda  with  tallow,  palm  oil,  and  resin ;  3d,  soft  soap, 
in  which  the  alkali  is  potash,  combined  with  whale  or  seal  oil,  and  some 
tallow.  The  difference  of  consistence  depends  principally  upon  the  af- 
kali ;  as  the  fatty  salts  of  soda  unite  with  water  to  form  true  hydrates, 
which  are  completely  solid,  while  the  potash  salts  absorb  water,  and  form 
a  semitransparent  gelatinous  mass,  such  as  is  the  ordinary  soft  soap. 

For  the  preparation  of  the  hard  white  soap,  a  solution  of  caustic  soda 
is  prepared,  of  specific  gravity  1*050,  by  decomposing  soda-ash  by  the 
proper  quantity  of  Hme  ;  the  soda-ley  being  brought  to  boil,  the  tallow 
is  added  in  small  portions  at  a  time,  until  the  free  alkali  has  been  all 
combined  with  fatty  acids,  and  the  ley  will  saponify  no  more.  The  li- 
quor contains  then  free  glycerine,  and  the  fatty  salts  of  soda,  all  dissolved 
together  in  the  water ;  and  as  the  soap  scarcely  crystallizes,  a  peculiar 
method  is  necessary  to  separate  it  from  the  solution.  This  is  founded 
on  the  fact  that  soap  is  insoluble  in  a  solution  of  common  salt.  If  to  a 
solution  of  soap  in  water,  as  much  common  salt  be  added  as  the  water 
can  dissolve,  the  soap  is  separated,  and  floats  on  the  surface  of  the  li- 
quor completely  deprived  of  water.  But  this  is  not  the  state  in  which 
the  manufacturer  wishes  it  to  be.  Hence  the  salt  is  added  but  gradually 
to  the  soap. ley,  and  the  water  then  dividing  itself  between  the  salt  and 
the  soap,  a  point  is  obtained  at  which  the  soap  is  in  its  proper  hyd  rated 
condition,  and  this  being  recognised  by  the  appearance  of  the  boil  and 
the  texture  of  the  layer  of  soap,  the  latter  is  run  into  wooden  boxes,  where 
it  congeals,  and  is  then  cut  by  a  wire  into  the  forms  it  has  in  commerce. 

The  hard  white  soap  thus  made  generally  contains  from  forty  to  fifty 
per  cent,  of  water.  When  very  hard  it  still  retains  above  thirty,  and 
may  hold  seventy  per  cent,  without  being  very  soft. 

The  formation  of  the  Yellow,  or  Resin  Soap,  depends  on  the  direct 
combination  of  an  acid  resin  (colophony,  p.  578)  with  soda.     In  this 


SPERMACET  I. E  T  H  A  L.  591 

case  no  glycerine  is  set  free,  as  there  is  no  proper  saponification.  A 
mere  compound  of  resin  and  soda  would  be,  however,  too  soft,  and  also 
act  too  powerfully  on  clothes  ;  and  hence  there  is  always  a  quantity  of 
fat  added,  generally  tallow,  and  some  palm  oil,  which  brightens  the  col- 
our, and  masks  the  disagreeable  odour  of  the  resin.  A  good  soap  should 
contain  two  parts  of  fatty  matter  to  one  of  resin. 

The  Soft  Soap  is  manufactured  by  heating  the  oils  in  shallow  pans, 
and  gradually  adding  a  strong  solution  of  caustic  potash,  boiling  and  con- 
tinually agitating  the  mass  until  the  milkiness  produced  by  the  oil  van- 
ishes,  the  mass  becomes  transparent,  and  the  froth  subsides.  As  this 
soap  cannot  be  separated  from  the  liquor  by  the  addition  of  common  salt, 
which  would  decompose  it,  forming  a  soda-soap  and  chloride  of  potassi- 
um, the  hquor  is  evaporated  until  the  operator  recognises  that  it  has  at- 
tained the  proper  strength,  and  it  is  then  cooled  as  rapidly  as  possible. 
The  glycerine  of  the  oils  exists,  therefore,  mixed  through  the  substance 
of  the  soap.  To  give  it  greater  consistence,  some  tallow  is  generally 
employed  ;  and  the  stearate  of  potash  crystallizing  gradually,  forms  the 
white  points  which  are  seen  in  most  specimens  of  soft  soap. 

Plasters  are  metallic  soaps.  Of  these,  the  only  one  of  pharmaceutic 
importance  is  the  Litharge  Plaster,  prepared  by  boiling  litharge,  olive  oil, 
and  water  together ;  oleate  and  margarate  of  lead  are  formed,  and  float 
upon  the  surface  ;  when  the  mass  has  obtained  the  proper  consistence, 
it  is  removed,  and  formed  into  rolls  for  use.  The  watery  solution  con- 
tains glycerine  and  a  large  quantity  of  oxide  of  lead  dissolved.  If  lith- 
arge  plaster  be  digested  in  ether,  oleate  of  lead  dissolves,  and  the  mar- 
garate of  lead  is  left  behind. 

Of  Spermaceti,  Ethal,  and  the  derived  Bodies. 

Spermaceti  exists  in  the  cavities  of  the  head  of  the  physeter  macro- 
cephalus,  and  some  allied  species  of  whales,  dissolved  in  the  spermaceti 
oil,  from  which  it  separates  by  crystallization  after  the  death  of  the  ani- 
mal. To  obtain  it  pure,  it  is  to  be  crystallized  repeatedly  from  its  alco- 
holic solution  by  cooling  ;  it  is  a  remarkably  beautiful  crystalline  fat, 
melting  at  120°,  and  volatilizing  at  680°  without  change,  if  the  air  be 
excluded.  By  boiling  with  very  strong  alkaline  solutions,  it  gradually 
saponifies,  a  margarate  and  an  oleate  being  formed  ;  but,  in  place  of 
glycerine,  a  peculiar  base,  which  is  termed  Ethal,  being  set  free.  To 
obtain  it  pure,  spermaceti  is  saponified  by  being  fused  with  half  its 
weight  of  potash  ;  the  resulting  mass  being  digested  with  water  and  mu- 
riatic  acid,  the  oily  acids  and  the  ethal  separate  from  the  liquor  and  float 
upon  the  surface.  Being  then  mixed  with  lime,  which  combines  with  the 
oily  acids,  and  boiled  in  absolute  alcohol,  the  ethal  dissolves,  and  crystal- 
lizes out  on  cooling. 

It  is  a  solid  crystalline  white  substance,  destitute  of  taste  or  smell ; 
neutral  to  test  paper  ;  it  melts  at  119°,  and  volatilizes  rapidly  at  250°  ; 
it  is  insoluble  in  water  ;  its  formula  is  C32H34O2,  or  CaaHgaO.  +  Aq.  The 
spermaceti  itself  consists  of 

2  atoms  of  margaric  acid,  =C68H6606    )  r>,    tt    r»  •    i    * 
1  atom  of  oleic  acid,           =C,,uZo:  i  C208H207p,6,  one  equivalent 

3  atoms  of  ethal,  =C69H,a206,  S  ^^  spermaceti. 

The  ethal  is  remarkable  for  its  analogy,  in  composition  and  properties, 
to  the  bodies  of  the  alcohol  group  ;  like  them,  it  may  be  looked  upon  as 


592    WAX,    CERINE,    MYRICINE,    AND     TARTARIC    ACID. 

formed  of  water  united  to  a  carbohydrogen,  isomeric  with  defiant  gas, 
and  by  distilling  ethal  with  glacial  phosphoric  acid,  this  body  is  actually 
obtained,  and  has  been  termed  Cetene,  It  is  an  oily  liquid,  -colourless, 
soluble  in  alcohol  and  ether  ;  it  boils  at  527°.  From  its  reactions  and 
the  specific  gravity  of  its  vapour,  7846,  it  results  that  its  formula  is 

If  ether  be  heated  with  perchloride  of  phosphorus,  a  heavy  liquid  is 
obtained,  having  the  formula  C32H33CI. ;  and  by  fusing  ethal  with  potassi- 
urn,  hydrogen  is  evolved,  and  a  white  solid  substance  formed,  consisting 
of  C32H33O.  +  K.O.,  which,  with  water,  gives  hydrate  of  potash  and  ethal. 
With  sulphuric  acid  ethal  forms  sulphoethalic  acid,  which  resembles  the 
sulphovinic  acid,  and  has  the  formula  C32H33O.  .  S.Og-f-S.Oa  .  H.O. 
Farther,  if  the  ethal  be  heated  with  potash,  hydrogen  gas  is  given  oflT, 
and  an  acid  formed,  the  formula  of  which  is  CagHgiOg+Aq. :  it  is  term- 
ed the  Ethalic  Acid. 

From  this  analogy  of  ethal  to  wine-alcohol,  a  compound  radical,  Cetyl, 
similar  to  ethyl,  may  be  assumed  to  exist  in  these  combinations,  and  its 
formula  be  written  C32H33  or  Ct.  Ethal  is  then  Ct.O.-j-Aq.  (See  p. 
566.) 

Wax. — Ordinary  beeswax  is  a  mixture  of  two  substances,  which  are 
separated  by  boiling  alcohol.  Cerine  dissolves ;  it  is  quite  white ;  its 
specific  gravity  is  0*969  ;  it  is  less  fusible  than  wax  ;  it  does  not  combine 
with  bases  ;  its  formula  is  C20H20O2.  The  substance  insoluble  in  alcohol 
is  Myricine,  which  melts  at  95°  ;  its  formula  is  C20H20O.  In  yellow  wax  a 
colouring  matter  is  present  which  has  not  been  examined.  When  wax 
is  bleached  by  nitric  acid,  oxygen  is  absorbed,  and  a  peculiar  substance 
formed,  Ceraic  Acid,  which  has  the  formula  C20H20O3.  All  these  bodies 
are  probably  derived  from  oils,  isomeric  with  otto  of  roses,  which  exist 
in  the  flowers  of  odoriferous  plants. 

When  cerin  is  boiled  with  solution  of  potash,  a  soap  is  formed,  and 
from  this  a  peculiar  waxy  substance  (Cerdine)  is  obtained,  as  ethal  is  from 
spermaceti :  its  properties  are  but  very  little  known ;  from  an  analysis 
by  Ettling,  its  formula  would  appear  to  be  CigHigOy. 


CHAPTER  XXIV. 

OF  THE  ORGANIC  ACIDS  WHICH  PRE-EXIST  IN  PLANTS,  AND  DO  NOT  BELONS 
TO  ANY  ESTABLISHED  SERIES. 

Tartaric  Acid. — C8H40,o+2Aq. 
This  important  acid  exists  in  most  kinds  of  fruit,  occasionally  free,  but 
more  usually  combined  with  potash,  forming  cream  of  tartar,  or  as  tar- 
trate of  lime.  For  the  purposes  of  commerce,  it  is  almost  exclusively 
prepared  from  the  bitartrate  of  potash.  This  salt  exists  abundantly  in 
grape-juice,  and  being  but  very  slightly  soluble  in  spirituous  liquors,  it 
gradually  separates  as  the  alcoholic  fermentation  proceeds,  and  collects 
in  irregularly  crystallized  layers  on  the  insides  of  the  casks  in  which  the 
wine  is  made.     It  is  purified,  as  will  be  elsewhere  described. 


TARTARIC     ACID. CREAM     OF     TARTAR.  593 

When  one  part  of  carbonate  of  lime  is  added  to  a  solution  of  four  parts 
of  bitartrate  of  potash,  one  half  of  the  tartaric  acid  combines  with  the 
lime,  carbonic  acid  being  expelled  with  effervescence.  Tartrate  of  lime 
precipitates  as  a  white  powder,  and  neutral  tartrate  of  potash  remainvS 
dissolved.  By  the  addition  of  chloride  of  calcium  to  the  liquor,  this  por- 
tion, also,  of  tartaric  acid  is  thrown  down,  and  chloride  of  potassium  is 
formed.  The  whole  quantity  of  tartrate  of  lime  being  then  collected  and 
washed,  it  is  to  be  digested  with  a  quantity  of  oil  of  vitriol,  half  the 
weight  of  the  cream  of  tartar  employed,  and  diluted  with  four  parts  of 
water ;  sulphate  of  lime  is  formed,  and  tartaric  acid  set  free.  The  mix- 
ture, having  been  boiled  for  a  short  time,  is  to  be  strained,  and  the  liquor 
evaporated  gently  to  a  pellicle ;  the  tartaric  acid  then  crystallizes  on 
cooling. 

The  tartaric  acid  forms  colourless  oblique  rhombic  prisms,  generally 
tabular,  as  in  the  figure,  where  i,  w,  u  are  primary,  and 
a,  c,  m  secondary  faces  ;  it  is  permanent  in  the  air,  and 
dissolves  readily  in  half  its  weight  of  water ;  it  is  also  /^ 
easily  soluble  in  alcohol;  its  taste  and  reaction  are  n^  u  ^)w{^ 
strongly  acid.  When  heated,  it  abandons  water,  and 
forms  two  acids  which  will  be  again  noticed.  When  a  solution  of  it  is 
long  exposed  to  the  air,  it  absorbs  oxygen,  and  forms  carbonic  and  acetic 
acids.  This  effect  may  be  instantly  produced  by  boiling  it  with  an  ex- 
cess of  oxide  of  silver,  metallic  silver  being  set  free. 

Tartaric  acid  is  known  by  its  not  being  volatile,  and  by  leaving  a  co- 
pious coaly  residue  when  heated.  If  it  be  fused  with  potash,  it  is  de- 
composed, acetic  and  oxalic  acids  bemg  produced  (p.  475) ;  with  other 
oxidizing  agents,  as  black  oxide  of  manganese  and  sulphuric  acid,  it  gives 
carbonic  and  formic  acids.  A  solution  of  tartaric  acid  precipitates  lime- 
water,  but  the  precipitate  is  redissolved  by  an  excess  of  acid  or  by  so- 
lution of  sal  ammoniac.  The  soluble  neutral  tartrates  give  white  pre- 
cipitates, which  are  not  crystalline,  with  the  neutral  salts  of  lead,  lime, 
and  silver,  which  all  redissolve  in  an  excess  of  acid. 

The  tartaric  acid  is  bibasic,  its  formula  being  C8H40io+2  Aq. ;  sev 
eral  of  its  salts  are  of  considerable  importance. 

Bitartrate  of  Potash,     Cream  of  Tartar, — C8H,o04-{-K.O.Aq. 

This  salt,  just  now  noticed  as  being  deposited  from  grape-juice,  accord- 
ing as  alcohol  is  formed,  is  sent  into  commerce  under  the  name  of  Argol, 
which  is  red  or  white,  according  to  the  kind  of  wine  it  was  deposited 
from.  This  is  dissolved  in  boiling  water,  and  mixed  with  some  pipe- 
clay, which,  combining  with  the  colouring  matter  of  the  grape,  renders  it 
insoluble  ;  the  clear  liquor  is  then  allowed  to  cool  slowly,  and  the  cream 
of  tartar  is  deposited  in  irregular  crystals  on  the  sides  of  the  vessel,  still 
containing  a  small  quantity  of  tartrate  of  lime.  It  crystallizes  in  right 
rhombic  prisms,  as  in  the  figure,  jp,  u,  u  being  primary, 
and  a,  a\  i,  m  secondary  planes.  It  is  but  very  sparingly 
soluble  in  cold  water,  requiring  80  parts  at  60°,  and  7 
parts  at  212°  ;  hence  an  excess  of  tartaric  acid  produces 
a  crystalline  precipitate  in  solutions  of  potash  which  are 
not  very  dilute.  By  calcining  cream  of  tartar  either  alone  or  with  nitre, 
the  black  or  white  fluxes  employed  in  metallurgy  are  formed  (p.  334).   Its 

4F 


594 


TARTRATES     OF     POTASH,    AMxMONiA,    ETC. 


calcination  furnishes  also  the  purest  source  of  carbonate  of  potash,  which 
hence  derives  its  name  of  Salt  of  Tartar  (p.  487). 

Neutral  Tartrate  of  Potash.  Soluble  Tartar.— C^YiJd.^-irK.O.  .  K.O. 
This  salt  is  formed  by  adding  cream  of  tartar  to  a  hot  solution  of  car- 
bonate of  potash,  until  this  be  completely  neutralized.  It  crystallizea 
with  difficulty  in  right  rhombic  prisms,  which,  when  pure,  are  not  deli- 
quescent. 100  parts  of  water  dissolve  130  parts  of  it  at  60°,  and  268 
parts  at  212°.  Any  acid  added  to  its  solution  takes  half  the  potash,  and 
precipitates  cream  of  tartar. 

The  Tartrates  of  Ammonia  resemble  closely  those  of  pota§h.  The 
neutral  Tartrate  of  Soda  crystallizes  in  large  rhombic  prisms  like  nitre  ; 
it  is  very  soluble  in  water;  its  formula  is  C8H40io+Na.O.  .  Na.O. 
,  ,  ..  +4Aq. 

i^L^^  Tartrate  of  Potash  and  Soda.  Rochelle  Salt,  CsH^Piq-^- 
K.O.  .  Na.O.  +  lO  Aq.,  is  prepared  by  neutralizing  a  hot 
solution  of  carbonate  of  soda  with  cream  of  tartar  :  by  evap- 
'p  oration  and  cooling  it  forms  large  prismatic  crystals,  with 
many  sides,  of  the  right  rhombic  system,  p,  u,  u  being 
X[~\^  primary,  and  ^,  i,  t,  e,  e  being  secondary  faces.  These 
^v•T■'"v-.-— ^  crystals  are  remarkable  for  being  often  but  half  formed,  so 
as  to  present  the  aspect  represented  in  the  lower  figure. 
Its  taste  is  mildly  saline,  and  not  very  disagreeable,  whence 
its  popularity  as  a  medicine.  It  is  permanent  in  the  air  ex- 
cept it  be  very  dry,  when  it  effloresces  slightly  at  the  sur- 
face;  it  dissolves  in  two  parts  of  cold  water. 
The  Tartrate  of  Lime  is  very  sparingly  soluble  in  water,  and  is  precipitated  as  a 
white  powder,  when  solutions  of  a  neutral  tartrate  and  of  a  salt  of  lime  are  mixed. 
It  dissolves  in  an  excess  of  acid ;  and  if  this  solution  be  neutralized,  it  is  deposited 
m  small  octohedral  crystals,  which  have  the  formula  C8H40io-}-Ca.O.  .  Ca.O.-f  8 
Aq.  Nolner  has  asserted  that,  when  tartrate  of  lime  is  mixed  with  yeast,  a  ferment- 
ation sets  in,  by  which  a  new  acid,  Pseudo-acetic  Acid,  is  produced ;  this  requires, 
however,  confirmation. 

Prototartrate  of  Iron,  C8H40io-f2Fe.O.,  is  a  white  powder,  very  sparingly  solu- 
ble in  water ;  it  is  formed  in  minute  crystals  when  hot  solutions  of  protosulphate  of 
iron  and  of  cream  of  tartar  are  mixed  together.  The  Prototartrate  of  Iron  and  Pot- 
ash, C8H40io-4-Fe.O.  .  K.O.,  is  formed  by  digesting  cream  of  tartar  and  water  with 
metallic  iron.  Hydrogen  gas  is  evolved,  and  a  white,  sparingly  soluble  salt  is  ob- 
tained, which,  when  exposed  to  the  air,  rapidly  absorbs  oxygen,  and  becomes  green- 
ish brown  or  black.  In  this  state  it  contains  magnetic  oxide  of  iron,  and  is  much 
more  soluble.  Pertartrate  of  Iron,  formed  by  dissolving  the  freshly  precipitated  red 
oxide  of  iron  in  a  solution  of  tartaric  acid,  gives  by  evaporation  a  brown  jelly.  If 
the  red  oxide  of  iron  be  boiled  with  a  solution  of  cream  of  tartar,  it  dissolves  abun- 
dantly, giving  a  fine  brown-red  liquor,  from  which,  by  cautious  evaporation,  small 
ruby-red  crystals  may  be  obtained ;  but  it  is  generally  dried  down  completely,  when 
it  forms  a  translucent  brown  mass,  deliquescent  in  damp  air.  An  excess  of  tartaric 
acid  should  be  avoided,  as  it  acts  on  the  peroxide  of  iron  during  the  evLporation, 
reducing  it  to  the  state  of  protoxide,  and  carbonic  acid  being  given  off.  Hence  the 
pharmacopoeias  direct  perfect  neutrality  of  the  liquor  to  be  secured  by  the  addition 
of  a  small  quantity  of  ammonia.  The  formula  of  this  salt  is  C8H4O10-I-K.O. .  IVOs. 
It  is  very  soluble  in  water,  and  its  solution  is  not  precipitated  by  an  excess  of  potash. 
Tartrate  of  Antimony. — 3(C3H40]o)-|-Sb.03.  This  salt  is  obtained  by  the  solution 
of  the  sesquioxide  of  antimony  in  tartaric  acid ;  it  is  colourless,  and  crystallizes  in 
short  deliquescent  prisms. 

Tartrate  of  Potash  and  Antimony.  Tartar- Emetic. — C8H4C,o+K.O.  . 
Sb.05+2  Aq.  This  salt,  a  most  important  compound  of  antimony,  is 
prepared  by  boiling  together  in  water  equal  weights  of  sesquioxide  of 
antimony  and  cream  of  tartar.     In  the  Dublin  and  Edinburgh  pharma- 


PROPERTIES     OF     TARTAR-EMETIC.  595 

Copceias,  the  Powder  of  Algarotti  (p.  453)  is  employed  as  the  source  of 
oxide  of  antimony,  but  by  the  London  college  an  impure  oxide  is  pre- 
pared, by  gently  deflagrating  together  sulphuret  of  antimony  and  nitre 
with  a  little  muriatic  acid,  and  washing  out  the  soluble  products.  In 
either  case  the  oxide  of  antimony  replaces  the  second  atom  of  base 
(water)  in  the  cream  of  tartar,  and  by  evaporation  and  cooling  it  may 
be  obtained  in  crystals,  which  are  right  rhombic  octohedrons,  with  many 
secondary  planes,  as  in  the  figure.  This  salt  dissolves 
in  fourteen  parts  of  cold  and  in  two  of  boiling  water. 
In  dry  air  it  effloresces,  losing  the  2  Aq.  Its  solution  is 
not  affected  by  alkalies ;  but  the  oxide  of  antimony  is 
precipitated  by  sulphuric  or  muriatic  acids,  and  by  am- 
monia. In  the  preparation  of  tartar-emetic,  the  whole 
product,  from  the  materials  used,  can  never  be  obtained 
crystallized ;  the  mother  liquor  contains  a  substance 
which  dries  down  to  a  transparent  mass,  like  gum  Ara- 
bic. By  alcohol  it  is  decomposed  into  tartar-emetic  and 
free  tartaric  acid.  According  to  Knapp's  analysis,  this 
salt  is  the  neutral  tartrate  of  potash  and  antimony,  having  the  formula 
C4HA  .  K.O.+(3C4H205+Sb.03)+2  Aq.  It  may  be  formed  by  dissolv- 
ing tartar-emetic  in  a  strong  solution  of  tartaric  acid,  and  then  crystal- 
lizes in  minute  oblique  rhombic  prisms.  In  order  to  form  this  salt, 
however,  from  cream  of  tartar  and  oxide  of  antimony,  a  quantity  of 
potash  must  enter  into  some  form  of  combination,  which  has  not  been 
explained. 

Owing  to  the  occasional  presence  of  arsenic  in  the  ores  of  antimony, 
the  tartar-emetic  of  commerce  is  not  unfrequently  contaminated  by  its 
presence,  and  should,  in  such  case,  be  absolutely  rejected  from  medi- 
cinal use. 

If  tartar-emetic  be  exposed  to  a  temperature  of  480^,  it  abandons,  be- 
sides its  crystal-water,  two  equivalents  of  water,  the  elements  of  which 
are  abstracted  from  the  constitution  of  the  tartaric  acid  as  generally 
assumed.  In  this  dried  tartar-emetic,  therefore,  the  organic  element  is 
not  C8H4O10,  but  CgHaOg.  When  redissolved  in  water,  it  resumes  the 
two  atoms  of  water,  forming  ordinary  tartar-emetic  again.  Of  the  other 
salts  of  tartaric  acid,  but  one  possesses  this  property,  the  borotartrate 
of  potash  being  also  reduced  by  loss  of  water  at  480°  to  the  formula 
C8H208+K!'0*  •  B.O3.  Chemists  are  not  unanimous  in  explaining  this 
peculiarity.  The  simplest  idea  is,  that  these  two  atoms  of  water  exist 
ready  formed  in  these  salts,  and  that  tartaric  acid  is  really  quadribasic ; 
being,  in  its  crystallized  form,  C8H20s-f4H.O.  ;  the  cream  of  tartar 
being  CsHA+K.O.  .  3H.0. ;  Rochelle  salt,  CgHaOs+K.O.  .  Na.O.  .  2 
H.O.  ;  and  for  tartar-emetic,  the  oxide  of  antimony  replacing  three  atoms 
of  a  protoxide,  the  formula  is  CgHgOs+K.O.  .  Sb.03+2  Aq.-i-2  Aq.,  and 
the  two  portions  of  water  being  retained  by  very  unequal  forces,  are  given 
off  at  very  different  temperatures.  Berzelius  considers  that  in  this  change 
the  nature  of  the  acid  is  totally  altered  ;  and  as  opinion  is  so  much  divided 
on  the  subject,  I  shall  not  enter  farther  into  its  discussion. 

Action  of  Heat  on  Tartaric  Acid. — When  tartaric  acid  is  cautiously  heated,  it  fuses 
into  a  mass  like  gum,  and  gives  off  water.  In  this  state  it  combines  with  bases, 
forming  salts  quite  different  from  the  tartrates  ;  it  retains  its  bibasic  character,  but 
its  atomic  weight  is  increased  to  one  and  a  half  times  that  of  tartaric  acid,  its  for- 
mula being  CiiHeOis-l-^  Aq.     It  thus  constitutes  Tartralic  Acid;  it  does  not  crys- 


598      RACE  MIC  kcm   and  its  salts. 

tallize,  and  in  solution  gradnally  passes  back  into  tartaric  acid.  If  the  tartralic  acm 
be  kept  long  melted  at  360°,  it  abandons  still  more  water,  and  forms  Tartrelic  Acid, 
in  which  the  bibasic  character  remains,  its  formula  being  Ci6H802o-|-2  Aq.  This 
acid  is  characterized  by  forming  insoluble  salts  with  lime  and  barytes,  thereby  dif- 
fering from  the  tartralic  acid.  If  the  heat  be  still  longer  kept  up,  a  porous  white 
mass  is  formed,  which  is  insoluble  in  water  and  in  alcohol.  It  is  Anhydrous  Tar- 
taric Acid;  its  formula  is  CSH4O10.  If  left  long  in  contact  with  water,  it  changes 
successively  into  the  tartrelic,  tartralic,  and  common  tartaric  acid.  This  change  is 
produced  more  rapidly  by  boiling  with  a  solution  of  potash  :  this  substance  appears 
to  hold  the  same  relation  to  tartaric  acid  that  the  white  sublimate  does  to  the  prop- 
er lactic  acid  (p.  536). 

If  tartaric  acid  be  distilled  at  a  still  higher  temperature,  it  abandons  water  and 
carbonic  acid,  and  forms  Pyrotartaric  Acid,  CSH4O10  giving  off  30. O2  and  H.O., 
and  C5H3O3  remaining.  The  process  succeeds  best  at  about  400°.  This  acid  is 
white ;  it  crystallizes  from  the  distilled  liquors  in  prisms,  which  are  to  be  purified 
from  empyreumatic  oil  by  recrystallization  and  digestion  with  animal  charcoal ;  it 
reacts  very  acid ;  it  melts  at  210°,  and  sublimes  at  360°  ;  is  very  soluble  in  wate. 
and  alcohol.  It  is  a  monobasic  acid,  forming  salts  which,  with  few  exceptions,  are 
soluble  and  crystallizable. 

Racemic  Acid, — C8H40,oH-2  Aq.  This  acid  is  found  in  grape-juice, 
replacing  tartaric  acid  to  a  greater  or  less  extent ;  its  formation  appears 
to  depend  on  very  peculiar  circumstances,  as  it  has  never  been  found 
except  in  the  district  about  the  Vosges  Mountains,  and  only  in  some  sea- 
sons.  It  is  combined  with  potash,  forming  a  kind  of  cream  of  tartar, 
which  is  biracemate  of  potash,  and  from  which  it  is  prepared  by  the 
same  methods  as  have  been  described  for  tartaric  acid. 

It  crystallizes  in  colourless  oblique  rhombic  prisms,  which  contain 
water,  of  which  one  half  is  lost  by  efflorescence  in  warm  dry  air;  the 
remaining  hydrate  is  identical  in  composition  with  crystallized  tartaric 
acid ;  it  tastes  and  reacts  as  strongly  acid.  In  its  relation  to  salts,  it 
follows  exactly  the  same  rules  as  the  tartaric  acid,  but  their  crystalline 
form  is  completely  different ;  it  is  a  bibasic  acid,  and  its  formula,  when 
crystallized,  is  C8H4O10+2H.O.+2  Aq.  The  characters  by  which  it 
is  distinguished  from  tartaric  acid  are,  first,  racemic  acid  requires  ten 
times  as  much  water  for  solution,  and  they  are  hence  easily  separated 
by  crystallization.  Second,  that  the  corresponding  salts  are  not  of  the 
same  crystalline  form.  Third,  the  racemate  of  potash  and  soda  is  un- 
crystallizable,  giving  merely  a  gummy  mass,  while  the  Rochelle  salt 
forms  very  large  crystals.  Fourth,  the  racemate  of  lime  is  insoluble 
in  a  solution  of  sal  ammoniac.  The  two  acids,  however,  form  a  most 
perfect  example  of  isomerism,  as  not  merely  their  composition,  but  their 
atomic  weight  is  absolutely  the  same. 

When  heated,  racemic  acid  passes  through  precisely  the  same  changes 
as  have  been  described  for  tartaric  acid,  abandoning  water,  and  forming 
bibasic  acids,  whose  formulae  are  respectively  C12H6O15+2H.O.  and  Cie 
H8O20+2H.O.  They  are  distinguished  by  their  salts,  which  differ  in 
characters  from  each  other,  and  from  those  of  the  bodies  formed  by  tar- 
taric acid. 

By  the  destructive  distillation  of  racemic  acid  is  generated  the  Pyro- 
racemic  Acid,  in  which  the  isomerism  with  the  tartaric  acid  series  is 
broken  through  ;  its  formula  being  CgHaOg.  It  differs  totally  in  proper- 
ties  from  the  pyrotartaric  acid ;  it  does  not  crystallize  ;  it  tastes  acid  ;  its 
salts  are  all  soluble  and  crystallizable,  but  pass  also  into  a  gummy  con- 
dition. If  a  little  crystal  of  copperas  be  laid  in  a  solution  of  one  of  these 
salts,  it  becomes  coloured  bright  red. 


CITRIC     ACID     AND     ITS     SALTS.  597 

Citric  ^cM.— C,2H50ii+3H.O.+2  Aq. 

This  acid  exists  in  the  juices  of  fruits,  especially  the  lemon,  orange, 
currant,  and  quince.  It  is  usually  prepared  from  lemon-juice,  which  is 
clarified  by  rest,  then  saturated  with  chalk,  and  the  neutral  solution  is 
boiled  until  the  citrate  of  lime  is  completely  deposited  ;  this  is  then  wash- 
ed  and  decomposed  by  a  quantity  of  oil  of  vitriol,  equal  in  weight  to  the 
chalk  employed,  and  diluted  with  six  volumes  of  water.  After  the  sul- 
phate of  lime  has  been  removed  by  straining,  the  liquor  is  evaporated, 
and  allowed  to  crystallize  by  very  slow  cooling ;  its  form  is  generally 
that  of  a  right  rhombic  prism,  very  much  modified,  as  in  the  figure, 
where  i,  u\  u  are  primary,  and  n',  y,  r  are  secondary  planes,  ^^^^p^^-v^^^ 
In  this  case  its  formula  is  that  given  above  ;  but  if  its  solu-  /i^v.,..^>S\ 
tion  be  evaporated  at  212°  to  a  pellicle,  it  crystallizes  while  Qy^  j 
hot  in  a  totally  different  form,  and  its  formula  is  then  CiaLH^Us.  1  4>.J 
H5O11+3H.O.  By  exposing  the  hydrated  crystals  in  vacuo  ^^<^^^iti>^ 
to  sulphuric  acid  or  to  a  gentle  heat,  the  2  Aq.  may  also  be  removed. 

The  citric  acid  possesses  an  agreeably  sour  taste ;  it  dissolves  in  less 
than  its  own  weight  of  cold,  and  in  half  its  weight  of  boiling  water  ;  it  i* 
sparingly  soluble  in  alcohol ;  when  heated,  it  fuses,  becomes  yellow,  and 
ultimately  gives  the  usual  pyrogenic  products  of  organic  acids.  It  is  a 
tribasic  acid,  and  gives  rise  to  three  classes  of  salts  ;  and,  as  these  con- 
tain different  quantities  of  combined  water,  their  history  was  very  confu- 
sed until  Liebig  explained  their  true  constitution.  Very  few  of  these 
salts  are,  however,  of  practical  or  medicinal  interest. 

Citrate  of  Soda  crystallizes  in  efflorescent  prisms,  having  the  formula  Ci2H50n-f- 
3Na.0.4-4  Aq.4-7  Aq.  By  exposure  to  a  heat  of  212°  the  7  Aq.  are  removed,  and 
at  400°  the  remaining  4  Aq.  are  driven  off:  Berzelius  is  of  opinion  that  in  this  ac- 
tion the  real  constitution  of  the  citric  acid  is  changed,  and  that  it  is  partly  convert- 
ed into  aconitic  acid ;  but  the  point  is  not  yet  experimentally  decided,  and  Liebig's 
views  explain  the  phenomena  with  such  beautiful  simplicity,  that  I  have  no  hesita- 
tion in  adopting  them,  at  least  provisionally. 

The  Citrate  of  Lime  is  obtained  by  mixing  solutions  of  a  soluble  citrate  and  of  a 
salt  of  lime ;  it  forms  a  white  powder,  sparingly  soluble  in  pure  water,  but  much 
more  so  if  the  liquor  be  acid.  Its  constitution  is  Ci2H50ii4-3Ca.O.-j-4  Aq.  When 
boiled  with  an  excess  of  lime-water,  citric  acid  forms  a  basic  Citrate  of  Lime,  which 
is  less  soluble  than  the  neutral  salt. 

The  Citrates  of  Lead  and  of  Barytcs  are  white  powders,  insoluble  in  water,  form- 
ed by  double  decomposition,  and  resembling  in  constitution  the  citrate  of  lime ; 
there  are  also  basic  salts,  the  formation  of  which,  as  in  that  of  lime,  appears  to  re- 
sult from  the  crystal- water  (2  Aq.)  of  the  acid  being  more  or  less  replaced  by  metal- 
lic oxide,  in  addition  to  that  which  fulfils  the  proper  basic  function. 

The  citric  acid  is  easily  recognised  by  forming  no  precipitate  with  lime-water  un- 
less the  liquor  be  heated.  Its  potash  salt  is  also  very  soluble,  even  with  an  excess 
of  acid  ;  it  is  thus  distinguished  from  the  racemic  and  tartaric  acids. 

When  citric  acid  is  heated,  it  fuses,  gives  off  water,  and  is  converted  into  an 
acid,  which,  from  being  found  in  the  aconitum  napellus,  is  called  Aconitic  Acid,  but 
it  exists  also  abundantly  in  various  species  of  equisetum,  and  is  hence  often  called 
Equisetic  Acid.  To  complete  the  change  of  the  citric  acid,  it  must  be  distilled  un- 
til the  gases  which  come  over  cease  to  be  inflammable,  and  oily  drops  appear  in  the 
receiver  ;  the  process  is  to  be  then  interrupted,  the  mass  remaining  in  the  retort  to 
be  dissolved  in  water,  the  solution  filtered  and  evaporated  to  a  pellicle.  On  cool- 
ing, it  forms  a  crystalline  mass,  from  which  ether  dissolves  out  the  aconitic  acid, 
and  leaves  unaltered  citric  acid  behind  ;  the  former  may  then  be  obtained  crystal- 
lized by  evaporation. 

Aconitic  acid  is  soluble  in  water,  alcohol,  and  ether ;  its  formula  is  C12H3O9-4- 
3  Aq.  ;  like  citric  acid,  it  is  tribasic  ;  it  forms  well-characterized  salts  :  the  aconi- 
tate  of  ether  had  been  mistaken  for  citric  ether ;  for,  when  citric  acid  is  put  in  con- 
tact with  alcohol  and  oil  of  vitriol,  it  changes  into  aconitic  acid. 


598  MALIC     ACID     AND     ITS     SALTS. 

If  aconitic  acid  be  heated  until  it  boils,  it  gives  off  carbonic  acid,  and  forms  Itor- 
konic  Acid,  which  distils  as  an  oily  liquid,  and  forms  a  crystalline  mass  as  it  cools ; 
by  solution  in  alcohol  and  slow  evaporation,  it  may  be  obtained  in  long  prismatic 
needles  ;  its  salts,  of  which  there  are  two  classes  (it  being  bibasic),  generally  crys- 
tallize very  well ;  its  formula  is  CioHiOe-l-^  Aq.  ;  formed  by  the  aconitic  acid  losing 
C2O4,  but  an  atom  of  water,  previously  basic,  entering  into  the  organic  element. 
When  the  Itakonic  Acid  is  redistilled,  it  is  copverted  into  water  and  a  heavy  oily 
liquid,  Citrakonic  Acid,  the  formula  of  which  is  CioHsOs-^-Aq.  In  contact  with  wa-^ 
ter,  it  forms  a  crystalline  mass  containing  2  Aq. 

All  these  products  are  simultaneously  and  successively  formed  in  the  distillation 
of  common  citric  acid.  Acetone  is  also  generated,  C12H12O12  giving  3(C3H30.),  with 
3H.0.  and  3(C.02). 

Malic  ^ciVZ.— C8H4O8+2H.O. 

This  acid  exists  in  most  fruits,  associated  with  citric  and  tartaric  acids, 
but  is  found  purest  and  most  abundant  in  the  berries  of  the  mountain  ash 
and  in  the  houseleek.  The  best  mode  of  extraction  is  the  following,  de- 
vised by  Liebig.  The  juice  of  the  berries  of  the  mountain  ash  (sorbus 
aucuparia)  is  to  be  nearly,  but  not  completely,  neutralized  by  lime,  and 
the  liquor  then  boiled  for  some  hours,  during  which  the  malate  of  lime 
precipitates  as  a  sandy  white  powder  ;  when  no  more  falls  down,  the 
neutralization  is  completed  by  adding  a  little  more  lime,  and  on  cooling, 
the  remainder  of  the  salt  is  obtained.  This  malate  of  lime  is  to  be  dis- 
solved by  boiling  in  the  smallest  possible  quantity  of  very  dilute  nitric 
acid.  On  cooling,  the  acid  malate  of  lime  crystallizes,  and  is  to  be 
purified  by  recrystallization.  This  salt  being  then  decomposed  by  ace- 
tate of  lead,  malate  of  lead  is  formed,  which,  being  acted  on  by  sulphu- 
retted hydrogen,  gives  sulphuret  of  lead  and  free  malic  acid  ;  by  evapo 
ration  of  the  liquor  and  cooling,  a  sirup. thick  liquid  is  obtained,  which, 
after  long  repose,  forms  a  white  crystalline  mass. 

Malic  acid  is  deliquescent,  and  very  soluble  in  water.  It  tastes  and 
reacts  strongly  acid  ;  its  relations  to  bases  are  very  curious  ;  thus  mag- 
nesia  is  the  only  earth  by  whose  carbonate  it  can  be  completely  neutral- 
ized. This  arises  from  its  tendency  to  form  salts,  in  which  one  atom  of 
basic  water  is  preserved,  it  being  a  bibasic  acid.  Another  peculiarity 
pointed  out  by  Hagen  is,  that  it  forms  with  many  bases  two  neutral  salts, 
of  which  one  retains  water  with  obstinacy  at  212°,  at  which  tempera- 
ture the  other  at  once  abandons  it.  When  crystallized  it  appears  to  con- 
tain  only  basic  water  ;  its  formula  is  hence  C8H4O8+2  Aq.  None  of  its 
salts  are  of  technical  or  medicinal  interest,  and  hence  require  but  brief 
notice. 

The  alkaline  malates  are  very  soluble  in  water,  scarcely  crystalliza- 
ble,  sparingly  soluble  in  alcohol. 

The  Malate  of  Lime  forms  as  a  granular  white  precipitate  when  malic  acid  is 
neutralized  by  lime.  Its  formula  is  C8H408+2Ca.O.  ;  it  separates  in  hard,  brilliant 
crystals,  which  contain  5  Aq.,  when  the  following  salt  is  neutralized  by  an  alkaline 
carbonate.  Bimalate  of  Lime,  C8H408-|-Ca.O.  .  H.O.-f  6  Aq.,  crystallizes  in  large 
right  rhombic  octohedrons.  Water  dissolves  it  abundantly  when  boiling,  but  very 
sparingly  when  cold. 

The  Malate  of  Lead,  C8H408-f  2Pb.O.,  precipitates,  on  mixing  solutions  of  a  solu- 
ble malate  with  acetate  of  lead,  as  a  white  curdy  mass,  which,  after  some  time, 
changes  into  minute  but  brilliant  crystalline  scales.  By  boiling  in  water,  a  small 
quantity  of  it  is  dissolved,  which  separates  in  brilliant  plates  on  cooling.  It  fuses 
below  212°,  and  is  then  nearly  insoluble  in  water. 

Malic  acid  is  distinguished  both  from  tartaric  and  citric  acids  by  not  giving  any 
precipitate  with  lime-water  either  by  heat  or  when  cold. 

When  malic  acid  is  heated  to  a  temperature  of  about  400°,  it  abandons  water  and 


MECONIC     ACID     AND     ITS     SALTS.  599 

gives  origin  to  two  acids,  of  which  one  is  remarkable  as  being  found  naturally  ex- 
isting in  several  plants.  They  are  the  Maleic  Acid  and  the  Fumaric  Acid,  the  latter 
so  called  from  having  been  first  discovered  in  the  fumaria  officinalis.  These  acids 
are  isomeric,  the  reaction  being  in  both  cases  that  C8H4O8  produces  2H.0.  and 
CsHzOe.  Both  acids  may  be  formed  in  the  same  process  ;  the  maleic  acid  passes 
over  with  the  water,  and  crystallizes  from  the  condensed  liquor ;  the  less  volatile 
fumaric  acid  constitutes  the  residue  in  the  retort,  which  solidifies  into  a  crystalline 
mass  as  it  cools.  From  the  plants  which  contain  this  acid,  it  may  be  obtained  by 
precipitating  the  clarified  juices  by  acetate  of  lead,  and  decomposing  the  salt  of  lead 
by  sulphuretted  hydrogen.  The  liquors  yield  the  acid  by  crystallization  when  con- 
centrated to  the  necessary  degree. 

The  Maleic  Acid,  which  had  been  thought  identical  with  the  Aconitic  Acid,  al- 
ready noticed,  forms  crystals  of  a  sour,  bitter  taste,  soluble  in  water,  alcohol,  and 
ether.  When  heated,  it  abandons  water,  and  the  anhydrous  acid  remains,  which, 
if  the  water  be  allowed  to  flow  back,  gradually  changes  into  fumaric  acid.  This 
anhydrous  acid  melts  at  167°,  and  sublimes  at  350°.  Of  its  salts,  that  of  barytes 
alone  is  remarkable  ;  it  is  a  white  precipitate,  which  changes  soon  into  a  mass  of 
brilliant  plates. 

The  Fumaric  Acid,  which  exists  also  in  Iceland  moss,  crystallizes  in  fine  long 
prisms,  which  fuse  with  difficulty,  and  volatilize  first  at  400°.  It  requires  200  parts 
of  water  for  its  solution.  When  heated,  it  is  decomposed  into  water  and  anhydrous 
maleic  acid.  The  fumarate  of  silver  is  so  insoluble,  that  one  part  of  the  acid,  dis- 
solved in  200,000  parts  of  water,  is  precipitated  by  nitrate  of  silver,  but  the  precipi- 
tate dissolves  in  nitric  acid.  The  salts,  with  copper,  iron,  and  lead,  are  also  very 
sparingly  soluble. 

When  muriatic  acid  gas  is  passed  into  a  solution  of  maUc  acid  in  absolute  alco- 
hol, Hagen  found  that  the  ether  formed  contains  fumaric,  and  not  malic  acid.  It  is 
a  liquid,  heavier  than  water,  of  an  agreeable  smell.  With  potash  it  gives  alcohol 
and  fumarate  of  potash.  Its  formula  is  C4H.034-Ae.O.  On  adding  water  of  am- 
monia to  this  ether,  a  substance  is  deposited  in  brilliant  white  scales,  insoluble  in 
cold  water  and  in  alcohol,  but  dissolved  by  boiling  water.  It  is  Fumaramid,  its 
formula  being  C4H.  .  02Ad.  By  potash,  ammonia  is  set  free,  and  fumarate  of  potash 
formed. 

Meconic  ^aVZ.— C,4H.Oh+3H.O.+2  Aq. 

This  acid  is  found  only  in  opium  ;  it  is  best  extracted  by  adding  chloride  of  cal- 
cium to  an  infusion  of  opium  in  cold  water.  A  white  precipitate  of  mixed  meconate 
and  sulphate  of  lime  occurs.  This,  being  washed  with  hot  water  and  with  alcohol, 
is  to  be  treated  with  dilute  muriatic  acid,  heated  to  about  180°.  The  meconate  of 
lime  dissolves,  and,  from  the  liquor  on  cooling,  bimeconate  of  lime  separates  in 
brilliant  crystalline  plates.  On  dissolving  these  in  warm,  strong  muriatic  acid,  and 
cooling  the  solution,  the  pure  meconic  acid  crystallizes.  It  may  be  freed  from  any 
adhering  colouring  matter  by  combination  with  potash,  decomposing  the  crystallized 
meconate  of  potash  by  muriatic  acid,  and  recrystalhzation. 

When  pure,  meconic  acid  is  in  brilliant  white  crystalline  scales,  containing  2  Aq., 
which  they  give  oflfat  212° ;  it  is  soluble  in  four  parts  of  boiling  water;  it  is  a  triba- 
sic  acid,  forming  salts,  of  which  those  with  the  earths  and  heavy  metallic  oxides 
are  generally  insoluble  in  water.  There  are  three  classes  of  Meconates,  according 
as  the  quantity  of  fixed  base  is  one,  two,  or  three  atoms.  Few  of  them  are  specifi- 
cally of  imp6rtance.  The  most  characteristic  properties  of  this  acid  are,  1st,  that 
it  produces  with  solutions  of  the  peroxide  of  iron  a  blood-red  colour,  analogous  to 
that  of  the  sulphocyanide  of  iron,  from  which  it  is  distinguished  by  the  fact  that, 
on  the  addition  of  the  acetate  of  lead,  a  white  precipitate  is  formed,  which,  when 
heated  to  full  redness  with  a  Uttle  sulphur  and  potassium,  and  treated  with  water, 
gives  no  red  colour  with  the  salts  of  iron  (see  page  525) ;  2d,  that  with  nitrate  of 
silver  it  gives  a  white  precipitate,  which  is  dissolved  by  dilute  nitric  acid;  the 
liquor,  however,  when  boiled,  becomes  milky,  and  deposites  cyanide  of  silver.  . 

If  a  strong  solution  of  meconic  acid  be  boiled  for  a  long  time,  or  if  the  crystallized 
acid  be  dissolved  in  strong,  boiling  muriatic  acid,  it  is  converted  into  Komenic  Acid, 
carbonic  acid  being  given  off.  The  crystallized  meconic  acid  undergoes  the  same 
phange  when  heated  to  400°.  This  acid  forms  granular  crystals,  which  are  soluble 
only  in  sixteen  parts  of  boiling  water,  and  have  the  formula  Ci2H208-{-2H.O.,  as  the 
C14H.O11  loses  C2O4  and  gains  H.O.  This  acid  is  bibasic  ;  the  third  atom  of  water, 
which  was  basic  in  the  meconic  acid,  entering  into  the  radical  here.    It  also  red- 


(>00  PREPARATION     OF     TANNIN. 

dens  the  per-salts  of  iron.  It  forms  two  series  of  salts,  which  in  properties  resem- 
ble closely  the  corresponding  meconates.  When  it  is  heated  to  500°,  it  gives  off 
water  and  carbonic  acid,  and  forms  Pyromekonic  Acid,  of  which  the  formula  is  Cio 
H3O5+H.O.  This  acid  forms  crystalhne  plates,  which  fuse  at  240°,  and  are  vola- 
tilized by  a  heat  little  higher.  It  is  very  soluble  in  water,  alcohol,  and  ether ;  it  is 
a  monobasic  acid,  forming  salts,  which,  with  the  exception  of  that  of  lead,  are  all 
soluble  in  water.  Like  the  acids  from  which  it  is  derived,  it  strikes  a  blood-red 
colour  with  solutions  containing  peroxide  of  iron. 

Tannic  Acid,  or  Tannin. — CigHsOg  +  SH.O. 

This  important  substance  exists  in  the  bark  of  most  exogenous  trees, 
particularly  the  oak  and  horse-chestnut,  accumulated  principally  in  the 
inner  layers  of  bark.  It  is  found  also  in  the  roots  of  the  tormentilla  and 
bistort,  in  the  leaves  of  roses  and  pomegranates  ;  but  its  most  abundant 
source  is  the  gall-nut  of  the  oak  (quercus  infecloria). 

To  distinguish  this  from  the  other  kinds  of  tannin,  of  which  there  is  a 
great  number,  it  may  be  suitably  termed  GaUo-tannic  Acid,  and  I  shall 
generally,  though,  perhaps,  not  uniformly,  employ  that  name. 

The  method  given  by  Pelouze  for  its  extraction,  and  which  serves  for 
the  preparation  of  a  variety  of  other  vegetable  principles,  is  as  follows  : 
Into  a  globular  funnel,  b,  which  can  be  closed  at  the  top  by  a 
stopper,  and  rests  in  a  bottle,  a,  as  in  the  figure,  is  to  be  intro- 
duced a  quantity  of  nut-galls  in  powder,  moderately  compress- 
ed, after  the  tube  of  the  funnel  has  been  stopped  with  a  little 
cotton.  The  upper  empty  part  of  the  funnel  is  to  be  then  filled 
with  ether,  as  it  is  usually  in  the  shops,  containing  about  one 
tenth  of  water  dissolved  in  it,  and  the  apparatus  allowed  to  stand 
for  some  days.  The  bottle  is  then  found  to  contain  two  lay- 
ers of  liquid.  The  inferior,  sirup-thick,  is  a  concentrated  so- 
lution of  tannic  acid  in  water,  with  very  little  ether.  The 
upper  is  ether,  containing  but  a  trace  of  tannic  and  gallic 
acids.  Being  separated,  the  lower  layer  is  to  be  washed  once 
or  twice  with  a  little  ether,  and  then  evaporated  in  vacuo  with 
a  capsule  of  sulphuric  acid.  A  faintly-yellowish  white  mass  remains,  of 
a  distinctly  crystalhne  structure,  which  is  pure  gallo-tannic  acid.  The 
theory  of  this  process  is,  that  the  tannic  acid  is  so  greedy  of  water  as  to 
withdraw  it  from  the  ether,  and  to  dissolve  it  to  the  exclusion  of  every 
other  constituent  of  the  gall-nut. 

The  watery  solution  of  gallo-tannic  acid  reddens  litmus ;  it  is  probably 
insoluble  in  absolutely  anhydrous  alcohol  and  ether  ;  its  taste  is  intense- 
ly astringent,  but  not  bitter.  The  most  characteristic  property  of  tannic 
acid  is,  that  it  combines  with  the  animal  substance  Gelatine,  and  forms  a 
compound  insoluble  in  water,  which  is  the  basis  of  most  kinds  of  leather ; 
hence  any  tissue,  as  skin,  which  contains  gelatine,  removes  gallo-tannic 
acid  from  its  watery  solution,  on  which  is  founded  the  art  of  Tanning, 
It  is  a  tribasic  acid,  and  forms  three  classes  of  salts,  which  are  of  inter- 
est from  the  colours  of  precipitates  it  gives  with  metallic  solutions,  being 
often  useful  as  a  test  for  the  presence  of  certain  metals.  Hence  an  in- 
fusion, or  tincture  of  Galls,  is  always  found  in  the  laboratory  as  a  rea- 
gent ;  it  does  not  affect  the  solutions  of  Zinc  or  Cadmium,  or  the  'protox- 
ides  of  Iron  and  Manganese,  nor  any  of  the  alkaline  or  earthy  salts. 
With  the  other  metals  it  gives  precipitates  which,  with  Lead  and  Anti^ 
mony,  are  white  ;  with  Copper,  gray ;  with  Tin,  Nickel,  Cohalt,  Cerium, 
Tellurium^  and  Silver,  are  various  shades  of  yellow  ;  with  Tantalum  and 


PREPARATION     OF     GALLIC     ACID.  601 

Bismuth,  are  orange  ;  with  Titanium,  blood-red  ;  with  Platinum,  greerf , 
with  Chrome,  Molybdenum,  Uranium,  and  Gold,  are  brown  ;  and  with  Os- 
mium and  peroxide  of  Iron,  are  rich  bluish  purple.  This  last  is  the  most 
important  of  all,  from  its  great  delicacy  and  distinctness.  If  the  solu- 
tions be  very  strong,  the  liquor  appears  absolutely  black,  and  constitutes 
the  material  of  ordinary  writing  ink. 

The  insolubility,  and  consequent  inactivity  of  tartrate  of  antimony,  is 
taken  advantage  of  in  medicine,  infusion  of  oak-bark  or  galls  being  em- 
ployed as  an  antidote  in  poisoning  by  tartar-emetic.     I  shall  have  occa 
sion  hereafter  to  notice  its  use  in  the  detection  and  neutralization  of  the 
vegetable  alkaloids. 

The  gallo-tannic  acid  is  not  the  only  kind  of  tanning  material  employ- 
ed in  the  manufacture  of  leather  ;  yet,  as  the  others  will  hereafter  come 
under  notice,  I  shall  give  Humphrey  Davy's  estimate  of  the  comparative 
power  of  such  substances  as  contain  true  tannic  acid.  He  found  the 
quantity  of  active  material  in  100  parts  of  the  following  bodies  to  be, 


Gall-nuts 27-4 

Oak  bark  entire 63 

Horse-chestnut  bark  entire    .    .    4-3 
Elm  bark  entire 2-7 


"White  inner  oak  bark     .    .    .  16*0 

White  inner  horse-chestnut     .  15-2 

Sicilian  sumach 16-2 

Malaga  sumach 10-4 


These  numbers  are  but  approximative,  and  such  as  are  given  by  very 
rough  processes,  the  true  quantity  of  tannic  acid  present  being  much  lar- 
ger ;  thus  the  gall-nuts  easily  yield,  by  Pelouze's  method,  forty  per  cent 
of  pure  product. 

VVhen  a  solution  of  tannic  acid  is  exposed  to  the  air,  it  is  decomposed , 
absorbing  oxygen  and  evolving  carbonic  acid,  the  liquor  becomes  colour 
ed,  and  a  large  quantity  of  gallic  acid  is  found  to  be  produced. 

Gallic  ^cifZ.— C7H.03-f2H.O.  +  Aq. 

This  remarkable  substance  does  not  appear  to  exist  naturally  formed 
in  plants,  but  is  generated  by  the  decomposition  of  gallo-tannic  acid. 
Powdered  galls  are  to  be  made  into  a  thin  paste  with  water,  and  exposed 
to  the  air  for  some  weeks,  at  a  temperature  of  about  80°,  water  being 
supplied  according  as  it  evaporates  away  ;  the  resulting  mass  is  to  be 
boiled  with  water,  and  the  gallic  acid  crystallizes  out  of  the  liquor  as  it 
cools.  By  digestion  with  ivory  black  and  recrystallization,  it  is  obtain- 
ed completely  pure. 

In  this  process  the  reaction  is  very  simple,  as  an  atom  of  tannic  acid, 
Cii-HgOiz,  absorbing  from  the  air  eight  atoms  of  oxygen,  produces  4C.O2 
and  2(C7H.03-f3  Aq.). 

The  conversion  of  gallo-tannic  acid  into  gallic  acid  may  occur,  howev- 
er,  without  the  access  of  air,  and,  indeed,  be  effected  almost  instantane- 
ously  ;  thus,  if  tannic  acid  be  boiled  in  a  strong  solution  of  potash  for  a 
few  minutes,  and  an  excess  of  sulphuric  acid  be  then  added,  a  copious 
product  of  gallic  acid  is  obtained  crystallized  on  cooling  ;  or,  if  sulphu- 
ric acid  be  added  to  a  strong  solution  of  gallo-tannic  acid,  and  the  pre- 
cipitate thus  formed  be  washed  with  a  small  quantity  of  water,  and  then 
added  gradually  to  boiling  dilute  sulphuric  acid,  it  dissolves,  and  on  cool- 
ing the  gallic  acid  crystallizes.  In  these  reactions,  which  succeed  also 
perfectly  with  infusion  of  galls,  some  other  substances  must  be  simulta- 
neously formed,  which  are  as  yet  not  known.  Gallo-tannic  acid  contains 
exactly  the  constituents  of  gallic  acid  and  acetic  acid,  as  Ci8H509=2(C- 

4  G 


602       PYROGALLIC,     MELANGALLIC     ACIDS,     ETC. 

H.03)+C4H303 ;  but  Liebig  has  determined  that  acetic  acid  is  not  pro- 
duced. 

This  change  may  occur  in  the  nut-gall  itself,  which  it  is  very  probable 
contains  a  principle  analogous  to  yeast,  which,  under  favourable  circum- 
stances, induces  this  kind  of  decomposition  in  the  gallo-tannic  acid.  This 
idea,  first  suggested  by  Robiquet,  has  derived  much  support  from  the  ex- 
periments  of  Larocque,  who  found  that  the  matter  of  the  nut-gall  which 
remains  after  the  extraction  of  the  tannin  has  the  power  of  exciting  the 
alcoholic  fermentation  in  solutions  of  sugar.  As  yet,  however,  we  pos- 
sess  no  accurate  knowledge  of  the  theory  of  this  interesting  transmuta- 
tion. 

Pure  gallic  acid  crystaUizes  in  colourless  oblique  rhombic  prisms,  as 
tt,  z  in  the  figure,  where  i  is  a  secondary  plane  ;  it  tastes  bitter  and  slightly 
^::^:^^..,^        acid,  and  requires  100  parts  of  cold,  but  much  less  of  boiling 
y^^Y^^^^    water  for  its  solution  ;  it  is  less  soluble  in  alcohol ;  its  crys- 
tals  contain  three  atoms  of  water,  of  which  one  is  expelled  at  a 
temperature  of  230°,  but  the  remaining  two  are  only  remov- 
I     i      ed  when  replaced  by  bases.     It  is  a  bibasic  acid,  forming  two 
M;~-.J,_J      classes  of  salts  ;  those  with  the  alkalies  are  very  soluble  ;  the 
^--^^    earthy  and  metallic  salts  are  insoluble  in  water.     With  a 
per-salt  of  iron,  gallic  acid  gives  a  blackish-blue  precipitate,  which  dif- 
fers from  the  tannate  of  iron  in  becoming  gradually  colourless,  the  acid 
being  decomposed,  and  the  iron  reduced  to  the  state  of  protoxide  ;  this  is 
effected  instantly  by  boiling,  carbonic  acid  gas  being  evolved.     The  gal- 
lie  acid  is  farther  distinguished  from  the  tannic  by  not  precipitating  gela- 
tine  nor  any  of  the  vegetable  alkalies. 

Products  of  the  Decomposition  of  Gallic  Acid. 

Pyrogallic  Acid. — When  gallic  acid  is  carefully  heated  to  about  400°,  it  is  totally 
decomposed  into  carbonic  acid  and  pyrogallic  acid  (C7H305=C6H603-|-C.02),  which 
sublimes  in  brilliant  white  plates  ;  it  is  easily  soluble  in  ether,  alcohol,  and  water  ; 
it  reacts  feebly  acid  ;  it  fuses  at  240°,  and  sublimes  at  400°.  If  a  solution  contain- 
ing peroxide  of  iron  be  added  to  a  solution  of  pyrogallic  acid,  a  black  colour  is 
struck,  but  the  iron  is  rapidly  reduced  to  the  state  of  protoxide,  and  the  liquor  as- 
sumes a  rich  red  tint.  If,  however,  a  salt  of  pyrogallic  acid  be  used,  the  solution 
remains  permanently  blue. 

Melangallic  Acid. — If,  in  the  distillation  of  pyrogallic  acid,  the  temperature  be  al- 
lowed to  rise  beyond  450°,  it  is  decomposed,  water  is  given  off',  and  a  shining,  jet- 
black  mass,  like  coal,  remains  in  the  retort,  which  is  this  body ;  its  formula  is 
C12H3O3,  being  formed  from  2(C6H303)  by  loss  of  3H.0. ;  it  is  insoluble  in  water, 
alcohol,  and  ether ;  at  a  temperature  of  500°  it  is  totally  decomposed  into  the  ordi- 
nary pyrogenic  products  ;  it  dissolves  in  alkaline  solutions,  forming  salts  of  a  black 
colour,  which  do  not  crystallize ;  these  salts  give  black  precipitates  with  solutions 
of  the  earthy  and  metallic  salts. 

If  gallo-tannic  acid  be  heated  to  about  400°,  it  is  resolved  totally  into  pyrogallic, 
melangallic,  and  carbonic  acids  and  water. 

Ellagic  Acid. — In  the  formation  of  gallic  acid  by  the  slow  fermentation  of  tannic 
acid,  a  certain  quantity  of  ellagic  acid  generally,  though  not  constantly,  appears. 
Being  insoluble  in  water,  it  remains  when  the  gallic  acid  has  been  dissolved  out ; 
and,  by  digesting  the  residue  with  a  weak  solution  of  potash,  it  is  taken  up,  and 
may  then  be  precipitated  by  muriatic  acid. 

It  forms  minute  crystals,  whose  formula  is  C7H.O3-4-H.O.+  Aq.  The  Aq.  is  driven 
ofTby  a  heat  of  212°,  and  the  dry  acid  is  then  isomeric  with  the  gallic  acid,  but  it  is 
monobasic ;  it  is  very  feebly  acid,  not  expelling  carbonic  acid  from  its  salts  ;  the 
earthy  and  metallic  Ellagatcs  are  all  insoluble,  and  all  white  or  yellow. 

If  gallic  acid  be  heated  to  280°  with  oil  of  vitriol,  it  dissolves,  and  on  cooling, 
brilliant  crystals  of  a  dark  scarlet  colour  are  deposited,  which  constitute  Parellagic 
Acid.    This  body  is  isomeric  with  ellagic  acid ;  it  forms  with  bases  salts  which  are 


CATECHUIC     AND     C  A  T  E  C  H  U  T'A  N  N  I  C     ACIDS.     603 

generally  red.  It  is  worthy  of  notice,  that  ellagic  acid  acted  on  by  oil  of  vitriol 
gives  no  parellagic  acid. 

It  is  here  probably  best  to  notice  the  forntiation  of  what  has  been  termed 
Artificial  Tannin ;  it  is  produced  by  mixing  one  part  of  almost  any  kind 
of  vegetable  substance  with  five  parts  of  oil  of  vitriol,  letting  the  mixture 
stand  for  some  days,  and  then  heating  it  as  long  as  any  sulphurous  acid 
gas  is  evolved.  A  black  mass  remains,  from  which  the  remaining  acid 
is  to  be  washed  with  water,  and  then  the  tannin  dissolved  out  by  alcohol ; 
the  solution  is  dark  brown,  and  when  evaporated  gives  a  black  extract- 
ive matter,  which  tastes  astringent,  smells  of  burned  sugar,  and  dissolves 
in  water ;  it  precipitates  gelatine,  but  does  not  affect  the  salts  of  iron 
like  true  tannin. 

Another  and  a  very  singular  manner  of  producing  artificial  tannin 
consists  in  boiling  pure  charcoal  in  nitric  acid  as  long  as  any  reaction 
occurs  ;  the  liquor  is  then  brown  ;  being  evaporated  to  the  consistence 
of  a  sirup  and  mixed  with  water,  a  brownish-yellow  substance  falls,  and 
the  filtered  solution  gives,  by  evaporation,  a  hard  black  mass,  which  red- 
dens  litmus,  tastes  astringent,  is  soluble  in  water  and  alcohol,  and  copi- 
ously precipitates  gelatine  ;  when  heated,  it  smells  like  horn,  and  contains 
nitrogen  ;  it  precipitates  most  metallic  salts  brown.  The  true  nature  of 
these  bodies  is  not  well  known,  as  they  have  not  been  much  studied  since 
the  methods  of  organic  chemistry  acquired  their  present  exactness  ;  they 
are  probably  mixtures  of  many  bodies,  as  ulmine  in  its  various  forms 
with  crenic  and  aprocrenic  acids. 

Caiechuic  Acid  and  Catechutannic  Acid, 

The  Catechu,  or  Terra  Japonica,  a  brown  extract  prepared  from  the  wood  of  the 
mimosa  catechu,  appears  to  contain  at  least  four  acids,  the  precise  composition  and 
connexion  of  which  have  not  yet  been  definitely  established.  The  rough  catechu, 
as  imported,  is  of  extensive  use  in  medicine,  and  in  the  arts  for  tanning  and  for  giv- 
ing a  rich  permanent  brown  dye.  Davy  estimated  that  100  parts  of  Bengal  catechu 
contain  forty-eight,  and  of  Bombay  catechu  about  fifty-four  per  cent,  of  useful  tan- 
ning material. 

If  catechu  be  treated  with  ether,  by  the  method  of  displacement  as  described  lor 
tannic  acid,  the  liquor  does  not  separate  into  two  layers,  but  a  strong  solution  of 
Catechutannic  Acid  in  ether  is  obtained,  which,  by  evaporation,  yields  it  as  a  pale 
yellow,  scarcely  crystalline  mass,  in  taste  and  appearance  similar  to  tannic  acid ; 
its  solution  in  water  precipitates  gelatine,  but  not  tartar-emetic  ;  with  the  salts  of 
peroxide  of  iron  it  strikes  an  intensely  olive-green  colour,  which  is  best  marked  with 
the  perchloride,  being  somewhat  purple  with  the  persulphate ;  exposed  to  the  air, 
its  solution  rapidly  absorbs  oxygen,  becomes  red,  and  finally  brown,  depositing  a 
brown  insoluble  matter.     This  change  is  instantly  effected  by  any  oxidizing  agent. 

The  catechutannic  acid  has  been  analyzed  by  Pelouze,  who  ascribes  to  it  the 
formula  CigHsOs-l-Aq. ;  it  would  thus  appear  to  be  formed  by  the  abstraction  of  four 
atoms  of  oxygen  from  tannic  acid. 

When  catechu  has  been  deprived  of  the  catechutannic  acid  by  ether  or  continued 
washings  with  cold  water,  the  residual  mass  is  to  be  boiled  in  alcohol,  and  the  fil- 
tered liquor  evaporated  to  one  third  of  its  volume  ;  on  cooling,  Catechuic  Acid  crys- 
tallizes. If  coloured,  it  is  to  be  dissolved  in  boiling  water,  precipitated  by  acetate 
of  lead,  the  catechuate  of  lead  diffused  through  boiling  water,  and  decomposed  by 
sulphuretted  hydrogen  ;  the  liquor  being  filtered,  gives,  on  cooling,  a  perfectly  white 
and  pure  catechuic  acid  ;  it  forms  satiny  flakes,  indistinctly  crystallized  ;  it  is  very 
little  soluble  in  cold  water,  but  abundantly  in  boiling  water  and  in  alcohol ;  it  is  in- 
soluble in  ether ;  its  solution  is  not  acid ;  it  appears  to  exist  in  very  different  states 
of  hydration,  or,  possibly,  different  kinds  of  catechu  contain  substances  which  are 
totally  distinct,  for  the  formulae  assigned  to  it  are  quite  discordant,  and  chemists 
are  not  agreed  quite  as  to  its  properties.  Svanberg,  who  examined  the  catechu 
from  the  mimosa  catechu,  gives  as  its  formula  CisHsOs+Aq.  Zwenger,  who  states 
the  substance  he  worked  with  to  be  the  produce  of  the  nauclea  gambir,  gives 


604    CINCHONATANNIC    AND    CINCHONIC    ACIDS,    ETC. 

C2oH908-|-Aq. ;  and  Hagen,  who  used  Bengal  catechu,  found  the  catechuic  acid  to 
be  CuHeOe-j-'^  Aq.,  and  its  lead  salt  Ci4H606-|-2Pb.O.  Additional  researches  are 
required  to  clear  up  this  confusion. 

When  catechuic  acid  is  heated,  it  fuses,  gives  off  water,  and,  finally,  a  white  crys- 
talline sublimate,  Pyrocatechin,  which  has  the  formula  CeHjO.-l-Aq. ,  its  character- 
istic property  is  that  of  forming  a  bright  green  solution  with  alcohol. 

If  a  solution  of  either  of  the  acids  now  described  be  exposed  to  the  air,  oxygen  is 
absorbed,  and  much  more  rapidly  in  presence  of  an  alkali.  The  substance  formed 
is  termed  Japonic  Acid ;  it  makes  up  the  mass  of  the  coloured  portion  of  catechu  ; 
it  is  almost  insoluble  in  water ;  soluble  in  caustic,  but  not  in  carbonated  alkalies. 
Svanberg  gives  for  it  the  formula  Ci2H204-}-Aq.  If  catechuic  acid  be  boiled  with  a 
solution  of  carbonate  of  potash,  Rubinic  Acid  is  formed,  whose  formula  is  said  to  be 
CisHeOg.  By  farther  absorption  of  oxygen  it  forms  japonic  acid.  None  of  these  re- 
sults, however,  can  be  considered  as  definitely  established. 

Cinchonatannic  Add  and  Cinchonic  Acid, 

These  substances  exist  in  the  barks  of  various  species  of  cinchona,  combined  with 
quinia  and  cinchonia.  The  first  is  extracted  by  digestion  in  dilute  muriatic  acid  and 
precipitation  with  magnesia.  The  precipitate  is  to  be  dissolved  in  acetic  acid  and 
precipitated  with  acetate  of  lead,  which  leaves  the  alkaloids  dissolved ;  the  cincho- 
natannate  of  lead  being  decomposed  by  sulphuretted  hydrogen,  the  filtered  liquor 
yields,  on  evaporation,  the  Cinchonatannic  Acid  pure,  and  of  a  very  pale  yellow  col- 
our, not  crystalline.  In  properties  it  resembles  closely  ordinary  tannic  acid;  it 
precipitates  gelatine  and  tartar-emetic.  An  infusion  of  cinchona  is  hence  recom- 
mended as  an  antidote  in  cases  of  poisoning  by  tartar-emetic.  It  colours  solutions 
of  the  per-salts  of  iron  green.  By  exposure  to  the  air,  it  is  converted  into  a  rust- 
coloured  substance  termed  Cinchona  Red.  Nothing  is  known  of  the  composition  of 
these  bodies. 

The  Cinchonic  Acid,  which  Berzelius  believes  to  exist  in  the  inner  bark  (albumen) 
of  fir  and  of  most  trees,  is  obtained  by  adding  lime  in  small  quantity  to  a  cold  infu- 
sion of  cinchona  bark.  The  alkaloids  being  thus  separated,  the  liquor  is  filtered  and 
evaporated  very  carefully  to  the  consistence  of  a  sirup.  On  standing  for  a  few  days, 
the  cinchonate  of  lime  crystallizes  in  needles,  which  are  to  be  decomposed  by  an 
exact  equivalent  of  sulphuric  acid.  The  gypsum  being  removed  by  the  filter,  the 
solution  is  concentrated,  and  the  cinchonic  acid  crystallizes.  It  forms  small  acid 
needles  ;  is  very  soluble  in  water  ;  its  salts  are  all  soluble  in  water ;  it  affects  nei- 
ther gelatine,  tartar-emetic,  nor  the  per-salts  of  iron ;  its  formula  appears  to  be 
C14H8O8-I-4  Aq.  When  it  is  heated,  a  substance  sublimes  in  brilliant  yellow  nee- 
dles, which  is  termed  Chinoyl,  and  consists  of  C3H.O. 

Kinoic  Acid,  or  Coccotannic  Acid, 

The  substance  known  in  pharmacy  as  Gum  Kino,  which  is  an  extract  of  the 
wood  of  the  coccoloba  uvifera,  is  to  be  dissolved  in  cold  water,  the  solution  precipi- 
tated by  sulphuric  acid,  the  precipitate  washed,  dissolved  in  boiling  water,  and  solu- 
tion of  barytes  added  until  the  sulphuric  acid  is  all  removed  ;  the  liquor  is  then  care- 
fully evaporated  to  dryness.  The  kinoic  acid  forms  a  crimson  transparent  mass, 
soluble  in  alcohol  and  water,  but  not  in  ether ;  its  taste  is  astringent,  but  not  bitter. 
The  salts  of  this  acid  are  not  known,  nor  has  its  composition  been  examined.  It 
does  not  precipitate  solution  of  tartar-emetic. 

Of  the  following  acids  we  possess  httle  more  than  a  knowledge  of  their  probable 
existence. 

Lactucic  Acid  is  said  to  exist  in  the  lactuca  virosa.  The  expressed  juice  is  pre- 
cipitated by  acetate  of  lead,  and  the  lactucate  of  lead  decomposed  by  sulphuretted 
hydrogen.  From  the  hquor  the  acid  crystaUizes  by  evaporation  and  cooling,  like 
oxalic  acid ;  it  tastes  acid,  and  gives  with  protosalts  of  iron  a  green,  and  with  salts 
of  copper  a  brown  precipitate. 

Fungic  Acid  exists  in  most  mushrooms  ;  their  expressed  juice  is  boiled,  and  the 
coagulated  albumen  removed  by  filtration  ;  the  liquor  is  then  evaporated  to  a  sirup, 
and  treated  with  alcohol.  Fungate  of  potash  remains  undissolved,  from  which  the 
acid  is  obtained  by  acetate  of  lead  and  sulphuretted  hydrogen.  The  fungic  acid  is 
colourless,  sour,  deliquescent,  and  not  crystalline. 

Boletic  Acid  is  obtained  from  the  boletus  ignarius,  in  the  same  way  as  the  last  acid 
is  from  other  mushrooms.  It  crystallizes  readily,  and  sublimes  without  decompo- 
sition. 


KRAMERIC     ACID,     ETC. PECTIN.  605 

Kramcric  Acid,  exists  in  rhatany  root  (krameria  triandria).  The  watery  infusion 
IS  precipitated,  first  by  gelatine,  and  then  by  copperas.  The  filtered  liquor  is  con- 
centrated, neutralized  by  lime,  precipitated  by  acetate  of  lead,  and  the  kramerate  of 
lead  decomposed  by  sulphuret  of  hydrogen ;  it  crystallizes  irregularly,  and  tastes 
strongly  acid  and  astringent ;  its  formula  is  probably  CioHsOs,  by  Liebig's  analysis. 

Cdincic  Acid  exists  in  the  root  of  the  chiococca  racemosa.  Its  mode  of  extraction 
resembles  that  of  the  krameric  acid ;  it  crystallizes  in  needles ;  is  but  sparingly  sol- 
uble in  water ;  its  solution  reacts  acid ;  it  appears  to  have  the  same  formula  as  kra 
meric  acid,  and  perhaps  they  are  really  identical. 

Verdous  aiid  Verdic  Acids  exist  in  a  variety  of  plants  of  the  families  (Mpsaceae, 
compositae,  and  eupatoriae  ;  it  is  best  prepared  from  the  roots  of  the  scabiosa  succi- 
sa.  They  are  to  be  digested  in  alcohol,  and  the  solution  mixed  with  ether.  Impure 
verdous  acid  is  thrown  down  ;  it  is  to  be  dissolved  in  water,  and  the  liquor  precip- 
itated by  acetate  of  lead ;  the  verdite  of  lead  being  collected  and  decomposed  by 
H.S.,  gives  the  pure  Verdous  Acid,  which  remains  after  evaporation  as  a  clear  yel- 
low mass,  which  is  not  altered  by  the  air ;  it  reddens  htmus  strongly.  If  it  be  neu- 
tralized by  an  alkaU,  it  then  absorbs  oxygen  rapidly,  and  the  solution  becomes  deep 
green ;  from  this,  acids  throw  down  a  brown-red  powder,  which  is  Verdic  Acid. 
Runge,  who  observed  these  facts,  considers  that  the  two  acids  are  different  oxides 
of  the  same  radical,  but  no  exact  researches  have  been  made  about  them. 

Other  acids,  of  which  the  existence  has  been  only  indicated,  will  be  noticed  in  de  • 
scribing  the  more  important  bodies  with  which  they  are  associated  in  the  plants. 


CHAPTER  XXV. 

OF   THE   NEUTRAL   ORGANIC   SUBSTANCES   AND   THE   PRODUCTS   OF   THEIR 
DECOMPOSITION. 

The  bodies  to  be  described  in  this  chapter  are  distinguished  by  the 
absence  of  distinct  acid  or  basic  characters,  and  also  that  they  are  at 
least  so  destitute  of  colour  as  not  to  be  included  in  the  list  of  colouring 
matters.  In  other  respects  they  possess  no  direct  connexion  with  each 
other,  and  are  united  only  for  convenience  of  arrangement. 

Pectin,  or  Vegetable  Jelly. 

This  substance,  which  is  to  be  carefully  distinguished  from  animal 
jelly,  or  Gelatine,  to  which  it  by  no  means  bears  the  relation  that  the 
albumen  of  plants  does  to  that  of  animals,  is  very  extensively  diffused, 
being  found  in  almost  every  kind  of  plant,  and  distributed  through  all 
their  parts.  It  is  very  easily  prepared  from  the  expressed  juice  of  white 
beet,  celery,  parsley,  currants,  cherries,  or  plums.  It  is  sufficient  to 
filter  the  juice  and  mix  it  with  alcohol ;  after  some  hours,  the  pectin 
separates  as  a  consistent  jelly,  which  is  to  be  collected  on  a  filter,  wash- 
ed with  alcohol,  and  dried  by  a  very  moderate  heat.  It  forms  a  trans- 
parent mass,  like  isinglass,  and  is  almost  insipid.  When  immersed  in 
water,  it  swells  up  ;  one  part  gives  a  firm  jelly  with  100  parts  of  water. 
When  acted  on  by  nitric  acid,  it  produces  pectic  and  the  mucic  acid.  It 
precipitates  the  salts  of  barytes,  lead,  copper,  and  sesquioxide  of  iron,  but 
does  not  affect  solutions  of  silver,  of  protosulphate  of  iron,  of  tartar- 
emetic,  of  tannic  acid,  or  of  silicate  of  potash.  Its  formula,  as  from  the 
experiments  of  Fremy,  is  C24Hn022.  By  long  boiling,  or  by  contact  with 
any  powerful  acid  or  base,  it  changes  into  the  following  substance : 


606    PECTIC    AND    METAPECTIC    ACIDS. S  A  L  I  C  I  N  E. 

Pectic  Acid  appears  to  exist  naturally  combined  with  lime  in  many  plants,  and  is 
precipitated  from  their  juice  on  the  addition  of  muriatic  acid.  The  precipitate  is  to 
be  boiled  with  a  little  lime,  and  the  solution  again  decomposed  by  muriatic  acid. 
The  pectic  acid,  which  then  separates  pure,  is  to  be  washed  with  distilled  water  and 
dried.  It  does  not  crystallize,  but  forms  white  transparent  scales,  tastes  distinctly 
acid,  and  reddens  litmus.  It  dissolves  very  sparingly  in  cold,  but  more  copiously 
in  boiling  water ;  the  solution  is  colourless,  and  does  not  gelatinize  on  cooling,  but 
is  coagulated  to  a  transparent  jelly  by  acids,  by  lime-water,  alcohol,  and  many 
salts.  Sugar  gradually  converts  the  solution  into  a  firm  jelly,  and  is  thus  useful  in 
the  mamifacture  of  the  preserves  of  juicy  fruits. 

The  pectic  acid  is  isomeric  with  pectin,  its  formula  being  C24H17O22.  It  appears 
to  be  bibasic,  the  pectate  of  lead  being  C24Hi7022H-2Pb.O.  Its  alkaUne  salts  are 
soluble  in  water,  but  the  others  are  insoluble,  and  form  transparent  jellies  while 
moist. 

If  pectin  or  pectic  acid  be  boiled  in  a  solution  of  potash,  the  alkali  being  in  ex- 
cess, until  the  liquor  ceases  to  give  any  precipitate  on  the  addition  of  muriatic  acid, 
Metapectic  Acid  is  formed.  On  the  addition  of  sugar  of  lead,  metapectate  of  lead  is 
thrown  down,  which,  being  decomposed  by  sulphuretted  hydrogen,  the  metapectic 
acid  dissolves,  and  is  obtained  by  cautious  evaporation  to  dryness.  Its  taste  and 
reaction  are  strongly  acid  ;  it  deliquesces,  and  dissolves  easily  in  alcohol  and  water; 
it  is  not  volatile.  When  dry,  it  is  isomeric  with  the  preceding  bodies,  its  formula 
also  being  C24H17O22 ;  but  its  salts  contain  five  atoms  of  base.  Those  of  the  alka- 
lies are  soluble  and  uncrystailizable,  but  those  of  the  earths  and  heavy  metallic  ox- 
ides are  insoluble  in  water. 

Of  Salicine,  and  the  Bodies  derived  from  it. 

This  substance  exists  in  the  leaves  and  bark  of  a  great  variety  of 
trees,  but  is  particularly  abundant  in  those  species  of  salix  which  have  a 
bitter  taste.  The  bark  is  to  be  boiled  three  or  four  times  with  water, 
the  decoction  evaporated  till  it  amounts  to  but  three  times  the  weight  of 
the  bark  employed,  then  digested  for  twenty-four  hours  with  oxide  of 
lead,  and  the  clear  liquid  evaporated  to  the  consistence  of  a  sirup.  After 
a  few  days  this  becomes  a  mass  of  crystalline  fibres,  which,  separated 
by  pressure  from  the  mother  liquor,  are  to  be  purified  by  solution,  diges- 
tion  with  animal  charcoal,  and  recrystallization. 

When  pure,  salicine  is  in  the  form  of  small  white  rectangular  crystal- 
line plates  or  prisms ;  its  taste  is  very  bitter.  It  dissolves  in  eighteen 
parts  of  cold  and  in  one  of  boiling  water ;  it  is  soluble  in  alcohol,  but 
not  in  ether ;  at  212°  it  melts,  and  on  cooling  solidifies  into  a  crystalline 
mass.  The  composition  of  salicine  has  been  very  accurately  determin- 
ed ;  its  formula  is,  when  crystallized,  C2iH,209+2  Aq. ;  it  precipitates  the 
basic  acetate  of  lead,  forming  a  white  compound,  the  formula  of  which  is 
C2,H,A+3Pb.O. 

The  products  of  the  decomposition  of  salicine  are  exceedingly  remarkable. 
When  it  is  boiled  with  dilute  sulphuric  acid,  it  is  decomposed  into  grape-sugar,  and 
a  resinous  substance  termed  Saliretine.  Three  atoms  of  salicine,  C63H36O27,  giving 
saliretine,  C51H24O15,  and  sugar,  C12H12O12.  When  quite  pure,  this  body  is  white  or 
pale  yellow.     It  is  insoluble  in  water,  but  soluble  in  alcohol  and  ether. 

With  sulphuric  acid  and  chromate  of  potash,  salicine  gives  hydruret  of  salicyl 
(oil  of  spiraea),  as  described  page  573.  Although  the  evolution  of  formic  and  car- 
bonic acids,  which  occur  in  this  reaction,  show  that  it  is  in  reality  complex,  yet  its 
result  may  be  expressed  by  the  simple  abstraction  of  water  from  the  salicine,  as 
2(C2iH,209)— 6H.O.=^3(C,4H604). 

When  salicine  is  boiled  with  nitric  acid,  it  is  totally  converted  into  picric  acid. 
As  this  body  is,  however,  more  closely  connected  with  indigo,  it  will  be  there  fully 
described. 

By  the  action  of  chlorine  on  salicine  two  bodies  are  produced,  one  crystalline, 
whose  formula  is  C21H12 .  CI2O9,  and  the  other  a  heavy  oil,  consisting  of  CaiHs . 
CI4O9.     They  are  both  soluble  in  alcohol,  but  sparingly  soluble  in  water. 

If  strong  oil  of  vitriol  be  poured  on  salicine,  it  is  decomposed  into  water  and  a 


PHLORIDZINE     AND    ITS     PRODUCTS.  607 

deep  olive-green  powder,  Olivin,  the  formula  of  which  is  C21H9O6.  This  action  is 
accompanied  by  the  disengagement  of  much  heat.  Olivin  is  crystalline,  insoluble 
in  M^ater,  alcohol,  and  ether.  If  the  oil  of  vitriol  be  in  great  excess,  it  becomes 
red-coloured,  and  the  salicine  dissolves.  The  red  substance  thus  formed  is  termed 
Rujin ;  it  is  obtained  more  simply  from  phloridzine.  If  a  large  quantity  of  sahcine 
be  acted  on  by  sulphuric  acid,  it  forms  a  tenacious  mass,  which,  when  treated  with 
water,  and  the  liquor  neutralized  by  hme,  gives  a  brown  resinous  body,  which  is 
termed  Rutilin.    This  contains  sulphuric  acid,  its  formula  being  C28Hi2044-S.03. 

Of  Phloridzine  and  its  Products. 

This  remarkable  substance  exists  in  the  bark  of  the  roots  of  the  various  species 
of  apple,  pear,  plum,  and  cherry  trees.  It  is  prepared  by  infusing  the  root-bark  in 
weak  spirit  for  eight  or  ten  hours  at  120°.  The  greater  part  of  the  spirit  may  then 
be  distilled  off,  and  on  cooling,  the  phloridzine  crystallizes  from  the  remaining  liquor. 
It  forms  brilliant  silky  plates  and  needles,  perfectly  white  when  pure.  It  is  easily 
soluble  in  alcohol,  ether,  and  in  boihng  water,  but  requires  iOOO  parts  of  cold  water 
for  its  solution.  Its  taste  is  bitter  and  astringent.  The  formula  of  the  crystals  is 
C2iHiiOg-|-4  Aq.  At  212°  it  gives  off  2  Aq. ;  it  melts  at  226°,  and  boils  at  360°, 
but  is  decomposed,  water  being  evolved,  and  a  new  substance  produced.  The  solu- 
tion of  phloridzine  precipitates  some  metallic  salts.  The  persulphate  of  iron  gives 
a  brown  precipitate,  but  the  perchloride  of  iron  produces  a  blood-red  liquor  and  no 
precipitate. 

The  decomposition  of  phloridzine  by  heat  is  not  complete  until  the  temperature 
rises  to  450° ;  it  then  forms  a  deep  red  mass  of  Rujin,  the  same  substance  as  is 
produced  by  the  action  of  oil  of  vitriol  on  salicine  ;  it  is  very  soluble  in  alcohol,  in- 
soluble in  ether ;  boiled  in  water,  it  dissolves,  but  loses  its  red  colour,  and  the  liquor, 
on  cooling,  becomes  milky.  It  dissolves  in  water  of  ammonia  or  potash  with  a  rich 
red  colour,  and  is  precipitated  on  the  addition  of  an  acid ;  its  formula  is  C14H7O5 ; 
it  combines  with  oil  of  vitriol,  forming  Rufin-sulphuric  Acid,  which  unites  with  the 
metallic  oxides,  forming  red  or  brown  salts,  which  possess  considerable  analogy  to 
the  sulphovinates. 

When  phloridzine  is  dissolved  in  dilute  sulphuric  acid,  and  the  liquor  boiled,  a 
white  crystaUine  substance  separates,  which  is  termed  Phloretine ;  the  liquor  then 
contains  much  grape-sugar.  The  formula  of  phloretine  is  C51H26O17 ;  its  taste  is 
sweet ;  it  is  sparingly  soluble  in  water,  but  very  soluble  in  alcohol ;  it  melts  at  300°; 
when  heated  with  nitric  acid,  it  forms  PUoretic  Acid,  the  formula  of  which  is  C51H24 . 
N2O25 ;  it  is  a  yellow-brown  powder,  of  a  velvety  aspect,  but  not  crystalline ;  insol- 
uble in  water,  and  soluble  in  alcohol. 

The  most  remarkable  action  on  phloridzine  is  that  exercised  by  ammonia  with 
access  of  air.  Over  a  capsule  containing  water  of  ammonia  are  arranged  several 
capsules  containing  phloridzine  in  very  thin  layers,  anri  the  whole  is  so  covered 
with  a  large  bell-glass  as  that  the  air  shall  have  free  acress  ;  after  a  few  days  the 
contents  of  the  capsules  are  changed  into  a  thick  sirupy  liquor,  nearly  black ;  the 
excess  of  ammonia  being  removed  by  exposure  in  vacuo  with  sulphuric  acid,  the 
excess  of  phloridzine  is  dissolved  out  by  alcohol,  and  the  residue  then  being  dis- 
solved in  water,  gives  a  magnificent  blue  liquor,  from  which  the  colouring  substance, 
Phloridze'in,  is  precipitated  by  the  cautious  addition  of  acetic  acid ;  it  is  not  crys- 
talline ;  it  forms  a  transparent  resinous  mass  of  a  rich  crimson  colour ;  its  taste  is 
bitter ;  boiling  water  dissolves  enough  of  it  to  be  coloured  red,  but  cold  water,  al- 
cohol, or  ether  appear  scarcely  to  act  upon  it. 

The  formula  of  phloridzein  is  C21H14 .  OisN.-fAq. ;  it  is  formed,  therefore,  by  the 
combination  of  phloridzine  with  five  atoms  of  oxygen  and  one  of  ammonia ;  it  is 
not,  however,  a  salt  of  ammonia,  for  the  alkalies  dissolve  phloridzein  without  alter- 
ation, forming  magnificent  blue  solutions  ;  from  metallic  solutions  it  precipitates 
purple  or  blue  lakes,  the  composition  of  which  renders  it  probable  that  the  equiva- 
lent of  phloridzein  is  C42H28  .  026N2-f  2  Aq. ;  then  the 

Phloridzelnate  of  ammonia,  =C42H28 .  N2O26-I-N.H3. 
Phloridzeinate  of  silver,        =C42H28 .  N20264-2Ag.O. 
Phloridzeinate  of  lead,  =042X128  •  N2026-|-2Pb.O. 

If  the  blue  solution  of  phloridzeinate  of  ammonia  be  put  in  contact  with  a  slip  of 
zinc,  protochloride  of  tin,  sulphuretted  hydrogen,  or  any  other  deoxidizing  agent,  it 
is  deprived  of  colour,  but  by  exposure  to  the  air  it  rapidly  reassumes  its  tint ;  with 
chlorine  the  colour  is  instantly  and  permanently  destroyed. 


608        ASPARAGINE,     CAFFEINEj     AND     PIPERINE, 

Asparagine.     Aspartic  Acid. 

Asparagine  is  found  in  the  young  shoots  of  asparagus  and  of  potatoes,  in  the 
roots  of  liquorice  and  marsh-mallow.  From  the  latter  it  is  easily  prepared.  The 
decorticated  roots  are  to  be  digested  in  cold  water  for  forty-eight  hours,  and  the  li- 
quor then  strained  and  evaporated  to  the  consistence  of  a  sirup.  By  standing  foi 
some  time,  the  asparagine  gradually  crystallizes,  and  the  crystals  are  to  be  purified 
in  the  ordinary  manner  by  animal  charcoal.  It  forms  rectangular  octohedrons  and 
prisms;  it  is  colourless  and  tasteless;  it  requires  about  sixty  parts  of  cold,  but  much 
less  of  hot  water  for  solution ;  it  is  insoluble  in  alcohol ;  it  contains  nitrogen,  its 
formula  being  N.C4 .  H4034-Aq. ;  the  water  goes  away  by  a  heat  of  230°. 

When  asparagine  is  boiled  with  a  strong  solution  of  barytes,  ammonia  is  expell- 
ed, and  aspartate  of  barytes  formed  ;  by  cautiously  adding  sulphuric  acid,  the  bary- 
tes may  be  precipitated,  and  the  liquor  yields,  on  evaporation  and  cooling,  crystal- 
lized aspartic  acid.  In  this  reaction  2(N.C4 .  H4O3)  produces  N.H3  and  N.Cs .  H5O6, 
which  is  the  formula  of  aspartic  acid.  This  substance  is  tasteless,  sparingly  solu- 
ble in  cold,  but  abundantly  in  boiling  water,  and  is  deposited  as  a  white  crystal- 
line powder  as  the  solution  cools  ;  it  reddens  litmus.  Its  salts  are  generally  solu- 
ble, except  those  of  lead,  silver,  and  black  oxide  of  mercury. 

It  is  not  easy  to  decide  whether  the  ammonia  exists  ready  formed  or  not  in  the 
asparagine  ;  if  so,  the  remaining  organic  element  may  be  aconitic  acid  (see  p.  597), 
and  then  there  should  be, 

Asparagine=ranhydrous  aconitate  of  ammonia=C4H.03-|-N.H3. 
Aspartic  acid=anhydrous  binaconitate  of  ammonia=2(C4H.03)-|-N.H3. 

In  the  case  of  the  anhydrous  compounds  of  ammonia  with  the  mineral  acids,  it  is 
retained  with  the  same  obstinacy  as  in  asparagine  (see  p.  508). 

Caffeine  or  The'ine.     Caffeic  Acid, 

This  has  been  found  only  in  the  coffee-berry,  the  tea-leaf,  and  the  paulinia  sor- 
baUs  (guarana).  To  prepare  it,  raw  coffee  is  to  be  boiled  in  water,  and  the  decoc- 
tion treated  with  subacetate  of  lead  as  long  as  the  precipitate  which  forms  is  col- 
oured. The  caffeine  crystallizes  from  the  filtered  liquor  by  evaporation  and  cooling ; 
if  it  be  coloured,  it  is  to  be  boiled  with  oxide  of  lead  and  ivory  black,  and  again 
crystallized  ;  when  pure,  it  forms  brilliant  long  needles  of  a  rich  satiny  lustre  ;  its 
taste  is  purely  bitter  ;  it  dissolves  in  fifty  parts  of  cold,  but  in  much  less  of  boiling 
water  ;  it  is  very  soluble  in  proof  spirit,  but  insoluble  in  absolute  alcohol ;  its  solu- 
tions react  neither  acid  nor  alkaline  ;  it  is  not  precipitated  by  any  metallic  salt. 
Caffeine  is  remarkable  for  the  large  quantity  of  nitrogen  it  contains  (29  per  cent.), 
being  more  than  any  other  vegetable  substance  ;  its  formula  is  NzCg.  H502H-Aq. 
When  caffeine  is  boiled  with  solution  of  barytes,  cyanuric  acid,  ammonia,  formic, 
and  carbonic  acids  are  produced. 

The  coloured  precipitate  produced  in  the  decoction  of  raw  coffee  by  acetate  of 
lead  contains  two  peculiar  substances,  which  may  be  extracted  from  it  by  treat- 
ment with  a  stream  of  sulphuretted  hydrogen  gas,  evaporation  to  the  consistence  of 
a  sirup,  and  digestion  of  the  residue  in  strong  alcohol.  That  which  dissolves  is 
Caffetannic  Acid ;  it  is  dark  brown  ;  tastes  acid  and  astringent ;  colours  the  per- 
salts  of  iron  emerald  green  ;  it  precipitates  the  salts  of  barytes  and  lime  yellow,  of 
copper  green,  but  does  not  affect  tartar-emetic.  The  substance  insoluble  in  alcohol 
is  a  white  powder,  which,  when  heated,  evolves  the  characteristic  aromatic  smell 
of  roasted  coffee  ;  its  solution  in  water  reddens  litmus  ;  it  is  termed  Caffeic  Acid. 

These  bodies  have  not  been  accurately  examined.  It  is  not  known  if  the  tannic 
acid  of  tea  and  coffee  be  the  same, 

Piperine. — N.C34 .  HigOe. 

This  substance  exists  in  white,  black,  and  long  pepper ;  it  is  prepared  from  white 
pepper  by  digestion  in  spirit  of  wine,  and  distilling  the  liquor  to  the  consistence  of 
an  extract,  from  which,  by  digestion  in  a  solution  of  caustic  potash,  a  quantity  of 
resin  is  to  be  removed  ;  the  residue  is  then  to  be  dissolved  in  alcohol,  and  the  solu- 
tion abandoned  to  spontaneous  evaporation,  when  the  piperine  gradually  crystallizes 
in  transparent  rhombic  prisms.  It  melts  at  212°  ;  is  tasteless  and  inodorous  ;  des- 
titute of  either  acid  or  basic  properties  ;  nitric  acid  colours  it  red  ;  when  heated 
strongly,  it  yields  ammoniacal  products. 


ONIA'E,     CETRARINE,     PICROTOXINE,     ETC. 


609 


CanZ/ianiirac— C10H6O4.  This  substance  is  extracted  from  the  blistering  fly  (va- 
rious species  of  cantharis  and  lytta)  by  digesting  a  watery  extract  of  the  flies  in  al- 
cohol, evaporating  the  solution  to  dryness,  and  treating  the  residue  with  ether, 
which  dissolves  out  the  cantharidine.  By  spontaneous  evaporation  it  is  obtained 
crystallized ;  it  forms  colourless  pearly  scales,  which  fuse  when  gently  heated, 
and  sublime  unaltered  at  a  higher  temperature  ;  it  is,  when  pure,  insoluble  in  water 
and  in  cold  alcohol ;  it  is  perfectly  neutral,  and  has  no  aftinity  either  to  acids  or 
bases. 

Anemonine.     Anemonic  Acid. 

This  substance  exists  in  various  species  of  anemone  ;  it  is  extracted  by  distilling 
the  plant  with  water ;  it  separates,  after  some  time,  from  the  distilled  water,  in 
brilliant  white  needles  ;  it  melts  and  volatilizes  at  a  high  temperature,  yet  not  with- 
out partial  decomposition ;  its  formula  is  C6H3O4 ;  when  it  is  dissolved  in  strong 
muriatic  acid,  and  the  liquor  evaporated  to  dryness,  Anemonic  Acid  is  formed  ;  its 
formula  is  CeR40r^-\-Aq.    It  is  not  important. 

«    Cetrarine,  or  Lichen  Bitter. 

This  substance  is  found  in  Iceland  moss  ;  to  extract  it,  the  lichen,  being  well 
crushed,  is  to  be  digested  in  alcohol  as  long  as  this  acquires  a  bitter  taste  ;  the  li- 
quor may  then  be  distilled  in  great  part  off,  and  the  cetrarine  is  deposited,  on  cool- 
mg,  m  granular  crystals  ;  these  are  to  be,  while  still  moist,  washed  with  ether  and 
cold  alcohol,  by  which  they  are  rendered  white,  and  then  being  dissolved  in  200 
times  their  weight  of  boiling  alcohol,  the  pure  cetrarine  separates  on  cooling  as  a 
white  powder  of  a  slightly  crystalline  aspect.  It  is  but  sparingly  soluble  in  any 
menstruum  ;  its  only  remarkable  character  is,  that  by  digestion  with  muriatic  acid 
it  forms  a  deep  blue  mass,  but  the  nature  of  the  reaction  is  not  known,  as  the  con- 
stitution of  these  bodies  has  not  been  accurately  investigated. 

Picrotoxine,  or  Cocculine. 

This  substance  exists  in  the  seeds  of  the  menispennum  cocculus  (cocculus  Indi- 
cus),  constituting  their  active  ingredient ;  to  prepare  it,  the  seeds,  freed  from  the 
capsules,  are  to  be  digested  in  alcohol,  and  the  solution  evaporated  to  an  extract ; 
this  is  to  be  then  treated  with  water  as  long  as  anything  is  dissolved,  and  then 
some  muriatic  acid  added  to  the  liquor ;  by  cooling,  the  cocculine  crystalhzes  in 
brilliant  wliite  needles.  Its  reaction  is  neutral ;  its  taste  intensely  bitter ;  it  dis- 
solves moderately  in  boiling,  but  sparingly  in  cold  water.  The  portion  of  the  alco- 
holic extract  which  does  not  dissolve  in  water  contains  another  substance,  Picro- 
toxic  Acid,  which  is  brown,  and  possesses  the  properties  of  a  resin  ;  it  dissolves  in 
alkahne  liquors,  from  which  acids  throw  it  down  unchanged.  The  formula  C10H6O4 
has  been  assigned  to  picrotoxine,  and  that  of  CiiHc04  to  picrotoxic  acid. 

Cciumbine. — Found  in  the  roots  of  the  menispermum  palmatum.  The  coarsely- 
powdered  columbo-roots  are  to  be  digested  in  ether,  and  by  the  spontaneous  evap- 
oration the  columbine  crystallizes  ;  or  by  digesting  the  roots  in  alcohol,  and  decol- 
orizing the  liquors  by  animal  charcoal,  it  may  also  be  prepared  ;  it  forms  brilliant 
right  rhombic  prisms ;  its  taste  is  intensely  bitter  ;  its  reaction  neutral ;  it  dissolves 
but  sparingly  in  water,  alcohol,  or  ether  ;  its  solution  does  not  precipitate  any  me- 
tallic salt ;  its  formula  appears  to  be  C24H12O7. 

Cusparinc. — This  is  the  active  principleof  the  true  angustura  (cusparia  febrifuga). 
The  bark  is  to  be  extracted  by  alcohol,  and  the  solution  concentrated  very  much  by 
spontaneous  evaporation  ;  on  cooling  then  below  32^,  granular  crystalline  masses 
of  cusparine  separate,  from  which  the  liquor  is  to  be  strained  ;  by  redissolving  in 
alcohol,  and  precipitation  of  the  colouring  matter  by  acetate  of  lead,  it  is  ultimately 
obtained  pure.  When  crystallized  from  a  solution  some  degrees  below  32°,  cuspa- 
rine forms  colourless  but  irregular  needles  ;  by  a  very  gentle  heat  it  melts  and  gives 
off  twenty-three  per  cent,  of  water  of  crystallization  ;  it  dissolves  readily  in  water 
and  alcohol,  but  is  insoluble  in  ether ;  by  heat  it  is  totally  decomposed  ;  its  solu- 
tions precipitate  most  metallic  salts.     Its  composition  is  not  known. 

Elatcrine  is  the  active  material  of  the  expressed  juice  of  the  momordica  elaterium ; 
the  juice,  being  evaporated  to  the  consistence  of  an  extract,  is  to  be  digested  in 
strong  alcohol ,  the  solution  thus  formed  is  to  be  distilled  to  a  small  bulk,  and  then, 
on  being  mixed  with  water,  it  deposites  the  elaterine  as  a  white  crystalline  powder. 
It  melts  at  about  320°,  but  is  totally  decomposed  by  a  stronger  heat ;  its  taste  is 

4H 


610     MECONINE,    PEUDECANINE,    iESCULINE,    ETC. 

intensely  bitter  ;  it  is  almost  insoluble  in  water,  but  abundantly  in  alcohol ;  it  pos- 
sesses no  characteristic  chemical  property. 

Meconine. — This  substance  exists  mixed  with  the  more  important  ingredients  m 
opium  ;  it  is  most  abundant  in  the  inferior  kinds  ;  its  preparation  is  very  circuitous, 
and  will  be  described  in  the  general  analysis  of  opium,  under  the  head  of  narceine. 
Meconine  crystallizes  in  white  six-sided  prisms  ;  it  melts  at  194°,  and  may  be  sub- 
limed unaltered  ;  it  dissolves  sparingly  in  cold,  but  moderately  in  boiling  water, 
abundantly  in  alcohol  and  ether ;  its  formula  appears  to  be  C2oH907-j-Aq.  By  nitric 
acid  it  is  dissolved,  and  a  substance  crystallizes  from  the  liquor  in  long  needles, 
which  is  termed  Nitromeconic  Acid;  its  formula  is  N.C20  •  H9O12 ;  its  solution  in  watei 
reddens  litmus  ;  it  volatilizes  at  370°,  but  is  partly  decomposed.  By  contact  with 
chlorine,  meconine  is  coloured  red,  and  substances  formed  whose  constitution  is^not 
well  known. 

Peudecanine. — This  substance  is  found  in  the  roots  of  the  peudecanum  officinale, 
and  is  extracted  by  digestion  with  alcohol  and  evaporation  ;  it  crystallizes  in  deli- 
cate white  needles  of  a  slightly  aromatic  taste  ;  it  fuses  at  140°  ;  it  is  insoluble  in 
water,  and  but  sparingly  in  cold  alcohol ;  it  dissolves  copiously  in  boiling  alcohol, 
in  ether,  and  the  oils. 

jEscuUne,  or  Polychrome. 

A  great  number  of  vegetables  give,  when  treated  with  hot  water,  a  solution  which 
appears  yellow  by  transmitted,  hut  violet  or  blue  by  reflected  light.  This  phenom- 
enon results  from  the  presence  of  a  body  hence  called  Polychrome,  and  aXsoJEsculine^ 
being  most  abundant  in  the  bark  of  the  horse-chestnut.  The  bark  is  to  be  digested 
in  alcohol,  and  the  liquor  to  be  concentrated  by  distillation  to  the  consistence  of  a 
sirup,  in  which,  when  set  aside  for  some  weeks,  the  aesculine  crystallizes ;  by  wash- 
ing with  ice-cold  water  it  is  freed  from  the  liquid  extractive  matter  ;  the  impure 
crystals  are  to  be  dissolved  in  a  boiling  mixture  of  five  parts  of  alcohol  with  one  of 
ether,  from  which,  by  cooling,  the  pure  substance  separates,  perfectly  colourless. 
and  generally  as  a  light  powder,  like  magnesia  alba.  It  tastes  bitter  ;  it  dissolves 
in  672  parts  of  water  at  50°,  and  in  thirteen  parts  at  212°  ;  its  cold,  watery  solution 
is  perfectly  colourless  by  transmitted,  but  slightly  blue  by  reflected  light ;  if  spring- 
water  be  used,  the  blue  becomes  much  stronger  ;  acids  destroy  this  property,  but  it 
is  restored  to  the  solution  by  the  addition  of  a  few  drops  of  any  alkali. 

The  watery  solution  of  aesculine  reddens  litmus,  yet  it  does  not  neutralize  the  al- 
kalies, nor  precipitate  any  of  the  ordinary  metallic  salts  ;  it  dissolves  abundantly  in 
alkaline  liquors,  and  the  solutions  give  a  magnificent  play  of  colours  with  reflected 
light ;  its  formula  is  CieHgOio- 

Populine  exists  in  the  bark  and  leaves  of  different  species  of  populus,  along  with 
salicine  ;  the  latter  is  removed  from  the  liquors  by  precipitation  with  acetate  of 
lead,  and  then,  by  evaporation,  the  populine  is  obtained  crystallized  ;  its  taste  is  bit- 
ter-sweet, like  liquorice  ;  it  is  very  sparingly  soluble  in  water  ;  when  heated,  it  fu- 
ses, and  is  then  decomposed  ;  like  salicine,  it  gives  with  nitric  acid,  picric  acid,  and 
with  sulphuric  acid,  rutilin  ;  its  composition  is  not  known. 

Quassine  constitutes  the  bitter  principle  of  the  quassia  amara  and  excelsa.  The 
rasped  wood  is  to  be  boiled  several  times  with  water,  and  the  fihered  decoction 
evaporated  down  to  three  fourths  the  weight  of  the  wood  employed.  The  liquid, 
when  cold,  is  to  be  mixed  with  slacked  lime,  and,  after  twenty-four  hours,  filtered 
and  evaporated  nearly  to  dryness  ;  the  residue  is  to  be  treated  with  alcohol,  and  the 
solution  distilled  in  a  water-bath  to  dryness  ;  it  is  then  impure  quassine  ;  it  is  to  be 
washed  with  ether,  and  then  redissolved  in  alcohol,  and  this  treatment  repeated 
until  it  becomes  completely  white. 

Quassine  forms  small  white  prisms  of  an  intense  but  purely  bitter  taste ;  but  spa- 
ringly soluble  in  water  or  in  ether,  it  dissolves  abundantly  in  alcohol ;  when  heated, 
it  fuses  like  a  resin  ;  its  solution  is  not  precipitated  by  any  metallic  salt,  but  abund 
antly  by  tannic  acid  ;  its  formula  is  C20H12O6. 

Santonine. — This  substance  exists  in  the  flowering  tops  and  seeds  of  a  number  of 
species  of  artemisia,  from  one  of  which  (art.  santonica)  it  derives  its  name.  To 
prepare  it,  four  parts  of  the  seeds  are  to  be  mixed  with  one  and  a  half  of  dry  lime, 
and  boiled  in  twenty  parts  of  alcohol  three  times  ;  the  united  decoctions  are  to  be 
distilled  to  fifteen  parts  ;  the  residue,  when  cold,  is  to  be  filtered,  evaporated  to  one 
half,  and,  having  been  rendered  slightly  acid  by  vinegar,  boiled  for  some  time  ;  on 
cooling,  the  santonine  crystallizes  in  large  featherv  crystals,  which  are  to  be  puri- 
fied from  an  adhering  resinous  substance  by  washing  with  alcohol.     Being  then  re- 


SAPONINEj-^SCILLITINE,    SENEGINE,    ETC.         611 

dissolved,  and  the  solution  slowly  cooled,  the  santonine  crystallizes  in  colourless 
rectangular  prisms  and  plates ;  it  is  tasteless ;  it  is  very  sparingly  soluble  in  water; 
more  so  in  alcohol  and  ether ;  at  338°  it  melts,  and  by  a  carefully-applied  heat  may 
be  sublimed  without  decomposition,  otherwise  it  becomes  brown,  and  a  yellow  crys- 
talline substance  is  formed.  Santonine  appears  to  possess  feeble  acid  properties  ;  it 
produces  with  the  alkalies  soluble,  and  with  the  earths  and  ordinary  metallic  oxides 
insoluble  compounds,  but  they  are  of  instable  constitution.  The  formula  of  santo- 
nine is  CioHsOa. 

By  exposure  to  light,  santonine  undergoes  a  change  apparently  isomeric  ;  it  be- 
comes gold-coloured,  and  forms  yellow  solutions,  which,  however,  soon  become 
colourless. 

Saponine. — This  substance  is  most  easily  extracted  from  the  roots  of  the  sapona- 
ria  officinalis  by  boiling  in  weak  spirit ;  on  cooling,  the  saponine  separates  ;  it  is 
purified  by  digestion  with  animal  charcoal ;  it  is  a  white  powder,  of  a  sharp,  piquant 
taste ;  very  soluble  in  water,  it  is  sparingly  soluble  in  alcohol,  and  insoluble  in  ether; 
its  formula  appears  to  be  C26H230)6.  By  the  action  of  nitric  acid,  saponine  forms 
mucic  acid  and  a  resinous  substance ;  when  dissolved  in  solution  of  caustic  pot- 
ash, it  forms  Saponinic  Acid,  which  is  precipitated  as  a  white  powder  on  adding  a 
stronger  acid  to  the  liquor.  The  formula  of  saponinic  acid  is  C26H22O12.  It  is  in- 
soluble in  cold,  but  soluble  in  boiling  water. 

Scillitine  is  the  active  principle  of  the  squill  (scilla  maritima).  The  fresh  juice  is 
evaporated,  and  the  extract  treated  with  alcohol.  The  spirituous  solution  is  to  be 
dried  down,  and  the  residue,  being  dissolved  in  water,  is  to  be  precipitated  with  ace- 
tate of  lead,  and  filtered  ;  sulphuretted  hydrogen  being  passed  through  the  clear  li- 
quor removes  the  excess  of  lead,  and  then,  by  filtration  and  evaporation,  the  scillitine 
may  be  crystallized. 

It  forms  a  hard,  brittle  mass,  like  resin,  of  an  intensely  bitter  taste ;  it  deliques- 
ces and  dissolves  readily  in  alcohol  and  water,  but  not  in  ether. 

Senegine. — This  substance  is  extracted  from  the  roots  of  the  polygala  senega  by 
boiling  with  water,  precipitating  the  concentrated  decoction  with  the  acetate  of  lead, 
filtering  and  removing  the  excess  of  lead  from  the  solution  by  sulphuretted  hydro- 
gen, and  evaporating  cautiously  to  dryness  ;  the  residue  is  to  be  digested  in  alcohol, 
and  this  solution  being  dried  down,  the  product  is  to  be  digested  in  ether.  The  ma- 
terial which  remains  undissolved  is  then  to  be  passed  through  the  same  series  of 
operations  until  it  becomes  a  white  pulverulent  mass,  which  is  pure  Senegine.  It  is 
sparingly  soluble  in  cold,  but  abundantly  in  boiling  water ;  it  is  very  soluble  in  alco- 
hol, but  insoluble  in  ether.  With  sulphuric  acid  it  produces  a  curious  play  of  col 
ours,  becoming  first  yellow,  after  some  time  rose-red,  and  then  dissolving;  the  so- 
lution gradually  becomes  violet,  after  some  time  grayish-blue,  and  finally  colourless, 
while  a  gray  precipitate  falls  down.  Senegine  appears  to  possess  feeble  acid  prop- 
erties. 

Smilacine,  or  Sarsaparilline. — This  substance  is  found  in  the  roots  of  the  smilax 
sarsaparilla  and  the  bark  of  the  China  nova.  It  is  obtained  by  boiling  with  alcohol, 
and  distilling  the  decoction  to  two  thirds  ;  on  cooling,  the  smilacine  crystallizes,  and 
is  purified  by  animal  charcoal  and  recrystallization.  It  is  white,  in  very  minute  nee- 
dles ;  its  taste  nauseous  and  slightly  bitter ;  very  sparingly  soluble  in  water,  more 
so  in  alcohol,  most  in  ether ;  with  sulphuric  acid  it  gives  colours  like  those  of  sen- 
egine. 

Absinthiine. — The  bitter  principle  of  the  wormwood  (artemisia  absinthium).  It  is 
prepared  by  a  succession  of  operations  almost  identical  with  those  described  for  ob- 
taining senegine  ;  it  is  hence  unnecessary  to  repeat  their  description.  When  com- 
pletely pure,  it  is  white  and  crystalline ;  its  taste  is  intensely  bitter ;  it  fuses  at  a 
high  temperature,  and  closely  resembles  a  resin ;  its  best  solvent  is  alcohol.  It 
possesses  the  characters  of  a  weak  acid,  being  much  more  soluble  in  alkaline  liquors 
than  in  pure  water,  and  being  precipitated  from  such  solutions  on  the  addition  of 
an  acid.    With  oil  of  vitriol,  it  is  coloured  first  yellow,  and  then  dark  reddish  purple. 

Lactucinc  is  obtained  by  digesting  the  inspissated  juice  of  the  lactuca  virosa  (lac- 
tucarium)  in  ether ;  by  the  spontaneous  evaporation  of  the  solution,  it  forms  a  mass 
of  crystalline  needles,  slightly  coloured  yellow  ;  it  has  a  strong  bitter  taste,  is  fusi- 
ble, and  may  be  partly  volatilized  ;  it  is  soluble  in  water,  alcohol,  and  ether.  It  is 
decomposed  by  strong  acids,  and  appears  not  to  have  any  tendency  to  form  salts. 


612  APOTHEME. EXTRACTIVE. 

Of  Extractive  Matter.     Apotheme.     Extracts. 

If  from  any  plant,  or  portion  of  a  plant,  the  soluble  ingredients  be 
dissolved  out  by  water,  a  variety  of  substances  exist  in  the  liquor,  some 
acid,  others  basic,  others  indifferent ;  of  these  bodies,  the  majority  pos- 
sess the  property  of  absorbing  oxygen  when  the  solution  is  exposed  to 
the  air,  and  often,  also,  of  evolving  carbonic  acid,  changing  thereby  into 
substances  insoluble,  or  scarcely  soluble  in  water.  Thus  gallo-tannic 
acid  first  forms  gallic  acid,  and  is  then  converted  into  a  brown  insoluble 
mass;  so  gum  and  sugar  ultimately  produce  certain  forms  of  ulmine; 
and  there  are  few  of  the  neutral  principles  described  in  the  present 
chapter  that  do  not  rapidly  undergo  a  similar  change. 

During  the  evaporation  of  a  vegetable  infusion  or  decoction,  these  re- 
actions rapidly  occur,  being  promoted  by  the  heat ;  the  liquor,  which  had 
been  at  first  clear,  becomes  turbid  and  brown,  a  deposite  forms,  and  when, 
finally,  it  has  been  evaporated  to  the  consistence  of  a  thick  sirup,  what 
remains  is  termed  an  extract;  it  is  a  mixture  of  the  constituents  of  the 
plant  in  great  part  decomposed.  If  this  extract  be  treated  with  water, 
and  tl^e  soluble  portion  again  evaporated,  the  same  changes  occur,  so 
that,  no  matter  what  may  have  been  the  original  nature  of  the  vegetable 
substances,  they  are  ultimately  reduced  to  this  insoluble  and  inert  con- 
dition. This  brown  substance  is  termed  Apotheme ;  its  true  nature  is 
not  known,  but  it  is  probable  that  its  composition  and  properties  vary  in 
some  degree  with  the  nature  of  the  substance  it  is  formed  from  ;  we  do 
not  even  know  of  its  relations  to  the  various  kinds  of  ulmine ;  though, 
from  its  solubility  in  alkaline  liquors,  and  its  precipitating  metallic  salts, 
its  being  separated  from  these  by  acids,  and  obstinately  retaining  a  por- 
tion of  the  acid  used  to  precipitate  it,  its  identity  with  ulmic  acid  or 
humic  acid  is  not  improbable. 

When  the  conversion  of  the  real  constituents  of  the  plant  into  apo. 
theme  is  yet  incomplete,  the  material,  which  dissolves  equally  in  water 
and  dilute  alcohol,  but  not  in  absolute  alcohol  or  in  ether,  is  termed 
extractive.  Such  a  mixture  can  have  no  distinctive  chemical  properties  ; 
it  is  more  or  less  coloured,  and  uncrystallizable  ;  it  precipitates  metallic 
salts  ;  it  absorbs  oxygen,  forming  apotheme  (oxidized  extractive).  The 
different  classes  of  plants  are  considered  by  pharmaceutic  writers  to  con- 
tain different  kinds  of  extractive  matter;  there  are  thus  hitter  extractive, 
gummy  extractive,  astringent  extractive,  and  so  on ;  but,  to  the  chemist, 
these  names  convey  only  the  idea  of  absolute  ignorance  of  the  real 
nature  of  these  bodies ;  the  chemist  recognises  no  such  substance  as 
extractive  matter,  or  Apotheme;  they  are  merely  complex  products  of 
decomposition  of  other  bodies,  and  have  not,  as  yet,  been  accurately  ex- 
amined. In  the  preparation  of  an  extract  of  a  plant,  the  ambition  of  the 
operator  should  be,  not  to  have  either  extractive  or  apotheme  produced, 
but,  by  employing  the  lowest  possible  temperature,  and  excluding  air  as 
much  as  possible,  to  obtain  the  constituents  of  the  plant  in  a  concentrated 
form,  but  not  destroyed,  as  they  too  frequently  are,  by  the  operation : 
accordingly,  in  the  manufacturing  laboratory  of  the  Apothecaries'  Hall 
of  Ireland,  the  greatest  precautions  are  taken  to  ensure  success  in  the 
preparation  of  extracts ;  but  details  of  the  methods  belong  to  pure  phar- 
macy, and  are  unfitted  for  the  present  work. 

A  great  number  of  bodies,  that  have  been  from  time  to  time  announced  as  the 
active  principles  of  many  plants  containing  them,  are  really  but  such  extracts,  prop- 


COLOURING     MATTERS.  613 

eriy  prepared,  but  still  not  the  pure  chemical  substances.  Thus,  from  colocynth, 
Colocynthine ;  from  hippo,  Emetine ;  from  rhubarb,  Rheine,  &c.  It  is  on  this  account 
that  many  bodies,  to  which  distinct  names  have  been  given  by  their  discoverers,  as 
chemical  species,  are  not  noticed  as  such  by  me. 

The  bitter  principle  of  the  Aloes  is  one  of  these  which  have  never  been  obtained 
chemically  pure,  and  yet  the  very  remarkable  products  of  the  action  of  nitric  acid 
on  it  show  that  it  is  a  truly  distinct  substance.  When  socotrine  or  hepatic  aloes 
are  digested  with  hot  nitric  acid,  red  fumes  are  abundantly  evolved,  and  four  dif- 
ferent acids  produced,  for  the  accurate  examination  of  which  we  are  indebted  to 
Schunk.  They  are,  the  Alo'ttic  Acid,  the  Alo'e-resinic  Acid,  the  Chrysammic  Acid, 
and  the  Chrysolepic  Acid,  and  they  are  generated  by  successive  oxidation  of  the  bit- 
ter principle  of  the  aloes,  in  the  order  in  which, their  names  stand. 

The  Alo'etic  Acid  is  a  yellow  powder,  insoluble  in  water,  but  forming  soluble  salts, 
of  which  that  with  potash  crystallizes  in  ruby-red  needles.  The  Alo'e-resinic  Acid 
is  soluble  in  water ;  its  potash  salt  uncrystallizable ;  its  combinations  with  the  me- 
tallic oxides  insoluble,  and  generally  brownish-red.  The  analyses  of  these  bodies 
are  not  yet  published. 

The  Chrysammic  Acid  is  a  greenish-yellow  crystalline  powder ;  it  is  very  spa- 
ringly soluble  in  water,  yet  tinges  it  purplish-red  ;  it  is  more  soluble  in  alcohol,  ether, 
and  acids ;  when  heated,  it  fuses,  and  is  then  decomposed  with  a  slight  explosion, 
and  a  bright  but  smoky  flame  ;  it  contains  nitrogen  ;  its  formula  is  C15H2  .  N2O12+ 
Aq.  The  chrysammate  of  barytes  is  a  red  insoluble  powder.  The  chrysammate 
of  potash  is  the  most  insoluble  of  all  the  salts  of  potash,  requiring  1250  parts  of  wa- 
ter at  60°  for  solution,  and  may  hence  serve  as  an  excellent  reagent  for  that  alkali ; 
it  is  a  dark  red  crystalline  powder  when  precipitated,  but  when  it  crystallizes  from 
a  hot  dilute  solution,  it  forms  gold-coloured  plates. 

The  Chrysolepic  Acid  is  distinguished  by  its  solubility  in  water  ;  it  crystallizes  ni 
beautiful  gold-coloured  plates,  closely  resembling  Picric  Acid,  with  which  it  is  isom- 
eric, its  formula  being  C12H2  ,  NaOia-f-Aq.  It  is  distinguished,  however,  by  the 
much  greater  solubility  of  its  potash  salt,  and  by  the  action  of  heat,  as  it  may  be 
fused  and  volatilized  without  decomposition,  if  cautiously  heated. 


CHAPTER  XXVI. 

OF    THE    COLOURING   MATTERS. 

The  substances  to  be  now  described  may  be  arranged  in  two  classes, 
according  as  they  pre-exist  in  the  plant,  or  as  they  are  merely  products 
of  the  decomposition  of  other  bodies  which  are  not  coloured ;  of  these 
last  an  example  has  already  been  given  in  the  formation  of  phloridzeine 
from  phloridzine. 

SECTION  I. 

OF    THE    PRE-EXISTING   COLOURING    MATTERS. 

Colouring  Principles  of  Madder, 

The  dried  roots  of  the  rubia  tinctorum  constitute  the  madder  of  com- 
merce,  which,  furnishing  the  well-known  Turkey  red,  is  perhaps  the 
most  important  of  the  dyestufFs.  The  constitution  of  madder  is  very 
complex ;  it  contains  five  different  colouring  matters  and  two  colourless 
acids,  the  general  preparation  and  properties  of  which  are  as  follows : 

Madder  Purple,  or  Purpurine. — Madder  roots  are  to  be  well  washed 
with  water  at  80°,  then  boiled  several  times  in  a  strong  solution  of  alum, 
and  each  liquor  filtered  while  very  hot.  On  cooling,  a  red-brown  sub- 
stance precipitates,  which  is  impure  Madder  Red;  it  is  to  be  separated 


G14  COLOURING    PRINCIPLES    OF     MADDER. 

by  trie  filter.  On  adding  to  the  clear  red  solution  some  sulphuric  acid, 
the  madder  purple  is  thrown  down.  To  obtain  it  quite  pure,  it  is  to  be 
dissolved  in  boiling  alcohol,  and  the  solution  allowed  to  evaporate  slowly. 
It  separates  as  a  fine  orange-red  crystalline  powder,  sparingly  soluble 
in  cold,  but  more  easily  in  boiling  water.  The  solution  is  rose-red  ;  its 
solutions  in  ether  and  alcohol  are  bright  red.  Acids  turn  it  yellow ;  al- 
kalies dissolve  it  with  a  rich  red  colour.  It  is  fusible,  and,  when  more 
strongly  heated,  a  portion  sublimes  as  a  red  powder,  but  the  greater  part 
is  decomposed. 

Madder  Red,  or  Alizarine,  as  precipitated  in  the  preparation  of  pur- 
purine,  is  to  be  purified  by  repeated  boiling  with  solution  of  alum,  and 
then  crystallized  by  solution  in  ether  and  spontaneous  evaporation.  It  is 
a  brownish -yellow  crystalline  powder.  When  heated,  it  sublimes,  form- 
ing brilliant  orange  needles ;  it  is  sparingly  soluble  in  water,  more  so  in 
alcohol  and  ether.  Ammonia  dissolves  it  with  a  purple  red,  and  potash 
or  lime  with  a  violet  colour.  The  formula  CarHjaOio  has  been  assigned 
to  this  body. 

Madder  Orange. — The  roots  are  to  be  digested  for  sixteen  hours  in 
eight  parts  of  water  at  70°  ;  the  infusion  is  to  be  filtered  and  set  aside ; 
small  orange  crystals  gradually  for4Ti ;  these  are  to  be  collected  and  dis- 
solved  in  boiling  alcohol.  On  cooling,  the  madder-orange  crystallizes  as 
a  yellow  powder.  When  heated,  it  fuses,  and  is  decomposed  in  great 
part,  some  of  it  subliming  in  yellow  fumes ;  it  is  most  easily  soluble  in 
eth^r ;  it  dissolves  in  alkaline,  forming  brown-red  liquors. 

Madder  Yellow,  or  Xanihin. — The  cold  infusion  of  madder  is  to  be 
mixed  with  an  equal  volume  of  lime  water.  The  dark-red  precipitate 
is  to  be  treated  with  dilute  acetic  acid  ;  the  lime  and  the  yellow  dissolve  ; 
any  traces  of  the  other  colouring  matters  are  removed  from  the  liquor 
by  a  woollen  cloth  mordanted  with  alum.  The  solution  is  to  be  then 
evaporated,  the  residue  dissolved  in  alcohol,  and  precipitated  by  sugar 
of  lead  ;  the  scarlet  precipitate  separated,  and  decomposed  by  sulphuret- 
ted hydrogen.  The  liquor  so  obtained  gives,  on  evaporation,  the  xan- 
thine pure;  it  is  yellow,  uncrystaUizable,  and  very  soluble  in  alcohol 
and  water. 

Madder  Brown  is  totally  insoluble  both  in  alcohol  and  water.  The 
acids  which  exist  in  madder  are  but  very  little  known,  and  do  not  possess 
any  interest  either  technical  or  scientific. 

Of  these  colouring  matters,  the  Red,  or  Alizarine,  is  the  most  important, 
as  it  forms  with  an  alumina  mordant  the  magnificent  Turkey  Red.  With 
an  iron  mordant  it  gives  a  permanent  black,  and  with  mixed  mordants 
of  the  two,  various  intermediate  shades  of  purple.  The  great  complexity 
of  the  process  for  dyeing  Turkey  red  arises  from  the  difficulty  of  dis- 
solving away  the  other  four  bodies,  so  that  only  pure  madder  red  may 
remain. 

Alkanna  Red,  or  Anchusic  Acid. 

This  substance  exists  in  the  roots  of  the  anchusa  tinctoria.  They  are  to  be  well 
boiled  in  water,  and  then  digested  in  a  solution  of  carbonate  of  potash  ;  on  the  ad- 
dition of  an  acid  to  this  liquor,  the  colouring  matter  precipitates ;  it  may  also  be 
obtained  by  digesting  the  roots  in  alcohol  and  evaporating ;  it  is  a  dark-red  resin- 
ous body,  insoluble  in  water,  soluble  in  alcohol,  ether,  and  the  essential  oils  ;  it 
combines  with  alkalies,  forming  blue  solutions,  which  give  blue  or  crimson  lakes 
with  metallic  salts.     The  formula  C17H10O4  has  been  assigned  to  this  body. 

Braziliine  is  the  colouring  matter  of  various  soeries  of  ca-sabina  (Brazil  wood, 


SAFFLOWER     RED,     ETC.  615 

fernambouc  wood).  The  decoction  of  the  wood  in  water  is  to  be  agitated  with  hy- 
drated  oxide  of  lead,  then  filtered  and  evaporated  to  dryness.  The  residue  is  to  be 
treated  with  alcohol,  the  solution  mixed  with  water  and  gelatine,  which  throws 
down  a  quantity  of  tannic  acid,  then  filtered,  again  dried,  mixed  with  alcohol,  and 
filtered  to  separate  the  excess  of  gelatine,  then  again  evaporated,  and  set  aside  to 
crystallize. 

When  pure,  brazilii'ne  forms  orange  crystals ;  it  is  soluble  in  water,  alcohol,  and 
ether ;  the  solutions  are  reddish-yellow  ;  alkalies  and  most  metallic  salts  give  pur- 
ple, and  alum  a  red  precipitate,  with  the  solution  of  braziliine 

Santaline  exists  in  the  red  sanders  wood  (pterocarpus  santalinus).  Its  extraction 
and  properties  are  exactly  similar  to  that  of  the  Alcanna  Red.  Its  formula  is 
CigHsOs. 

Hcematoxyline. — This  substance,  the  colouring  principle  of  the  logwood  (haema- 
toxylon  Campechianum),  is  frequently  met  with  naturally  crystaUized  in  stellated 
groups  of  prisms,  sometimes  of  considerable  size,  in  clefts  of  the  wood ;  it  may  also 
be  prepared  by  a  process  similar  to  that  described  for  braziliine ;  it  is  slightly  bitter 
and  astringent ;  it  is  very  sparingly  soluble  in  w^ater,  but  copiously  in  alcohol  and 
ether,  forming  brownish-red  liquids.  Acids  colour  its  solutions  yellow,  alkalies 
purple ;  with  the  earths  and  metallic  oxides  it  forms  purple  or  blue  lakes. 

Saffiower  Red,  or  Carthamine, 

The  petals  of  the  safQower  (carthamus  tinctorius)  contain  a  red  and  a  yellow  ma- 
terial ;  the  former  alone  is  of  technical  importance.  The  flowers  are  to  be  washed 
with  water  acidulated  with  acetic  acid  until  all  the  Saffiower  Yellow  is  removed. 
By  digestion  then  in  a  solution  of  carbonate  of  soda,  the  carthamine  is  dissolved, 
and  may  be  precipitated  by  any  acid,  but  citric  acid  answers  best ;  it  forms  a  dark 
red  powder,  insoluble  in  water  and  in  acids,  and  but  sparingly  soluble  in  alcohol  oi 
ether ;  it  reddens  litmus,  and  gives  with  the  alkalies  yellow  solutions ;  its  com- 
pound with  soda  crystallizes  in  silky  needles  ;  with  alumina  it  forms  a  beautiful 
red  lake,  Rouge,  used  as  a  cosmetic  and  in  dyeing.  This  substance  is  much  em 
ployed  for  dyeing  silk  of  various  shades  of  pink  and  rose  colour. 

I  have  found  in  the  petals  of  the  salvia  fulgens  a  colouring  matter  possessing  con- 
siderable analogy  to  carthamine,  and  capable  of  being  substituted  for  it. 

Qmrcitrine. — This  substance  is  extracted  from  the  bark  of  the  quercus  infectoria 
by  simple  decoction  in  water ;  after  some  days  the  colouring  matter  separates  in 
crystals ;  or,  better,  by  digesting  the  bark  in  alcohol,  precipitating  the  tannin  by  gel- 
atine and  evaporation :  when  pure,  it  resembles  very  minute  crystals  of  yellow 
prussiate  of  potash ;  it  is  easily  soluble  in  water  and  in  alcohol,  and  appears  to  pos- 
sess feeble  acid  properties.  Its  formula,  by  BoUey's  analysis,  appears  to  be  CieHgO 
-|-Aq.     With  metaUic  oxides  it  gives  brilliant  yellow  lakes. 

Chrysorhamnine.     Xanihorhamnine, 

I  have  found  the  unripe  berries  of  the  rhamnus  tinctorius  (Persian  berries,  grains 
d' Avignon)  to  contain  a  substance  soluble  in  alcohol  and  ether,  and  crystallizing 
from  its  ethereal  solution  in  minute  silky  needles  of  a  brilliant  yellow  colour ;  it 
gives  with  metallic  oxides  yellow  lakes.  When  cautiously  heated  it  fuses,  but  is 
not  volatile.  In  the  ripe  berry,  this  substance,  to  which  I  have  given  the  name 
Chrysorhamnine,  is  totally  replaced  by  another,  which  I. term  Xanthorhamnine, 
which  is  of  a  much  less  beautiful  yellow,  and  does  not  crystallize  ;  this  change  is 
effected,  also,  by  boiling  the  chrysorhamnine  for  a  few  minutes  with  water,  or  by 
contact  with  alkalies.  The  xanthorhamnine  is  totally  insoluble  in  ether,  but  easily 
soluble  in  alcohol  and  water.  It  is  formed  by  the  union  of  the  elements  of  water 
with  chrysorhamnine.  Its  silver  salt  is  yellow  when  first  thrown  down,  but  rap- 
idly becomes  black,  metallic  silver  separating,  and  a  colourless  organic  substance 
being  formed.  The  Persian  berries  are  much  used  for  dyeing  yellow,  but,  from  the 
processes  employed,  the  xanthorhamnine  alone  is  actually  brought  into  play. 

Luteoline  is  the  colouring  principle  of  the  weld  (reseda  luteola),  and  probably  of 
the  dyers'  broom  (genista  tinctoria).  Its  mode  of  preparation  resembles  that  of 
quercitrine.  It  is  soluble  in  water,  alcohol,  and  ether  ;  it  combines  with  both  acids 
and  alkalies,  forming  yellow  compounds.  With  alumina  and  the  oxides  of  tin  and 
lead,  it  gives  brilliant  yellow  lakes  ;  with  iron,  a  dark  brown  precipitate. 

Morinc  is  the  colouring  principle  of  the  yellow-wood  (morus  tinctorius) ;  it  is  pre 
pared  like  quercitrine,  with  which  its  properties  accurately  agree. 

OreUina.—ThQ  seed  of  the  bixa  orellana  are  imbedded  in  an  orange-red  colouring 


616  COCHINEAL     RED,     ETC, 

matter,  which  is  separated  by  washings  and  a  kind  of  fermentation  ;  when  deposit- 
ed from  the  hquors,  so  as  to  form  a  consistent  paste,  it  is  sent  into  commerce  under 
the  names  of  Kocou,  Orleans,  or  Anotta.  To  obtain  the  colouring  principle  pure,  the 
orange-red  mass  is  digested  in  alcohol,  and  the  solution  distilled  nearly  to  dryness ; 
the  residue  is  tlien  treated  with  ether,  which  dissolves  the  orelline,  and  yields  it,  on 
evaporation,  as  an  orange-red,  somewhat  crystalline  powder ;  it  colours  water  pale 
yellow ;  it  is  more  soluble  in  alcohol,  but  gives  with  ether  or  oils  deep  red  solutions ; 
it  dissolves  in  alkalies,  and  is  precipitated  therefrom  by  acids.  With  alumina,  ox- 
ide of  tin,  and  oxide  of  lead,  it  gives  fiery  red  precipitates.  It  is  extensively  used 
in  dyeing,  and  also  to  heighten  the  colour  of  cheese  and  butter. 

Curcumine  is  found  in  the  roots  of  the  curcuma  longa  (turmeric),  and  is  obtained 
by  treatment  with  boiling  alcohol,  evaporation  to  dryness,  and  digestion  of  the  resi- 
due in  ether,  which  dissolves  the  pure  colouring  matter,  and  yields  it  by  spontane- 
ous evaporation.  Curcumine  melts  at  104°  ;  it  possesses  the  properties  of  a  resin  ; 
alkahes  brown  it,  on  which  its  employment  for  a  test-paper  rests ;  acids  render  its 
proper  yellow  much  paler,  except  boracic  acid,  which  stains  it  yellowish-red. 

Berberine  exists  in  the  roots  of  the  berberis  vulgaris  ;  it  is  prepared  by  boiling  the 
roots  in  water,  and  evaporating  the  decoction  to  the  consistence  of  an  extract, 
which  is  to  be  treated  with  spirit  of  wine  as  long  as  this  acquires  a  bitter  taste. 
The  spirit  is  to  be  distilled  in  great  part  off,  and  the  residue  suffered  to  stand  in  a 
cool  place  for  twenty-four  hours ;  the  crystals  which  form  are  to  be  recrystallized, 
first  from  water,  and  then  from  alcohol  Pure  berberine  forms  a  lig-ht  crystalline  yel- 
low pov/der  of  a  strongly  bitter  taste ;  it  is  very  sparingly  soluble  in  cold,  but  abun- 
dantly in  boiling  water  and  in  alcohol ;  it  is  insoluble  in  ether.  At  268°  it  melts, 
and,  if  farther  heated,  is  decomposed,  giving  ammoniacal  products ;  by  chlorine 
it  is  converted  into  a  brown-red  substance  ;  it  combines  with  bases,  acting  feebly  as 
an  acid ;  its  alkaline  compounds  crystalhze ;  those  with  the  earths  and  heavy  me- 
tallic oxides  are  insoluble,  and  generally  yellow  ;  a  solution  of  it  precipitates  the 
iodide,  cyanide,  ferrocyanide,  and  sulphocyanide  of  potassium.  Berberine  contains 
nitrogen,  its  formula  being  N.C33  .  HisOja. 

Cochineal  Red,  or  Carmine. 

This  veiy  remarkable  substance  diflfers  from  all  of  the  other  colouring  matters 
here  described,  in  being  a  product  of  the  animal  kingdom.  It  exists  in  many  in- 
sects of  the  genus  coccus,  as  the  coccus  cacti  (the  true  cochineal),  the  coccus  ilicis 
(kermes),  the  coccus  ficus  (lac  dye),  &c.  For  its  preparation  the  cochineal  is  to  be 
digested  in  ether  to  remove  a  quantity  of  fat,  and  then  boiled  in  alcohol  as  long  as 
this  is  coloured.  The  alcoholic  liquors,  being  mixed,  are  to  be  concentrated  by  dis- 
tillation, and  then  cautiously  dried  ;  the  impure  carmine  thus  obtained  is  digested 
in  alcohol,  and  the  solution  mixed  with  ether,  which  precipitates  the  colouring  mat 
ter  quite  pure. 

It  is  a  purple  red  powder,  easily  soluble  in  water  and  alcohol,  insoluble  in  ether. 
It  melts  at  122°,  but  is  decomposed  by  a  high  heat ;  chlorine  turns  it  yellow ;  al- 
kalies colour  cold  solution  of  carmine  red,  but  it  becomes  yellow  by  exposure  to  the 
air  or  by  boiling.  With  alumina  it  forms  a  precipitate,  which  is  crimson  when  pre- 
pared with  a  cold,  but  violet  if  with  a  hot  solution.  All  metallic  salts  give  lakes 
with  the  alkaline  solution  of  carmine ;  that  of  the  protoxide  of  tin  is  a  rich  scarlet. 
The  carmine  of  commerce  is  an  alumina  lake  more  or  less  pure ;  that  called  Chi- 
nese Carmine  is  the  compound  with  oxide  of  tin. 

The  carmine  contains  nitrogen ;  the  formula  N.C32  .  H26O20  has  been  assigned  to 
it,  but  cannot  be  considered  as  definitely  estabhshed. 

Of  Indigo,  and  the  Bodies  derived  from  it. 

The  blue  indigo  of  commerce  is  derived  from  the  leaves  of  a  variety 
of  plants  of  difFereni  genera.  The  genus  indigofera  includes  a  number 
of  productive  species,  also  the  genera  nerium  and  isatis,  marsdeiiia,  as- 
clepias,  and  polygonum,  galega,  spilanthus,  and  amorpha.  Of  these  the 
great  majority  are  natives  of  the  tropics  ;  but  a  few,  as  the  isatis  tincto- 
ria  and  the  polygonum  tinctorium,  belong  to  temperate  regions,  the  for- 
mer being  indigenous  both  to  Ireland  and  to  England. 

The  indigo  is  secreted  in  the  cellular  tissue  of  the  leaf,  in  a  form  (white 


BLUE     A^D     WHITE     INDIGO.  61 

mdigo)  which  can  also  be  artificially  produced  ;  it  is  then  colourless, 
and  remains  so  as  long  as  the  tissue  of  the  leaf  is  perfect.  When  the 
leaf  begins  to  wither,  oxygen  is  absorbed,  and,  the  indigo  assuming  its 
colour,  the  leaves  become  covered  with  a  number  of  blue  points,  the  first 
appearance  of  which  shows  that  the  period  for  collecting  them  has  arri- 
ved. The  fresh  leaves  are  thrown  into  large  vats  with  some  water,  and 
pressed  down  by  weights.  After  some  time,  a  kind  of  mucous  ferment- 
ation sets  in,  carbonic  acid,  ammonia,  and  hydrogen  gases  are  evolved, 
and  a  yellow  liquor  is  obtained,  which  holds  all  the  indigo  dissolved. 
This  is  separated,  mixed  with  lime-water,  and  then  exposed  to  the  air  un- 
til the  indigo  becomes  blue  and  insoluble,  and  is  completely  deposited  as 
a  precipitate.  The  theory  of  this  action  is,  that,  by  the  putrefaction  of 
the  vegeto-animal  matter  of  the  leaves,  the  indigo  is  kept  in  the  same 
white,  soluble  condition  in  which  it  exists  in  the  plant,  and  a  clear  solu- 
tion of  it  being  thus  obtained,  it  is  precipitated,  according  as  it  absorbs 
oxygen,  in  a  much  purer  form  than  otherwise  could  be  effected. 

The  putrefying  pasty  mass  of  leaves  obtained  from  the  isatis  tinctoria 
constitutes  the  woad  or  wad  employed  in  the  hot  indigo  bath  for  dyeing 
cloth. 

The  blue  indigo,  as  thus  obtained,  is  still  a  mixture  of  several  bodies, 
as  indigo. red,  indigo-brown,  indigo-gluten,  which  are  removed  by  repeat- 
ed treatment  with  alcohol  and  dilute  acids  and  alkalies.  When  pure,  the 
precipitated  indigo  is  a  rich  blue  powder,  which,  when  rubbed  by  a  knife,. 
assumes  the  colour  of  metallic  copper  ;  it  is  perfectly  insoluble ;  when 
cautiously  heated,  it  sublimes  in  rectangular  prisms  of  a  dark  purple  col- 
our and  metallic  lustre  ;  its  vapour  is  of  a  rich  purple  ;  it  contains  nitro- 
gen, its  formula,  as  fully  established  by  Dumas,  being  N.C,6.  H5O2. 

White  Indigo. — When  indigo  is  acted  upon  by  deoxidizing  agents,  as 
protochloride  of  tin,  protoxide  of  iron,  or  sulphurous  acid,  it  loses  its  blue 
colour,  and  the  white  indigo,  which  is  insoluble  in  water,  but  soluble  in 
alkaline  solutions,  is  produced.  Its  mode  of  preparation  is  simple  :  one 
and  a  half  parts  of  commercial  indigo,  two  and  a  half  parts  of  slacked 
lime,  and  two  parts  of  green  copperas,  are  to  be  well  mixed  up  with  six- 
ty parts  of  water,  in  a  vessel  from  which  the  air  is  carefully  excluded. 
The  protoxide  of  iron,  formed  by  the  action  of  the  lime  on  the  copperas, 
peroxidizes  itself  at  the  expense  of  the  indigo  and  v/ater,  and  the  white 
indigo  thus  formed  dissolves  in  combination  with  lime.  On  adding  mu- 
riatic acid  to  the  clear  solution,  the  white  indigo  precipitates,  and  may 
be  obtained  dry,  as  a  crystalline  powder,  by  suitable  precautions  to  pre- 
vent the  access  of  air. 

The  simplest  theory  of  this  process  should  be,  that  the  oxide  of  iron 
directly  abstracted  oxygen  from  the  indigo :  hence  the  names  o^ Deoxidized 
Indigo  and  Indigogene  were  given  to  the  white  substance  ;  but  the  anal- 
yses of  Dumas  have  proved  that  the  white  indigo  is  a  compound  of  hy- 
drogen with  the  blue  indigo,  its  formula  being  CieHj .  N.Oi+H.  In  its 
formation,  therefore,  water  is  decomposed,  the  elements  of  it  combining 
respectively  with  the  blue  indigo  and  the  deoxidizing  body. 

On  the  properties  of  this  white  indigo  depend  the  important  application 
of  indigo  as  a  dyeing  material.  The  indigo  is  rendered  soluble  either  by 
lime  and  copperas  (cold  indigo  bath),  or,  being  diffused  through  warm  wa- 
ter with  a  quantity  of  woad,  by  the  fermentation  of  which  ammonia  and 
hydrogen  are  evolved,  a  soluble  compound  of  ammonia  and  white  indigo 

4  I 


618  SULPHATES     OF     INDIGO,    ETC. 

IS  obtained  (hot  indigo  bath) ;  the  former  is  employed  for  cotton,  and  the 
latter  for  woollen  cloth.  The  cloth  is  immersed  in  the  bath  until  it  has 
fully  imbibed  the  solution ;  it  is  then  exposed  to  the  air,  the  oxygen  of 
which  carries  off  the  hydrogen  of  the  white  indigo,  and  the  blue  insoluble 
indigo  attaches  itself  to  the  fibres  of  the  cloth  so  firmly  at  the  moment 
of  its  formation,  as  to  constitute  the  most  permanent  ajid  the  most  beau- 
tiful of  our  blue  dyes. 

Sulphate  of  Indigo, — When  blue  indigo,  in  very  fine  powder,  is  digest- 
ed with  strong  oil  of  vitriol,  for  which  purpose  the  German  or  fuming  sul- 
phuric acid  answers  best,  it  dissolves  in  great  part,  and  two  acids  are 
formed,  the  Sulphopurpuric  and  Sulphindylic ;  the  former  is  the  prin- 
cipal product  when  the  indigo  is  in  excess,  the  latter  when  the  oil  of  vit- 
riol preponderates  ;  they  are  separated  by  dilution  with  water,  the  sul- 
phopurpuric acid  being  insoluble,  while  the  sulphindylic  acid  dissolves. 

The  sulphopurpuric  acid,  though  insoluble  in  dilute  acids,  dissolves 
readily  in  pure  water ;  it  forms,  with  the  alkalies  and  earths,  blue  com- 
pounds, which  are  sparingly  soluble  in  water,  but  soluble  in  alcohol.  By 
the  analysis  of  Dumas,  it  appears  to  consist  of  C32H10.  N2O4+2S.O3,  and 
in  its  potash  salt  to  contain  one  atom  of  alkali. 

The  sulphindylic  acid,  CigHg.  N.02-{-2S.03,  when  dried  from  its  solu- 
tion in  water,  forms  a  dark  blue  mass.  Its  salts  are  of  a  rich  blue  col- 
our ;  those  of  the  alkalies  are  soluble,  those  of  the  earths  and  metallic  ox- 
ides insoluble  in  water.  They  consist,  according  to  Dumas's  analysis,  of 
an  atom  of  indigo,  two  of  sulphuric  acid,  and  one  of  base.  The  sulpho- 
purpuric  and  sulphindylic  acids  thus  contain  the  same  organic  element 
(indigo),  but  in  different  proportions,  united  to  sulphuric  acid. 

Berzelius  considers  that,  besides  these  two,  there  are  generated,  by  the 
action  of  sulphuric  acid  on  indigo,  several  other  acids  of  complex  nature  ; 
but,  as  we  possess  no  exact  results  concerning  them,  and  as  they  are 
of  no  technical  importance,  it  is  unnecessary  to  describe  them  in  detail. 

This  solution  of  indigo  in  oil  of  vitriol  constitutes  the  Saxon  Blue,  or 
Chemic  Blue,  used  extensively  in  dyeing ;  on  neutralizing  the  liquor  by 
an  alkali  (carbonate  of  soda),  and  immersing  the  tissue,  whether  wool, 
silk,  or  cotton,  the  indigo  combines  with  the  fibre  of  the  cloth,  and  the 
sulphuric  acid  remains  combined  with  the  alkali. 

By  the  gradual  oxidation  of  indigo,  a  substance  is  formed  which  crystallizes  in 
large  red  prisms,  and  is  termed  by  Laurent  Isatine;  its  formula  is  CieHs  .  N.O4.  If 
tlie  process  be  more  violently  carried  on,  the  constitution  of  the  indigo  is  broken  up, 
and  a  new  type  formed,  thus :  by  the  action  of  an  excess  of  nitric  acid  on  indigo, 
two  remarkable  bodies  are  formed,  the  Anilic  and  the  Picric  Acids.  A  mixture  of 
one  part  of  fuming  nitric  acid  and  ten  of  water  being  brought  to  boil,  indigo  is  to  be 
added  in  fine  powder  as  long  as  any  effervescence  occurs ;  the  liquor  is  to  be  then 
filtered  while  hot.  Both  acids  crystallize  on  cooling ;  the  crystals  are  to  be  drain- 
ed, redissolved  in  water,  and  precipitated  by  acetate  of  lead  ;  picrate  of  lead  falls  ; 
anilate  of  lead  remains  dissolved,  and,  being  decomposed  by  sulphuretted  hydrogen, 
the  Anilic  Acid  crystallizes  in  white  needles  ;  its  taste  is  bitter  and  acid  ;  it  requires 
1000  parts  of  cold,  and  but  ten  of  boiling  water  ;  its  salts  are  all  soluble  ;  its  for- 
mula is  C14H4  .  N.Og-fAq. 

The  Picric  Acid  may  be  obtained  by  diffusing  the  picrate  of  lead  through  boiling 
water,  and  decomposing  it  by  sulphuretted  hydrogen  gas ;  on  filtering  and  cooling, 
the  picric  acid  crystallizes.  It  may  be  obtained,  however,  much  purer  and  more 
abundantly  by  digesting  salicine  in  nitric  acid  (p.  606),  and  directly  from  the  sub- 
stance which  exists  in  coal  gas  naptha,  termed  by  Laurent  hydrate  of  phenyl ;  it 
forms  yellow  prisms,  sparingly  soluble  in  cold  water ;  when  heated,  it  explodes,  a.^ 
do  also  its  salts ;  its  potash  salt  requires  260  parts  of  cold  water  for  solution,  and 
it  is  hence  sometimes  used  as  a  reagent  for  that  alkaU ;  its  formula  is  C12H3 .  N3O13 
+Aq. 


ACTION    OF     CHLORINE     ON     INDIGO.  619 

When  indigo  is  mixed  with  a  strong  boiling  solution  of  caustic  potash,  it  dissolves, 
Q.m.,ChrysanUic  Acid  is  formed,  which  may  be  precipitated  by  muriatic  acid  as  an 
orange-red  powder ;  it  dissolves  in  alcohol  and  ether,  and  crystallizes  by  the  evap- 
oration of  the  solutions  ;  its  formula  appears  to  be  C28H10  .  N.Os-f-Aq.  By  exposure 
to  the  air  while  hot,  or  directly  by  contact  with  peroxide  of  manganese,  this  acid  is 
converted  into  another,  Anthranilic  Acid,  the  properties  of  which  are  remarkable ; 
it  is  soluble,  crystallizes,  gives  very  well-marked  and  crystallizable  salts,  fuses  at 
375°,  and  sublimes  a  little  above  that  temperature  unchanged ;  if  it  be  strongly 
heated,  however,  it  is  decomposed,  the  sole  products  being  carbonic  acid  and  a  vol- 
atile liquid,  Anilene.  The  formula  of  the  hydrated  anthranilic  acid  is  C14H7  .  N.O4, 
and  it  gives  2C.O2  and  C12H7N. 

This  liquid,  anilene,  is  a  body  closely  analogous  to  the  melamine  (p.  526) ;  it  acts 
as  a  powerful  base,  combining  with  the  hydracids  directly,  and  with  the  oxacids  by 
mcluding  an  atom  of  water ;  it  thus  resembles  ammonia.  These  important  sub- 
stances, for  whose  discovery  we  are  indebted  to  Fritzche,  are  still  under  examina- 
tion. 

Action  of  Chlorine  on  Indigo. — This  subject,  so  important  in  relation  to  the  theory 
of  the  bleaching  of  colouring  matters,  has  been  very  minutely  investigated  by  Erd- 
man,  of  whose  numerous  and  complex  results  the  elementary  nature  of  this  work 
will  allow  but  a  general  notice  to  be  given.  Dry  chlorine  has  no  action  on  indigo, 
but  in  presence  of  water  it  converts  it  into  a  yellow  mass,  from  which  is  separated, 
by  distillation,  a  substance  termed  Chlorindopten,  which  sublimes  in  white  scales 
and  needles  ;  its  formula  is  CieHj .  O2CI4 ;  it  is  sparingly  soluble  in  water,  copiously 
in  alcohol  and  ether.  This  appears  to  be  a  secondary  product.  The  substance 
which  remains  behind  in  the  retort,  on  being  dissolved  in  boiling  alcohol,  yields,  on 
cooling,  red  prismatic  crystals  of  Chlorisatine :  its  formula  is  C16H4CI.  .  N.O3;  it  is 
hence  indigo,  in  which  an  equivedent  of  hydrogen  is  replaced  by  chlorine,  and  united 
to  an  atom  of  oxygen  ;  with  an  excess  of  chlorine  it  gives  Bichlorisatine,  which  con- 
sists of  C16H4CI2 .  N.O3.  If  these  bodies  be  treated  with  sulphuretted  hydrogen, 
sulphur  is  set  free,  and  the  hydrogen  enters  into  combination ;  in  contact  with  pot- 
ash, the  elements  of  an  atom  of  water  are  assimilated,  and  an  acid  formed,  which 
unites  with  the  potash.  In  this  way  chlorisatine  gives  Chlorisatyd,  C16H5CI.  .  N.O3, 
and  Chlorisatic  Acid,  CieHsCl.  .  N.O4,  and  bichlorisatine  gives  two  corresponding 
bodies. 

If  chlorisatyd  be  heated,  it  produces  water,  chlorisatine,  and  a  violet  powder,  CMo- 
rindine,  which  has  the  formula  C16H5CI. .  N.O2,  and  is  hence  a  compound  of  indigo- 
blue  with  chlorine.  By  heating  bichlorisatyd,  the  Bichlorindine,  C16H5N.  .  O3CI2,  is 
similarly  formed. 

By  passing  chlorine  through  a  solution  of  chlorisatine  in  alcohol,  all  hydrogen  is 
removed,  and  a  substance  formed  which  crystallizes  in  pale  yellow  plates,  anc^  has 
the  formula  OeOzCla  ;  it  is  termed  Chloranil.  By  the  secondary  reactions  of  these 
bodies,  a  number  of  others  are  generated,  which  it  is  not  necessary  specially  to  de- 
scribe. 

Notwithstanding  the  attention  devoted  by  the  most  distinguished  chemists  to  the 
compounds  and  derivatives  of  indigo,  the  theory  of  that  body  remains  very  obscure. 
The  derivation  of  picric  acid  from  the  body  Ci2H50.-|-Aq.  (Hydrate  of  Phanyl),  dis- 
covered as  a  product  of  destructive  distillation  by  Laurent,  may  serve  as  a  connect- 
ing point  for  many  of  the  bodies  derived  from  indigo,  and  which  otherwise  had  ap- 
peared totally  unconnected.  Thus  the  picric  acid  is  evidently  formed  by  the  sub- 
stitution of  3N.O4  for  3H.  in  C12H5O.,  and  the  anilene  is  probably  C12H5-J-N.H2  ; 
other  speculative  ideas  might  be  brought  forward,  but  I  shall  only  mention  that  the 
blue  indigo  contains  exactly  the  elements  of  cyanogen  and  benzyl,  C2N.-I-C14H5O2, 
and  that,  as  the  cyanogen  is  converted  so  easily  into  oxahc  acid  and  ammonia,  the 
derived  bodies,  which  contain  C,4,  may  thus  have  their  origin. 

Of  the  Colouring  Matters  derived  from  the  Lichens, 
Many  species  of  lichen  contain  substances  which,  although  colourless  themselves, 
produce,  by  contact  with  air  and  ammonia,  the  rich  purple  or  blue  colouring  mat- 
ters constituting  the  archil  and  litmus  of  commerce.  The  species  of  lichen  that 
have  been  in  this  respect  most  accurately  examined  are  the  variolaria  dealbata  by 
Robiquet  and  Dumas,  and  the  rocella  tinctoria  by  myself. 

The  useful  substance  in  the  variolaria  is  termed  Orcine ;  it  is  obtained  by  digest- 
ing the  lichen  in  alcohol,  evaporating  to  dryness,  dissolving  the  extract  in  water, 
concentrating  the  solution  to  the  thickness  of  a  sirup, -and  setting  it  aside  to  crvs- 


620  ORCEIN  E,    ERYTHRYLINEj    ETC. 

tallize  ;  it  forms,  when  quite  pure,  colourless  prisms  of  a  nauseous-sweet  taste  i  it 
fuses  easily,  and  may  be  sublimed  unaltered  ;  its  formula  is  Ci8H703-j-2  Aq.  vsKen 
sublimed  ;  when  crystallized  from  its  aqueous  solution,  it  contains  5  Aq. 

If  orcine  be  exposed  to  the  combined  action  of  air  and  ammonia,  exactly  as  de- 
scribed for  phloridzine  (p.  607),  it  is  converted  into  a  crimson  powder,  Orceine,  which 
is  the  most  important  ingredient  in  the  archil  of  commerce.  The  orceine  may  also 
be  obtained  by  digesting  dried  archil  in  strong  alcohol,  evaporating  the  solution  in 
a  water-bath  to  dryness,  and  treating  it  with  ether  as  long  as  anything  is  dissolved  ; 
it  remains  as  a  dark  blood-red  powder,  being  sparingly  soluble  in  water  or  ether, 
but  abundantly  in  alcohol ;  its  formula  is  CigHio .  N.Og.  The  orceine  in  archil  is, 
however,  frequently  found  to  contain  less  oxygen,  and  to  be  represented  by  the 
formula  CisHio .  N.O5.  I  have  termed  the  first  kind  Alpha-orce'ine,  and  the  second 
Beta-orcetne  ;  in  properties  they  are  identical. 

Orceine  dissolves  in  alkaUne  liquors,  with  a  magnificent  purple  colour  ;  with  me- 
tallic oxides  it  forms  lakes,  also,  of  rich  purple,  of  various  shades.  In  contact  with 
deoxidizing  agents  it  combines  with  hydrogen,  as  indigo  does,  and  forms  Leucor- 
cetne,  CigHio .  N.08-|-H.  When  bleached  by  chlorine,  a  yellow  substance  is  formed, 
Chlororcdne,  the  formula  of  which  I  have  found  to  be  CisHio.N.Os-^-Cl.,  analogous 
to  the  other. 

In  the  rocella  tinctoria  there  is  no  orcine  ;  the  origin  of  the  coloured  substances 
is  a  body  which  I  have  termed  Erythryline ;  it  is  soluble  in  ether  and  alcohol,  insol 
uble  in  water,  but  is  gradually  decomposed  by  it ;  its  formula  is  C22H16O6.  By  the 
action  of  the  air  it  is  gradually  changed  into  Erythrine,  a  substance  which  dissolves 
sparingly  in  cold,  but  abundantly  in  boiling  water,  from  which  it  separates  on  cool- 
ing in  brilliant  micaceous  plates ;  it  is  very  soluble  in  alcohol  and  ether ;  its  formula 
is  C22H13O9.  By  prolonged  boiling  in  water,  erythrine  is  changed  into  a  substance 
very  soluble  in  water  and  in  alcohol,  Amarythrine,  the  formula  of  which  is  C22Hi30i4; 
and,  finally,  by  the  still  farther  action  of  the  air,  Telerythrine  is  formed,  which  crys- 
tallizes in  small  grains,  and  has  the  formula  C22H9O18. 

If,  however,  in  addition  to  the  air,  ammonia  have  access  to  these  bodies,  the 
crimson  colour  is  produced,  and  the  two  varieties  of  orceine  are  formed.  I  conceive 
the  oxidizing  stage  to  proceed  as  far  as  amarythrine,  and  that,  by  combination  with 
ammonia  and  oxygen,  a  substance  is  formed,  to  which  I  have  given  the  name  of 
Azoerythrine.  Its  formula  is  C22H16  .  N.Oi9-j-3  Aq.  By  the  loss  of  4C.O2  and 
6H.0.,  it  gives  alpha-orcei'ne,  CigHio .  N.O5,  which,  absorbing  oxygen,  gradually 
forms  the  true  or  beta-orceine,  CigHio .  N.Og. 

When  an  alkaline  solution  of  orceine  is  exposed  to  the  air,  it  absorbs  more  oxy- 
gen, and  a  substance  is  produced  which  constitutes  a  great  part  of  the  colouring 
material  of  litmus.  I  have  termed  it  Azolitmine  ;  its  formula  is  CisHio  .  N.Oio  ;  it  is 
a  dark  red  powder,  which  is  insoluble  in  alcohol  or  ether,  and  but  sparingly  soluble 
in  water ;  it  dissolves  better  in  acid  liquors,  which  render  it  a  pale  red,  and  with 
zilkalies  it  gives  the  rich  blue  colour  of  htmus.  With  the  earths  and  metallic  ox- 
ides it  forms  purple  or  blue  lakes  ;  with  deoxidizing  agents  it  is  decolorized,  form 
ing  Leucolitmine,  and  by  chlorine  a  yellow  substance  is  produced,  having  the  foi 
mulaCisHio.N.Oio-fCl. 

Besides  the  bodies  of  the  erythrine  series,  the  lichen  rocella  contains  a  substance, 
termed  Rocclline,  which  is  white,  fusible,  insoluble  in  water,  soluble  in  alcohol  and 
ether  ;  its  formula  is  C26H24O6.  By  exposure  to  the  air,  it  is  converted  into  a  fatty 
substance  of  a  rich  crimson  colour,  which  I  have  termed  Erythrolcic  Acid ;  this  body 
exists  in  archil,  and  is  separated  from  the  orceine  by  means  of  its  solubility  in  ether. 
Its  formula  is  C26H22O8 ;  it  is  capable,  under  circumstances  which  are  not  yet  well 
understood,  of  being  broken  up  into  two  substances,  which  are  both  found  to  exist 
in  litmus  ;  they  are  Erythroleine,  which  has  the  formula  C26H22O4,  and  Erythrolit- 
viine,  which  consists  of  C26H22O12.  The  erythroleine  and  erythroleic  acid  are,  like 
the  alpha  and  beta  orceines,  distinguished  only  by  their  composition  ;  they  have  the 
same  colour,  are  sparingly  soluble  in  water,  but  copiously  in  alcohol  and  ether;  they 
dissolve  in  alkaline  liquors  with  a  rich  crimson  colour,  and  give  crimson  lakes  with 
the  metallic  salts.  The  erythrolitmine,  on  the  other  hand,  is  bright  red,  very  spa- 
ringly soluble  in  water  or  ether,  but  soluble  in  alcohol.  Alkalies  turn  it  bright  blue  ; 
in  a  solution  of  potash  it  dissolves,  but  its  compound  with  ammonia  is  insoluble, 
and  consists  of  C26H220i2-t-N.H40. 

The  brief  history  of  these  substances  now  given  will  render  intelligible  the  process 
of  manufacture  of  archil  and  litmus,  and  the  principles  of  their  use  in  the  arts  and 
in  the  laboratory.     The  lichens  employed  are  ground  up  with  water  to  a  uniform 


COLOURING  MATTERS  OP  LEAVES,  ETC.    621 

pulp,  and  this  is  then  mixed  with  as  much  water  as  makes  the  whole  thick- fluid. 
Amraoniacal  liquors  from  the  gas  or  ivory-black  works,  or  even  stale  urine,  are  from 
time  to  time  added,  and  the  mass  frequently  stirred,  so  as  to  promote  the  action  of 
the  air.  The  orcine  or  erythrine  which  existed  in  the  lichen  absorbs  oxygen  and 
ammonia,  and  forms  orceine  ;  the  rocelline  absorbs  oxygen,  and  forms  erythroleic 
acid  ;  these  being  kept  in  solution  by  the  excess  of  ammonia,  the  whole  liquid  is  of 
an  intensely  rich  purple  tint,  and  constitutes  ordinary  archil.  If  the  oxidizing  ac- 
tion of  the  air  be  allowed  to  go  too  far,  we  have  the  purple  colour  replaced  by  a 
shade  more  or  less  blue  ;  the  orceine  changes  to  azoliimine,  and  the  erythroleine 
gives  erythrolitmine  ;  a  quantity  of  chalk  and  plaster  of  Paris  is  then  added  to  the 
liquor,  so  as  to  form  a  consistent  paste,  and  this,  cut  into  little  cubical  masses  and 
dried,  forms  the  Litmus  of  commerce.  From  the  constitution  of  archil  and  litmus, 
such  must  be  the  general  principles  of  the  manufacture,  although,  particularly  for 
litmus,  the  details  are  kept  very  secret  by  those  engaged  in  the  trade. 

The  use  of  litmus  paper  as  a  test  for  the  presence  of  a  free  acid  arises  from  the 
blue  colour  belonging  to  compounds  of  the  erythrolitmine  and  azoerythrine  with  an 
alkali,  and  as  this  is  taken  by  even  the  weakest  acid,  the  red  colouring  materials 
are  set  free. 

Of  the  Colouring  Matters  of  Leaves  and  Flowers. 

The  green  colour  of  plants  is  due  to  the  presence  of  a  substance  termed  ChloT- 
ophyll.  Even  deeply-coloured  plants  contain  but  very  little  of  it,  and  it  has  not,  as 
yet,  been  obtained  in  a  state  of  such  purity  as  that  any  formula  can  be  assigned  to 
it.  It  does  not  contain  nitrogen ;  it  is  insoluble  in  water,  soluble  in  alcohol  and 
ether ;  it  is  dissolved  by  strong  acids,  and  precipitated  therefrom  by  dilution  ;  it 
enters  into  union  with  bases,  and  gives  pale  green  lakes.  With  deoxidizing  agents 
it  shows  the  same  process  of  decoloration  as  most  other  bodies  of  this  class. 

Berzelius  has  noticed  that  there  are  really  three  kinds  of  chlorophyll :  the  first, 
which  exists  in  fresh  leaves,  dissolves  in  acetic  acid  with  a  rich  grass-green  col- 
our ;  the  second,  formed  from  the  first  by  drying,  gives  an  indigo-blue  solution  with 
the  same  acid  ;  and  the  solution  of  the  third,  which  exists  principally  in  the  pyrus 
aria  and  other  dark-leaved  plants,  is  brownish-green.  So  excessive  is  the  colouring 
power  of  this  body,  that  Berzelius  has  calculated  that  the  entire  mass  of  leaves  of 
a  large  tree  seldom  contains  ten  grains  of  chlorophyll. 

It  is  known  that  in  autumn  the  leaves  of  many  trees,  as  the  sorbus  aucuparia, 
cornus  sanguinea,  &c.,  assume  a  fine  red  colour,  while  the  foliage  of  others,  partic- 
ularly of  forest-trees,  becomes  bright  yellow.  Berzelius,  who  has  examined  the 
nature  of  this  change,  found  the  chlorophyll  to  be  replaced  in  such  leaves  by  a  red 
and  a  yellow  colouring  matter,  to  which  he  gave  respectively  the  names  Erythro- 
fhyll  and  Xanthophyll.  The  former  is  an  extractive  matter,  easily  soluble  in  alcohol 
and  water ;  by  the  air  it  is  gradually  changed  into  a  brown  insoluble  matter;  with 
alkalies  it  forms  rich  green  solutions,  and  with  metaUic  oxides,  green  lakes ;  by 
acids  the  red  colour  is  restored ;  a  green  leaf  containing  chlorophyll  is,  however, 
not  reddened  by  an  acid.  It  is  remarkable,  that  all  trees  in  whose  leaves  erythro- 
phyll  forms  in  autumn  bear  red  fruit,  as  the  cherry,  currant,  &c. 

Xanthop/iyll  is  a  deep  yellow,  fatty  substance,  which  melts  between  100°  and 
120°  ;  it  is  insoluble  in  water,  but  dissolves  copiously  in  alcohol  and  ether ;  its  so- 
lution, exposed  to  the  air  and  light,  is  rapidly  bleached  :  alkalies  dissolve  it  sparing- 
ly v/ith  a  yellow  colour,  which  is  bleached  by  light. 

We  possess  but  very  little  accurate  knowledge  of  the  colouring  matters  of  flow- 
ers :  they  constitute  a  very  remarkable  group  of  bodies,  closely  related  to  each 
other,  and  distinct  from  the  colouring  matters  that  have  been  as  yet  examined.  It 
has  been  stated  that  the  colours  of  all  flowers  result  from  two  ;  one  blue  {Anthocy- 
an),  which  is  soluble  in  water  and  alcohol,  reddened  by  acids,  rendered  green  by 
alkalies,  and  from  these  changes  producing  the  red,  and  all  intermeidiate  shades  of 
purple  and  violet ;  the  yellow  substance  {Anthoxanthine)  is  likewise  easily  soluble 
in  alcohol  and  water,  and  is  coloured  intensely  blue  by  oil  of  vitriol.  These  sub- 
stances possess  most  analogy  to  hematoxylin  and  to  safiiower-yellow ;  but  it  is 
highly  probable  that  a  great  number  of  species  of  colouring  matters  exist  in  flowers 
as  they  do  in  woods.  The  quantity  present  in  the  flower  is  generally  so  excess- 
ively minute,  that  the  accurate  examination  of  their  properties  is  exceedingly  dif- 
ficult 


622 


THEORY     OF     DYEING,    ETC. 


On  some  general  Characters  of  Colouring  Matters,  and  on  the  Principle* 

of  Dyeing, 

In  addition  to  the  detailed  history  of  the  individual  colouring  matters, 
there  are  a  few  remarks  belonging  to  them  as  a  class  which  deserve 
notice. 

Under  the  heads  of  indigo  and  of  orceine,  I  have  described  the  forma- 
tion of  white  compounds,  by  the  action  of  deoxidizing  agents,  and  that 
in  those,  which  are  the  only  cases  that  have  been  accurately  examined, 
it  resulted  from  the  direct  combination  of  hydrogen  with  the  colouring 
matter.  This  character  of  forming  a  colourless  compound  with  hydro- 
gen appears  to  belong  to  all  colouring  substances.  If  an  infusion  of  log- 
wood, of  cochineal,  of  violets,  of  immerin,  be  rendered  acid  by  muriatic 
acid,  and  a  slip  of  zinc  immersed  therein,  the  liquor  becomes  gradually 
colourless,  and  on  adding  ammonia,  a  white  lake  is  precipitated,  consist- 
ing of  the  hydruret  of  the  colouring  matter  combined  with  oxide  of  zinc. 

With  oxygen  all  colouring  matters  appear  also  to  combine  to  form  bod- 
ies quite  or  nearly  destitute  of  colour.  Thus,  if  the  chrysorhamnate  of 
silver  be  boiled  in  water,  metallic  silver  separates,  and  oxidized  colour- 
ing matter  dissolves.  This  illustrates  the  manner  in  which  colours  fade, 
and  they  are  more  or  less  fugitive,  according  as  their  tendency  thus  to 
combine  with  oxygen  is  greater.  On  this  principle  was  founded  the  old 
process  of  bleaching,  by  exposing  the  cloth  to  the  conjoined  agencies  of 
water,  air,  and  light.  The  bodies  whose  colour  injured  the  whiteness  of 
the  cloth  were  gradually  changed  by  oxidation  into  others,  less  coloured 
and  more  easily  removable  by  washing.  In  the  majority  of  cases,  how- 
ever, the  process  is  not  limited  to  simple  oxidation,  but  carbonic  acid  is 
evolved,  and  the  colouring  matter  is  totally  broken  up  in  constitution. 

The  colour  of  many  substances,  as  logwood,  archil,  litmus,  indigo,  of 
most  flowers,  &c.,  is  removed  by  sulphuretted  hydrogen  and  by  sulphur- 
ous acid.  In  these  cases  there  is  direct  combination,  and  the  colour  is 
restored  by  expelling  the  combined  gas,  by  heat,  or  by  a  strong  acid. 
For  commerce,  many  bodies,  particularly  those  of  a  yellow  colour,  are 
given  a  temporary  whiteness  by  stoving  or  smoking  with  sulphurous 
acid,  by  placing  them  in  a  room  where  sulphur  is  burned  ;  this  is  done 
with  corn,  with  straw  for  hats,  with  sponges,  &c.  The  sulphurous  acid 
gradually  goes  off  afterward,  and  the  yellow  colour  returns. 

The  destruction  of  colours  by  means  of  chlorine  is  the  most  important 
decomposition  to  which  this  class  of  bodies  is  subject,  as  on  it  the  modern 
processes  of  bleaching  all  our  woven  tissues,  paper,  &c.,  is  founded. 
Innumerable  niceties  in  the  application  of  coloured  patterns  on  cloth 
would  be  impossible,  and  the  art  of  the  calico  printer  restrained  to  very 
narrow  limits,  were  it  not  for  the  power  which  chlorine  gives  him  of  re- 
moving the  original  colour  from  any  chosen  space,  and  replacing  it  by 
others  of  various  tints.  The  theory  of  this  action  of  chlorine,  which 
had  been  formerly  thought  to  depend  upon  a  mere  oxidation  of  the  col- 
ouring matter,  water  being  decomposed,  has  been  shown  by  my  results 
with  orceine,  and  confirmed  by  those  of  Erdman  on  indigo,  to  consist  in 
the  formation  of  new  substances  containing  chlorine.  The  chlorine  in 
some  cases  replaces  hydrogen  ;  in  others  it  combines  directly  with  the 
colouring  matter ;  in  others,  again,  water  is  decomposed,  and  the  prod- 
uct, besides  containing  chlorine,  is  also  more  highly  oxidized.     The 


FIXING  OF  COLOURS  ON  CLOTH,  ETC.     62'6 

action  of  chlorine  on  colouring  matter  is  therefore  subjected  to  thfe  same 
laws  as  when  it  acts  upon  other  organic  substances,  the  series  of  bodies 
derived  from  indigo  by  chlorine  having  much  analogy  to  the  series  of 
bodies  formed  with  alcohol  or  olefiant  gas. 

In  relation  to  the  processes  of  dyeing,  colouring  substances  are  divi- 
ded  into  two  classes,  the  substantive  and  adjective.  The  substantive 
colours  are  those  which,  being  very  sparingly  soluble  in  water,  and 
having  a  strong  affinity  for  the  fibre  of  the  cloth,  combine  directly  with 
it ;  such  are  carthamine  and  indigo ;  the  adjective  colours  are  incapable 
of  so  permanently  fixing  themselves,  and  the  necessary  insolubility  and 
affinity  for  the  cloth  is  given  through  the  intervention  of  a  base  with 
which  the  colouring  substance  may  combine.  The  cloth  is  mordanted 
with  alumina  (p.  436),  or  iron  (p.  558),  or  tin  (p.  448),  or  mixtures  of 
these  metallic  oxides,  and  as  the  lakes  so  formed  are  of  different  colours, 
a  great  variety  of  tints  may  be  produced.  The  field  of  application  of 
substantive  colours,  also,  is  greatly  enlarged  by  the  use  of  mordants  ; 
the  simple  colouring  matter  could,  of  course,  give  but  its  own  tints,  while 
it  forms,  with  the  bases,  lakes  of  various  colours. 

The  resources  of  the  dyer  are  by  no  means  limited  even  by  the  vast 
number  of  coloured  substances  described  in  the  present  chapter.  From 
the  mineral  kingdom,  some  of  the  richest  colours  are  now  procured,  as 
has  been  already  noticed  in  the  special  history  of  the  salts  of  chrome,  of 
iron,  of  copper,  of  lead,  of  manganese,  and  of  antimony.  It  is  remarka- 
ble, that  hitherto  no  true  green  colouring  matter  has  been  found  capable 
of  application  in  the  processes  of  dyeing,  the  only  greens  which  exist  in 
nature  being  the  chlorophyll  and  the  green  of  the  stems  of  buck-thorn 
(sap-green),  neither  of  which  is  capable  of  being  attached  to  cloth :  all 
greens  are,  therefore,  in  practice,  formed  by  the  superposition  of  a  blue 
findigo  or  Prussian  blue)  and  a  yellow  (chromate  of  lead  or  chrysotham- 
mine). 

The  details  of  the  processes  of  dyeing  and  printing  in  patterns,  al- 
though embracing  some  of  the  most  refined  applications  of  the  properties 
of  the  colouring  matters,  do  not  enter  into  the  plan  of  an  elementary  and 
general  work,  such  as  this  should  be. 


CHAPTER  XXVII. 

OF    THE    VEGETABLE    ALKALIES. 

The  substances  now  to  be  described  constitnte  a  very  remarkable 
family  of  bodies.  They  exist  naturally  in  the  plants  from  which  they 
are  derived,  and  confer  upon  them  their  most  active  medicinal  prop- 
erties ;  they  act  as  bases,  forming,  with  few  exceptions,  well-char- 
acterized and  neutral  salts  even  with  the  strongest  acids,  and  they 
are  distinguished  from  most  substances  of  vegetable  origin  by  con 
taining  nitrogen.  The  presence  of  this  element,  indeed,  has  been 
considered  as  standing  in  immediate  connexion  with  the  source  of 
their  alkaline  power,  and  has  given  rise  to  theories  of  their  intimate 


624  QUININE     AND     ITS     SALTS. 

constitution,  of  which  I  shall  notice  the  most  important  at  the  con- 
clusion of  their  special  histories. 

Quinine:— (N.C^o .  HisO^)  or  Qu.     Eq.  163-1  or  2039. 

The  bark  of  the  various  species  of  cinchona  contains  three  vege- 
table alkalies,  combined  with  the  cinchonic  and  cinchonatannic 
acids  already  described.  These  are  quinine,  cinchonine,  and  ari- 
cine ;  of  these,  the  quinine  is  by  far  the  most  important,  and  is  gen- 
erally extracted  from  the  yellow  bark.  The  coarsely-powdered  bark 
is  to  be  boiled  with  eight  or  ten  parts  of  water,  to  which  two  parts 
of  muriatic  acid  have  been  added.  When  the  liquor  will  dissolve 
no  more,  it  is  to  be  allowed  to  cool,  and  strained ;  lime  is  then  to 
be  added  in  very  fine  powder  until  the  liquor  has  a  marked  alkaline 
reaction  j  the  precipitate  is  to  be  collected  on  a  linen  cloth,  washed 
once  or  twice  with  water,  and  then  dried ;  from  this,  boiling  alco- 
hol dissolves  out  quinine  and  cinchonine  j  the  solution  being  mixed 
with  water,  the  alcohol  may  be  distilled  off  and  saved;  the  residue 
is  to  be  then  neutralized  by  dilute  sulphuric  acid,  and  a  slight  ex- 
cess added  to  form  acid  salts.  On  evaporating  this  liquor  to  the 
proper  point,  the  sulphate  of  quinine  crystallizes,  while  the  sulphate 
of  cinchonine  remains  in  solution. 

To  obtain  pure  quinine,  solution  of  sulphate  of  quinine  is  to  be 
decomposed  by  caustic  potash,  and  the  white  curdy  precipitate,  be- 
ing carefully  dried,  is  to  be  dissolved  in  the  smallest  possible  quan- 
tity of  spirit  of  wine.  By  then  allowing  it  to  evaporate  spontane- 
ously in  a  warm  place,  the  pure  quinine  crystallizes  with  an  atom 
of  combined  water. 

When  heated  cautiously,  the  quinine  abandons  its  crystal-water, 
and  then  fuses ;  its  taste  is  intensely  bitter  j  it  requires  200  parts 
of  boiling  water  for  solution,  and  is  almost  insoluble  in  cold  water; 
it  dissolves  easily  in  alcohol  and  ether. 

The  salts  of  quinine  are  generally  crystallizable,  and  soluble  in 
alcohol  and  water ;  those  with  the  oxygen  acids  contain  an  atom  of 
water,  in  which  they  agree  with  the  salts  of  ammonia,  of  melamine, 
and  of  anilene  ;  it  combines  directly  with  the  hydracids. 

The  Muriate  of  Quinine,  (Qu.-f-H.CL),  forms  pearly  needles.  It 
dissolves  easily  in  water ;  with  corrosive  sublimate  and  with  bichlo- 
ride of  platinum  it  forms  double  salts,  soluble  in  water,  and  crys- 
tallizable. 

The  Basic  Sulphate  qf  Quinine  is  the  most  important  preparation 
of  this  base ;  its  manufacture  is  conducted  on  a  very  large  scale, 
according  to  the  process  just  now  given  for  preparing  quinine,  or 
various  analogous  methods.  When  crystallized,  it  contains  water, 
its  formula  being  (Qua+S.Og+S  Aq.).  It  effloresces  when  gently 
heated  or  in  very  dry  air,  giving  off  six  atoms  of  water  and  retain- 
ing two,  Avhich  cannot  be  expelled  without  partial  decomposition ; 
it  is  but  sparingly  soluble  in  water,  requiring  thirty  parts  of  boiling 
and  740  parts  of  cold  water ;  it  requires  eighty  parts  of  cold  alco- 
hol, but  much  less  of  hot ;  its  crystals  are  small  pearly  plates  or 
needles,  which,  when  heated,  phosphoresce  strongly  and  fuse  ;  by 
a  strong  heat  it  is,  of  course,  totally  decomposed. 

The  JVeutral  Sulphate  of  Quinine  crystallizes  in  rectangular  prisms 


SALTS     OF     QUININE. C  I  N  C  H  O  N  I  N  E.  625 

which  have  the  formula  (Qu.  +  S.O3  +  8  Aq.).  They  effloresce  easily, 
dissolve  in  ten  parts  of  water  at  60^,  and  undergo  aqueous  fusion  at 
212°.  It  is  also  very  soluble  in  alcohol;  though  neutral  in  consti- 
tution, its  solution  reddens  litmus. 

The  sulphate  of  quinine  of  commerce  is  sometimes  adulterated 
with  sulphate  of  lime  and  with  boracic  acid,  which  are  known  by 
remaining  when  the  organic  substance  is  burned  away,  and  also 
with  sugar  and  with  margaric  acid.  The  latter  is  detected  by  its 
insolubility  in  dilute  acids ;  the  former  by  washing  the  sample  with 
a  little  water,  and  precipitating  the  quinine  that  is  dissolved  by  a 
drop  of  solution  of  carbonate  of  soda,  when  the  taste  of  the  sugar 
is  recognised. 

Phosphate  of  Quinine  crystallizes  in  small  but  very  brilliant  nee- 
dles, which  are  soluble  in  water  and  alcohol. 

The  Tannate  of  Quinine  is  formed  by  adding  solution  of  tannic 
acid  or  infusion  of  galls  to  any  salt  of  quinine.  A  white  precipi- 
tate appears,  which  is  totally  insoluble  in  water,  but  dissolves  in 
acetic  and  muriatic  acids. 

Ferroprussiate  of  Quinine  is  formed  by  boiling  together  one  part 
of  sulphate  of  quinine  and  one  and  a  half  of  yellow  prussiate  of 
potash  with  seven  parts  of  water.  The  newly-formed  salt  separates 
as  a  greenish-yellow  oily  substance.  When  the  liquor  is  cold,  it  is 
to  be  poured  off,  and  the  ferroprussiate  of  quinine  dissolved  in 
boiling  alcohol,  from  which  it  crystallizes  in  greenish-yellow  nee- 
dles by  spontaneous  evaporation. 

The  action  of  chlorine  on  quinine  and  its  salts  is  very  character- 
istic. If  sulphate  of  quinine  be  dissolved  in  a  large  quantity  of 
chlorine  water,  and  some  water  of  ammonia  added,  a  deep  green 
precipitate  is  formed,  and  the  liquor  becomes  also  intensely  green. 
To  the  body  so  formed  the  name  Dalleiochin  has  been  given.  If 
the  green  solution  be  evaporated  with  contact  of  air,  it  becomes 
dark-red  coloured,  sal  ammoniac  is  formed,  and  two  bodies,  of 
which  one  is  soluble  in  alcohol,  and  the  other  not ;  the  former  is 
called  Rusiochin,  and  the  latter  Melanochin.  Formulae  have  been 
proposed  for  these  bodies,  but  as  no  security  for  their  accuracy 
has  been  given,  I  think  it  better  not  to  bring  them  forward.  These 
reactions,  combined  with  the  action  of  tannic  acid,  serve  as  tests 
for  quinine. 

Cinchonine.—N.Q>2o  -  HjzO.  or  Ci.    Eq.  155-1  or  1939. 

This  alkali  exists  most  abundantly  in  the  gray  bark  (cinchona 
micrantha),  from  which  it  may  be  obtained  by  the  same  kind  of 'pro- 
cess as  the  yellow  bark  is  subjected  to  for  the  extraction  of  quinine; 
but  it  is  usually  prepared  from  the  mother  liquors  which  remain 
after  the  crystallization  of  the  sulphate  of  quinine,  as  just  now  de- 
scribed I  from  its  alcoholic  solution  it  crystallizes  in  thin  colourless 
prisms ;  its  taste  is  peculiar  and  bitter  ;  it  requires  2500  parts  of 
boiling  water  for  solution,  but  dissolves  easily  in  alcohol  and  in 
ether.  At  330°  it  fuses,  without  losing  weight.  Its  salts  resemble 
very  closely  those  of  quinine. 

Muriate  of  Cinchonine^  Ci.-f  H.CL,  crystallizes  easily  in  brilliant 

4K 


626  A  R  I  C  I  N  E. M  O  R  P  H  I  A. 

interwoven  needles ;  it  forms  double  salts  with  the  metallic  chlo- 
rides, similar  to  those  of  quinine. 

^ulyhate  of  Cinchonine. — The  basic  sulphate,  Cij-}-S.034-2  Aq., 
crystallizes  in  rhombic  prisms  j  it  requires  fifty-four  parts  of  cold 
water  for  solution.  The  neutral  salt,  Ci.  -f  S.O3-I  8  Aq.,  is  much  more 
soluble,  and  crystallizes  in  large,  well-formed  rhombic  octohedrons. 
The  Tannate  of  Ci?ickomne  is  a  white  insoluble  powder. 

In  contact  with  chlorine,  cinchonine  forms  a  dark  red  solution, 
and  after  some  time  a  brown  precipitate  appears.  If  iodine  and 
cinchonine  be  dissolved  together  in  alcohol,  and  the  liquor  evap- 
orated spontaneously,  a  compound  crystallizes  in  saffron-coloured 
needles,  which  is  described  as  Iodide  of  Cinchonine^  which  it  cannot 
be,  as  hydriodic  acid  is  formed. 

Aricine.—N.G^, .  H,A  or  Ar.     Eq.  171-1  or  2139. 

This  alkaloid  is  found  in  the  bark  known  as  China  de  cusco,  or 
arica  bark,  with  which  the  genuine  cinchona  bark  is  often  adulter- 
ated; the  tree  yielding  it  is  not  known.  It  is  obtained  by  precisely 
the  same  process  as  cinchonine  and  quinine  are  procured  from  the 
pale  and  yellow  barks. 

It  crystallizes  in  brilliant  white  needles;  it  is  totally  insoluble  in 
water,  but  easily  dissolves  in  alcohol  and  ether.  These  solutions 
have  an  intensely  bitter  taste  ;  by  nitric  acid  it  is  coloured  green ; 
its  salts  have  been  but  very  little  examined,  but  they  appear  to  cor- 
respond very  closely  in  constitution  and  properties  to  the  salts  of 
quinine  and  cinchonine. 

JlforpAt«.— N.C35  .  H20O6  or  Mr.     Eq.  293-8  or  3673. 

To  this  body  is  due,  in  most  part,  the  medicinal  activity  of  opium, 
as  a  substitute  for  which  it  is  prepared  upon  a  very  large  scale* 
The  processes  adopted  in  the  British  pharmacopoeias  for  this  pur- 
pose are  very  simple,  and  deliver  a  product  which,  although  by  no 
means  chemically  pure,  is  yet  sufficiently  so  for  all  medicinal  ob- 
jects ;  as  they  are,  however,  more  especially  applied  to  the  prep- 
aration of  the  muriate  of  morphia,  I  shall  describe  them  under  that 
head. 

To  obtain  pure  morphia,  the  process  invented  by  Wittstock  is 
perhaps  the  best.  One  part  of  opium,  eight  of  water,  and  two  of 
muriatic  acid  are  to  be  digested  together  for  six  hours  ;  when  the 
mixture  has  cooled,  the  brown  solution  is  to  be  poured  off,  and  the 
residue  treated  twice  more  with  water  and  acid.  The  liquors  so 
obtained,  being  mixed,  are  to  be  saturated  with  common  salt,  on 
which  they  become  milky,  and  after  a  few  hours,  a  brown  clotty 
precipitate  forms  ;  this  being  removed  by  the  filter,  ammonia  is  to 
be  added  in  slight  excess,  and  the  whole  allowed  to  stand  for  twen- 
ty-four hours.  The  precipitate  which  forms  in  this  time  is  to  be 
collected  on  a  filter,  washed  with  a  little  water,  dried,  and  digested 
in  spirit  of  specific  gravity  0*820,  which  dissolves  out  the  morphia. 
By  distillation,  the  greater  part  of  the  spirit  is  removed,  and  the 
morphia,  being  dissolved  in  a  small  quantity  of  boiling  alcohol,  crys- 
tallizes on  cooling.  In  this  process  the  narcotine  is  separated  by 
the  addition  of  the  common  salt,  in  a  solution  of  which  it  is  insolu- 


PROPERTIES     OF     MORPHIA.  627 

l)le  ;  the  meconic  acid,  codeine,  and  thebaine  remain  dissolved  after 
the  addition  of  the  ammonia  in  excess,  and  the  other  principles 
present  in  the  opium  remain  in  the  mother  liquor  after  the  morphia 
crystallizes. 

The  process  of  Merck  is  founded  on  the  insolubility  of  morphia 
in^  a  solution  of  sal  ammoniac,  and  its  solubility  in  lime-water. 
Opium  is  to  be  digested  in  three  times  its  weight  of  water,  then  ex- 
pressed, and  this  repeated  three  or  four  times  j  these  solutions  be- 
ing mixed,  are  brought  to  boil,  and  milk  of  lime  added  in  slight  ex- 
cess j  the  precipitate  which  forms  is  to  be  collected  on  a  strainer 
and  strongly  pressed  j  the  liquor  is  then  to  be  evaporated  until  it  is 
about  twice  the  weight  of  the  opium  employed,  and  to  be  then  fil- 
tered, brought  to  boil,  and  for  each  pound  of  opium,  one  ounce  of 
sal  ammoniac  added  in  powder.  The  morphia  separates  in  crystals, 
and  may  be  purified  by  boiling  with  some  lime  and  ivory  black,  and 
precipitation  again  by  sal  ammoniac. 

Morphia  crystallizes  in  right  rhombic  prisms,  as  in  the  figure,  2, 
u  being  primary,  and  m  a  secondary  plane,  containing 
2  Aq.,  which  they  lose  by  efflorescence  in  a  gentle  heat, 
and  become  opaque  ;  its  taste  is  strongly  and  permanent- 
ly bitter  j  it  is  almost  insoluble  in  water,  requiring  400 
parts  when  boiling,  and  separating  almost  completely  as 
the  liquor  cools.  The  solution  reacts  strongly  alkaline  ;  it  dissolves 
readily  in  alcohol,  but  very  sparingly  in  ether.  It  dissolves  in  so- 
lutions of  the  caustic  alkalies  or  earths.  If  morphia  or  any  of  its 
salts  be  brought  into  contact  with  nitric  acid,  they  become  coloured 
red  ;  this  property  belongs  also  to  some  other  vegetable  alkalies, 
and  appears  not  to  be  possessed  by  morphia  when  absolutely  pure. 
With  chlorine  water,  morphia  is  first  coloured  orange-red,  and  then 
dissolved.  If  iodic  acid  be  brought  into  contact  with  morphia,  it  is 
immediately  decomposed,  and  iodine  set  free. 

If  morphia  or  any  of  its  salts  be  added  to  a  solution  of  sesquichlo- 
ride  of  iron,  the  solution  assumes  a  rich  blue  colour,  which  is  re- 
moved by  an  excess  of  acid,  but  returns  on  the  neutralization  of  it 
by  an  alkali.  With  tannic  acid  it  gives  a  copious  white  precipitate. 
By  these  remarkable  reactions,  the  recognition  of  morphia  is  ren- 
dered more  simple  than  that  of  any  other  body  of  its  class. 

Morphia  completely  neutralizes  the  strongest  acids,  forming  salts 
which  are  generally  soluble  and  crystallizable. 

Muriate  of  Morphia,  Mr.  +  H.Cl.,  is,  for  medicinal  objects,  the 
most  important  compound  of  morphia ;  its  preparation,  as  directed 
by  the  British  pharmacopoeias,  is  as  follows :  the  soluble  parts  o( 
opium  having  been  dissolved  out  by  digestion  in  water,  the  united 
liquors  are  to  be  evaporated  to  the  consistence  of  a  sirup,  and  then 
cold  water  added,  by  which  a  quantity  of  feculent  matter  (apotheme) 
is  separated ;  the  clear  liquor  is  to  be  decomposed  by  a  slight  ex- 
cess of  chloride  of  lead  (London)  or  of  chloride  of  calcium  (Edin- 
burgh). The  meconate  of  morphia,  which  exists  in  the  opium,  be- 
ing decomposed,  meconate  of  lime  or  lead  is  precipitated,  and  mu- 
riate of  morphia  remains  dissolved  5  the  liquor  is  to  be  carefully 
strained  and  evaporated  to  a  pellicle ;  on  cooling,  the  salt  crystalli- 
nes J  this  is  to  be  pressed  between  folds  of  cloth,  to  remove  the 


628  NARCOTINE. CODEINE. 

dark  mother  liquor,  and  then  dissolved  in  boiling  water,  digested 
with  ivory  black,  and  recrystallized  until  the  crystals  become  per- 
fectly white. 

The  product  of  this  method,  although  not  chemically  pure,  is  suf 
ficiently  so  for  medicinal  uses.  It  contains  codeine,  and  sometimes 
others  of  the  opium  alkaloids.  To  obtain  the  pure  salt,  pure  mor- 
phia should  be  dissolved  in  dilute  muriatic  acid,  and  the  solution 
crystallized. 

Sulphates  of  Morphia, — The  neutral  sulphate,  which  crystallizes  in 
groups  of  soft  needles,  and  dissolves  in  twice  its  weight  of  water, 
has  the  formula  Mr.H.O. .  S.Og+S  Aq.  The  Bisulphate  of  Morphia 
does  not  crystallize. 

Acetate  of  Morphia  is  formed  by  dissolving  the  alkali  in  acetic 
acid,  or  by  decomposing  muriate  of  morphia  by  acetate  of  lead ;  it 
is  soluble  in  water  and  in  alcohol,  and,  after  the  muriate,  is  the  most 
important  salt  of  morphia. 

Morphia  is  precipitated  by  ammonia  and  by  tannic  acid  from  so- 
lutions of  any  of  these  salts. 

JVarcoifme.— N.C46 .  H^aOja  or  Nr.     Eq.  5230  or  418. 

This  alkaloid  may  be  obtained  at  once  from  opium  by  digestion 
with  ether,  or  when  the  impure  morphia  is  thrown  down  by  ammo- 
nia, ether  dissolves  out  the  narcotine  from  it.  It  crystallizes  in  col- 
ourless rhombic  prisms,  which  are  generally  larger  than  those  of 
morphia  5  it  fuses  at  338^,  and  remains  liquid  until  cooled  to  266°, 
when  it  congeals  as  a  mass  of  radiated  needles.  It  is  almost  insol- 
uble in  water,  but  easily  soluble  in  alcohol  and  ether  j  its  salts  have 
but  little  stability,  few  of  them  crystallize,  and  most  are  decompo- 
sed by  dilution  with  much  water.  Bj'^  ammonia  and  tannic  acid  they 
are  precipitated. 

From  morphia,  narcotine  is  very  easily  distinguished  by  its  solu- 
bility in  ether,  insolubility  in  caustic  alkalies  and  earths,  and  its  not 
giving  the  reactions  characteristic  of  morphia  with  nitric  acid  or 
with  sesquichloride  of  iron.  But  if  narcotine  be  put  in  contact  with 
sulphuric  acid,  and  oxygen  is  supplied  either  by  the  air  or  by  a 
trace  of  nitric  acid,  it  becomes  red.  Under  these  circumstances, 
however,  morphia  becomes  green. 

Cotfeme.— N.C35 .  H20O5  or  Cdn.     Eq.  3573  or  285-8. 

This  alkali  remains  dissolved  after  the  morphia,  narcotine,  and 
other  substances  have  been  precipitated  by  ammonia.  The  filtered 
liquor  is  to  be  evaporated  to  dryness,  and  digested  in  solution  of 
potash ;  a  substance  remains  undissolved,  which  gradually  becomes 
crystalline.  This  is  to  be  washed  with  water,  and  then  dissolved  in 
boiling  ether,  from  which,  by  spontaneous  evaporation,  the  codeine 
separates  in  colourless  prismatic  crystals,  which  contain  2  Aq. 

Crystallized  codeine  fuses  at  300°,  giving  off  its  crystal  water.  It 
dissolves  copiously  in  water  ;  the  solution  reacts  strongly  alkaline  ; 
it  is  insoluble  in  alkaline  liquors,  but  forms  with  acids  perfectly 
neutral  crystallizable  salts.  These  are  precipitated  copiously  by 
tannic  acid,  but  not  by  ammonia;  it  does  not  produce  any  of  the 
reactions  described  as  characterizing  morphia.    As  none  of  its  salts 


T  H  E  B  A  I  N  E. ^N  A  R  C  E  I  N  E. S  T  R  Y  C  H  N  I  N  E.  629 

are  employed  in  pharmacy  or  medicine,  they  need  not  be  specially 
noticed. 

TAeiame.— N.C25 .  H.A  or  Tb.     Eq.  2542  or  203-4. 

The  watery  infusion  of  opium  being  treated  with  milk  of  lime,  so 
that  the  morphia  may  rest  undissolved,  the  precipitate  is  to  be 
washed  with  water  until  it  becomes  white,  and  then  dissolved  in  a 
dilute  acid.  From  this  solution  thebaine  is  precipitated  by  ammo- 
nia. The  precipitate  being  dissolved  in  ether,  and  the  solution 
evaporated,  pure  thebaine  crystallizes  in  colourless  short  rhombic 
prisms,  which  taste  sharp  and  styptic,  and  have  a  strong  alkaline 
reaction.  At  300^  it  fuses,  and  solidifies  then  only  when  cooled  to 
230^.  It  is  scarcely  soluble  in  water,  but  abundantly  so  in  alcohol 
and  ether. 

By  acids  thebaine  is  decomposed,  a  resinous  substance  and  a  salt 
of  ammonia  being  formed.  In  its  other  characters  it  completely 
resembles  narcotine. 

J^arceine. — The  watery  solution  of  opium  is  to  be  heated  first  by 
ammonia,  which  throws  down  morphia,  narcotine,  thebaine,  and 
some  other  bodies,  and  these  being  removed  by  filtrations,  the  me- 
conic  acid  and  codeine  are  to  be  precipitated  by  an  excess  of  solu- 
tion of  barytes.  The  excess  of  barytes  being  then  removed  by  a 
current  of  carbonic  acid  gas,  the  filtered  liquor  is  to  be  evaporated 
to  the  consistence  of  a  sirup  and  set  aside ;  after  some  time  crys- 
tals form,  which  are  a  mixture  o{  meconine  (see  p.  610)  and  narceine. 
These  are  separated  by  ether,  which  dissolves  the  meconine,  and 
the  residual  narceine  being  dissolved  in  alcohol  and  decolorized  by 
animal  charcoal,  crystallizes,  by  the  cooling  of  its  solution,  in  deli- 
cate needles. 

It  tastes  bitter,  fuses  at  200°,  and  forms  a  crystalline  solid  on 
cooling  ;  it  dissolves  in  230  parts  of  boiling  water  ;  it  is  very  solu- 
ble in  alcohol,  but  insoluble  in  ether  j  its  solution  does  not  react  al- 
kaline, and  it  is  decomposed  by  strong  acids  ;  in  its  constitution, 
however,  it  resembles  the  true  vegetable  alkalies,  its  formula  being 

Pseudomorphine^  N.C54 .  H,sOj4,  occurs  but  very  rarely  in  opium. 
For  its  mode  of  preparation,  when  present,  I  shall  refer  to  the  lar- 
ger systematic  works ;  in  its  reactions  it  is  absolutely  identified 
with  morphia,  from  which  it  is  distinguished,  however,  by  its  com- 
position, by  crystallizing  in  plates,  and  by  not  forming  any  well- 
characterized  salts,  although  it  dissolves  very  readily  in  dilute  acids 

Strychnine.— N^C,^ .  H22O4  or  Stc.     Eq.  4355  or  348. 

This  alkaloid  exists  associated  with  brucine  in  several  species  of 
strychos  (nux  vomica,  ignatia,  colubrina,  «fec.),  also  in  the  substance 
used  by  the  natives  of  Borneo  for  poisoning  their  arrows,  and  term- 
ed Upas-tieuta^  or  Woorara  ;  it  is  obtained  most  easily  from  the  Ig- 
natius's  beans,  which  contain  but  little  brucine  ;  but,  as  these  are  not 
often  found  in  commerce,  the  nux  vomica  is  most  generally  em- 
ployed. The  seeds  are  to  be  boiled  for  some  time  in  strong  alco- 
hol, which  dissolves  out  a  quantity  of  fatty  matter  ;  being  then  dried 
in  a  stove,  they  are  easily  reduced  to  powder  j  this  powder  is  to  be 


630  STRYCHNINE,     ITS     PROPERTIES,     ETC. 

then  boiled  two  or  three  times  in  alcohol,  and  the  liquor  distilled 
until  the  greater  part  of  the  alcohol  has  come  over.  To  the  resi- 
due, acetate  of  lead  is  to  be  added  as  long  as  any  precipitate  oc- 
curs ;  by  this  means  more  fat,  colouring  matter,  and  some  organic 
acids  are  removed.  The  filtered  liquor  is  to  be  then  evaporated  so 
far,  that  from  sixteen  ounces  of  nux  vomica  it  amounts  to  six  or 
eight  ounces.  To  this  quantity  two  drachms  of  magnesia  are  to  be 
added,  and  the  whole  allowed  to  stand  aside  for  some  days ;  the 
precipitate  which  forms  is  to  be  collected  on  lineu,  pressed,  dried, 
and  dissolved  in  alcohol,  from  which  the  strychnine  crystallizes  on 
cooling,  while  the  brucine  remains  in  the  mother  liquor.  As  the 
strychnine,  how^ever,  is  not  yet  pure,  it  is  to  be  dissolved  in  dilute 
nitric  acid,  and  the  solution  evaporated  to  a  pellicle.  On  cooling, 
the  nitrate  of  strychnine  crystallizes  in  brilliant  white,  soft,  feathery 
prisms,  while  the  nitrate  of  brucine  separates  afterward  in  large, 
hard,  rhombic  prisms.  From  sixteen  ounces  of  nux  vomica,  forty 
grains  of  nitrate  of  strychnine  and  fifty  grains  of  nitrate  of  brucine 
may  be  obtained ;  from  the  solution  of  the  pure  nitrate  in  water, 
the  strychnine  may  be  precipitated  by  ammonia,  and,  being  dissolv- 
ed in  spirit  of  wine,  it  crystallizes,  by  spontaneous  evaporation,  in 
small  white  four-sided  prisms. 

Strychnine  has  an  intensely  bitter,  somewhat  metallic  taste  j  it 
requires  7000  parts  of  cold  water  for  solution  ;  and  yet,  if  one  part 
of  this  be  diluted  with  100  parts  more  of  water,  this  liquor  tastes 
strongly  bitter ;  it  is  insoluble  in  absolute  alcohol  and  in  ether,  but 
dissolves  readily  in  spirit  of  wine.  With  acids  strychnine  unites, 
forming  well-characterized  and  crystallizable  salts  j  it  differs  from 
the  other  vegetable  alkalies  in  containing  two  atoms  of  nitrogen  in 
its  equivalent.  With  chlorine  strychnine  gives  a  white  precipitate  ; 
also  with  tannin  ;  when  completely  pure,  it  is  not  reddened  by  nitric 
acid,  but  such  as  it  exists  in  commerce  it  generally  is  so,  owing  to 
the  presence  of  traces  of  brucine. 

Muriate  of  Strychnine^  Stc.-j-H.Cl.,  crystallizes  in  crowded  rhom 
bic  needles,  which  dissolve  readily  in  water.     With  corrosive  sub- 
limate, with  bichloride  of  platinum,  and  with  cyanide  of  mercury, 
it  gives  insoluble  double  salts. 

Hydrocyanate  of  Strychnine  is  obtained  by  dissolving  strychnine  in 
prussic  acid ;  it  crystallizes  in  needles,  which  are  decomposed  even 
by  a  gentle  heat.  If  solution  of  sulphocyanide  of  potassium  be  ad- 
ded to  a  solution  of  any  salt  of  strychnine,  the  liquor,  when  agitated, 
deposites  the  Sulphocyanate  of  Strychnine  in  fine  radiated  needles, 
which  are  insoluble  in  water.  By  this  means  one  part  of  strychnine 
may  be  recognised  in  375  of  water,  and  hence  Artus  has  proposed 
this  reaction  as  the  best  medico-legal  test  for  strychnine. 

Sulphate  of  Strychnine  forms  small  cubic  crystals,  which  contam 
4  Aq.,  and  are  soluble  in  ten  parts  of  water. 

The  characters  of  the  JS'^itrate  of  Strychnine  have  been  described  in 
the  method  of  preparing  the  alkaloid. 

Strychnine  is,  perhaps,  after  pure  prussic  acid;  the  most  intense 
of  poisons.     It  kills  by  producing  tetanus. 


B  R  U  C  I  N  E. D  E  L  P  H  I  N  I  N  E. V  E  R  A  T  R  I  N  E.  631 

Brucine.—N,C,s .  H^gOg  or  Br.  'Eq.  408  or  5107. 

This  substance  is  found  associated  with  strychnine,  as  already  de- 
scribed, and  also  in  the  bark  of  the  false  angustura,  which  is  now 
known  to  be  the  strychnos  nux  vomica,  though  formerly  supposed 
to  be  the  brucia  antidysenterica,  whence  the  name  of  this  alkaloid 
is  derived.  Its  mode  of  preparation  from  the  nux  vomica  has  been 
sufficiently  described  in  the  preceding  article. 

From  its  solution  in  spirit,  brucine  crystallizes  in  colourless 
rhombs,  containing  water,  which  they  abandon  on  melting  at  220°. 
It  dissolves  in  850  parts  of  cold  and  in  500  parts  of  boiling  water ; 
these  solutions  react  alkaline,  and  taste  intensely  bitter  ;  it  dissolves 
readily  in  alcohol,  but  is  insoluble  in  ether. 

With  nitric  acid,  brucine  becomes  of  a  rich  red  colour,  which,  on 
the  addition  of  protochloride  of  tin,  changes  to  a  fine  violet;  this 
distinguishes  it  from  the  red  of  morphia,  which  is  completely 
bleached  by  protochloride  of  tin  and  by  sulphurous  acid. 

With  chlorine,  brucine  gives  a  yellowish-red,  and  with  iodine  a 
chocolate-brown  precipitate. 

The  salts  of  brucine  have  a  bitter  taste,  are  generally  crystalliza- 
ble,  and  give  with  tannin  and  with  ammonia  white  precipitates. 

The  Curara,  or  Urari  poison,  used  in  the  Indian  Archipelago  for 
poisoning  arrows,  contains  a  vegetable  alkaloid,  Curarine^  which 
lorms  a  yellow  uncrystallizable  mass,  which  dissolves  easily  in  wa- 
ter and  in  alcohol,  but  is  insoluble  in  ether ;  it  reacts  alkaline,  and 
combines  with  acids ;  its  salts  do  not  crystallize  5  its  solution  is  pre- 
cipitated by  tannic  acid. 

The  tree  from  which  curara  is  derived  is  not  accurately  known, 
but  is  supposed  to  be  a  strychnos. 

Delphinine.—N.C,, .  H,  A  or  De.  Eq.  2659  or  2124.— This  sub- 
stance  is  extracted  from  the  seeds  of  the  stavesacre,  delphinium 
staphisagria^  by  digestion  in  water,  to  which  some  sulphuric  acid 
had  been  added.  The  acid  liquor  is  to  be  decomposed  by  a  slight 
excess  of  magnesia,  and  the  precipitate  being  washed  and  dried,  is 
to  be  boiled  in  alcohol,  which  dissolves  the  delphinine.  To  obtain 
it  quite  pure,  it  is  to  be  redissolved  in  a  dilute  acid,  boiled  with  ani- 
mal charcoal,  filtered,  precipitated  with  ammonia,  and  the  precipitate 
dissolved  in  alcohol,  from  which  the  delphinine  separates  on  cooling 
as  a  white  crystalline  powder. 

It  is  soluble  in  ether  and  alcohol  j  almost  insoluble  in  water;  its 
solution  has  an  intolerably  sharp  taste  ;  it  melts  at  250^  ;  chlorine 
turns  it  green  j  oil  of  vitriol  colours  it  red,  and  then  carbonizes  it ; 
its  salts  are  very  soluble,  but  crystallize  badly ;  Courbe  states  that 
the  stavesacre  contains  also  a  substance,  Stephysaine,  (N.C32 .  H23O4 1), 
which  is  distinguished  by  its  insolubility  in  ether ;  it  is  a  yellow 
resinous  mass,  insoluble  in  water,  but  dissolving  in  dilute  acids  with- 
out neutralizing  them. 

Veratnne.—'N.Cs^ .  H2i06  or  Ve.     Eq.  3647  or  289. 

This  alkaloid  is  found  in  the  roots  of  the  veratrum  album,  and  in 
the  seeds  of  the  veratrum  sabadilla  j  the  best  process  for  its  extrac- 
tion is  that  given  by  Vasmer. 


632  SABADILLIN  E. J  E  R  V  I  N  E. C  O  L  C  H  I  C  I  N  E, 

The  sabadilla  seeds  are  to  be  infused  in  water,  containing  an  ounce 
of  oil  of  vitriol  for  each  pound  of  seeds,  as  long  as  anything  is  dis- 
solved. The  filtered  liquor  is  wine-yellow  5  it  is  to  be  accurately 
neutralized  by  carbonate  of  soda,  and  evaporated  to  the  consistence 
of  an  extract.  While  yet  warm,  alcohol  is  to  be  poured  on  it,  and 
digested  until  everything  soluble  is  taken  up.  From  this  solution 
the  alcohol  is  then  to  be  distilled  off,  the  residue  digested  in  dilute 
sulphuric  acid,  and  from  this  liquor  the  veratria  precipitated  by  car- 
bonate of  soda.  The  precipitate  must  be  redissolved  in  a  dilute 
acid,  digested  with  ivory  black,  and  again  precipitated  by  a  carbon- 
ated alkali  in  order  to  obtain  it  pure. 

Pure  veratrine  appears  as  a  white  uncrystallized  resinous  powder  ; 
it  melts  at  230°,  reacts  alkaline,  has  no  smell,  but  produces  violent 
sneezing ;  its  taste  is  exceedingly  sharp,  but  without  bitterness  j  it 
is  insoluble  in  water,  but  dissolves  readily  in  alcohol  and  ether  5  its 
salts  are  mostly  crystallizable  and  neutral,  but  if  mixed  with  much 
water  they  are  decomposed,  acid  being  set  free,  and  a  basic  salt  pre- 
cipitated. Veratrine  itself  is  actively  poisonous,  and  is  much  used 
in  medicine,  but  none  of  its  salts  are  important. 

Sabadilline.—'N.C^o .  H.aO^  or  Sa.     Eq.  2351  or  188-1. 

This  body,  which  accompanies  veratrine,  is  separated  from  it  by  boiling  the  pre- 
cipitate produced  by  the  carbonate  of  soda  with  water.  From  the  liquor  the  sabadil- 
line  gradually  separates  in  radiated  crystalline  needles,  of  a  pale  rose  colour,  but 
when  purified  it  becomes  white ;  its  taste  is  intolerably  sharp ;  it  is  sparingly  soluble 
in  water  or  in  ether,  but  abundantly  soluble  in  alcohol ;  it  reacts  strongly  alkaline, 
and  forms  crystallizable  salts  with  acids. 

Jervine.— 1^2^00  -  HsOg  or  Je.     Eq.  5952  or  476. 

This  alkaloid  accompanies  veratrine  in  veratrum  album;  it  is  prepared  by  a  pro- 
cess similar  to  that  for  veratrine,  from  which  it  is  separated  by  the  facility  with 
which  it  crystallizes  from  its  alcoholic  solution,  and  by  the  very  sparing  solubility 
of  its  sulphate.  When  pure  it  is  white,  easily  fusible,  totally  decomposed  at  400°, 
nearly  insoluble  in  water,  but  copiously  soluble  in  alcohol.  Of  its  salts,  the  sul- 
phate, nitrate,  and  muriate  are  sparingly  soluble  in  water  or  in  mineral  acids;  the 
acetate  dissolves  readily.  Muriate  of  jervine  forms,  with  bichloride  of  platinum,  a 
very  sparingly  soluble  iouble  salt.    Crystallized  jervine  contains  4  Aq. 

Colchicine. — (Formula  not  established.) 

This  alkaloid  is  obtained  from  the  seeds  of  the  meadow  saffron  (colchicum  autum- 
nale)  by  digestion  in  a  mixture  of  weak  alcohol  and  sulphuric  acid.  The  excess 
of  acid  in  the  liquor  is  to  be  then  neutralized  by  lime,  and  the  alcohol  distilled  oif. 
The  residual  liquor  is  to  be  decomposed  by  carbonate  of  potash  in  excess,  the  pre- 
cipitate washed,  dried,  dissolved  in  absolute  alcohol,  decolorized  by  animal  charcoal, 
and  gently  evaporated,  a  few  drops  of  water  being  added.  The  pure  colchicine 
crystallizes  in  colourless  needles.  Its  taste  is  intensely  bitter,  but  not  biting,  like 
that  of  veratrine,  nor  does  it  produce  the  violent  sneezing;  it  is  pretty  soluble  in  wa- 
ter, and  very  soluble  in  alcohol  and  ether;  its  solution  reacts  feebly  alkaline,  but 
neutralizes  acids  perfectly.  Tincture  of  iodine  precipitates  it  of  a  rich  orange  col- 
our. Nitric  acid  colours  it  dark  violet  and  blue.  Though  most  abundant  in  the 
seeds,  all  parts  of  the  meadow  saffron  contain  colchicine. 

Emetine. — (Formula  not  established.)  This  substance  exists  in  all 
those  plants  whose  roots  are  sent  into  commerce  under  the  name 
of  Ipecacuanha,  or  Hippo.  The  roots  are  to  be  powdered  and  digest- 
ed in  ether,  by  which  a  fatty  substance  is  taken  up.  They  are  then 
to  be  boiled  with  alcohol,  the  decoction  mixed  with  water,  and  the 
spirit  distilled  off.  The  residual  liquor  is  to  be  filtered,  and  then 
boiled  with  magnesia  j  the  precipitate  is  to  be  dried  and  digested  in 


SOLANINE. CH  E  LERYTHR  INE,    ETC.  633 

alcohol,  which  dissolves  the  emetine.  This  solution  is  to  be  evap- 
orated to  dryness,  the  residue  dissolved  in  a  dilute  acid,  the  liquor 
boiled  with  ivory  black  until  completely  decolorized,  then  filtered, 
and  the  emetine  precipitated  by  an  alkali. 

When  completely  pure,  emetine  is  white  and  nearly  tasteless  j  it 
is  very  poisonous ;  scarcely  soluble  in  water  or  in  ether,  it  dis- 
solves readily  in  alcohol ;  it  possesses  strong  alkaline  properties  ,* 
its  salts  are  completely  neutral,  but  cannot  be  crystallized  j  they 
dry  down  to  gummy  masses.  Tannic  acid  and  corrosive  sublimate 
produce  white  precipitates ;  iodine,  bichloride  of  platinum,  brown 
ish-yellow  precipitates  with  the  salts  of  emetine. 

Solanine.—lS(.C,s  .  H^aO^s  or  So.     Eq.  7519  or  601. 

This  alkaloid  is  found  in  the  berries  of  the  solanum  nigrum ;  in  the  berries,  leaves, 
and  stems  of  the  solanum  dulcamara  (bitter-sweet)  and  tuberosum  (potato). 

The  powdered  stems  of  bitter-sweet  are  to  be  digested  with  spirit  of  sp.  gr.  0-865, 
mixed  with  one  third  of  sulphuric  acid.  The  liquid  is  to  be  supersaturated  with 
milk  of  lime,  the  spirit  distilled  off,  the  residue  washed  with  water,  and  what  remains 
treated  with  dilute  sulphuric  acid.  From  the  solution  thus  obtained  the  solanine  is 
to  be  precipitated  by  an  alkali,  washed  with  water,  dissolved  in  alcohol,  decolorized 
by  animal  charcoal,  and  then  obtained  by  evaporation.  It  forms  a  white  brilliant 
powder,  of  a  slightly  bitter,  nauseous  taste ;  it  does  not  brown  turmeric,  but  restores 
the  blue  colour  of  reddened  litmus ;  it  melts  a  little  above  212° ;  it  is  almost  insolu- 
ble in  water,  sparingly  soluble  in  ether,  but  copiously  in  alcohol.  With  acids  it 
forms  neutral  salts,  which  do  not  crystallize,  and  are  strong  narcotic  poisons. 

The  injurious  properties  of  unripe  potatoes  result  from  the  presence  of  this  body. 
It  exists  abundantly  in  the  early  shoots  (under  ground)  and  buds  of  the  tubers. 

Chelerythrine. — (Formula  not  established.) 

This  substance  is  extracted  from  the  roots  of  the  chelidonium  majus  by  digestion 
with  dilute  sulphuric  acid.  The  liquor  so  obtained  is  to  be  evaporated  and  mixed 
with  ammonia.  The  brown  precipitate  which  falls  is  to  be  washed,  prised  between 
folds  of  paper,  and  digested  in  alcohol  with  some  sulphuric  acid.  The  alcoholic 
solution  being  mixed  with  water  and  the  spirit  distilled  off,  the  residual  liquor  is 
precipitated  by  ammonia,  and  the  precipitate  being  washed  and  dried  by  pressure,  is 
to  be  digested  in  ether,  and  the  ethereal  solution  evaporated  to  dryness.  The  mass 
so  obtained  is  then  digested  in  dilute  muriatic  acid,  which  leaves  a  resinous  sub- 
stance undissolved.  The  deep  red  liquor  evaporated  to  dryness  and  washed  with 
ether,  leaves  a  mixture  of  muriate  of  chelerythrine  and  muriate  of  cheledoline,  the 
fojrmer  of  which  is  dissolved  by  washing  with  a  small  quantity  of  water,  while  the 
latter  remains  undissolved. 

From  the  solution  of  the  muriate,  the  chelerythrine  is  precipitated  by  ammonia 
as  a  white  curdy  powder.  From  its  ethereal  solution  it  remains  as  a  resinous  mass, 
which  remains  soft  for  a  long  time;  it  is  insoluble  in  water;  its  solutions  in  alcohol 
and  ether  are  pale  yellow.  With  acids  it  forms  salts  of  a  rich  crimson  colour, 
which  generally  crystallize.    Tannic  acid  produces  in  their  solutions  a  precipitate 


soluble  in  alcohol. 


Chelidonine. — N3C40 .  HgoOg  or  Ch. 


The  preparation  of  this  substance  has  been  in  great  part  described  in  the  prece- 
ding article.  By  digesting  the  sparingly  soluble  muriate  with  ammonia,  then  dis- 
solving in,  sulphuric  acid,  and  precipitating  with  muriatic  acid,  it  is  freed  from  all 
traces  of  chelerythrine,  and  finally  the  pure  chelidonine,  separated  by  ammonia,  is 
dissolved  in  boiling  alcohol,  from  which  it  crystallizes,  on  cooling,  in  brilliant  c'ol- 
ouriess  tables.  It  isj  insoluble  in  water,  soluble  in  alcohol  and  ether;  it  tastes  bitter, 
and  reacts  alkaline ;  its  salts  are  colourless,  and  those  with  the  mineral  acids  crys* 
tallize ;  its  solutions  give  with  tannic  acid  a  precipitate. 

Aconitine. — (Formula  not  established.) 

The  fresh-expressed  juice  of  the  monkhood  (aconitum  napellus)  is  to  be  boiled 
and  filtered,  and  the  clear  liquor  mixed  with  an  excess  of  carbonate  of  potash.    The 

4L 


634         A  T  R  O  P  I  N  E. B  ELLADONIN  E. D  A  T  U  R  I  N  E. 

mixture  is  to  be  agitated  with  ether  as  long  as  anything  is  taken  up,  and  by  evapo- 
rating this  solution  the  aconitine  remains.  From  the  dry  plant  or  from  the  seeds, 
the  aconitine  may  be  obtained  by  processes  similar  to  those  described  for  veratrine 
and  colchicine, 

Aconitine  partly  crystallizes  from  its  ethereal  or  alcoholic  solution  in  white  grains, 
but  for  the  most  part  forms  a  colourless,  vitreous-looking  mass ;  it  tastes  sharp  and 
bitter,  and  is  intensely  poisonous ;  it  reacts  strongly  alkaline,  and  neutralizes  the 
strongest  acids  ;  alkalies  precipitate  its  solution  white ;  chloride  of  gold  and  tannic 
acid  also  give  white  precipitates,  and  iodine  throws  it  down  orange. 

Atropine. — N.C34  .  HgaOg  or  At. 

This  alkaloid  exists  in  all  parts  of  the  atropa  belladonna,  but  most  abundantly  in 
the  roots.  To  prepare  it,  the  fresh  roots  are  to  be  powdered  and  digested  in  alcohol, 
of  specific  gravity  0820.  The  liquor  obtained  is  to  be  mixed  with  lime,  in  the  pro- 
portion of  one  part  to  twenty-four  parts  of  roots,  and  laid  aside  for  twenty-four  hours 
with  frequent  agitation;  the  mixture  is  to  be  then  filtered,  and  the  deposite  treated 
with  dilute  sulphuric  acid :  the  filtered  solution  is  distilled,  and  the  spirit  being  thus 
removed,  the  residual  liquor  is  concentrated  by  evaporation  until  it  equals  one 
twelfth  of  the  roots  employed.  To  this  liquor,  when  cold,  is  to  be  added  a  strong 
solution  of  carbonate  of  potash,  until  a  dirty  brown  precipitate  occurs,  which  is  to 
be  removed  by  the  filter,  and  then  more  carbonate  of  potash  added  as  long  as  any 
precipitate  is  formed.  This  last,  which  is  impure  atropine,  is  to  be  washed  with 
water,  then  dried,  and  dissolved  in  strong  alcohol,  the  solution  decolorized  by  boil-, 
ing  with  animal  charcoal,  filtered,  and  gradually  evaporated,  whereby  the  atropine 
separates  in  small  white  silky  prisms. 

The  taste  of  atropine  is  sharp,  bitter,  and  metallic.  It  dilates  the  pupil  perma- 
nently and  strongly ;  if  impure,  it  is  brown,  does  not  crystallize,  and  has  a  horrible 
smell,  but  if  quite  pure  it  has  no  smell ;  it  requires  2000  parts  of  cold  water  for  so- 
lution, but  dissolves  in  thirty-four  parts  of  boiling  water,  from  which  some  crystalli- 
zes by  cooling,  but  the  greater  part  is  decomposed ;  it  dissolves  readily  in  alcohol 
and  ether. 

The  alkaline  properties  of  atropine  are  feeble ;  most  of  its  salts  are  decomposed 
by  boiling  with  water  into  ammonia  and  a  substance  of  an  excessively  disagreeable 
smell ;  this  decomposition  is  instantly  eflfected  by  the  caustic  fixed  alkalies.  Most 
of  the  salts  1^  atropine  crystallize;  tannic  acid  precipitates  their  solutions  white ; 
t^e  chlorides  of  platinum  and  gold,  yelloAv ;  and  iodine,  orange-yellow. 

Belladonine. — (Formula  not  established.)  The  dried  root  of  belladonna  is  to  be 
mixed  with  a  strong  solution  of  caustic  potash  and  rapidly  distilled ;  the  distilled 
liquor  is  to  be  decomposed  by  bichloride  of  platinum,  and  the  white  precipitate  which 
forms  being  washed  and  dried,  is  to  be  mixed  with  carbonate  of  potash  and  gently 
heated.  Belladonine  sublimes  and  condenses  in  colourless  rectangular  prisms,  with 
a  penetrating  odour  like  ammonia ;  it  dissolves  in  water ;  the  solution  reacts  alka- 
line ;  it  is  not  very  poisonous ;  its  salts  resemble  closely  the  corresponding  salts  yf 
ammonia. 

It  appears  to  me  likely  that  this  substance  is  a  product  of  the  decomposition  of 
the  atropine  by  the  caustic  potash,  and  does  not  exist  in  the  plant. 

Daturine. — This  substance  is  obtained  from  the  seeds  of  the  thorn  apple  (datura 
stramonium),  by  the  same  process  as  has  been  described  for  the  preparation  of  aconi- 
tine. From  its  solution  in  spirit,  it  crystallizes  in  very  brilliant  colourless  groups 
of  needles.  When  perfectly  pure  it  is  inodorous,  but  when  impure  it  smells  dis- 
gustingly narcotic ;  its  taste  is  bitter,  and  like  that  of  tobacco ;  it  dissolves  in  seven- 
ty-two parts  of  boiling,  and  in  250  of  cold  water,  in  twenty-one  of  ether,  and  in  three 
of  alcohol ;  it  melts  below  212°,  and  volatilizes  unchanged,  at  a  stronger  heat  in  white 
clouds. 

A  solution  of  daturine  reacts  strongly  alkaline,  and  forms  crystallizable  neutral 
salts,  which,  like  pure  daturine,  are  very  poisonous.  Towards  reagents  it  acts  like 
atropine. 

Hyoscyamine. — This  alkaloid,  which  is  the  active  principle  of  the  henbane  (hyos- 
cyamus"  niger  and  albus),  is  best  prepared  from  the  seeds,  in  the  same  way  as  atro- 
pine, except  that  to  the  spirit  in  which  the  seeds  are  digested  some  sulphuric  acid 
should  be  added.  It  crystallizes  in  radiated  groups  of  silky  needles,  but  is  more 
usually  obtained  as  a  transparent  vitreous  mass.  In  its  properties  it  resembles  so 
perfectly  atropine  and  daturine,  that  they  need  not  be  specially  detailed.  It  neutral- 
izes acids  perfectly;  its  salts  are  intensely  poisonous;  they  are  decomposed  very 
easily,  even  by  boiling  with  water. 


C  O  N  E  I  N  E. N  I  C  O  T  I  N  E.  635 

Coneine.—'N.C,^  .  OhH.  or  Cn.     Eq.^  1359  or  108-7. 

This  remarkable  substance  is  ihe  active  principle  of  the  hemlock  (conimn  macui 
latum),  in  all  parts  of  which  it  exists,  but  is  more  easily  extracted  from  the  seeds. 
These  are  to  be  bruised,  mixed  with  one  fourth  of  a  strong  solution  of  caustic  pot- 
ash and  eight  parts  of  water,  and  distilled  as  long  as  the  water  which  comes  over 
has  any  smell.  This  is  to  be  neutralized  by  dilute  sulphuric  acid,  and  evaporated 
to  the  consistence  of  a  sirup.  The  residue  is  treated  two  or  three  times  with  a  mix- 
tui-e  of  one  part  of  ether  and  two  of  alcohol,  sp,  gr.  0820,  wherein  the  sulphate  of 
coneine  dissolves.  From  this  solution  the  ether  and  spirit  are  distilled  off,  then  some 
water  added,  and  the  liquor  evaporated  to  dryness.  The  residue  is  to  be  mixed 
with  half  its  weight  of  strong  solution  of  potash,  and  rapidly  distilled  to  dryness. 
The  receiver  should  be  carefully  cooled.  The  oily  coneine  should  be  separated 
from  the  watery  liquor,  and  this  last  distilled  again  with  some  lime.  If  the  coneine 
contain  ammonia,  it  may  be  got  rid  of  by  exposure  for  a  lew  hours  in  vacuo,  beside 
a  capsule  of  oil  of  vitriol. 

Pure  coneine  is  a  colourless  transparent  liquid,  of  sp.  gr.  089 ;  its  odour  is  highly 
penetrating  and  nauseating,  partly  like  that  of  the  plant;  its  taste  is  disgustingly 
sharp ;  it  is  extremely  poisonous.  100  parts  of  cold  water  dissolve  one  of  coneine, 
and  the  solution  becomes  turbid  when  heated,  Coneine  itself  dissolves  one  fourth  oi 
water,  and  this  liquor  becomes  milky  even  by  the  heat  of  the  hand  ;  it  mixes  with 
alcohol,  ether,  and  oils  in  all  proportions;  in  close  vessels  it  distils  unaltered  at 
■  370°,  but  at  a  much  lower  temperature  if  water  be  present.  When  completely  an- 
hydrous, coneine  has  no  alkaline  properties,  but  acts  very  powerfully  if  water  is 
present ;  it  saturates  acids  completely,  and  has  the  smallest  atomic  weight  of  any 
organic  alkali  known.  Its  salts  crystallize  but  imperfectly;  they  are  decomposed 
by  much  water ;  they  dissolve  readily  in  water,  alcohol,  or  a  mixture  of  alcohol  and 
ether,  but  in  pure  ether  they  are  insoluble.  Their  watery  solution  is  precipitated 
by  iodine,  saffron-yellow ;  and  by  tannic  acid,  white.  Coneine  itself  is  coloured  by 
nitric  acid  blood- red ;  by  exposure  to  the  air,  especially  if  warm,  coneine  is  decom- 
posed ;  it  becomes  brown,  ammonia  is  evolved,  and  a  bitter,  inodorous,  resinous 
substance  is  produced,  which  has  no  poisonous  properties. 

J^icotine. — (Formula  not  established.) 

This  substance  is  the  characteristic  ingredient  of  tobacco  (nicotiana  tabacum, 
and  many  other  species).  For  its  preparation,  precisely  the  same  process  is  to  be 
followed  as  has  been  described  for  coneine,  to  which  it  has  a  very  great  similarity. 
When  pure,  nicotine  is  a  colourless  oily  liquid,  of  a  pungent  tobacco  smell,  and  a 
sharp,  burning  taste ;  it  differs  from  all  other  organic  bases  in  mixing  with  water  in 
all  proportions ;  it  mixes  also  with  alcohol  and  ether.  When  anhydrous,  it  gives 
off  white  fumes  at  212°,  and  distils  at  480" ;  but  the  greater  part  of  it  is  decomposed. 
Jf  water  be  present,  it  distils  easily  at  a  much  lower  temperature. 

Nicotine  possesses  a  strong  alkaline  reaction,  and  neutralizes  acids  perfectly.  Its 
salts  are  generally  very  soluble,  some  crystallizable,  inodorous,  but  with  a  strong 
K)bacco  taste.    With  alkalies  they  evolve  the  characteristic  odour  of  the  plant. 

Menispcnni'ne. — N.Cis .  H12O2.  This  substance  is  found  in  the  capsules  of  the  coc- 
culus  Indicus,  associated  with  picrotoxine  (page  609).  The  alcoholic  extract  is  to  be 
boiled  with  acidulated  water,  and  when  the  picrotoxine  has  crystallized  from  the  fil- 
tered liquor,  an  excess  of  alkali  is  to  be  added.  The  precipitate  is  to  be  dissolved 
in  alcohol,  decolorized  by  animal  charcoal,  and  evaporated  to  dryness.  The  residue 
is  to  be  digested  with  ether,  which  dissolves  Menispermine,  and  leaves  another  body, 
Paramenispermine,  undissolved. 

From  the  ethereal  solution,  menispermine  crystallizes  in  white  square  prisms.  It 
is  tasteless,  and  not  poisonous ;  it  forms  neutral  crystallizable  salts.  The  parame- 
nispermine  dissolves  in  acids,  but  does  not  neutralize  them. 

Cissampdinc  exists  in  the  roots  of  the  cissampelos  pareira  (pareira  brava),  and  is 
prepared  by  the  same  kind  of  process  that  has  been  frequently  described.  From  the 
evaporation  of  its  ethereal  solution,  it  remains  as  a  yellowish,  transparent,  vitreous 
mass,  which  combines  with  water,  forming  a  white  powder  like  magnesia.  It  is  very 
easily  decomposed ;  it  is  a  powerful  organic  base ;  its  salts  form  gummy  masses, 
but  scarcely  crystallize. 

Glaucine  exists  in  the  glaucium  luteum  (homed  poppy).  Its  preparation  is  sim- 
ilar to  that  of  aconitine ;  it  crystallizes  in  pearly  scales ;  it  possesses  the  same  range 
of  properties  as  the  other  vegetable  bases,  and  forms  crystallizable  salts.  The 
homed  poppy  contains  another  crystalline  principle  (^Glauco-picritie),  which  appears 
also  to  act  as  a  base. 


636     CONSTITUTION     OF     VEGETABLE     ALKALOIDS. 

A  great  number  of  plants  are  stated  to  contain  organic  bases,  which,  howevef, 
have  been  as  yet  so  imperfectly  examined  and  described  as  to  render  their  intro- 
duction here  useless.  Of  such  substances,  the  most  important  are :  in  the  croton 
tiglium,  Crotonine,  which  is  crystalline,  but  is  not  the  active  principle ;  in  the  aathusa 
cynapium,  Cynapine,  crystalline ;  and  in  the  digitalis  purpurea,  Digitalhie,  which  ap- 
pears most  to  resemble  coneine. 

Of  the  Constitution  of  the  Vegetable  Alkaloids. 

From  the  period  of  the  first  discovery  of  this  class  of  bodies, 
chemists  have  endeavoured  to  ascertain  on  what  depended  the  ba- 
sic properties  by  which  they  are  so  remarkably  characterized.  The 
discovery,  by  Liebig,  that  each  equivalent  of  an  organic  base  con- 
tained an  equivalent  of  nitrogen,  suggested  the  very  plausible  idea 
that  they  contained  ammonia  ready  formed,  and  that  in  their  salts 
the  acid  was  neutralized  by  the  ammonia,  and  the  organic  substance 
remained  combined  with  the  salt,  as  it  had  been  with  the  ammonia 
before.  This  idea,  however,  cannot  be  sustained,  as  we  cannot  ob- 
tain ammonia  from  any  vegetable  alkaloid,  unless  by  processes 
which  totally  destroy  its  constitution,  and  which,  indeed,  eliminate 
ammonia  from  any  organic  substance  containing  nitrogen.  More- 
over, it  is  now  known  that  Liebig's  rule  is  not  universally  true  ;  the 
equivalents  of  strychnine  and  of  brucine  contain  each  two  atoms  of 
nitrogen,  and  we  know  of  other  organic  bases,  as  melanine,  amiline, 
jervine,  and  urea,  in  which  the  quantity  of  nitrogen  in  the  equiva- 
lent goes  much  beyond  one  atom.  We  may  hence  conclude  that 
there  is  no  reason  to  suppose  that  the  vegetable  alkalies  contain 
ammonia,  or  owe  their  basic  properties  to  its  presence. 

Some  remarkably  simple  relations  of  composition  occur  among 
certain  bodies  of  this  class,  which  would  at  first  appear  to  throw 
light  upon  their  constitution.  Thus  morphine  and  codeine  differ 
in  composition  only  by  morphia  containing  an  atom  of  oxygen 
more  5  and  if  we  supposed  (N.C35 .  H20O4)  to  be  a  compound  radical 
R.,  then  codeine  should  be  protoxide,  R.  +  O.,  and  morphia  deutox- 
ide,  R.4-20.  In  like  manner,  if  we  take  the  cinchona  alkalies,  we 
find  them  to  differ  only  in  the  quantity  of  oxygen  they  contain,  and 
making  (N-CjoHia)  a  compound  radical,  cinchonine  should  be  R.-f 
O.,  quinine  R.-f-^O.,  and  aricine,  R.4-30.  These  remarkable  facts 
might  lend  considerable  support  to  the  idea  that  these  alkaloids  are 
oxygen  bases,  oxides  of  compound  radicals  j  but  a  closer  examina- 
tion of  their  relations  does  away  with  all  probability  of  its  truth. 
Thus,  if  morphia  were  R.-|-20.,  then  by  muriatic  acid  we  should 
have  a  bichloride  formed,  R.-}-2Cl.,  and  water  separated  ;  in  place 
of  which,  the  morphia  combines  directly  with  one  atom  of  muriatic 
acid,  and  so  in  all  other  cases  ;  we  cannot  find  in  the  compounds  of 
these  vegetable  alkalies  any  of  the  laws  which  govern  the  formation 
of  salts  by  metallic  oxides.  In  addition,  the  salts  formed  by  these 
alkaloids  with  the  oxygen  acids  contain  an  atom  of  water,  which 
cannot  be  expelled  without  decomposition.  In  this  they  resemble 
ammonia,  and  I  think  that  it  is  the  only  analogy  which  we  can  estab- 
lish by  the  facts  at  present  known ;  but  whether,  in  these  vegetable 
alkalies,  the  nitrogen  makes  part  of  a  compound  radical  analogous 
to  amidogene,  remains  to  be  decided  by  future  investigations 


ULMINE     BODIES     FROM     SUGAR.  637 


CHAPTER  XXVIII. 

OF    THE   PRODUCTS    OF    THE    DECOMPi)SITION    OF    WOOD    AND    THE    ALLIED 

BODIES. 

SECTION  I. 

OF   THE    SLOW   DECOMPOSITION    OF    WOOD.      CONSTITUTION   OF   ULMINE 
OF    TURF    AND    COAL. 

The  gradual  decomposition  of  the  woody  tissues  of  plants  gives 
origin  to  a  class  of  bodies  which  had  been  long  confounded  under 
the  name  of  Ulmine,  but  which  are  now  recognised  to  consist  of 
several  distinct  substances,  differing  in  their  origin,  and  still  more 
essentially  in  their  properties.  From  the  influence  which  they  ex- 
ercise in  agricultural  operations,  by  forming  an  element  of  the  soil, 
and  their  importance  as  fuel,  by  constituting  the  great  mass  of  turf, 
they  deserve  a  somewhat  detailed  notice.  I  have  already  stated, 
that  by  the  action  of  acids  upon  sugar  (p.  532),  lignine,  starch,  and 
similar  bodies  (page  528),  brown  substances  are  produced,  the  com- 
position of  which  was  not  definitely  established.  Mulder  has,  how- 
ever, recently  reinvestigated  the  history  of  this  class  of  bodies,  and, 
from  his  known  accuracy,  his  results  may  be  looked  upon  as  satis- 
factory. 

When  sugar  is  acted  upon  by  a  very  dilute  acid,  and  the  liquor 
not  allowed  to  boil,  two  brown  substances  are  formed,  of  which  one 
is  soluble  in  solution  of  carbonate  of  soda,  but  the  other  not.  For 
these  bodies  the  names  Sacchulmine  and  Sacckulmic  Acid  maybe  re- 
tained. From  the  alkaline  solution  the  latter  may  be  precipitated 
by  any  stronger  acid.  These  bodies  are  insoluble  in  water  and  in 
alcohol.  The  formula  of  the  Sacchulmine  is  C4oHi60,4 ;  that  of  the 
Sacckulmic  Acid  is  C4oH,40i2.  They  differ,  therefore,  in  the  former 
containing  the  elements  of  water,  which,  however,  cannot  be  expell- 
ed without  total  decomposition. 

If  the  sacchulmic  acid  be  dissolved  in  water  of  ammonia  and  pre- 
cipitated by  an  acid,  it  retains  a  quantity  of  the  alkali ;  and  if  the 
ammoniacal  solution  be  decomposed  by  a  metallic  salt,  the  precipi- 
tate which  forms  is  a  double  compound  of  sacchulmic  acid,  ammo- 
nia and  the  metallic  oxide.  It  was  the  unsuspected  existence  of 
ammonia  in  these  cases  which  produced  the  discordance  of  former 
results. 

If  the  sugar  be  acted  on  by  a  stronger  acid,  and  the  solution  kept 
boiling  for  a  considerable  time,  the  ulmine  bodies  disappear,  and  ar6 
replaced  by  two  dark  brown  or  black  substances,  possessing  very 
analogous  properties,  the  Saccharo-humine  and  Saccharo-humic  Acid. 
This  change  takes  place  more  readily  if  the  air  have  free  access. 
Both  are  insoluble  in  water  and  alcohol ;  they  are  separated  by  al- 
kaline liquors,  which  dissolve  the  acid  body.  From  this  solution  it 
is  thrown  down  by  any  stronger  acid.     The  composition  of  saccha- 


638  ULMINE     BODIES     FROM     WOOD. 

ro-humine  is  expressed  by  the  formula  C4oH,50i5 ;  that  of  the  sac» 
charo-humic  acid  by  C4oH,20i2.  Like  the  former  bodies,  these  differ, 
therefore,  in  the  elements  of  water. 

Mulder  found  that  access  of  air  was  not  necessary  for  the  forma- 
tion of  sacchulmine  or  its  acid,  but  that  without  air  no  saccharo- 
humine  nor  its  acid  could  be  produced.  In  this  action,  even  with- 
out access  of  air,  formic  acid  appears,  although  but  in  small  quantity ; 
at  the  same  time,  glucic  acid  (p«  534),  and  another  body  first  de- 
scribed by  Mulder,  Jlpoglucic  Jlcid^  are  generated. 

When  wood  remains  long  in  contact  with  air  and  moisture,  it  is 
gradually  converted  into  a  mixture  of  two  brown  substances,  which, 
from  their  having  been  originally  found  as  a  product  of  the  decom- 
position of  elm,  are  specially  termed  Ulmine  and  Ulmic  Acid.  The 
latter  is  insoluble  in  alcohol  and  water,  soluble  in  alkaline  solutions; 
in  its  natural  state  it  contains  ammonia,  which  can  only  be  expelled 
by  boiling  with  caustic  potash,  by  which  the  greater  part  of  the  ul 
mic  acid  is  itself  decomposed.  Its  formula,  as  derived  from  the 
analysis  of  a  specimen  furnished  by  a  rotten  willow,  was  C4oHj20i2, 
being  isomeric  with  saccharo-humic  acid,  but  distinguished  from  it 
by  many  minor  characters,  especially  that  when  treated  with  acids 
it  retains  twice  as  much  ammonia  as  the  artificial  product.  Mulder 
considers  the  natural  ulmine  to  contain  more  hydrogen  ;  its  formula 
should  then  be  C4oH,40,2,  and  by  the  continued  action  of  the  air  it 
should  change  into  ulmic  acid.  The  formation  of  these  bodies  from 
the  woody  fibre  results  from  the  absorption  of  oxygen  and  the  evo 
lution  of  carbonic  acid  and  water  :  thus  four  atoms  of  lignine,  C48 
H32O32,  with  fourteen  of  oxygen,  produce  8C.O2  with  18H.0.,  and  an 
atom  of  ulmine,  C4oH,40,2. 

Another  kind  of  decomposition  to  which  wood  is  subject  is  the 
conversion  of  the  ligneous  fibre  into  a  white  friable  substance,  which 
is  formed  abundantly  in  the  interior  of  dead  trees;  its  composition 
is  found  to  be  expressed  by  the  formula  C33H27O24.  It  is  evidently 
formed  by  the  lignine  combining  with  oxygen  from  the  air  and 
with  the  elements  of  water,  and  then  giving  ofT  carbonic  acid  gas, 
C3GH24O24  with  30.  and  3H.0.  forming  C33H27O24  and  3C.O2. 

The  rotting  of  wood  is,  however,  by  no  means  necessarily  in- 
duced by  the  mere  presence  of  air  and  water  ;  for  lignine  may  be 
exposed  to  these  agents  for  centuries  without  being  altered  in  any 
sensible  degree.  Precisely  as  in  the  alcoholic  and  acetous  ferment- 
ations, it  is  necessary  that  an  azotized  substance  should  be  present, 
which,  being  first  decomposed,  and  forming,  probably,  crenic  and 
apocrenic  acids,  communicates  the  action  to  the  lignine  ;  the  albu- 
minous juices  which  exist  in  the  vessels  of  the  wood  act  thus  as  a 
ferment,  and  the  decomposition  of  the  wood  may  be  prevented  by 
precisely  the  same  methods  as  counteract  the  tendency  to  the  fer 
mentation  of  sugar  or  of  alcohol ;  any  deoxidizing  substance,  as 
sulphurous  acid;  any  metallic  salt,  as  corrosive  sublimate  or  blue- 
stone,  which  may  combine  with  the  albumen  and  render  it  insolu- 
ble, will  thus  protect  wood  from  decomposition,  and  are  at  present 
extensively  used  as  preservatives  against  what  is  technically  termed 
the  dry  rot. 

It  is  by  a  similar  decomposition  that  the  roots  and  other  remains 


ULMINE     BODIES     FROM     THE     SOIL,    ETC.  639 

of  plants  are  converted  into  a  substance  which,  by  virtue  of  its  di 
rect  absorption,  or  by  means  of  the  products  of  its  farther  change, 
contributes  powerfully  to  the  nutrition  of  the  succeeding  race  of 
plants,  and  thereby  constitutes  the  essential  element  of  every  fertile 
soil ;  but  though,  like  ulmine,  derived  from  the  rotting  of  vegetable 
matters,  and  for  the  most  part  of  the  same  composition,  the  organic 
substance  of  the  soil  is  by  no  means  identical  with  it.  It  would 
even  appear,  from  Mulder's  results,  that  the  vegetable  constituent 
of  the  soil  varies  in  composition  according  to  the  nature  of  the 
crop.  For  distinction,  I  shall  apply  to  the  ulmic  acid  of  the  soil  the 
name  of  Ge'ic  Acid^  proposed  by  Berzelius.  To  extract  it,  the  soil 
is  washed  with  boiling  water  until  this  passes  away  quite  clear,  and 
then  boiled  with  carbonate  of  soda ;  the  brown  filtered  liquor  is 
precipitated  by  muriatic  acid,  and  the  precipitafe  boiled  with  alco- 
hol to  dissolve  out  two  organic  acids,  which  will  be  shortly  descri- 
bed. In  this  state  the  substance  is  really  an  ammoniacal  salt,  its 
formula  being  C40H12O12+N.H3  +  4H.O.,  and  even  by  caustic  potash 
it  cannot  be  completely  deprived  of  ammonia.  In  the  ge'ic  acid  of 
a  meadow,  the  same  organic  element  was  found  to  be  united  with 
twice  as  much  ammonia  j  and  in  one  case,  where  the  substance  had 
been  obtained  from  the  soil  of  an  orchard,  the  geic  acid  had  the 
formula  C4oH,20,4.  The  geic  acid,  C4oH,20i2,  though  isomeric  with 
the  saccharo-humic  and  ulmic  acids,  is  proved  not  to  be  identic£il 
hy  numerous  minor  characters,  which  need  not  be  described  here. 

In  that  decomposition  of  vegetable  matter  which  gives  origin  to 
turf,  water  is  present  in  much  greater  quantity  than  in  any  of  the 
former  cases,  in  many  instances  the  plants  being  totally  immersed, 
and  so  matted  together,  from  their  mode  of  growth,  that  the  access 
of  air  must  be  very  much  prevented.  Hence  we  no  longer  find  in 
turf  the  comparatively  simple  decomposition  of  the  wood  into  an 
ulmine  and  an  ulmic  acid,  but,  in  addition  to  these  bodies,  the  turf 
allies  itself  to  the  varieties  of  coal,  in  containing  several  kinds  of 
fossil,  resinous,  and  waxy  substances,  which  are  produced  by  sec- 
ondary and  more  complicated  reactions.  Here  it  is  necessary,  how- 
ever, to  describe  only  such  constituents  of  the  turf  as  are  analogous 
to  those  already  noticed,  and  for  distinction  I  shall  term  them  Hu- 
mous and  Humic  Acids.  The  former  is  found  principally  in  the 
light,  pale  brown  turf,  which  is  not  imbedded  in  water  ;  the  latter, 
on  the  contrary,  in  the  heavy  black  turf,  to  which  water  has  had 
free  access.  They  are  prepared  precisely  as  noticed  for  the  geic 
acid,  the  turf  containing  in  abundance  the  same  organic  acids,  sol- 
uble in  alcohol,  as  does  vegetable  soil. 

The  Humous  Acid  resembles  perfectly  in  its  properties  the  sac- 
chulmic  acid,  with  which  it  is  isomeric,  its  formula  being  C4oH,40,2, 
but  it  has  no  tendency  to  retain  ammonia  when  precipitated  by  an 
acid  from  its  combination  with  that  alkali.  The  Humic  Acid,  on 
the  contrary,  combines  with  ammonia  so  intimately  that  they  can- 
not be  separated  by  any  reagent ;  and  it  even  absorbs  ammonia  in 
the  laboratory,  from  the  small  quantity  of  the  gas  which  may  be  set 
free  in  other  operations.  As  extracted  from  the  black  turf,  its  for- 
mula is  CjoHj50,5  +  N.H40.  It  is,  therefore,  when  free  from  ammo- 
nia, isomeric  with  the  saccharo-humine,  but  differs  totally  in  com- 


640  FORMATION     OF     COAL. 

position  from  the  saccharo-humic  acid,  with  which  it  is  so  identified 
in  properties. 

The  azotized  acids  which  have  been  noticed  as  existing  in  vege- 
table soil  and  in  turf,  are  termed  the  Crenic  and  Apocrenic  Acids  } 
they  derive  their  origin  from  the  rotting  of  those  elements  of  the 
plant  which  contain  nitrogen,  as  albumen,  &c.,  and  are  formed,  also, 
in  the  decomposition  of  animal  substances  under  peculiar  circum- 
stances 5  thus  certain  soft  minerals,  as  polishing  slate  and  rotten- 
stone,  contain  so  much  organic  matter  as  to  be  used  for  food  in 
time  of  distress  in  the  north  of  Europe,  and  Berzelius  found  this  to 
consist  of  crenic  acid,  formed  from  the  bodies  of  the  microscopic 
animals,  whose  silicious  skeletons  constitute  the  mineral  portion  of 
the  rock. 

These  acids  were  first  discovered  in  mineral  springs,  whence 
their  name  (KprjvT]),  and  are  most  easily  obtained  pure  from  the 
ochery  deposites  which  form  on  the  sides  of  the  spring,  and  in 
which  they  are  combined  with  oxide  of  iron  and  silica.  They  are 
separated  by  means  of  their  copper  salts,  the  white  crenate  of  cop- 
per being  soluble,  while  the  brown  apocrenate  of  copper  is  insolu- 
ble in  a  liquor  containing  free  acetic  acid  3  from  the  copper  salts 
they  may  be  set  free  by  sulphuretted  hydrogen. 

The  Crenic  Acid  is  a  pale  yellow  gummy  mass,  of  an  astringent 
taste,  very  soluble  in  alcohol  and  water ;  its  formula  is  N.C,4 .  Hie 
0,2;  by  exposure  to  the  air  it  changes  into  Apocrenic  Acid;  this 
is  brown,  of  an  astringent  taste,  reddens  litmus,  and  is  much  less 
soluble  in  alcohol  and  water  than  the  crenic  acid  j  its  formula  is 
NA3.H„0«_. 

The  relations  of  these  acids,  and  of  the  several  species  of  ulmine 
to  the  nutrition  of  plants,  will  be  hereafter  considered. 

The  circumstances  under  which  coal  is  formed  have  been  already 
noticed  generally  in  p.  476  and  563,  but  i*  remains  to  examine  spe- 
cially the  mode  of  decomposition  to  which  the  wood  is  subjected 
during  that  change.  The  coal  appears  to  require  for  its  production 
that  the  ligneous  fibre  should  be  in  presence  of  water,  with  little 
or  no  access  of  air,  and  that  in  most  cases  the  temperature  shall  be 
elevated.  Thus,  while  ulmine  is  produced  when  the  woody  mate- 
rial is  on  the  surface,  or,  at  least,  only  immersed  in  water,  the  for- 
mation of  any  of  the  varieties  of  coal  requires  the  conjoined  influ- 
ence of  moisture,  of  great  pressure,  arising  from  the  superposition 
of  beds  of  rock  or  soil,  of  a  high  temperature,  given  by  the  prox- 
imity of  volcanic  foci,  or  generated  by  the  decomposition  of  the 
wood  itself,  and,  finally,  that  the  access  of  air  shall  be  much  more 
limited  than  in  the  former  cases.  Then,  according  to  the  age  of 
the  geological  formation,  the  nature  of  the  superincumbent  rock, 
and  the  degree  to  which  the  temperature  is  raised,  the  coaly  mate- 
rial varies  in  composition.  The  more  recent  species  {Lignite  or 
Fossil  Wood),  which  peculiarly  belong  to  the  tertiary  formations, 
are  characterized  by  the  perfect  preservation  of  the  organized 
structure  of  the  wood,  and  a  more  or  lees  deep  brown,  but  not 
black  colour.  Their  composition  may  generally  be  expressed  by 
formulae  which  indicate  that,  without  any  absorption  of  oxygen  from 
an  external  source,  the  wood  has  given  off  carbonic  acid  and  water. 


COMPOSITION,    ETC.,     OF     COAL 


641 


In  the  coals  of  the  secondary  strata  (the  proper  coal  formation) 
great  diversity  of  constitution  exists,  depending  on  local  circum- 
stances. It  would  appear  that,  where  the  conversion  from  lignite 
into  true  coal  is  perfect,  the  proportion  of  carbon  and  hydrogen  be- 
comes uniformly  CgaHis,  these  elements  being  united  with  small 
quantities  of  oxygen,  generally  amounting  to  from  three  to  five 
atoms.  The  cannel  coal  of  Wigan,  the  splint  coal  of  Workington, 
and  the  caking  coal  of  Newcastle,  have  been  ascertained,  by  John- 
stone, to  be  so  constituted.  Here,  also,  the  change  arises  from  the 
elimination  of  the  elements  of  water  and  carbonic  acid  from  the 
wood,  as  C36H24O24  produces  exactly  40. O2  and  12H.0.,  with  C32 
H,20,. 

AVhen  the  mass  of  decomposing  vegetable  matter  has  been  sub- 
jected to  a  very  high  temperature,  as  by  the  direct  contact  of  vol- 
canic rocks,  it  becomes  almost  completely  carbonized,  and  the  va- 
riety of  coal  termed  Anthracite  is  formed.  The  small  quantity  of 
hydrogen  and  oxygen  which  anthracite  contains,  can  only  be  refer- 
red to  traces  of  the  proper  coal  that  have  escaped  decomposition, 
and  if  pure,  it  would  be  a  Mineral  Coke,  identical  in  nature  with  the 
coke  artificially  prepared. 

The  formulae  here  given  as  expressing  the  constitution  of  the  pro- 
ducts of  the  decomposition  of  wood,  are  to  be  considered  only  as 
illustrative  of  the  kind  of  reaction  which  goes  on  between  its  ele- 
ments 5  for  none  of  these  products  are  pure  chemical  substances ; 
they  form  no  definite  compounds  j  they  have  no  precise  equivalent 
number,  and  hence  it  is  only  for  illustration  that  a  formula  can  be 
legitimately  employed  to  express  their  composition. 

The  following  table  contains  the  ordinary  composition  of  the  most 
Important  varieties  of  coal  and  turf.  The  numbers  given  were  se- 
lected from  those  obtained  in  the  analyses  byEichardson  and  Reg- 
lault. 


Turf .  .  . 
Lignite  .  . 
Splint  Coal 
Cannel  Coal 
Cherry  Coal 
Caking  Coal 
Anthracite 


68  09 
71-71 
82-92 
83  75 
84-84 
87-95 
91  98 


Hydrogen. 


593 
485 
6-49 
566 
5  05 
524 
3-92 


Oxygen   and 
Mtrogen. 

31  37 
21  67 
10-86 
8  04 
8-43 
541 
3  16 


Asbes. 


4-61 
1  77 
0  13 
255 
1-68 
1-40 
0  94 


Economic 
Value  of 
100  Parts. 


171 
208 
262 
260 
258 
271 
273 


At  the  same  time  that  the  great  masses  of  fossil  fuel  are  thus  gen 
erated  by  the  decomposition  of  wood,  a  great  number  of  other  pro- 
ducts make  their  appearance,  which,  although  much  inferior  in  quan- 
tity, possess,  at  least  in  some  cases,  considerable  interest.  Thus 
the  fire-damp  of  mines  (p.  563)  consists  in  most  part  of  marsh  gas, 
but  contains  in  some  cases,  also,  olefiant  gas  and  free  hydrogen. 

Interspersed  through  the  masses  of  coal  are  found  small  quantities  of  a  great  va- 
riety of  bodies,  principally  carbohydrogens,  resembling  the  oils  and  stearoptens  of 
plants  closely  in  properties  and  constitution.  Thus  Ozocherit,  or  jTossil  Wax,  is  found 
in  cavities  in  the  rocks  lying  upon  coal ;  it  is  brown,  of  a  foliated  structure  ;  it  fuses 
at  143*^'.  Paroffifie,  which  is  an  important  constituent  of  the  tar  produced  in  the 
destructiv^e  distillation  of  wood,  is  also  found  associated  with  coal.  It  is  while, 
crystallizes  in  brilliant  plates ;  it  fuses  at  111*^,  and  maybe  distilled  unaltered;  it 
dissolves  readily  in  ether  and  alcohol ;  it  is  not  acted  upon  by  any  reagent,  whence 

4M 


642 


MANUFACTURE     OF     WOOD     VINEGAR. 


its  name  {parum  affinis).  Both  these  bodies  have  the  same  composition  as  olefiam 
gas,  consisting  of  C.H.  Many  waxy  fossil  substances  are  isomeric  with  oil  of  tur- 
pentine, and  one,  which  is  interesting  as  being  the  matrix  in  which  the  native  cin  • 
nabar  of  Idria  is  imbedded  (page  402),  has  the  formula  C2iH'7;  it  is  termed  Idria- 
line. 

Others  of  these  products  are  liquid,  and  frequently  issue  forth  from  the  surface  of 
the  ground,  constituting  springs,  which,  from  theirinflammability,  have  been  invested 
in  uncivilized  countries  with  a  sacred  character.  Such  liquids  are  known  as  Rock 
OU,  or  Petroleum.  Some  specimens  of  it  that  have  been  accurately  examined  are, 
like  paraffine,  isomeric  with  olefiant  gas,  while  others  are  isomeric  with  oil  of  tur- 
pentine, and,  absorbing  oxygen,  are  gradually  converted  into  a  resinous  substance 
Asphalt,  for  which  the  formula  C40H32O6  has  been  assigned. 

SECTION  II. 

OF  THE  PRODUCTS  OF  THE  DESTRUCTIVE  DISTILLATION  OF  WOOD,  COAL, 

AND  RESIN. 

The  results  of  the  action  of  heat  on  an  organic  substance  are 
strictly  analogous  to  those  of  an  imperfect  combustion.  A  quanti 
ty  of  carbon  is  removed,  as  carbonic  acid,  and  a  quantity  of  hydro- 
gen, as  water.  The  other  products  contain,  therefore,  relatively- 
less  oxygen.  If  the  substance  upon  which  we  operate  be  pure,  and 
the  heat  be  carefully  managed,  the  result  is  in  all  cases  perfectly- 
simple  and  distinct,  as  where  acetic  acid  gives  acetone  and  carbon- 
ic acid  ;  malic  acid  gives  water,  carbonic  acid,  and  maleic  acid  ;  but 
if  the  temperature  change,  another  set  of  reactions  occurs,  and  oth- 
er  products  are  generated,  which  arise,  properly  speaking,  from  the 
decomposition  of  the  first.  Thus  acetic  acid  gives  marsh  gasj  ma- 
lic acid  gives  fumaric  acid.  Hence,  if  substances  be  taken,  through 
which,  either  from  their  mass  or  their  non-conducting  power,  the 
jieat  cannot  be  uniformly  diffused,  a  number  of  different  reactions 
takes  place  in  different  portions  at  the  same  time,  according  to  their 
irespective  temperatures ;  the  bodies  generated  in  the  interior  are 
altered  according  as  they  approach  the  surface,  and  hence  a  very 
high  degree  of  complexity  is  given  to  the  ultimate  results. 

When  the  substances  operated  on  are  not  pure,  but,  as  common  wood,  coal,  turf, 
&c.,  contain  various  organic  bodies  of  different  natures  mixed  together,  it  becomes 
quite  impossible  to  express  the  precise  reactions  which  occur,  and  the  number  ot 
bodies  generated  becomes  very  great.  It  is  to  the  classes  of  bodies  thus  produced 
that  I  wish  to  direct  attention  in  the  present  section,  as  in  all  cases  where  the  mode 
of  origin  of  a  pyrogenic  product  is  accurately  known,  I  have  described  it  in  connex- 
ion with  the  body  from  whence  it  is  usually  derived. 

According  as  the  object  of  the  process  is  the  manufacture  of  vinegar  or  of  tar,  the 

rdistiilation  of  wood  is  very  differently  managed.    For  the  first,  a  cast  iron  cylinder, 

— — ^  «,  is  built  into  a  furnace, 

\llSy     <    .  ,  rpP         r  hff^  of  which  c  is  the  grate,  d 

^^    CT'  <  -XJLbe   I      f^  n.^'""^  -g^,^^      the  fire-door,  and  e,  e,  e  the 

5^1^  R5JSK       ^^^jg^  which  winds  spiral- 

ly round  the  cylinder,  so 
as  to  heat  it  as  uniformxy 
as  possible.  The  wood,  in 
pieces  which  fit  accurate- 
ly the  interior  of  the  cylin- 
der, is  introduced  by  an 
opening  in  the  top,  which 
is  then  closed  by  the  plate 
b.  The  volatile  and  gas- 
eous products  of  the  dis- 
tillation pass  off  by  the 
tube  g,  which  is  bent  zig- 
zag, and  is  surrounded  at  i,  i  by  larger  tubes,  through  which  a  stream  of  cold  water 
constantly  passes.    This  water  is  supplied  from  a  reservoir,  n,  by  the  tube  I,  and, 


PYROXYLIC     SPIRIT,     ETC.  643 

entering  below  at  w,  passes  from  one  jacket  to  another  by  the  cross  pipes  o,  o,  and 
escapes  ultimately  above  atp;  this  cooling  arrangement  being  a  form  of  Liebig's 
condensing  tube  (p.  543),  convoluted,  as  it  were,  in  order  to  occupy  less  room.  The 
Jiquids  which  are  thus  condensed  collect  in  the  tubs  r,  and  the  gases  which  come 
over  are  allowed  by  the  cock  t  to  issue  from  the  tube  s,  and,  being  set  on  fire,  play 
on  the  bottom  of  the  cylinder,  and  thus  economize  a  certain  quantity  of  fuel. 

The  liquid  products  separate,  on  standing,  into  two  layers,  the  upper  formed  of 
oily  and  tarry  matters,  the  lower  of  water,  acetic  acid,  pyroxylic  spirit,  &c.  By  the 
connecting  tube,  this  heavier  liquid  passes  into  the  second  tub,  while  the  tar  remains 
in  the  first.  The  impure  acetous  liquor  is  neutralized  by  carbonate  of  lime ;  the 
acetate  of  lime  decomposed  by  sulphate  of  soda  or  sulphuret  of  sodium ;  the  acetate 
of  soda  crystallized  and  fused  in  order  to  expel  the  adhering  tar,  then  dissolved,  re- 
crystallized,  and  decomposed  by  oil  of  vitriol.  Pure  acetic  acid  is  thus  obtained, 
which  is  then  diluted  with  water  to  the  various  degrees  of  strength  required  in  com- 
merce (p.  557). 

When  the  acetous  liquor  has  been  neutralized  by  the  lime,  it  is  concentrated  by 
distillation,  whereby  a  spirituous  liquid  is  obtained,  which  is  termed  Pyroxylic  Spirit^ 
and  has  a  close  analogy  to  alcohol  in  its  characters.  In  this  state  it  is,  however,  a 
mixture  of  a  variety  of  bodies  ;  some  of  these,  as  aldehyd  and  acetone,  have  been 
already  noticed,  and  the  others  will  now  be  described.  Mr.  Scanlan  first  recognised 
the  various  constituents  of  the  impure  pyroxylic  spirit,  and  their  history  was  accu- 
rately investigated  by  Dumas  and  Peligot,  by  Lowig  and  by  myself. 

The  impure  pyroxylic  spirit  having  been  deprived  of  water  by  repeated  rectifica- 
tions over  lime,  as  much  chloride  of  calcium  as  it  can  dissolve  is  to  be  added  to  it,  and 
the  mixture  allowed  to  stand  for  a  few  days.  Being  then  distilled  in  a  water-bath, 
the  body  to  which  the  name  of  pyroxylic  spirit  is  specially  applied  remains  in  the 
retort,  combined  with  the  chloride  of  calcium,  while  there  distils  over  a  mixture  of 
two  liquids,  Xylit  and  Mesit,  which  are  separated  from  each  other  by  frequent  rectifi- 
cation, as  their  boiling  points  difier.  Besides  these  three  bodies,  there  exist  in  the 
rough  liquor  an  oil,  Methol,  and  a  solid  substance,  discovered  by  Mr.  Scanlan,  and 
termed  Eblanine. 

This  last  body  remains  behind  when  the  spirit  is  rectified  over  lime,  from  which 
it  is  separated  by  adding  muriatic  acid,  and  being  then  dissolved  in  boiling  alcohol,  it 
crystallizes  on  cooling;  it  forms  deep  orange-yellow  needles;  it  fuses  at  350°,  and 
volatilizes  in  a  current  of  air  or  of  vapour,  but  is  decomposed  if  heated  by  itself;  it 
is  insoluble  in  water,  but  dissolves  in  alcohol  and  volatile  oils  ;  sulphuric  acid  col- 
ours it  indigo  blue;  its  formula  is  C21H9O4.    No  combinations  of  it  are  known. 

The  Methol  contains  no  oxygen,  its  formula  being  C4H3.  It  boils  at  350°,  and 
possesses  the  general  characters  of  an  essential  oil. 

Xylit  resembles  alcohol  closely  in  its  properties.  Its  odour  is  agreeable  and  ethe- 
real; its  specific  gravity,  0816;  it  boils  at  143°;  with  acids  it  produces  ethereal 
compounds,  which  have  not  been  closely  examined;  its  formula  appears  to  be 

Cl2H,205. 

Medt  can  scarcely  be  considered  as  having  been  as  yet  obtained  pure;  in  its 
properties  it  closely  resembles  xylit,  but  has  a  higher  boiling  point;  its  formula  has 
been  stated  to  be  C6fe602.  I  shall  have,  on  another  occasion,  to  notice  tne  probable 
constitution  of  these  bod  ies. 

The  proper  Pyroxylic  Spirit  is  obtained  pure  from  its  combination  with  chloride 
of  calcium  by  the  addition  of  water  and  distillation ;  by  rectification  in  a  water- 
bath  with  dry  lime  it  is  freed  from  water.  When  quite  pure,  it  is  a  colourless 
liquid,  of  a  peculiar  aromatic  smell;  it  bums  with  a  flame  still  less  luminous  than, 
that  of  spirit  of  wine;  its  specific  gravity  is  0*798;  it  boils  at  140°;  its  formula  is 
C2H4O2;  the  specific  gravity  of  its  vapour  is  1-1105;  in  its  action  upon  other  bodies, 
this  substance  ranges  itself  completely  with  wine-alcohol,  and  it  is  hence  frequently 
termed  Mdhylic  Alcohol,  from  the  Greek  words  [j.edv  and  vIt],  In  the  history  of  its 
combinations,  it  will,  therefore,  be  sufficient  to  fix  attention  on  those  points  which 
are  more  specially  characteristic  of  it,  its  series  being  in  many  respects  more  com- 
plete than  that  of  ordinary  alcohol. 

Pyrox}dic  spirit  combines  with  bases  and  with  salts  to  form  compounds  similar  to 
the  alcoates.  It  is  decomposed  by  the  chlorides  of  zinc  and  alcohol,  by  the  fluorides 
of  silicon  and  boron;  methylic  ether  is  evolved,  the  reactions  being  precisely  as  in 
the  case  of  ordinary  alcohol. 

When  treated  with  sulphuric  acid,  the  methylic  alcohol  produces  an  ether,  an  or- 
ganic acid,  and  a  heavy  oil,  precisely  similar  to  those  formed  by  spirit  of  wine. 
But  the  reaction  is  much  more  distinct;  all  the  products  remain  properly  in  the  se- 
ries of  the  methylic  alcohol,  no  gas  equivalent  to  olefiant  gas  being  evolved. 


644    METHYLIC  ETHER  AND  ITS  COMPOUNDS. 

The  Methylic  Ether  is,  at  ordinary  temperatures  and  pressures,  a  colourless  gas, 
of  an  ethereal  odour;  it  burns  with  a  blue  flame.  Water  absorbs  thirty-seven  times 
its  volume  of  it;  its  formula  is  C2H3O.;  it  hence  is  isomeric  with  Vine-alcohol, 
with  the  vapour  of  which  it  has  the  same  specific  gravity,  =1601-5,  but  its  atomic 
weight  is  only  one  half  that  of  alcohol ;  it  combines  directly  with  anhydrous  sul- 
phuric acid,  forming  a  heavy  oily  liquid,  and  with  the  other  acids  to  form  compound 
ethers.  For  the  same  reasons  as  have  been  fully  discussed  under  the  head  of  wine- 
alcohol,  it  is  assumed  to  be  an  oxide  of  a  compound  radical,  Methyl,  C2H3  or  Me., 
and  the  formula  of  tha  pyroxylic  spirit  is  theretbre  Me.O.-f-Aq. 

The  Stilphomethijlic  Acid  is  formed  precisely  as  the  sulphovinic  acid,  which  it 
closely  resembles  in  properties,  except  that  it  may  be  obtained  crystallized  in  white 
needles  by  cautious  evaporation  of  its  solution.  Its  formula  is  Me.O. .  S.O3+S.O3. 
H.O. ;  its  salts  are  generally  more  permanent,  and  crystallize  more  easily  than  the 
sulphovinates. 

Sulphate  of  Methyl. — Me.O.+S.Os.  This  substance  passes  over  as  a  heavy  oil 
when  one  part  of  pyroxylic  spirit  is  distilled  with  five  or  six  parts  of  oil  of  vitriol, 
and  is  formed  also  by  the  direct  union  of  methylic  ether  and  dry  sulphuric  acid.  It 
has  a  strong  garlic  odour;  its  specific  gravity  is  1-324;  it  boils  at  370°.  By  boiling 
water  or  strong  bases,  it  is  immediately  removed  into  its  constituents.  With  dry 
ammonia  it  forms  a  white  crystalline  mass,  Sulphomethylan,  which  consists  of  Me> 
O. .  S.03+S.02Ad. 

Chloride  of  Methyl,  C2H3CI.  or  Me.Cl.,  is  formed  by  heating  a  mixture  of  common 
salt,  pyroxylic  spirit,  and  oil  of  vitriol.  A  permanent  gas  is  evolv6d,  which  may  be 
collected  over  water,  which  absorbs  but  twice  its  volume  of  it;  it  burns  with  a 
greenish-white  flame. 

Iodide  of  Methyl,  C2H3I.  or  Me. I.,  is  prepared  by  distilling  a  mixture  of  phospho- 
rus, iodine,  and  pyroxylic  spirit.  On  the  addition  of  water  to  the  distilled  liquor, 
the  iodide  of  methyl  separates  as  a  heavy  oily  liquid,  of  sp.  gr.  2-237 ;  it  boils  at 
about  112^. 

Fluoride  of  Methyl,  C2H3F.  or  Me.F.,  is  formed  by  heating  a  mixture  of  sulphate 
of  methyl  and  fluoride  of  potassium,  and  collecting  the  gas  evolved  over  water.  It 
is  colourless,  and  burns  with  a  M^hitish  flame,  evolving  fumes  of  hydrofluoric  acid. 

Methylene-mercaptan.  Sulphuret  of  Methyl. — These  bodies  are  prepared  precisely 
as  the  corresponding  substances  in  the  series  of  ordinary  alcohol. 

Nitrate  of  Methyl,  Me.O. .  N.O5,  is  prepared  by  distilling  nitrate  of  potash,  pyrox- 
ylic spirit,  and  oil  of  vitriol,  mixed  together  in  a  capacious  retort.  The  receivers 
are  to  be  carefully  cooled,  and  a  gentle  heat  applied  to  the  retort  to  commence  the 
reaction,  which  then  continues  to  the  end  without  any  farther  external  heat.  The 
product,  when  purified  by  redistillation  over  some  oxide  of  lead,  is  a  colourless  li- 
quid, neutral,  of  an  ethereal  odour;  it  burns  with  a  yellow  flame;  its  sp.  gr.  is  1-182; 
it  boils  at  151°.  If  a  drop  of  it  be  heated  to  300°,  it  explodes,  and  this  takes  place 
much  more  easily  if  there  be  a  quantity;  hence  its  distillation  must  be  very  cau- 
tiously conducted. 

Carbomethylic  Acid  is  formed  by  passing  a  jtream  of  dry  carbonic  acid  into  a  so- 
lution of  barytes  in  pyroxylic  spirit.  Carbomethylate  of  bar5rtes  forms  in  minute 
plates,  which  are  insoluble  in  spirit,  but  dissolve  easily  in  wate'r.  This  salt  rapidly 
decomposes  into  carbonate  of  barytes,  free  carbonic  acid,  and  methylic  alcohol. 
With  chlorocarbonic  acid  and  sulphuret  of  carbon,  the  pyroxylic  spirit  gives  com- 
pounds precisely  similar  to  those  already  described  in  the  series  of  ordinary  alcohol. 

Oxalate  of  Methyl,  Me.O. .  C2O3,  is  best  formed  by  distilling  a  mixture  of  equal 
parts  of  oxalic  acid,  pyroxylic  spirit,  and  oil  of  vitriol.  The  product  crystallizes  in 
large  rhombic  plates  ;"it  fuses  at  124°,  and  boils  at  312°;  it  dissolves  easily  in  water 
and  alcohol.  With  water  of  ammonia  it  produces  oxamid  and  methylic  alcohol ; 
with  dry  ammonia  it  forms  a  crystalline  body,  Me.O. .  C203+C202Ad.,  OxavietJiylan. 

Acetate  of  Methyl. — Me.O. .  AC.O3.  Formed  by  distilling  together  oil  of  vitriol, 
pyroxylic  spirit,  and  acetate  of  soda.  It  forms  a  colourless  liquid,  which  boils  at 
l36°;"^its  specific  gravity  is  0-919,  The  substance  known  as  Mesit  may  be  consid- 
ered as  a  compound  of  methylic  alcohol  and  aldehyd,  C2H30,^-C4H30.,  and  the 
xylit  is  probably  a  mixture  of  that  body  with  the  acetate  of  methyl. 

The  combinations  of  methylic  ether  with  the  other  acids  resemble  so  closely 
those  of  vinic  ether  that  they  need  not  be  specially  described. 

Products  of  the  Oxidation  of  Pyroxylic  Spirit. 

If  pyroxylic  spirit  be  distilled  wnth  chromate  of  potash  and  sulphuric  acid,  it 
is  totally  converted  into  c:irbonic  acid  and  water.  If  black  oxide  of  manganese 
be  used,  and,  after  the  first  violent  efiervescence  has  ceased,  a  gentle  heat  be  ap- 


PREPARATION     OF     FORMIC     ACID,     ETC.  645 

plied,  a  .liquid  distils  over,  which,  when  completely  pure,  has  the  formula  GfrHaO^ ; 
U  boils  at  104°  ;  its  sp.  gr.  is  0-855 ;  it  is  termed  MetkylaL 

Ifpyroxylic  spirit  be  brought  into  contact  with  oxygen  by  means  of  spongy  plati- 
uum,  as  described  for  ordinary  alcohol  in  p.  554,  hydrogen  is  removed  and  oxygen 
absorbed  in  equivalent  proportion,  and  the  melhylic  alcohol  is  totally  converted  into 
hydrated  Farniic  Acid,  C2H4O2  and  20.  giving  2H.0.  and  C2H2O4.  In  this  reac- 
tion there  does  not  appear  to  be  any  intermediate  state  equivalent  to  that  of  aldehyd, 
which  body  appears  to  be  without  a  representative  in  the  pyroxylic  series,  at  least, 
except  in  co/nbination.  Fox  practical  purposes,  tliis  mode  of  preparing  formic  acid 
is  not  had  recourse  to,  as  it  may  be  derived  more  easily  from  the  oxidation  of  most 
organic  bodies. 

The  formic  acid  derives  its  name  from  existing  in  a  very  concentrated  form  in 
the  common  ant  (formica  rufa),  and  produces  the  pain  of  their  sting  on  being  in- 
jected into  the  puncture  which  the  animal  makes ;  it  was  Ibrmeriy  prepared  by  dis- 
tilling the  ants  with  a  little  water;  but  the  process  of  Dobereiner  is  now  generally 
followed.  It  consists  in  mixing  one  part  of  starch,  or  sugar,  or  tartaric  acid,  with 
four  of  black  oxide  of  manganese,  four  of  water,  and  four  of  oil  of  vitriol.  Con- 
siderable etiervescence  occurs,  owing  to  the  escape  of  carbonic  acid.  When  this  is 
over,  the  mixture  is  to  be  distilled  until  four  and  a  half  parts  have  passed  over  j 
this  acid  liquor  is  to  be  neutralized  by  carbonate  of  soda,  and  the  formiate  of  soda 
crystallized  by  evaporation  and  cooling.  From  this  salt  the  formic  acid  may  be  ob- 
tained in  any  required  degree  of  concentration,  by  distillation  with  oil  of  vitriol,  in 
precisely  the  manner  described  for  acetic  acid  (p.  556). 

If  sugar,  or  starch,  or  barley  be  simply  heated  with  dilute  sulphuric  acid  until  it 
becomes  brown,  a  certain  quantity  of  formic  acid  is  produced,  along  with  ulmine  and 
ulmic  acid.  The  generation  of  this  acid  as  a  product  of  the  decomposition  of  prus- 
sic  acid,  of  chloral,  and  of  hydrated  oxalic  acid,  has  been  already  noticed. 

Pure  hydrated  ibrmic  acid  is  a  limpid  colourless  liquid,  which  fumes  slightly  in 
the  air;  its  odour  is  intensely  pungent;  when  cooled  below  33°,  it  crystallizes  in 
brilliant  plates;  it  boils  at 212°;  its  specific  gravity  is  1-235.  In  this  most  concen- 
trated form  it  is  an  absolute  caustic  if  applied  to  the  skin,  producing  a  sore  very 
difficult  to  heal ;  its  formula  is  C2H.O3+H.O.,  and,  like  acetic  acid,  it  is  supposed 
to  contain  a  radical,  Formyl,  C2H,  or  Fo.,  and  its  rational  formula  to  be  F0.O3+H. 
O.  Combining  with  water,  it  forms  at  least  one  other  definite  hydrate,  the  formula 
ofwhichisFo.03+2H.O. 

The  resemblance  of  formic  acid  to  acetic  acid  is  very  close,  but  they  are  at  once 
distmguished  by  their  behaviour  to  certain  reagents.  When  heated  with  an  excess 
of  oil  of  vitriol,  it  is  decomposed,  with  lively  effervescence,  into  water  and  carbonic 
oxide  (C2H.03=C202  and  H.O.).  If  a  solution  of  formiate  be  mixed  with  a  cold  so- 
lution of  nitrate  of  silver,  a  white  crystalline  precipitate  of  formiate  of  silver  falls, 
which,  when  heated,  is  totally  decomposed  into  metallic  silver,  water,  and  carbonic 
acid,  C2H.03+Ag.O.  giving  2C.O2  with  H.O.  and  Ag.  If  formic  acid  be  digested 
on  red  oxide  of  mercury,  carbonic  acid  is  given  off,  and  a  sparingly  soluble  crystal- 
line formiate  of  the  black  oxide  of  mercury  is  produced  :  this,  when  boiled,  is  total- 
ly decomposed,  metallic  mercury  separating,  and  carbonic  acid  and  water  being 
evolved. 

The  alkaline  formiates  are  soluble  and  crystallizable  ;  that  of  ammonia  crystal- 
lizes in  right  rhombic  prisms,  which  melt  at  250°,  and  sublime  without  alteration. 
If  its  vapour  be  passed  through  a  red-hot  porcelain  tube,  it  is  totally  converted  into 
prussic  acid  and  water,  C2H.O3+N.H4O.  giving  C2N.H.  and  4H.6. 

Formiate  of  Soda  crystallizes  in  rhombic  prisms,  which  have  the  formula  Na.O. . 
F0.O3-I-2  Aq.  When  heated,  it  undergoes  aqueous  fusion,  and  by  a  higher  tempera- 
ture is  decomposed.  A  solution  of  this  salt,  when  boiled  with  the  salts  of  silver, 
mercury,  gold,  palladium,  or  platinum,  precipitates  the  metal,  and  is  hence  useful  in 
analysis. 

Fonniate  of  Barytes. — Ba.O. .  F0.O3.  It  is  obtained  in  large 
rhombic  prisms,  as  in  the  figure,  where  w,  y  are  primary,  and  i  a 
secondary  plane,  which  have  a  bitter  taste,  and  are  not  altered 
by  the  aif.  It  is  very  soluble  in  water,  but  insoluble  in  alcohol. 
Formiate  of  Lime  is  easily  produced  by  neutralizing  lime  with 
dilute  formic  acid ;  it  is  equally  soluble  in  cold  and  in  hot  water, 
so  that  it  is  only  obtained  crystallized  by  slow  evaporation ;  it 
dissolves  in  ten  parts  of  cold  water;  it  is  insoluble  in  alcohol. 

Formiate  of  Lead. — Pb.O. .  Fo.Os.    If  formic  acid  be  added  to  a 
solution  of  acetate  of  lead,  this  salt  separates  after  a  short  time  in  stellated  groups 
of  brilliant  needles,  which  are  anhydrous,  and  require  forty  parts  of  water  fcr  solu- 


1)40         PRODUCTS     OF     DISTILLATION     OF     COAL. 

tion ;  it  is  totally  insoluble  in  alcohol.  By  the  formation  of  this  salt,  the  formic 
iicid  is  readily  distinguished  from  the  acetic  acid,  and  the  two,  if  present  together, 
may  be  thus  separated. 

Foriniate  of  Copper  crystallizes  in  large  rhomboidal  prisms,  as  in 
the  figure,  where  i,  u,  u  are  primary,  and  m  a  secondary  plane, 
which  are  very  regular,  transparent,  and  of  a  fine,  clear  blue  colour. 
It  eflioresces  in  dry  air. 

The  Formiaies  of  Mercury. — That  of  the  red  oxide  is  very  soluble; 
it  can  only  exist  at  ordinar}^  temperatures ;  by  a  very  gentle  heat  it 
changes  into  the  formiate  of  the  black  oxide,  and  this,  when  boiled, 
gives  metallic  mercury,  as  already  described  among  the  tests  for 
formic  acid.  The  formiate  of  the  black  oxide  may  also  be  prepared 
by  mixing  solutions  of  formiate  of  soda  and  of  subnitrale  of  mercury ;  it  separates 
in  small  pearly  plates  of  four  and  six  sides,  which  may  be  dried  between  folds  of 
blotting  paper,  and  have  a  fine  silky  lustre. 

Chlorides  and  Iodides  of  Formyl. — When,  under  the  Influence  of  powerful  reagents, 
the  constitution  of  the  compounds  of  acetyl  or  elayl  is  broken  up,  a  series  of  bodies 
is  generally  produced,  which  are  supposed  to  contain  as  their  radical  formyl.  Thus, 
by  the  action  of  chlorine  on  the  chloride  of  elayl,  a  heavy  oily  liquid  is  formed,  C2 
H.CI2  or  F0.CI2,  Bichloride  of  Formyl;  and  by  acting  on  chloral  by  caustic  potash, 
formic  acid  is  produced,  and  a  heavy  oily  liquid,  which  is  termed  Chlorofoi-m,  and 
consists  of  C2H.CI3  or  F0.CI3,  being  Perchloride  of  Formyl.  This,  which  is  the  most 
interesting  of  these  bodies,  is  easily  prepared  by  distilling  alcohol,  acetone,  or  py- 
roxylic  spirit  with  chloride  of  lime  ;  it  is  colourless,  of  an  agreeable  ethereal  odour; 
its  specific  gravity  is  1-480;  it  boils  at  141°;  the  specific  gravity  of  its  vapour  is 
4-llb;  with  an  excess  of  chlorine  it  gives  bichloride  of  carbon. 

Periodide  of  Formyl.  Iodoform,  F0.I3,  is  produced  by  adding  caustic  potash  to  a 
solution  of  iodine  in  alcohol  until  it  is  completely  decolorized,  but  avoiding  an  ex- 
cess of  alkali;  on  then  evaporating,  the  iodoform  is  deposited  in  brilliant  gold-col- 
oured plates;  it  is  insoluble  in  water,  but  very  soluble  in  alcohol  and  ether;  it  vola- 
tilizes at  218° ;  with  potash  it  gives  iodide  of  potassium  and  formiate  of  potash. 
There  exist  also  bromides,  cyanides,  and  sulphurets  of  formyl,  which  do  not  require 
notice. 

By  acting  on  the  methylic  ether  and  on  the  chloride  of  methyl  with  chlorine, 
Regnault  obtained  two  series  of  bodies,  which  follow  precisely  the  same  principles 
of  constitution  as  have  been  described  fully  when  speaking  of  wine-alcohol  (p.  565). 
Malaguti  also  obtained,  from  the  oxalate  and  acetate  of  methyl,  bodies  similar  to 
those  generated  by  chlorine  with  the  ordinary  oxalic  and  acetic  ethers,  and  hence 
it  is  only  necessary  to  say  that  all  the  conclusions  there  drawn  respecting  the  nature 
of  these  bodies,  and  the  theory  of  the  chlorine  radicals,  may  be  applied  to  explain 
tlie  origin  of  the  bodies  derived  from  the  methylic  alcohol  also. 

"Products  of  the  Distillation  of  Coal. 

The  products  of  the  distillation  of  coal  in  close  vessels  possess 
a  remarkable  analogy  to  those  that  have  been  now  described,  and, 
indeed,  in  many  instances,  are  identical  with  them.  Thus  the  gas- 
eous products  are  marsh  gas,  olefiant  gas,  and  carbonic  acid.  The 
liquid  products  consist  of  various  bodies  closely  analogous  to  pe- 
troleum, and  the  solids  consist  of  napthaline  and  paraffine.  The 
relative  proportions  of  these  products  vary  with  the  temperature. 
The  lower  the  heat  employed,  the  less  gas,  and  the  more  solids 
and  liquids  are  produced  j  the  higher  the  temperature,  the  greater 
is  the  quantity  of  carburetted  hydrogen  ;  but,  for  the  purposes  to 
which  the  practical  process  is  applied,  the  temperature  must  not 
be  raised  too  high,  for  then  the  gas  evolved  would  be  mostly  marsh 
gas  and  pure  hydrogen,  which  possess  little  illuminating  power, 
while  a  great  deal  of  illuminating  power  may  be  derived  from  the 
vapours  of  some  highly  volatile  liquid  products.  In  the  manufac- 
ture of  coal  gas  for  the  purpose  of  illumination,  the  object  is,  there- 
fore, to  maintain  a  temperature  too  high  for  the  production  of  much 
napthaline  or  paraffine,  but  not  high  enough  to  produce  hydrogen 


COMPOUNDS     OF     NAPTHALINE.  647 

or  marsh  gas,  and  thus  ohtain  the  greatest  possible  quantity  of  a 
gaseous  product  of  olefiant  gas  and  vapours  of  liquid  carbohydro- 
gens. 

From  the  albuminous  constituents  of  the  wood,  coal  always  con- 
tains a  certain,  though  small  quantity  of  nitrogen,  and  hence  ammo- 
nia is  evolved  in  its  distillation.  The  gas  liquor  so  obtained  is  ex- 
tensively used  in  the  manufacture  of  sal  ammoniac.  From  the  sul- 
phates existing  in  the  plants,  or  in  water  which  has  filtered  through 
the  bed  of  coal,  or  from  iron  pyrites,  which  is  generally  associated 
abundantly  with  the  rocks  of  the  coal  formation  (p.  363),  a  small 
quantity  of  sulphur  always  exists  in  coal,  which  is  evolved  during 
the  distillation  as  sulphuretted  hydrogen,  and  requires  to  be  care- 
fully separated  from  the  other  gases,  which  is  effected  by  washing 
them  with  the  milk  of  lime,  which  absorbs  also  the  carbonic  acid. 
The  apparatus  used  for  making  coal  gas  does  not  differ  in  principle, 
although  very  much  in  arrangement,  from  that  figured  in  p.  642. 
The  ammoniacal  liquor  and  the  tar  are  collected  in  the  tubs,  and 
the  gas,  in  place  of  being  burned  at  the  orifice  of  the  tube  5,  is  con- 
ducted to  the  purifiers,  and  thence  to  the  gasometers  for  use. 

Most  of  the  substances  produced  in  this  process  have  been  already  noticed.  It 
only  remains  now  to  describe,  as  briefly  as  possible,  the  properties  of  such  others  as 
are  important. 

Of  Napthaline  aTid  its  Derivatives. — This  substance  is  a  very  usual  product  of  the 
decomposition  of  organic  substances  by  heat;  it  is  obtained  abundantly  by  rectifying- 
coal-gas  tar;  it  crystallizes  in  white  silvery  plates ;  its  specific  gravity  is  1-048;  it 
melts  at  136^,  and  boils  at  413'^,  but  sublimes  rapidly  at  much  lower  temperatures ; 
it  burns  with  a  strong  smoky  flame ;  its  smell  is  powerful  and  very  peculiar ;  it  is 
insoluble  in  water,  but  abundantly  soluble  in  ether,  alcohol,  and  oils ;  its  formula  is 
CmHs;  the  specific  gravity  of  its  vapour  is  4488.  It  is  remarkable  for  the  number 
of  compounds  to  which  it  gives  rise.  When  digested  with  nitric  acid,  it  forms  two 
combinations ;  the  first,  Nitrofiapthalid,  crystallizes  in  sulphur-yellow  prisms ;  its 
formula  is  C20H7.  N.O4;  the  second,  Nltronaphdehyd^  is  a  white  crystalline  powder, 
having  the  formula  C10H3 .  N.O4,  Both  these  bodies  are  insoluble  in  water,  but  dis- 
solve easily  in  alcohol  and  ether,  from  which  solutions  they  crystallize  on  cooling. 
When  nitronapthalid  is  distilled  with  lime,  a  substance  is  obtained  which  resem- 
bles eblanine  (p,  643)  in  properties,  but  consists  of  C20H7O.  Laurent  termed  it 
Oxvk  of  Napthcdese. 

Chlorine  forms  with  napthaline  a  heavy  oily  liquid,  which  has  the  formula  C20H8 
CI2.  It  gradually  evolves  muriatic  acid  gas,  and  deposites  a  crystalline  substance. 
This  change  is  effected  immediately  by  heat  or  by  a  base.  This  solid  body  is  tenn- 
ed  ChlornaptMid ;  it  consists  of  C20H7CI.  If  this  be  melted  and  submitted  to  the 
continued  action  of  chlorine,  hydrogen  is  removed  and  a  crystalline  solid  formed, 
Cfdornaptlidehyd,  C  0H4CI2.  By  acting  on  napthaline  with  an  excess  of  chlorine,' 
and  distilling  the  product,  a  solid  substance  is  obtained,  which  crystallizes  in  large 
prisms,  and  has  the  formula  C20H6CI2.  All  of  these  bodies  are  insoluble  in  water, 
but  dissolve  in  alcohol  and  ether. 

When  these  chlorine  compounds  are  boiled  in  nitric  acid,  a  series  of  substances 
are  obtained  containing  chlorine  and  oxygen.  Thus  from  C20H8CI2  is  formed  C20 
H5.O3CI2,  which  is  a  brilliant  yellow  crystalline  matter,  insoluble  in  water,  and 
melting  at  206°.  By  farther  treatment  with  nitric  acid,  the  Chloronapthalic  Acid  is 
formed,  the  formula  of  which  is  C20H5 .  O6CI2.  This  body  is  insoluble  in  water,  but 
dissolves  in  ether,  and  crystallizes,  on  cooling,  in  short,  brilliant  yellow  prisms ;  It 
melts  at  400°,  and  may  be  sublimed  unchanged.  With  bases  it  forms  well-charac- 
terized salts,  which  are  orange  or  red-coloured ;  those  of  the  alkalies  and  earths  are 
soluble  and  crystallizable ;  those  of  the  heavy  metals  are  insoluble  in  water.  In 
this  process  there  is  also  formed  a  substance  which  does  not  contain  chlorine  ;  it  re- 
sembles closely  benzoic  acid ;  it  is  termed  Napthalic  Acid-,  but  its  composition  is  not 
yet  decided ;  another  product  noticed  by  Marignac  is  an  acid  possessing  the  remark- 
able constitution  of  C.Cl.  .N.O4. 

The  action  of  sulphuric  acid  on  napthaline  varies,  as  the  acid  is  hydrated  or  an- 
hydrous.   In  the  latter  case,  sulphurous  acid  is  evolved  and  a  series  of  products 


648  BODIES     OF     THE     PHENYL     SERIES. 

formed,  vrhich  have  been  described  by  Berzelius  as  follows:  Sulphonapthaline,  Cu 
Hg.  S.O2,  crystallizes  in  white  plates,  which  melt  below 212o  to  a  colourless  liquid; 
Sidphonapthalid,  C24H10  •  S.O2,  is  a  snow-white  powder,  which  may  be  separated 
from  the  former  by  means  of  its  insolubility  in  cold  alcohol.  In  addition  to  these 
bodies  there  are  formed  two  acids,  the  Sidfkonwplhalic  and  the  Sulplwnapthic ;  they 
are  isolated  by  taking  advantage  of  the  insolubility  of  the  barytes  salt  of  the  latter  in 
cold  alcohol,  and  then,  by  decomposing  the  barytes  salts  by  dilute  sulphuric  acid, 
these  organic  acids  may  be  obtained  crystallized.  The  SulpJionapthic  Acid  forms 
soft  crystalline  scales,  of  a  soapy  feel,  like  talc,  which  taste  bitter  and  sour.  Its  for- 
mula is  C22H9 .  S4O12+2  Aq. ;  it  combines  with  two  atoms  of  fixed  base.  The  SuU 
'phanapihalic  Acid  forms  a  hard  crystalline  mass,  which  is  acid  and  bitter,  inodorous, 
tiisible  below  21*2=';  it  is  very  deliquescent;  its  formula  is  C20H8 .  S2O3.  The  salts 
of  these  acids  are  all  soluble  in  water.  There  is  still  another  acid  product,  termed 
by  Berzelius  Sidphoglucic  Acid,  the  constitution  of  which  is  not  known. 

Notwithstanding  that  few  subjects  have  been  so  often  investigated  as  the  history 
of  napthaline  and  its  derivatives,  there  are  few  bodies  whose  theory  is  more  obscure- 
It  would  appear  that  all  its  hydrogen,  or  at  least  six  atoms  of  it,  is  capable  of  re- 
placement by  chlorine  or  nitrous  acid,  and  there  does  not  exist  any  distinct  charac- 
ter by  which  the  existence  of  a  compound  radical,  either  primitive  or  derived,  as  a 
basis  of  these  combinations,  could  with  reason  be  assumed.  The  hypothesis  of 
Marignac  is,  that  napthaline  itself  is  a  compound  of  two  carbohydrogens,  C16H4+ 
C4Bb',  by  the  diverse  action  of  reagents  upon  which  the  various  bodies  may  be  de- 
rived ;  but  this  idea  does  not  afford  sufficient  advantages  to  justify  its  adoption. 

Paranaptkaline. — This  substance  is  associated  with  napthaline  in  the  gas-tar,  and 
is  isomeric  with  it,  its  formula  being  C20H8;  it  differs  in  its  fusing  and  boiling  points, 
which  are  very  much  higher ;  it  may  be  distilled  unaltered  ;  it  is  insoluble  in  water, 
very  sparingly  soluble  in  alcohol  or  ether,  but  copiously  so  in  oil  of  turpentine ;  its 
relations  to  other  bodies  are  not  well  known;  with  nitric  acid  it  produces  a  colour- 
less crystalline  body,  having  the  formula  C15H4O2. 

The  liquid  products  of  the  distillation  of  coal  have  been  as  yet  studied  only  by 
Laurent,  of  the  most  interesting  of  whose  results,  as  yet,  but  the  general  nature  has 
been  published.  This  liquid,  which  is  properly  termed  Gas-7iaptha,  contains  a  crys- 
talline solid,  which  volatilizes  without  decomposition,  and  acts  as  an  acid;  its  for- 
mula is  Ci2H50.+Aq.  Its  discoverer  considers  it  as  a  hydrated  oxide  of  a  com- 
pound radical,  which  he  terms  Phenyl;  it  combines  with  potash  and  barytes,  forming 
crystalline  compounds.  With  sulphuric  acid  it  forms  Sulphophe7iic  Acid,  C12H5O.  . 
S.O3+S.O3  .  H.O.,  which  forms  salts  resembling  the  sulphovinates ;  with  chlorine  it 
forms,  first,  Cfilorophenesic  Acid,  C12H3  .  Cl20.-f-Aq.,  which  crystallizes  in  rhombo- 
hedrons,  and  possesses  a  very  nauseous  odour;  and  afterward  Chlo'rophenic  Acid, 
the  formula  of  which  is  C12H2  .  ClsO.+Aq. 

With  nitric  acid,  the  hydrated  oxide  of  phenyl  produces,  first,  Nitrophencsic  Acid, 
Ci2H3(N208)0.-i-Aq.,  and  by  continuing  the  action,  the  Nitrophenic  Add,  C12H2 
(N30i2)0.+Aq.,  which  is  the  Picric  Acid  described  p.  618,  as  formed  from  indigo 
and  salicine.  This  phenyl  series  appears,  therefore,  to  be  the  final  result  of  the  ox- 
idation of  a  great  number  of  organic  bodies.  As  yet,  our  knowledge  of  the  proper- 
lies  of  these  bodies  is  not  sufficiently  detailed  to  justify  any  discussion  of  their  na- 
ture, but  the  connexion  with  the  bodies  derived  from  indigo  is  exceedingly  remark- 
able. If  we  consider  the  radical  as  C12H5,  then  amilene  is  Amidide  of  Phenyl,  and 
all  the  characters  of  its  salts  are  easily  explained.  The  substance  termed  by  Lau- 
rent ChloraWine,  CaHeCb,  is  probably  CzHsCl.+H.Cl. 

In  preparing  olefiant  gas  for  the  purposes  of  illumination,  by  the  destmctive  dis- 
tillation of  resin,  a  number  of  substances,  some  solid,  others  liquid,  are  produced, 
which  have  been  examined  by  Pelletier  and  Walter.  Those  not  already  described 
are  as  follows:  Retisteren,  a  white  crystalline  solid,  which  melts  at  152«  and  boils  at 
(517®.  In  its  properties  it  resembles  napthaline ;  its  formula  is  C32H14.  Betinol  is 
a  colourless  liquid,  tasteless  and  inodorous ;  specific  gravity  =:0-9 ;  it  boils  at  400° ; 
its  formula  is  C32H1  ,  being  isomeric  with  benzin ;  the  specific  gravity  of  its  vapour 
is  7-25.  Retinaptha  is  a  colourless  liquid,  of  an  agreeable  odour;  its  specific  gravi- 
ty is  0-86;  it  boils  at  226®;  its  formula  is  CmHs.  Reti^iyl,  also  a  liquid,  boils  at 
300° ;  it  consists  of  C18H12,  being  polymeric  with  mesitylene. 

When  the  gas  obtained  by  the  destructive  distillation  of  oil  is  strongly  compress- 
ed, a  liquid  separates,  which  was  found  by  Faraday  to  contain  three  distinct  sub- 
stances. Of  these  the  most  abundant  was  the  benzin  described  already  (page  571), 
as  produced  in  the  decomposition  of  benzoic  acid.  Of  the  others,  one  is  known  as 
Faraday's  Quadricarhv/ret  of  Hydrogen ;  it  is  also  formed  abundantly  in  the  distillation 
of  caoutchouc ;  its  specific  gravity  is  0627 ;  it  boils  below  32'' ;  it  combines  with 


KREOSOTE,     KAPNOMOR,     ETC.  649 

chlorine,  forming  a  heavy  oil ;  it  is  isomeric  with  olefiant  gas,  its  formula  being  Ca 
H4,  and  the  specific  gravity  of  its  vapour  is  double  that  of  the  gas,  being  1-962.  The 
third  liquid  boils  at  183°.  Its  formula  is  probably  C6H4,  being  isomeric  with  mesit- 
ylene  and  retinyl. 

During  an  elaborate  examination  of  the  nature  of  the  tar  produced 
from  the  destructive  distillation  of  wood,  Reichenbach  described  a 
number  of  bodies,  of  which  one,  Kreosote^  has  become  of  much  in- 
terest, from  its  remarkable  properties,  but  the  others  are  still  very- 
little  known.  For  the  preparation  of  kreosote,  the  tar  is  rectified  by- 
successive  distillations,  until  the  oil  which  passes  over  becomes 
heavier  than  water,  and  then  digested  with  a  solution  of  caustic 
potash,  which  dissolves  the  kreosote  5  when  this  liquor  is  exposed  to 
the  air,  it  becomes  brown,  and  being  then  neutralized  by  an  acid, 
the  kreosote  separates.  This  process,  of  solution  in  an  alkaline 
liquor  and  precipitation  by  an  acid,  is  to  be  repeated  until  the  solu- 
tion is  no  longer  browned  by  exposure  to  the  air ;  the  kreosote  is 
then  pure.  It  is  an  oily,  colourless  liquid,  with  a  penetrating  odour 
of  smoke  ;  its  taste  is  sharp  and  burning ;  its  specific  gravity  is 
1037  J  it  boils  at  400^^ ;  it  burns  with  a  strong  smoky  flame  ;  with 
water  it  unites  in  two  ways :  100  parts  of  water  dissolve  1*25  of 
kreosote,  and  100  parts  of  kreosote  take  up  ten  of  water  ;  the  solu- 
tion is  quite  neutral ;  kreosote  mixes  with  ether,  alcohol,  and  acetic 
acid  in  all  proportions.  It  unites  with  alkalies  and  with  acids,  but 
without  appearing  to  form  any  definite  compounds,  and  it  is  not  cer- 
tain that  it  has  ever  been  obtained  really  pure.  The  formula  as- 
signed to  it  is  C,4H902. 

The  most  remarkable  property  of  kreosote  is,  that  it  coagulates 
albumen  and  the  colouring  matter  of  the  blood,  and  these  bodies  are 
then  no  longer  susceptible  of  putrefaction.  Fibrine,  or  muscular 
flesh,  immersed  in  a  solution  of  kreosote  for  some  minutes,  has  no 
tendency  to  putrefy  even  if  exposed  to  the  heat  of  the  sun  after- 
ward ;  from  this  is  its  name  derived  (xps^f  aw^w).  Kreosote  is  the 
antiseptic  principle  in  pyroligneous  acid,  and  in  turf  or  wood  smoke. 
If  placed  on  the  tongue,  it  makes  a  white  mark,  with  violent  pain. 
Its  use  as  a  caustic  remedy  for  toothache  is  well  known. 

Kiipnomor  accompanies  kreosote  in  tar;  it  is  a  colourless  liquid ;  it  smells  like 
rum ;  with  oil  of  vitriol  it  forms  a  purple  solution ;  it  boils  at  360''.  Picamar  is 
also  liquid;  it  boils  at  518° ;  it  combines  with  bases.  Cedriret  crystallizes  in  fine  red 
needles,  insoluble  in  all  liquids  except  oil  of  vitriol  and  kreosote,  the  former  pro- 
ducing a  blue,  and  the  latter  a  purple  solution.  Pittakal  forms  a  dark  blue  solid 
mass,  which,  when  rubbed,  assumes  a  golden  lustre ;  it  contains  nitrogen ;  it  is  in- 
soluble in  water,  but  dissolves  in  acids,  and  is  thrown  down  again  by  alkalies. 
With  metallic  salts,  its  solution  gives  blue  precipitates,  which  may  be  attached  by 
mordants  upon  Avoollen  and  cotton  cloths.  The  constitution  of  these  bodies  has  not 
been  examined. 

By  the  action  of  reagents  on  the  coal-gas  naptha,  Runge  obtained  a  series  of  bod- 
ies, a  re-examination  of  which  would  be  of  the  highest  interest  to  science ;  they  are 
liquid,  and  appear  to  possess  strong  alkaline  properties,  and  generate  salts,  which 
with  one  ( Cyatiot)  are  of  a  rich  blue  colour.  They  belong  apparently  to  the  same 
class  of  bodies  as  anilene. 

By  the  destructive  distillation  of  animal  substances,  a  series  of  oily  bodies  is  gen- 
erated, of  a  strong  odour  {Animal  Oil  of  Dippel,  Oil  of  Hartshorn),  which  is  described 
by  Unverdorben  as  a  mixture  of  several  bodies,  to  which  he  has  given  names;  but, 
as  we  possess  no  accurate  knowledge  whatsoever  of  their  properties,  I  do  not  think 
it  necessary  to  give  his  account  of  their  preparation. 

4N 


H50  GERMINATIO  N. M  A  L  T  I  N  G. 


CHAPTER  XXIX. 

OF    THE    CHEMICAL    PHENOMENA    OF    VEGETATION. 

In  the  seed  of  a  plant,  the  gerrne  of  the  future  individual  is  associated 
with  one  or  more  organs,  termed  cotyledons,  which  contain,  in  general, 
starch  and  some  form  of  azotized  matter,  as  albumen,  gluten,  or  legu- 
mine,  which  substances  are  so  disposed  in  order  to  supply  the  nutriment 
necessary  for  the  development  of  the  embryo,  until  its  organs  are  fitted 
for  the  collection  of  nutriment  from  external  sources. 

The  first  act  of  growth  in  the  seed  is  termed  germination,  and  is 
accompanied  by  a  remarkable  change  in  the  constitution  of  the  cotyle- 
donous  mass.  For  perfect  germination,  it  is  necessary  that  the  seed  be 
moderately  supplied  with  water  and  with  air,  and  that  it  be  either  in  the 
dark,  or  exposed  but  to  little  light ;  all  these  circumstances  are  perfectly 
secured  by  the  ordinary  mode  of  sowing  seeds  in  a  moistened  soil,  which 
shall  be  so  loose  as  to  admit  air,  and  yet  exclude  the  light. 

A  seed  so  circumstanced  gradually  swells  to  much  beyond  its  original 
volume,  and  its  temperature  rises  ;  it  absorbs  oxygen  from  the  air,  and 
evolves  water  and  carbonic  acid,  and  the  starch  of  the  cotyledon  gradu- 
ally  disappears,  being  changed  into  sugar.  From  the  point  of  the  seed 
where  the  embryo  is  situated,  two  shoots  spring  forth,  one  of  which,  the 
radical,  takes  its  direction  downward  into  the  soil,  while  the  other,  the 
plumula,  strikes  up  towards  the  air,  to  become  the  origin  of  the  stem  ; 
according  as  this  growth  proceeds,  the  quantity  of  sugar  in  the  seed 
diminishes,  and  by  the  time  that  the  radical  is  fit  for  the  performance  of 
its  functions,  as  root,  in  absorbing  nutriment  from  the  soil,  nothing  re. 
mains  of  the  seed  but  its  ligneous  husk,  which  in  some  cases  completely 
perishes  under  ground,  but  in  others  rises,  and,  assuming  the  functions  of 
leaves  (seed-leaves),  assists  in  providing  nutriment  for  the  young  plants, 
until  the  stem  has  been  furnished  with  leaves  by  which  it  may  act  upon 
the  surrounding  air. 

This  process  of  germination  is  artificially  produced,  for  the  purposes  of 
the  arts,  by  the  operation  of  malting ;  the  grain  is  steeped  in  water  until 
it  has  absorbed  the  proper  quantity  of  it ;  it  is  then  spread  on  the 
floor  of  the  malthouse,  and  its  temperature  prevented  from  rising  too 
high  by  the  mass  being  frequently  spread  out,  and  new  surfaces  ex- 
posed to  the  air.  When  the  seed  contains  the  maximum  quantity  of 
sugar,  that  is,  when  the  conversion  of  the  starch  is  most  complete, 
and  yet  before  much  sugar  has  been  assimilated  by  the  germe,  which 
is  practically  found  to  be  when  the  radical  has  grown  as  long  as  the 
grain,  but  does  not  project  beyond  it,  the  young  plant  is  killed  by  ex- 
posing the  malted  corn  to  a  current  of  hot  dry  air  in  the  malt-kiln,  and 
the  malt  is  then  employed  as  a  source  of  sugar  in  the  fermentative  pro- 
cesses of  the  brewer  and  distiller. 

The  saccharine  fermentation  which  thus  furnishes  nutriment  for  the 
young  plant  in  the  first  stage  of  its  existence,  resembles  the  transforma- 
tion of  starch  by  means  of  sulphuric  acid,  described  in  p.  528,  and  is  ex- 


CONSTITUTION     OF     PLANTS.  651 

cited  by  the  presence  of  a  peculiar  ferment  produced  by  the  decomposi- 
tion of  the  vegetable  albumen  which  the  seed  contains.  This  active 
substance  is  termed  Diastase;  it  does  not  pre-exist  in  the  seed,  but  is 
itself  produced  by  the  action  of  the  air  and  water  upon  the  albumen  ;  it 
is  not  identical  with  the  ferment  which  induces  the  alcoholic  fermenta- 
tion, but  they  appear  to  be  but  successive  stages  of  the  decomposition  of 
the  same  substance.  The  diastase  may  be  obtained  solid  by  bruising 
malt  with  a  small  quantity  of  water,  and  expressing  the  liquor  ;  to  this 
alcohol  is  to  be  added,  which  precipitates  a  quantity  of  unaltered  albu- 
men, and  on  evaporating  the  filtered  liquor  to  dryness,  the  diastase  re- 
mains, though  by  no  means  pure ;  it  is  a  white  gummy  mass  ;  it  is  pre- 
cipitated by  infusion  of  galls  and  most  metallic  salts ;  one  part  of  it  rap- 
idly and  completely  converts  a  solution  of  2000  parts  of  starch  in  water, 
first  into  dextrine,  and  finally  into  grape-sugar.  It  has  been  suggested 
by  Saussure  that  diastase  is  identical  with  the  substance  termed  mucin 
in  p.  537,  but  this  is  doubtful ;  it  contains  nitrogen,  and  is  most  proba- 
bly, as  already  stated,  the  first  product  of  the  putrefaction  of  the  gluten 
or  albumen. 

When  the  process  of  germination  is  over,  the  plant  is  found  provided, 
by  its  roots  and  leaves,  with  the  means  of  procuring  such  nutriment  as 
its  future  offices  require,  from  the  atmosphere  and  the  soil.  For  the 
constitution  of  its  proper  ligneous  tissue,  carbon,  hydrogen,  and  oxygen 
are  required,  and  these  serve  also  for  the  formation  of  the  majority  of  its 
excreted  products,  as  sugar,  gum,  starch,  resin,  oils,  and  acids  ;  but,  in 
addition,  nitrogen  is  required  ;  and  although  the  proportion  of  nitrogen 
in  any  plant  is  small,  compared  with  that  of  the  other  elements,  yet  it 
is  of  great  importance  as  a  constituent  of  the  active  principles  of  most 
medicinal  plants,  as  the  vegetable  alkalies,  amygdaline,  &c. ;  and  of  still 
higher  interest,  as  Bousingault  has  shown  the  nutritive  power  of  each 
plant,  when  used  as  food,  to  be  proportional  to  the  quantity  of  nitrogen 
which  it  contains.  In  every  plant  there  exists  also  certain  inorganic 
elements,  acids,  and  bases,  which,  though  small  in  quantity,  are  yet  es- 
sential to  its  healthy  growth.  The  examination  of  the  modes,  chemical 
and  vital,  by  which  these  various  substances  are  supplied  to  the  plant 
and  assimilated  by  its  organs,  constitutes  an  important  branch  of  vege- 
table physiology,  which  can  here  be  but  superficially  sketched  ;  and,  in 
its  relation  to  practice,  the  manner  of  supplying  these  materials  so  as  to 
favour  the  growth  of  plants,  and  develop  their  most  useful  principles, 
must  be  the  basis  of  every  system  of  enlightened  agriculture. 

Of  the  Assimilation  of  Carbon  hy  Plants. 

In  describing  the  constitution  of  the  atmosphere  (p.  269),  I  have  had 
already  occasion  to  notice  the  beautiful  provision  by  which  the  two  great 
classes  of  organized  beings  mutually  compensate  for  the  change  which 
each  produces  in  its  nature,  and  thus  retain  it  in  the  condition  most 
conducive  to  the  healthful  existence  of  both.  That  while  the  animal,  in 
his  respiration,  throws  off"  carbonic  acid  and  absorbs  oxygen,  the  plant, 
from  the  surfaces  of  its  green  leaves,  in  sunlight,  absorbs  carbonic  acid 
and  gives  out  oxygen.  It  only  remains  here  to  examine  the  circumstan- 
ces of  this  change  with  reference  to  the  other  functions  of  the  plant. 

As  water  is  abundantly  absorbed  by  plants,  both  with  the  roots  and 
leaves,  the  assimilation  of  carbon  from  the  air  should,  with  it,  supply  at 


652  FORMATION     OF     WOODY     TISSUE. 

once  the  elements  of  the  woody  matter,  as  well  as  of  those  other  bodies, 
as  sugar,  starch,  and  gum,  which  contain  oxygen  and  hydrogen  in  the 
proportions  to  form  water.  But  this  respiratory  function  of  the  leaves 
does  not  in  reality  possess  the  simplicity  and  uniformity  of  effect  which 
has  been  just  assigned  to  it.  It  is  found  that  the  absorption  of  carbonic 
acid  and  the  liberation  of  oxygen  occur  only  under  the  influence  of  sun- 
light, and  from  the  green  portions  of  the  plant,  while  the  coloured  por. 
tions,  as  the  flowers  and  fruits,  and  even  the  green  leaves  during  the 
night,  absorb  oxygen  and  give  out  carbonic  acid,  thus  tending  to  in- 
crease the  vitiation  of  the  atmosphere  produced  by  animals  in  place  of 
counteracting  it.  The  existence  of  these  opposing  actions  had  induced 
some  physiologists  to  doubt  whether  they  did  not  neutralize  each  other, 
and  hence  to  seek  for  the  source  of  the  carbon  of  the  plant  in  the  action 
of  the  roots  upon  the  organic  substances  of  the  soil.  But  the  experi- 
ments  of  Daubeny  have  conclusively  established  that  a  healthy  plant 
evolves  so  much  more  oxygen  in  the  day  than  it  absorbs  during  the 
night,  and  inversely  absorbs  so  much  more  carbonic  acid  during  the  day 
than  it  evolves  at  night,  as  may  satisfactorily  account  for  the  growth  of 
the  woody  material  of  the  plant,  and  compensate  for  the  influence  of  ani- 
mal  respiration  and  combustion  upon  the  air. 

It  has  been  already  shown,  that  the  grains  of  starch,  when  elaborated 
by  the  organs  of  the  plant,  possess  a  structure  totally  different  from  that 
which  characterizes  bodies  constituted  in  virtue  of  mere  affinity,  and 
more  analogous  to  certain  animal  organs,  as  the  crystalline  lens  of  the 
eye.  In  the  diflTerent  varieties  of  starch,  it  is  not  diflficult  to  trace  the 
gradual  transition  to  lignine,  and,  as  stated  in  page  530,  ordinary  wood 
siiU  retains  in  the  tubes  and  cells  formed  by  the  arrangement  of  the  par- 
ticles of  lignine,  a  considerable  quantity  of  unaltered  starch.  In  the  me- 
dulla of  various  trees,  the  passage  from  starch  to  lignine  is  still  more 
evident.  Now  for  the  formation  of  starch  there  are  required  but  water 
and  carbon,  its  formula  being  C,2HioO,o,  and  this  I  consider  as  the  actual 
result  of  the  true  respiratory  process  of  the  plant ;  carbonic  acid  being 
absorbed,  and  an  equal  volume  of  oxygen  being  exhaled,  the  carbon  is 
assimilated  by  the  vital  power  of  the  plant,  and,  with  the  elements  of 
water,  produces  a  substance  partially  organized  in  structure,  the  starch 
globule.  The  outer  layer  of  this  gradually  increasing  in  density,  and 
water  being  separated  from  the  internal  portion,  should  give  a  cell,  or,  by 
the  reunion  of  many,  a  continuous  fibre  or  tube  of  true  lignine.  The 
change  being  simply  the  loss  of  water,  the  formula  of  the  lignine  becomes 
C12H8O8.  The  nature  of  the  starch  globule,  and,  hence,  the  structure  and 
physical  properties  of  the  ligneous  fibre,  varies  in  different  plants.  Thus 
1  consider,  in  the  adult  plant,  starch  to  be  the  first  product  of  the  assimi- 
lation of  carbon  and  water,  that  it  is  already  possessed  of  a  low  degree 
of  organization,  and  is,  in  structure  and  composition,  adapted  for  the 
change  (growth  rather  than  transformation)  into  true  wood. 

By  contact  with  the  albuminous  or  fermentative  principles,  the  starch, 
whether  accumulated  in  the  seed  or  roots,  or  distributed  throughout  the 
substance  of  the  plant,  undergoes  changes  of  an  opposite  kind.  Its  or- 
ganized  character  is  lost ;  it  successively  forms  gum  and  sugar.  We 
cannot  yet  form  cane-sugar  artificially  from  starch,  but  we  can  have  no 
doubt  that  it  arises,  as  grape-sugar  does,  from  the  catalytic  metamorphosis 
of  the  starch,  arrested,  in  virtue  of  the  vital  power  of  the  plant,  at  a  point 


SECRETION     OF     PLANTS,    ETC.  653 

where  we  cannot  seize  it  in  the  laboratory.  These  are  the  truly  nutri- 
tious elements  of  the  plant,  whether  designed  for  the  support  of  the  adult 
individual,  or,  collected  in  proper  reservoirs,  to  serve  for  the  sustenance 
of  the  future  individual  in  the  seed. 

In  the  conversion  of  the  starch  into  the  numerous  secondary  products, 
as  acids,  colouring  matters,  oils,  &c.,  the  presence  of  which  characterizes 
the  generality  of  plants,  we  may  find  the  source  of  that  inverse  respira- 
tory action  which  so  much  masks  the  real  and  simple  nutritive  process. 
Of  the  circumstances  of  the  formation  of  these  bodies,  we  have  an  exam- 
ple admirably  illustrative  of  the  point,  in  the  conversion  of  lignine  into 
ulmine.  Here,  though  the  change  would  at  first  appear  to  require  only 
the  loss  of  the  elements  of  water,  we  find  it  to  be  much  more  profound  j 
the  constitution  of  the  lignine  is  totally  broken  up ;  oxygen  is  abundant- 
ly absorbed  from  the  air  ;  a  quantity  of  its  carbon  is  carried  off  as  car- 
bonic  acid,  and  a  quantity  of  its  hydrogen  as  water.  This  action,  which 
may  be  looked  upon  as  equivalent  to  the  various  processes  of  secretion 
performed  upon  the  blood  by  the  organs  of  animals,  by  which  substances 
adapted  to  the  use  or  structure  of  diflTerent  parts  are  there  deposited, 
while  others  unfitted  for  the  purposes  of  the  organized  being  are  thrown 
off,  is  carried  on  by  the  leaves,  probably  by  all  portions  of  the  surface  of 
the  plant,  and  is  the  source  of  the  continued  exhalation  of  water  and  car- 
bonic acid  w4Hch  occurs.  During  the  day,  and  especially  in  bright  sun- 
shine, the  assimilating  power  of  the  plant  being  in  full  action,  carbonic 
acid  is  taken  in,  and  oxygen  given  out ;  during  the  night,  while  the  plant 
is  in  repose,  this  nutritive  action  ceases.  Through  the  whole  time,  how- 
ever, the  process  of  the  secretion  is  carried  on,  water  and  carbonic  acid 
given  off,  though  in  such  proportion  only  as  to  secure  at  the  end  of  the 
twenty-four  hours  an  excess  of  assimilated  carbon  sufficient  fully  to  se- 
cure and  account  for  the  rapidity  of  growth. 

The  changes  of  constitution  which  accompany  the  ripening  of  fruit 
deserve  to  be  considered  more  in  detail  than  those  of  which  the  general 
nature  has  been  just  noticed.  If  we  examine  the  composition  of  a  young 
apple,  we  find  it  to  be  nearly  tasteless,  and  to  consist  of  a  loose  ligneous 
tissue,  in  which  is  imbedded  a  quantity  of  ordinary  starch  ;  as  its  growth 
proceeds,  the  starch  diminishes  in  proportional  amount,  and  the  fruit  be- 
comes intensely  sour,  from  the  presence  of  tartaric  acid  ;  after  some  time 
the  acidity  becomes  of  a  much  less  disagreeable  kind,  and  the  tartaric 
acid  is  found  to  be  replaced  by  malic  acid  ;  and  in  the  next  and  conclu- 
ding stage  of  maturity,  this  acid  disappears,  its  place  being  taken  by  pec- 
tine  and  by  sugar.  During  the  whole  of  these  actions,  oxygen  is  absorb- 
ed from  the  air,  and  water  and  carbonic  acid  given  off.  Their  theory  is 
simply  indicated  :  thus  starch,  which  is  C,2H,oO,o,  absorbing  140.,  pro- 
^  duces  6  Aq.  and  4C.O2,  with  tartaric  acid,  CsH40,o ;  and  of  this,  three 
atoms,  absorbing  60.,  produce  8C.O2  and  4  Aq.,  with  two  atoms  of  malic 
acid,  2(C8H408).  The  change  of  tartaric  to  malic  acid  may  also  occur 
without  the  absorption  of  oxygen  from  the  air,  as  6(C8H40,o)  may  pro- 
duce 5(C8H408)  with  8C.O4  and  4  Aq. ;  but  as  fruits  do  not  ripen  in  close 
vessels,  unless  when  they  absorb  oxygen,  the  former  is  more  probably 
the  process  which  actually  takes  place.  The  formation  of  the  pectine 
and  sugar  from  the  malic  acid  may  be  produced  by  the  absorption  of  ox- 
ygen and  the  giving  off  of  water  and  carbonic  acid,  as  8(C8H408)  with 
9H.0.  and  50.,  produce  pectine,  C24H17O22,  sugar,  2(C,2Hi20j2)  with  16C 


654        SOURCE  OF  CARBON  IN  PLANTS. 

O2.  That  neither  pectine  nor  sugar  is  derived  originally  from  the  starch, 
is  evident,  as  the  starch  abounds  but  in  the  very  earliest  stage,  and 
gives  place  to  the  tartaric  acid,  while  the  increase  in  quantity  of  the 
gelatinous  and  saccharine  matter  is  proportional  to  the  disappearance 
of  the  acid  constituents  of  the  fruit. 

When  our  knowledge  of  the  ultimate  effect  of  the  complex  actions  of 
plants  upon  the  atmosphere  was  still  uncertain,  it  was  considered,  and 
upon  very  rational  grounds,  that  the  plant  was  indebted  for  its  carbon  to 
the  organic  substances  of  the  soil,  and  the  necessity  for  a  continued  sup- 
ply of  animal  or  vegetable  manure  to  keep  up  the  fertility  of  the  soil,  was 
thus  satisfactorily  explained  ;  it  was  considered  that  the  roots  and  leaves 
remaining  from  the  preceding  crop,  or  intentionally  mixed  up  with  the 
soil,  were  converted,  as  already  described,  into  ulmine,  which,  either  by 
itself,  or  in  combination  with  inorganic  bases,  was  taken  up  by  the  ab- 
sorbing rootlets  of  the  plant,  carried  into  its  vessels,  and  assimilated  to 
the  constituents  of  its  tissues  ;  for,  in  fact,  if  we  examine,  at  any  moment, 
any  kind  of  fertile  soil,  we  find  it  to  contain  abundance  of  a  kind  of  ul- 
mine (geic  acid,  p.  639) ;  we  find  this  ulmine  to  be  a  product  of  the  de- 
composition of  the  organic  substances  used  as  manure  ;  we  find  that,  in 
barren  soils,  the  ulmine  is  either  absent,  or  it  exists  in  another  isomeric 
form  (humine,  &c.),  and  hence  the  vegetation  appeared  distinctly  con- 
nected with,  and  attributable  to  the  quantity  of  geine  present.  But,  not- 
withstanding such  plausible  evidence,  Liebig  has  brought  forward  very 
strong  proof  that  the  action  of  the  ulmine  can  be  but  secondary  towards 
the  nutrition  of  the  plant.  His  arguments  are  derived  from  the  facts  : 
first,  that  the  plant  may  fully  vegetate,  though  totally  unconnected  with 
the  ground,  as  has  been  proved  by  experiments  upon  cellular  plants,  sus- 
pended in  the  air,  and  supplied  with  water ;  second,  that,  from  the  insol- 
ubility of  every  kind  of  ulmine,  either  free  or  when  combined  with  earthy 
bases,  which  alone  are  presented  in  sufficient  quantity  in  the  soil,  it  can- 
not be  directly  absorbed  by  the  rootlets  of  the  plant,  which  totally  reject 
every  kind  of  solid  matter  ;  and,  third,  that  if  we  compare  the  quantity  of 
ulmine  in  a  soil  before  the  growth  and  after  the  collection  of  a  crop,  we 
find  the  diminution  to  be  so  small  when  compared  with  the  great  quanti- 
ty of  carbon  contained  in  the  mass  of  vegetable  matter  that  has  been  ob- 
tained, as  fully  to  prove  the  produce  of  carbon  in  the  crop  to  bear  but  an 
indirect,  if  any,  proportion  to  the  quantity  of  ulmine  in  the  soil.  The  true 
office  of  the  organic  matter  in  the  soil  appears  to  be,  that,  by  its  gradual 
decomposition,  a  constant  supply  of  carbonic  acid  is  afforded  to  the  plant, 
by  which,  during  the  first  stages  of  its  development,  and  while  destitute 
of  the  expanse  of  leaf  requisite  to  collect  the  necessary  quantity  of  nutri- 
ment from  the  air,  a  more  concentrated,  and,  as  it  were,  richer  food  is 
applied  to  the  absorbing  roots,  and  its  healthful  and  rapid  growth  thus 
provided  for  ;  it  is  not,  therefore,  the  ulmine  of  the  soil,  but  the  organic 
matter  generally,  in  changing  into  ulmine,  that  may  supply  carbon  to  the 
young  plant,  the  office  of  the  soil-ulmine  (geic  acid)  being  different,  as 
will  be  shortly  shown  ;  and,  even  in  this  action  of  the  organic  matters, 
the  functions  of  the  plant  remain  the  same,  being  the  absorption  of  car- 
bonic acid  and  evolution  of  oxygen. 

Assimilation  of  Nitrogen  hy  Plants. 
The  organic  substances  which  contain  nitrogen  belong  to  two  classes ; 


SOURCE     OF    NITROGEN     IN     PLANTS.  655 

those  of  the  first,  which  constitute  the  active  or  characteristic  principles 
of  many  plants,  although  of  much  interest  in  relation  to  medicine  and  to 
abstract  science,  are  of  very  little  importance  with  reference  to  the  growth 
of  the  plant,  and  its  use  as  food.  The  bodies  whose  origin  and  proper- 
ties are  here  of  interest,  belong  to  that  class  of  vegeto-animal  substan- 
ces, as  albumen,  gluten,  legumine,  of  whose  extraordinary  power  in  in- 
ducing catalytic  decompositions  of  other  bodies  I  have  so  often  spoken ; 
they  are  found  in  all  parts  of  the  plant,  dissolved  or  diffused  through  its 
juices,  but  especially  collected  where  transformations  necessary  for  growth 
or  germination  are  to  be  accomplished.  Although  present  in  but  small 
quantity,  no  function  of  the  plant,  in  any  stage  of  its  existence,  could  be 
accomplished  witltout  their  aid.  The  conversion  of  starch  into  sugar  for 
the  nutrition  of  the  germe ;  of  starch  or  lignine  into  the  vast  variety  of 
secretory  products  in  the  adult  plants  ;  the  elaboration  of  the  fruit,  its  ri- 
pening, and  even  the  ultimate  destruction  of  the  vegetable  tissues,  have 
their  origin  in  a  series  of  actions,  induced  and  maintained  by  communi- 
cation from  the  active  fermentation  of  these  azotized  materials. 

Not  merely  does  the  presence  of  this  class  of  bodies  regulate  the  prop- 
er performance  of  the  functions  of  the  plant,  but  they  play  an  equally  im- 
portant part  in  favouring  the  assimilation  of  vegetable  matter  when  used 
as  food  by  animals.  Bousingault  has  shown  by  experiments,  to  which 
I  shall  have  occasion  again  to  refer,  that  in  herbivorous  animals,  the  to- 
tal quantity  of  nitrogen  assimilated  for  the  growth  of  its  muscular  and 
other  tissues  is  derived  from,  and  equal  to  that  contained  in  the  vegeta- 
ble substances  used  as  food,  and  that  hence,  to  ascertain  the  nutritive 
value  of  any  organic  substance,  it  is  only  necessary  to  determine  the  quan- 
tity of  nitrogen  which  it  contains.  The  results  so  calculated  agree  with 
the  mean  experimental  results  of  the  most  enlightened  agriculturists, 
within  limits  as  narrow  as  could  be  expected  in  experiments  of  that  kind, 
and  may,  by  farther  research,  be  brought  to  still  greater  accuracy. 

Like  the  carbon,  the  nitrogen  of  plants  is  obtained,  in  great  part,  by 
absorption  from  the  air,  but  yet  it  is  not  merely  gaseous  nitrogen  which 
is  assimilated.  The  atmosphere  always  contains  a  quantity  of  ammonia, 
derived  from  the  putrefaction  of  organifc  bodies.  This  is  absorbed,  and 
passes  into  the  constitution  of  a  new  set  of  plants,  and  from  them  to  an- 
imals, to  be  again  thrown  into  the  air  after  their  death,  and  thus  circulate 
from  age  to  age,  entering  into  the  constitution  of  each  successive  race  of 
organized  beings.  We  cannot  refer,  however,  the  total  quantity  of  ni* 
trogen  in  plants  to  this  one  source  ;  for  if  the  produce  of  one  year  deri- 
ved its  nitrogen  only  from  the  decomposition  of  the  plants  of  the  previous 
year,  the  total  quantity  should  be  constant ;  whereas  experience  teaches 
us  that,  by  proper  methods,  the  quantity  of  vegetables  produced  on  a  soil 
may  be  continuously  increased,  and  for  this  the  nitrogen  must  be  derived 
strictly  by  absorption  from  the  air. 

Plants  vary  exceedingly  in  the  faciUty  with  which  they  derive  nitrogen 
from  the  air,  whether  by  direct  absorption  of  gas  or  as  ammonia.  Thus 
trefoil  vegetates  and  thrives  nearly  as  well  when  planted  in  pure  sand, 
and  supplied  only  with  water  and  air,  as  when  sown  in  ordinary  soil ; 
and  when  fully  grown,  the  quantity  of  nitrogen  is  found  to  be  increased 
twenty-six  per  cent.  ;  but,  on  the  contrary,  wheat  grows  but  slowly  un- 
der the  same  circumstances,  makes  no  attempt  to  flower,  and,  on  analy- 
sis, the  whole  plant  is  found  to  contain  even  a  little  less  nitrogen  than 


iJ56  ASSIMILATION    OF     HYDROGEN,     ETC. 

had  originally  existed  in  the  seed.  Wheat  has,  therefore,  no  power  to 
assimilate  nitrogen  from  the  air,  while  trefoil  possesses  that  character  in 
probahly  its  greatest  vigour.  Yet  wheat,  when  fully  grown,  is  rich  in 
nitrogen  ;  its  seed  is  more  nutritious  than  that  of  any  other  corn,  as  it 
contains  more  gluten ;  its  nitrogen  must,  therefore,  be  derived  from  an- 
other source :  it  is  extracted  from  the  organic  matters  of  the  soil. 

Without  entering  here  into  the  question  of  the  nature  of  manures, 
which  will  require  especial  consideration,  it  may  be  stated  that,  though 
wheat  is  thus  peculiar  in  deriving  its  supply  of  nitrogen  exclusively  from 
the  soil,  yet  all  plants  do  so  in  a  greater  or  less  degree.  In  the  soil,  how- 
ever, the  nitrogen  is  not  present  uncombined.  It  is  evolved  as  ammonia 
from  the  decomposing  organic  substances  of  the  manufes,  and  hence  an- 
imal manures,  as  producing  more  of  it,  are  proportionally  richer.  It 
has  been  already  noticed  (p.  639)  that  the  ulmine  of  the  soil  is  always 
combined  with  ammonia,  which  it  retains  with  exceeding  force.  But  in 
presence  of  strong  bases,  such  as  lime,  which  all  fertile  soils  contain,  the 
ulmine  is  slowly  decomposed,  the  elements  of  carbonic  acid  and  of  am- 
monia are  eliminated  from  it,  and  these  both  being  in  a  state  fit  for  ab- 
sorption by  the  rootlets  of  the  plant,  are  assimilated,  and  supply  carbon, 
nitrogen,  and  water.  Independent  of  the  ammonia  derived  from  the  or- 
ganic substances  actually  contained  in  the  soil,  much  of  that  diffused 
through  the  atmosphere  is  carried  to  the  roots  of  plants  by  showers  of 
rain,  and  by  the  direct  absorption  of  the  gas  by  the  porous  clay.  There 
are  few  specimens  of  clay,  especially  if  they  contain  iron,  which  do  not 
give  out  ammonia  when  heated,  and  the  absorption  occurs  with  greater 
power  when  the  clay  has  been  strongly  dried.  Hence  the  increased  fer- 
tility often  given  to  a  soil  by  burning  the  surface  to  the  depth  of  a  few 
inches. 

.Assimilation  of  Hydrogen^ 

I  have  described  (p.  653)  as  the  source  of  the  carbonic  acid  evolved 
by  plants  during  the  night,  the  conversion  of  the  starchy  substance,  which 
I  conceive  to  be  that  first  elaborated  by  the  plant,  into  the  various  se- 
cretory products,  acids,  colourirTg  matters,  &c.  But  there  are  many 
classes  of  important  vegetable  products  in  which  hydrogen  so  far  pre- 
dominates, that  we  must  conceive  for  their  formation  water  to  be  decom- 
posed,  and  its  oxygen  to  be  evolved,  either  free  or  in  combination  with 
carbon.  Of  such  bodies,  glycerine,  all  of  the  fixed  and  many  of  the  vol- 
atile oils,  wax,  and  caoutchouc,  are  examples.  The  secretory  action 
may  thus,  in  place  of  opposing  that  of  the  respiration  of  the  plant,  coin- 
cide with  it  in  result,  according  to  the  nature  of  the  substances  formed, 
since,  if  all  the  carbon  of  the  starch  remains  in  the  constitution  of  the 
secretion,  oxygen  is  evolved  from  the  water  which  is  decomposed  to  sup- 
ply the  necessary  quantity  of  hydrogen. 

Of  the  Inorganic  Constituents  of  Plants. 

If  we  make  a  plant  vegetate  in  water  which  holds  dissolved  small  quan- 
tities of  inorganic  salts,  we  find  that,  as  long  as  the  plant  remains  in 
health,  it  exercises  upon  these  salts  a  remarkable  discretionary  power  of 
absorption,  taking  up  some  and  rejecting  others,  which  pass  into  its  sub- 
stance only  when,  by  the  death  or  weakness  of  the  plant,  the  liquor  enters 
the  tubes  by  merely  physical  capillarity.     If  a  plant,  whose  tissues  have 


RELATION     OF     SOIL    TO     PLANT.  657 

»jeen  thus  imbibed  with  saline  matters  by  its  own  spontaneous  power  of 
absorption,  be  placed  in  a  vessel  of  pure  water,  it  will  be  found  to  give 
out  certain  of  the  saline  matters  it  had  taken  up,  but  to  retain  others. 
In  this  manner  we  may  recognise  the  action  of  inorganic  salts  upon  plants 
to  be  of  three  kinds  :  first,  directly  poisonous,  which  are  rejected  by  the 
plant  as  long  as  it  is  in  health,  and  to  this  class  belong  most  substances 
poisonous  to  man  ;  2d,  those  to  which  the  plant  appears  indifferent,  which 
are  taken  up  by  it  and  given  off  again,  without  any  apparent  influence  on 
its  growth  ;  and,  3d,  those  which,  when  absorbed  by  the  plant,  are  assim- 
ilated to  its  proper  tissues,  and  are  not  given  up  by  the  plant  to  water  in 
which  it  may  be  immersed. 

The  bodies  of  this  last  class  are  all  combinations  of  alkalies  and  earths, 
and  principally  with  organic  acids  ;  they  form  the  ashes  of  the  plant 
when  the  organic  matter  is  burned  away,  and  then  always  possess  an  al- 
kaline reaction  from  the  formation  of  carbonates.  As  a  general  princi- 
ple, we  may  say  that  each  plant  requires  for  its  healthy  growth  inorganic 
substances  in  certain  quantity  and  of  a  certain  nature  ;  but  replacement 
of  one  base  by  another  may  occur  in  certain  cases,  without  positive  injury 
to  the  plant.  Thus  the  plants  which  yield  soda  when  grown  upon  the 
seashore  (salsola,  salicornia),  if  transplanted  to  the  interior,  gradually 
lose  the  soda,  and  acquire  potash  in  its  place  ;  so  that,  after  a  generation, 
no  trace  of  the  former  alkali  remains.  The  ashes  of  oaks  or  pines  grown 
upon  a  granitic  or  basaltic  soil  contain  abundance  of  magnesia  and  of 
potash,  while  trees  of  the  same  species  will  flourish  on  a  limestone  soil, 
and  in  their  ashes  lime  will  be  the  predominant  ingredient.  But  these 
cases  of  substitution  of  one  base  for  the  other  in  a  plant  are  still  but  rare 
exceptions  to  the  principle,  that  each  kind  of  plant  requires  for  its  vigor- 
ous and  healthy  growth  to  be  supplied  with  inorganic  substances  of  a 
specific  nature  and  in  certain  quantity. 

It  is  this  principle  which  determines  the  more  successful  cultivation  of 
certain  plants  in  certain  soils.  Thus,  if  we  examine  the  composition  of 
■the  ashes  of  wheat,  we  find  abundance  of  silica,  phosphoric  acid,  magne- 
sia, lime,  and  potash.  If  we  sow  wheat  in  a  soil  which  contains  neither 
potash  nor  phosphoric  acid,  some  of  the  materials  necessary  for  the  per- 
fection  of  the  plant  being  absent,  the  crop  cannot  be  productive ;  but  if 
we  previously  manure  the  soil  with  bonedust,  with  ashes  of  weeds,  or 
other  substances  which  may  supply  the  necessary  inorganic  elements, 
these  will  be  absorbed,  and  the  plants  obtain  their  full  development. 
Even  when  the  quantity  of  the  required  inorganic  base  is  but  exceeding, 
ly  minute,  it  will  still  be  collected  by  the  vital  action  of  the  plant  in  the 
necessary  quantity.  Thus,  in  most  sea-plants,  iodide  of  magnesium  ex- 
ists  in  such  proportion  as  that  it  affords  the  universal  source  of  iodine  for 
all  technical  and,  scientific  objects ;  and  yet  that  salt,  which  is  excess- 
ively soluble,  is  removed  by  the  plant  from  the  sea-water,  which  con- 
tains but  minute  traces  of  it,  and  is  retained  in  the  vegetable  tissue  by  a 
power  which  prevents  its  being  washed  out  again.  It  is  this  power  of  a 
plant  to  search  for  and  remove  from  the  soil  all  traces  of  those  inorganic 
bases  which  it  most  requires,  that  renders  many  soils  incapable  of  bear- 
ing  successive  crops  of  the  same  kind,  without  the  intermediate  applica- 
tion of  suitable  mineral  manures.  But  if  the  soil  be  of  such  nature  as  to 
contain  itself  those  elements,  it  may  become  truly  inexhaustible  for  the 
growth  of  most  species  of  plant.     It  is  hence  that  soils  formed  by  the  de- 

40 


658  CONSTITUTION     OF     SOILS. 

composition  of  basaltic  rocks  or  of  modern  lavas  are,  for  every  kind  of 
crop,  some  of  the  most  productive  ;  the  facility  with  which  these  rocks 
are  decomposed  by  the  action  of  air  and  water,  provides  a  constant  sup. 
ply  of  soil  absolutely  new,  and  from  the  constitution  of  these  rocks,  the 
great  variety  of  their  mineral  components  renders  such  soil  abundant  in 
every  element  that  plants  in  general  require. 

Of  the  Constitution  of  Soils  and  of  Manures, 

From  what  has  been  already  said,  it  is  easy  to  judge  of  the  circum- 
stances which  render  a  soil  barren  or  productive,  but  from  the  importance 
of  the  subject  to  vegetable  physiology  and  to  agriculture,  it  requires  more 
detailed  examination. 

The  organic  elements  of  the  plant  being  derived  for  the  most  part  from 
the  atmosphere,  the  office  of  the  soil,  so  far  as  they  are  concerned,  is  re- 
duced to  supplying  to  the  roots,  during  those  periods  when  there  is  not 
a  sufficient  expanse  of  foliage  to  absorb  nutriment  from  the  air,  the  car- 
bonic acid  produced  by  the  gradual  rotting  of  the  ligneous  matter,  and 
ulmine,  and  ammonia  from  the  azotized  elements  of  the  manure.  For 
this  purpose  the  soil  is,  in  respect  to  its  mineral  composition,  unimpor- 
tant ;  it  should  be  porous,  in  order  to  admit  of  the  easy  penetration  of  the 
rootlets,  and  to  allow  free  access  of  oxygen  to  the  organic  matter  to  form 
carbonic  acid ;  it  should  yet  be  close  enough  to  retain  moisture  in  the 
average  intervals  of  rain,  in  order  that  the  water  necessary  for  vegeta- 
tion may  not  be  absent. 

These  physical  conditions  are  not,  however,  combined  in  any  one  kind 
of  mineral  material.  If  we  take  a  soil  of  pure  sand  or  of  pure  limestone, 
we  find  them  so  loose  and  porous  that  the  water  filters  off  almost  imme- 
diately after  falling,  and  the  plants  necessarily  perish.  If  a  soil  consist 
of  pure  clay,  its  tenacity  wf)uld  be  such  as  totally  to  prevent  the  access 
of  air,  and  all  growth  of  the  absorbing  filaments  of  the  roots.  To  com- 
bine the  two  proper  conditions  of  a  soil,  the  clay  should  be  mixed  with 
the  porous  material,  in  proportions  which  vary  with  the  nature  of  the 
plant  to  be  cultivated  ;  and  thus  the  simplest  soil,  in  order  to  fulfil  its 
physical  conditions,  as  supplemental  to  the  atmosphere,  should  contain  two 
mineral  substances,  of  which  one  should  be  clay,  and  the  other  lime  or 
silica ;  and  as  in  practice,  unless  for  some  special  object,  the  presence  of 
caustic  lime  would  prove  injurious  to  the  absorbing  rootlets,  this  should 
be  present,  combined  with  carbonic  acid,  as  in  any  of  the  usual  varieties 
of  limestone  rocks. 

The  proper  action  of  the  soil,  that  which  it  exercises  independently  of 
its  office  in  replacing  the  atmosphere,  is  to  supply  to  the  plant  those  in- 
organic constituents,  the  importance  of  which  have  been  already  shown. 
For  this  purpose,  a  far  greater  complexity  of  constitution  is  required. 
Thus  there  is  no  plant  that  does  not  contain  both  lime  and  silica,  and 
hence,  in  the  simplest  soil,  both  must  be  present.  There  is  scarcely  a 
plant  whose  ashes  do  not  contain  a  fixed  alkali,  generally  potash  ;  and 
hence  minerals  which  may  yield,  by  their  decomposition,  the  necessary 
quantity  of  that  base,  should  be  present  in  a  fertile  soil.  For  most  plants, 
also,  magnesia  must  be  supplied  ;  and  for  many,  and  especially  the  vari- 
ous kinds  of  corn,  phosphoric  acid.  In  average  soils,  most  of  these  bodies  . 
are  naturally  present  in  the  necessary  degree.  When  the  soil  has  origi- 
nated in  the  decomposition  of  granitic  or  of  slaty  rocks,  the  silica,  the  al 


EXCRETIONS     OF     PLANTS,     ETC.  659 

umina,  and  the  potash  are  abundantly  supplied  from  feldspar  and  from 
mica :  ^.ime  and  magnesia  also  may  be  derived  from  associated  minerals ; 
but,  in  general,  it  is  necessary  to  add  lime  to  such  soils,  in  order  that  the 
quantity  necessary  to  full  fertility  may  be  present.  In  purely  limestone 
soils,  clay  and  silicious  gravel  must  be  added  ;  and  to  make  up  the  defi- 
ciency in  potash,  the  ashes  of  other  plants  and  cinders  of  coal.  If  the 
soil  be  purely  silicious,  the  addition  of  clay  and  lime  (marl)  may  bring  it 
to  the  proper  composition. 

In  these  few  words  are  contained  the  theory  of  what  are  termed  miner- 
al manures,  with  few  exceptions.  In  adding  lime  or  marl,  bonedust  or 
cinders,  to  a  soil,  we  either  render  its  physical  condition  of  porosity  and 
tenacity  more  suitable  to  the  circumstances  of  the  plant,  or  we  supply 
some  ingredient  which  was  either  primitively  deficient  in  the  soil,  or  had 
been  removed  from  it  by  a  previous  crop  of  the  same  kind.  On  this  last 
condition  is  founded  also  the  necessity,  in  an  economic  agriculture,  of 
alternating  crops  which  take  up  from  the  ground  materials  of  different 
kinds.  Thus,  if  wheat  be  grown  upon  a  soil,  the  rocky  substance  of  which 
is  rich  in  potash  and  phosphoric  acid,  the  crops  will,  afler  a  few  years,  be 
unproductive,  and  the  soil  impoverished,  because  the  rock  decomposes  too 
slowly  to  supply  materials  for  the  wheat  as  fast  as  they  are  required;  but 
if  we  take  from  that  soil  a  crop  of  wheat  but  once  in  three  years,  and  in- 
terpose  some  other  plant,  as  trefoil,  which  takes  up  but  little  potash  and 
no  phosphoric  acid,  the  soil  has  time  to  recover  its  constitution,  and  the 
series  of  crops,  thus  arranged  in  rotatory  order,  so  far  from  impoverishing 
the  soil,  may  bring  it  to  a  higher  degree  of  richness,  by  the  additions  made 
to  its  azotized  organic  components  by  the  roots  and  rejected  leaves  of  the 
various  crops  which  are  left  upon  it,  and  the  manure  derived  from  the  con- 
sumption of  its  produce  by  animals. 

The  advantage  of  a  rotation  of  crops  may  be  thus  deduced  from  the 
necessity  of  the  soil  -renewing  its  mineral  constituents,  by  the  gradual 
decomposition  of  the  subjacent  rocky  matter  (subsoil).  But  the  obser- 
vations of  Macaire  and  Decandolle  indicate  another  and  not  less  im- 
portant reason  for  its  use.  These  physiologists  have  found,  that  from 
the  rootlets  of  a  plant  the  same  process  of  excretion  is  carried  on  as  by 
its  stem  and  leaves,  and  that  brown-coloured  substances  are  exuded, 
which  possess  much  analogy  with  tannin,  and  which  are  poisonous  to 
plants  of  the  same  kind  when  dissolved  in  the  water  with  which  their 
roots  are  supplied.  On  the  other  hand,  the  excretory  products  of  one 
plant  may  be  used  without  injury,  and  even  advantageously,  for  the 
growth  of  another  plant  of  a  different  natural  family ;  and  in  this  respect 
the  grasses  and  the  leguminous  plants  are  most  remarka«b]e.  It  is  hence, 
probably,  for  example,  that  wheat  unfits  the  soil  for  the  growth  of  an- 
other crop  of- wheat,  not  merely  by  removing  the  potash  and  phosphoric 
acid  which  is  required  for  the  perfection  of  its  parts,  but  it  also  gives  out 
a  substance  poisonous  to  a  plant  of  the  same  kind,  but  which  acts  bene- 
ficially upon  the  rootlets  of  a  leguminous  plant,  favouring  its  growth, 
while  the  soil  has  time  to  regain  from  the  subsoil  the  inorganic  mate- 
rials of  which  it  had  been  deprived. 

The  utility  of  manures  may  now  be  easily  understood;  their  action  is 
either  as  bone-earth,  marl,  lime,  cinders,  or  silicious  gravel,  to  supply  to 
the  soil  some  mineral  ingredient  in  which  it  had  been  deficient,  or  to 
provide,  as  by  the  ordinary  vegetable  or  animal  manures,  soot,  &c.,  or- 


660  ACTION     OF     ORGANIC     MANURES. 

ganic  matter,  which,  by  its  decomposition,  may  give  ot:it  trmtbonpr  -Ai^id 
and  ammonia  for  the  nutrition  of  the  young  plants,  kn  some  few  *.a«es 
the  action  of  manures  is  more  indirect;  thus  the  leguminous  plants  (tre- 
foil) require  but  little  inorganic  matter,  but  much  ammonia,  and  yet 
there  is  no  manure  so  efficient  in  the  promotion  of  their  growth  as  plas- 
ter of  Paris  (sulphate  of  lime).  The  plant,  however,  contains  no  sul- 
phate of  lime ;  it  is  not  absorbed.  The  action  of  this  manure  appears 
to  be,  as  was  first  suggested  by  Liebig,  that,  acting  on  those  substances 
of  the  ulmine  family  which  always  retain  a  large  quantity  of  ammonia 
intimately  united  in  the  soil,  it  forms,  by  double  decomposition,  ulmate 
of  lime  and  sulphate  of  ammonia,  which  last,  being  soluble,  is  easily  ab- 
sorbed by  the  rootlets  of  the  plant,  and  the  nitrogen  assimilated  to  its 
tissues. 

With  regard  to  organic  manures,  their  great  value  depends  on  the  pro- 
portion of  nitrogen  they  supply.  In  plants,  the  great  mass  of  nitrogen  is 
always  deposited  in  organs,  as  the  seed,  the  tuber,  &c.,  which,  for  that 
very  reason,  are  sought  after  and  collected  by  man,  either  as  food,  or  for 
medicinal  purposes,  from  the  active  (azotized)  principles  they  contain. 
The  roots,  stems,  and  leaves  of  plants,  such  as  are  rejected  in  the  col- 
lection of  the  crop,  contain  little  nitrogen,  they  being  rejected  as  useless 
for  that  very  reason.  Hence  the  residue  of  a  former  season  may  manure 
the  land  abundantly  so  far  as  carbon  is  concerned,  but  be  quite  incapable 
of  supplying  nitrogen,  and  in  providing  materials  for  a  future  abundant 
crop.  The  object  of  the  agriculturist  must  be,  so  far  as  organic  mate- 
rial is  concerned,  to  supply  nitrogen,  especially  for  such  plants  as  the 
different  species  of  corn,  which  are  incapable  of  deriving  that  important 
element  directly  from  the  atmosphere.  The  value  of  an  organic  manure 
may  therefore,  for  practical  purposes,  be  considered  as  being  measured 
by  the  quantity  of  nitrogen  which  it  contains,  and  the  directness  or  in- 
directness of  the  benefit  derivable  from  it  depends  upon  the  manner  in 
which  the  nitrogen  is  combined.  If  mere  ammoniacal  salts  be  used,  or 
materials,  as  animal  manures,  urine,  &c.,  which  soon  form  ammoniacal 
salts  by  their  putrefaction,  the  whole  benefit  of  the  manure  is  given  to 
the  crops  immediately  succeeding  its  application  ;  but  if  organic  sub- 
stances be  employed  which  resist  decomposition,  their  nitrogen  is  evolved 
but  slowly ;  and  though  little  immediate  amelioration  be  observed  from 
their  addition  to  the  soil,  their  influence  is  gradually  and  steadily  exerted, 
and  becomes  ultimately  sensible  to  the  full  degree  proportional  to  the 
nitrogen  they  contain. 

A  mode  of  restoring  to  the  soil  the  principles  it  had  lost  by  indiscreet 
cultivation,  is  that  of  fallowing.  It  is  a  method  synonymous  with  an 
ignorant  and  improvident  agriculture.  The  soil  having,  by  over  work, 
lost,  on  the  one  hand,  some  of  its  essential  mineral  ingredients,  requires 
time  to  gather,  by  the  decomposition  of  the  undenying  subsoil  or  rock, 
a  proper  quantity  of  them  to  supply  the  elements  of  the  succeeding  crops, 
and  having  been  deprived  of  its  organic  elements,  especially  the  nitrogen, 
it  must  be  allowed  to  gain  from  the  atmosphere  a  suitable  quantity  of  am- 
monia, or  by  the  gradual  rotting  of  the  roots  of  the  preceding  crop,  a  quan- 
tity of  carbonic  acid  suitable  to  the  wants  of  that  which  is  to  follow.  But 
all  of  these  effects  may  be  more  perfectly  and  more  profitably  secured  by 
.he  intervention,  in  a  succession  suitably  arranged,  of  other  crops,  which 
exercise  upon  the  soil  actions  alternately  opposed.     Thus,  if  we  arrange 


ACTIVE     PRINCIPLES     OF     PLANTS.  661 

that  wheat,  which  probably  removes  from  the  soil  a  greater  quantity  and 
a  greater  number  of  elements  than  any  other  crop,  shall  be  succeeded  by 
sown  grasses,  for  forage  or  hay,  which,  as  they  are  not  allowed  to  mature 
their  seeds,  exercise  but  little  deteriorating  action  ;  these,  again,  by  oats, 
the  exhausting  power  of  which  is  but  one  sixth  that  of  wheat ;  then  pease 
or  beans  manured  ;  that  these  be  followed  by  barley,  the  exhausting  power 
of  which  is  one  third,  and  this  by  a  manured  green  crop,  the  soil  may  be 
brought  into  a  condition  superior  to  that  from  which  we  had  set  out,  and 
the  series  may  be  recommenced  with  wheat,  the  soil  being  every  season 
economized.  This  is  but  one  of  the  many  kinds  of  rotation  which  have 
been  found  by  experienced  agriculturists  to  be  as  beneficial  in  practice  as 
theory  indicates  that  they  ought  to  be  ;  and  no  other  reason  can  be  assign- 
ed for  allowing  a  field  to  lie  idle  every  second  or  third  year,  but  ignorance 
on  the  part  of  the  farmer  of  what  could  otherwise  be  done  with  it. 

It  remains  only  to  notice,  in  relation  to  the  theory  of  the  growth  of 
plants,  a  few  additional  circumstances  connected  with  the  formation  of 
some  of  their  peculiar  principles.  It  is  not  unusual  to  hear,  from  even 
intelligent  agriculturists,  objections  to  the  cultivation  of  certain  plants,  on 
the  grounds  of  their  exhausting  the  soil  too  much.  A  plant  exhausts  the 
soil  only  in  consequence  of  its  forming  in  proportional  quantity  some  sub- 
stance, the  elements  of  which  are  derived  from  the  soil,  and  which  con- 
stitute in  almost  every  case  the  valuable  portion  of  the  plant.  Wheat 
exhausts  the  soil,  because  it  derives  therefrom  the  large  quantity  of  nitro- 
gen which  its  grain  contains ;  but  it  is  precisely  that  great  quantity  of 
nitrogen  which  renders  wheat  more  valuable  in  the  market  than  oats  or 
barley.  Tobacco  exhausts  the  soil,  because  it  takes  up  abundance  of 
nitrogen,  with  which  it  forms  its  nicotine  ;  the  more  of  the  active  princi- 
ple the  plant  produces,  the  more  it  exhausts  the  soil ;  but  in  the  same 
proportion,  the  greater  value  does  it  possess  when  sold.  To  produce 
indigo,  nitrogen  must  be  supplied  to  the  plants  by  abundance  of  rich 
manure ;  no  crop  is  more  exhausting  ;  but  without  the  nitrogen  no  col- 
ouring matter  could  be  formed,  and  the  plant  would  be  completely  worth- 
less. Examples  of  this  kind  might  be  adduced  in  any  number;  but  these 
suffice  to  place  in  a  distinct,  though  popular  aspect,  the  general  principle, 
that  where  a  plant  exhausts  the  soil,  especially  as  to  its  nitrogen,  it  is  for 
the  production  of  the  substance  which  gives  the  plant  its  commercial 
value  and  importance,  and  that  hence  the  quantity  of  manure  necessary 
for  the  production  of  an  abundant  crop  is  fully  repaid  by  the  improved 
quality  of  the  produce. 

Without  seeking  to  enter  into  the  general  question  of  the  influence  of 
the  physical  agents  on  vegetation,  which  for  its  discussion  would  require 
more  extended  limits,  and  lead  to  considerations  too  far  removed  from 
chemistry  to  justify  its  introduction,  I  shall,  in  concluding  this  sketch  of 
the  chemistry  of  vegetation,  notice  the  peculiar  action  which  light  exer- 
cises upon  plants.  It  is  not  merely  that  it  acts  as  a  general  stimulus,  and 
thus  provokes  the  activity  of  nutrition,  which  determines  the  ultimate  re- 
suh  of  the  purification  of  the  atmosphere  by  plants,  and  that  its  withdraw- 
al is  followed,  with  plants  as  with  higher  beings,  by  a  torpor  and  tendency 
to  rest,  which  closes  their  petals,'  and  folds  their  leaves  at  night.  But  in 
the  production  of  the  coloured  parts  of  plants  the  agency  of  light  is  indis- 
pensable. A  plant  which  grows  in  darkness,  as  in  the  gallery  of  a  mine, 
no  matter  to  what  size  its  form  may  reach  by  means  of  a  copious  supply 


662      ACTION     OF     LIGH  T. A  NIMAL    CHEMISTRY. 

of  food,  remains  soft,  its  wood  unformed,  its  colour  pale  ;  the  chlorophyll 
not  being  generated,  unless  under  the  influence  of  light.  For  culinary 
purposes,  precisely  this  effect  is  produced  by  covering  up  the  stems  of 
celery  and  asparagus,  the  softness  and  whiteness  admired  upon  the  table 
being  the  evidence  of  the  sick  and  abortive  organization  of  the  stem. 

The  action  of  light  in  favouring  the  production  of  colour  in  plants  is, 
however,  accompanied  by  a  more  material  change.  The  petals,  and  all 
coloured  parts  of  plants,  except  the  j^eaves,  absorb  oxygen  from  the  air. 
This  is  precisely  what  we  find  a  number  of  bodies  to  effect,  when  pass- 
ing from  their  colourless  condition  to  that  in  which  their  proper  colour 
is  displayed.  Thus  white  indigo  becomes  blue  by  absorbing  oxygen. 
Thus  rocelline,  by  absorbing  oxygen  and  giving  off  water,  forms  ery- 
throlitmic  acid.  It  is  thus,  too,  by  deoxidizing  agents,  we  may  remove  the 
colour  from  logwood,  archil,  and  the  flowers  of  most  plants,  and  restore 
their  tints  by  again  admitting  it.  Frequently,  also,  the  generation  of  the 
coloured  substance  is  accompanied  not  merely  by  an  absorption  of  oxy. 
gen,  but  by  an  escape  of  carbonic  acid ;  this,  which  is  shown  in  the  la- 
boratory in  forming  orceine  from  erythrine,  appears  to  take  place  in  the 
tissues  of  most  flowers,  which  rapidly  give  out  carbonic  acid  for  some 
time  after  they  have  first  opened. 

In  similar  actions,  carried  on  in  the  laboratory  by  ineans  of  chlorine, 
the  influence  of  light  in  furthering  the  removal  of  hydrogen,  and  even  of 
carbon,  if  water  be  present,  is  most  remarkable,  and  illustrates  the  opera- 
tion of  that  physical  agent  in  producing  the  colours  of  plants  in  a  distinct 
and  satisfactory  way.  This  action  has  been,  however,  so  fully  noticed 
in  describing  the  general  chemical  agencies  of  light  (p.  172)  and  the  ac- 
tion of  chlorine  on  colouring  matters  (p.  622),  that  1  deem  it  necessary 
only  to  refer  to  what  has  been  there  said  upon  the  subject. 


CHAPTER  XXX. 

OF    ANIMAL   CHEMISTRY 

In  describing  the  various  classes  of  organic  bodies  which  have  hitherto 
come  under  our  notice,  I  have  made  no  distinction  as  to  their  animal  or 
vegetable  origin,  for  the  point  of  view  under  which  they  were  then  con- 
sidered,  and  the  properties  which  they  manifested,  were  independent  of 
their  source.  It  was  thus  with  ethal,  the  fatty  acids,  and  colouring  mat- 
ters  ;  and,  indeed,  in  many  instances,  the  same  substances  were  found  to 
be  products  of  both  kingdoms  of  organized  nature.  In  the  present  chap- 
ter I  purpose  to  describe,  so  far  as  our  accurate  knowledge  extends,  the 
chemical  history  of  those  bodies  which  I  characterized  in  another  place 
(p.  468)  as  being  rather  organized  than  organic ;  as  constituting,  not 
merely  a  product  of  the  vital  operations  of  the  being,  but  the  mechanism 
itself  by  which  these  vital  operations  are  carried  on  ;  as  making  part  of 
the  tissues  essential  to  its  proper  organization  and  life,  and  as  being, 
while  in  connexion  with  the  animal,  and  participating  in  its  life,  protect- 


'  FIBRIN  E,     ITS     PROPERTIES.  663 

ed  from  the  truly  chemical  reactions  of  their  proper  elements,  whi^h, 
after  the  death  of  the  animal,  especially  in  contact  with  air  and  water, 
rapidly  assume  simpler  forms  of  union,  and,  breaking  up  the  complex  an- 
imal tissue  into  a  crowd  of  binary  compounds,  induce  the  change  well 
known  as  putrefaction. 

In  connexion  with  these  substances,  which  form  the  basis  of  the  tissues 
and  organs  of  the  animal  frame,  I  will  bring  under  survey  the  processes 
by  which,  from  the  atmosphere,  or  from  the  materials  of  our  food,  the 
substance  of  our  organs  is  continually  renewed,  their  growth  provided 
for,  and  the  conditions  necessary  for  the  continuance  of  health  and  life 
maintained.  The  functions  of  respiration  and  of  digestion,  so  far  as  the 
chemical  phenomena  which  they  embrace  are  known  ;  the  composition  of 
those  secretions  and  excretions,  whose  agency  in  the  furtherance  of  those 
processes  has  been  studied,  will  here  be  described  ;  and,  finally,  the  com- 
position  of  those  excretions  which  have  for  their  office  the  separation  of 
elements  unfit  for  the  nutrition  of  the  beings,  or  which  are  not  intended 
for  its  support. 

In  each  of  these  divisions  I  shall  add  to  the  description  of  the  compo- 
sition Smd  properties  of  these  tissues  or  secretions  in  the  state  of  health, 
such  facts  in  reference  to  the  modifications  introduced  by  disease,  as 
have  been  observed  with  proper  accuracy. 

SECTION  I. 

OF  THE  COMPOSITION  OF  THE  ANIMAL  TISSUES. 

A.   Of  the  Albuminous  Materials  of  the  Tissues. 
Of  Fibrine. 

This  substance  constitutes  the  basis  of  the  muscular  tissue,  and  forms 
an  important  constituent  of  the  blood.  In  the  latter  it  exists  dissolved 
during  life,  but  separates  after  death  or  extraction  from  the  body,  produ- 
cing, with  the  colouring  material,  the  phenomenon  of  coagulation.  In 
the  muscles,  the  fibrine  is  arranged  in  a  truly  organized  and  living  con- 
dition, constituting  the  contractile  fibres,  in  which  it  is  so  interwoven 
with  nervous  and  vascular  filaments  as  to  render  its  isolation  impossible. 
To  obtain  pure  fibrine,  therefore,  we  have  recourse  to  blood,  which,  if  im- 
mediately on  being  drawn  it  be  briskly  agitated  with  a  little  bundle  of  twigs, 
does  not  coagulate,  but  the  fibrine  is  deposited  on  the  twigs  in  soft  tenacious 
masses,  which,  being  washed  to  remove  any  adhering  colouring  matter, 
and  digested  in  alcohol  and  ether  to  remove  some  traces  of  fatty  substan- 
ces which  adhere  to  it,  constitute  pure  fibrine,  which  may  be  dried  by  a 
gentle  heat,  and  appears  then  as  a  yellowish  opaque  mass,  hard,  tasteless, 
and  inodorous  :  if  it  be  at  all  transparent,  this  results  from  traces  of  ad- 
hering fat.  It  is  insoluble  in  water,  alcohol,  and  ether  ;  it  absorbs,  how. 
ever,  so  much  water  as  to  treble  its  weight,  and  thereby  recovers  the 
volume,  softness,  and  flexibility  it  possessed  before  being  dried.  This 
moisture  is  not  sensible  to  the  hand,  but  by  strong  pressure  between  folds 
of  bibulous  paper  it  may  be  removed,  and  the  fibrine  rendered  complete- 
ly dry.  When  boiled  with  water  for  a  great  length  of  time,  fibrine  is  de- 
composed and  dissolves,  but  it  does  not  form  any  kind  of  gelatine. 

Fibrine  is  remarkable  for  decomposing  deutoxide  of  hydrogen  rapidly 
by  catalytic  force  (p.  235,  258),  evolving  oxygen.  Several  of  the  animal 
tissues  produce  this  effect,  though  not  containing  fibrine.  Albumen  is, 
however,  totally  destitute  of  it. 


664  ALBUMEN. 

Fibrine  absorbs  cold  oil  of  vitriol,  and  swells  ap  to  a  yellow  transpa- 
rent jelly.  On  the  addition  of  water,  it  shrinks  up  and  becomes  hard  ; 
but  if  all  the  excess  of  acid  be  washed  away,  thb  residual  mass,  which  is 
a  neutral  compound  of  fibrine  and  sulphuric  acid,  dissolves  in  pure  water. 
With  nitric  acid,  fibrine  evolves  nitrogen  and  nitric  oxide,  and  forms  a 
yellow  powder,  xanthoproteic  acid,  to  which  I  snail  shortly  recur.  Tri- 
basic  phosphoric  acid  and  acetic  acid  dissolve  librme.  'I'he  solution  is 
precipitated  by  the  mineral  acids  and  by  caustic  potash,  an  excess  of 
which  last,  however,  redissolves  the  precipitate.  The  mono,  or  bi basic 
phosphoric  acids,  act  as  sulphuric  acid  towards  fibrine.  If  perfectly  dry 
fibrine  be  digested  in  strong  muriatic  acid,  it  swells  up,  and  after  a  few 
minutes  dissolves  into  a  rich  dark  blue  liquid.  No  gas  is  evolved.  This 
blue  liquor  is  precipitated  by  yellow  prussiate  of  potash. 

Fibrine  is  dissolved  even  by  a  dilute  solution  of  caustic  potash,  and 
appears  thereby  to  neutralize  the  alkali  almost  completely.  This  solu- 
tion is  coagulated  by  alcohol  and  by  acids,  but  not  by  heat.  The  pre- 
cipitates given  by  acetic  and  tribasic  phosphoric  acids  are  redissolved  by 
an  excess. 

If  sulphate  of  soda  or  nitrate  of  potash  be  added  to  newly-drawn  blood, 
its  coagulation  is  prevented  ;  and  if  fibrine  be  digested  in  a  strong  solution 
of  nitre,  it  dissolves,  forming  a  thick  liquid,  which  is  coagulated  by  heat, 
by  alcohol,  and  acids,  and  is  precipitated  by  the  salts  of  mercury,  lead,  and 
copper,  and  by  yellow  prussiate  of  potash.  This  property  of  fibrine  will 
again  come  under  notice. 

The  composition  of  fibrine  is  expressed  by  the  formula  CgooHgio .  N,oo 
O240-I-P.S2.  It  contains,  besides,  minute  quantities  of  lime  and  magne- 
sia, so  that,  when  incinerated,  it  leaves  0*77  per  cent,  of  sulphates  and 
phosphates  of  those  bases. 

Of  Albumen. 

This  substance  is  even  more  extensively  distributed  through  the  animal 
frame  than  fibrine.  Like  fibrine,  it  exists  in  two  conditions,  one  soluble, 
and  the  other  insoluble  in  water ;  but  whereas  the  fibrine  becomes  insol- 
uble almost  instantly  on  being  withdrawn  from  the  body,  albumen  may 
retain  that  state  for  an  indefinite  time,  and  its  history  is  therefore  more 
complete.  In  its  soluble  form  it  exists  in  the  blood,  the  egg,  in  the  serous 
secretions,  in  the  humours  of  the  eye,  &c. ;  in  the  soluble  or  coagulated 
form,  it  constitutes  a  portion  of  most  of  the  solid  tissues.  Albumen  de- 
rives its  name  from  its  constituting  the  mass  of  white  of  egg. 

Soluble  Albumen. — This  is  obtained  in  the  solid  form  by  evaporating 
to  dryness,  at  a  temperature  which  does  not  exceed  120°,  the  serum  of 
blood,  or  white  of  egg,  the  membranous  investments  of  the  latter  having 
been  torn  up  by  triturating  with  some  angular  fragments  of  glass.  The 
dry  mass  is  yellow,  transparent,  hard,  tough,  and  contains,  besides  the 
albumen,  the  salts  and  some  other  constituents  of  the  blood,  or  white  of 
«gg,  in  minute  quantity.  These  are  extracted  by  digestion  in  alcohol 
and  ether,  which  leave  the  albumen  pure.  When  thus  completely  dry, 
it  may  be  heated  beyond  212'^  without  passing  into  the  coagulated  condi 
tion.  If  digested  in  cold  water,  it  gradually  swells  up,  and  finally  dis- 
solves. This  solution,  when  heated  to  a  temperature  between  140**  and 
150°,  coagulates.  If  dilute,  the  solution  may  even  be  heated  to  165° 
without  coagulating,  and  when  present  in  very  small  quantity,  the  albu- 


STATES     OF     ALBUM  E  N. P  R  O  T  E  I  N  E,  6^6 

men  may  not  separate  until  the  water  boils.  When  once  coagulated  in 
this  manner,  albumen  is  totally  insoluble  in  water  j  it  is  changed  into  its 
second  form.  The  solution  of  albumen  is  precipitated  by  alcohol,  by 
acids,  and  metallic  salts,  exactly  as  the  solution  of  fibrine  in  saltpetre. 
The  only  distinction  that  can  be  drawn  between  the  two  is,  that  the  saline 
solution  of  fibrine  is  partially  decomposed  by  the  addition  of  a  large  quan- 
tity  of  water. 

The  precipitates  yielded  by  solution  of  albumen  with  metallic  salts  a?© 
mixtures  of  two  distinct  substances,  one  a  compound  of  albumen  with  the 
acid,  the  other  a  compound  of  albumen  with  the  metallic  oxide ;  the  for- 
mer is  generally  somewhat  soluble,  the  latter  insoluble ;  and  hence  results 
the  application  of  albumen  as  an  antidote  to  mineral  poisons,  as  corrosive 
sublimate  and  bluestone. 

Albumen  is  also  coagulated  by  many  organic  bodies,  as  tannic  acid 
and  kreosote,  which  last  acts  catalytically,  as  a  very  minute  quantity  of 
it  coagulates  a  large  quantity  of  albumen,  without  entering  into  combina- 
tion with  it. 

Coagulated  Albumen  is  obtained  by  heating  serum  of  the  blood,  or  white 
of  egg,  to  between  140°  and  150°,  so  that  they  solidify ;  washing  the  mass 
with  water,  digesting  with  alcohol  and  ether  until  all  soluble  is  removed, 
and  then  drying  with  care.  Thus  prepared,  it  retains  some  inorganic 
salts,  principally  phosphate  of  lime,  from  which  it  may  be  obtained  free 
as  follows  :  The  serum  of  the  blood  is  to  be  coagulated  by  muriatic  acid  ; 
the  coagulum  washed  with  acidulated  water,  and  then  so  much  pure  water 
added  as  may  dissolve  it.  This  solution  being  then  decomposed  by  car- 
bonate of  ammonia,  the  pure  albumen  is  separated  as  a  flocculent  white 
precipitate. 

When  dry,  it  is  yellow  and  transparent ;  in  every  chemical  character 
except  its  relation  to  deuloxide  of  hydrogen,  it  identifies  itself  with  fibrine, 
and  it  is  hence  unnecessary  to  repeat  the  details  of  these  reactions ;  in 
its  composition  it  is  very  closely  related  to  it ;  their  organic  element  is 
the  same,  and  they  diflfer  only  in  the  quantity  of  sulphur,  the  formula  of 
albumen  bemg  CsooHe^  .  N,oo024o+P.S4.  The  quantity  of  ashes  remain- 
ing from  albumen  is  greater  than  from  fibrine. 

The  comparative  history  of  these  bodies,  as  now  given,  leads  to  con- 
siderable doubt  as  to  how  far  they  are  chemically  distinct,  although  their 
physiological  characters  are  so  different.  Mulder,  to  whose  accurate 
researches  we  are  indebted  for  the  greater  part  of  our  knowledge  of  the 
constitution  of  these  bodies,  looks  upon  both  as  compounds  of  the  real 
organic  substance,  which  he  terms  Prote'ine,  with  sulphurets  of  phos- 
phorus.  In  fact,  the  sulphur  and  phosphorus  may  be  removed  by  very 
simple  methods,  and  the  body  (proteine)  which  then  remains  deserves 
attentive  study. 

When  albumen,  fibrine,  cheese,  or  flesh  is  freed,  by  digestion  in  wa- 
ter, alcohol,  and  ether,  from  all  bodies  soluble  in  these  Hquids,  and,  by 
dilute  muriatic  acid,  all  earthy  salts  have  been  removed,  it  is  to  be  dis- 
solved in  a  dilute  solution  of  caustic  potash,  and  heated  to  120°,  whereby 
the  sulphur  and  phosphorus  form  phosphate  of  potash  and  sulphuret  of 
potassium.  From  the  filtered  liquor  the  proteine  may  then  be  precipi- 
tated by  acetic  acid,  which  must  be  added  only  in  very  slight  excess,  as 
oftherwise  the  precipitate  would  be  redissolved. 

Proteine  forms  grayish-white  gelatinous  flocks,  which,  when  dried,  be* 

4  P 


666  COMPOUNDS     OF     PROTEIN  E. 

come  hard  and  yellow,  and  give  an  amber-coloured  powder.  It  absorbs 
^ater,  swells  up,  and  regains  the  appearance  it  had  before  being  dried. 
By  long  boiling  with  water  it  is  decomposed  and  dissolved. 

Proteine  dissolves  in  all  very  dilute  acids,  forming  neutral  compounds 
which  are  insoluble  in  strong  acid  liquors,  and  are  hence  precipitated  on 
the  addition  of  strong  acids,  except  the  acetic  and  tribasic  phosphoric 
acids.  With  oil  of  vitriol  it  combines  as  described  under  the  head  of 
fibrine,  and  forms  Proteosulphuric  Acid.  It  combines  also  with  earthy 
and  metallic  oxides,  forming  insoluble  compounds,  which  are  identical  in 
characters  with  those  obtained  with  albumen. 

The  composition  of  proteine,  as  found  by  Mulder,  and  confirmed  by 
the  analyses  of  its  acid  and  basic  combinations,  is  expressed  by  the  for. 
mula  C40H32 .  N5O12.  We  may  evidently  consider  albumen  and  fibrine 
as  compounds  of  proteine ;  for  if  we  represent  proteine  by  the  symbol 
Prt.,  albumen  becomes  Prt2o+P.S4,  and  fibrine  is  Prtgo+P.Sa-  I  consider, 
however,  that  the  state  of  combination  of  these  bodies  requires  some  far- 
ther  consideration. 

It  is  found  that  proteine  constitutes  the  basis,  not  merely  of  the  animal 
substances  now  under  examination,  but  that  it  is  obtained  also  from  ve- 
getable albumen,  gluten,  and  legumine  (p.  538),  and  constitutes  the  pure 
caseous  matter  of  milk,  and  that  the  similarity  of  properties  and  compo- 
sition  in  these  bodies  is  such  as  to  justify  us  in  looking  upon  them  as 
identical.  We  have  seen  that,  between  albumen  and  fibrine,  the  dis- 
tinctive chemical  characters  are,  if  any,  so  trivial  as  to  leave  no  firm 
ground  for  their  distinction  in  that  way ;  and  if  we  examine  the  evidence 
of  their  being  compounds  of  proteine  with  sulphur  and  phosphorus,  wo 
shall  find  them  quite  inconclusive.  First,  it  is  not  certain  that  such  sul- 
phurets  of  phosphorus  exist  as  P.S2  and  P.S4;  second,  the  compounds  of 
sulphur  and  phosphorus  do  not  manifest  any  tendency  whatsoever  to 
combination  ;  and,  third,  in  all  the  reactions  of  albumen  and  fibrine,  the 
proteine  on  the  one  hand,  the  sulphur  and  phosphorus  on  the  other,  act 
as  if  they  were  totally  distinct.  I  look  upon  albumen  and  fibrine,  while 
in  connexion  with  the  body,  as  organized  and  living  substances,  in  whose 
functions  the  minute  quantity  of  sulphur  and  phosphorus  may  act  an  im. 
portant  part  as  a  catalytic  body.  The  proteine  I  consider,  not,  with 
Mulder,  as  the  basis  of  our  tissues,  but  as  the  simplest  product  of  their 
decomposition.  It  enters  in  combination  with  acids  and  with  bases,  as 
indigo  or  morphia  do,  which  I  look  upon  as  totally  foreign  to  the  char- 
acter of  a  body  possessed  of  vital  properties. 

Having  thus  described  what  I  consider  to  be  the  true  place  of  proteine, 
m  relation  to  albumen  and  fibrine,  I  shall  briefly  notice  some  of  its  de- 
rived compounds. 

Chloroproieic  Acid  is  formed  by  passing  chlorine  into  a  solution  of  al- 
bumen.  It  is  a  white  powder.  Its  formula  is  C40H3,  .  N50i2+C1.04. 
By  ammonia  it  is  decomposed,  nitrogen  being  evolved,  and  a  white  sub- 
stance formed,  Oxyproteine,  the  formula  of  which  is  C40H3,  .  N5O15. 

The  formation  of  Xanthoproteic  Acid,  by  the  action  of  nitric  acid  on 
fibrine,  has  been  already  noticed.  It  is  an  orange-yellow  powder ;  when 
washed  from  adhering  acid,  tasteless  and  inodorous,  but  reddens  moist 
litmus  paper.  Insoluble  in  water,  alcohol,  and  ether,  it  unites  with  acids, 
forming  compounds  which  are  pale  yellow,  and  insoluble ;  with  bases  it 
forms  soluble  salts,  generally  deep  red  coloured.     Its  formula  is  CsiHj, . 


SOURCES,  ETC.,  OF  GELATINE.         667 

B.  Of  the  Gelatinous  Constituents  of  the  Tissues. 
Of  Gelatine. 

When  the  skin,  cellular  or  serous  tissues,  tendons,  and  some  forms  of 
cartilage,  as  that  of  bones,  are  boiled  in  water,  they  dissolve  in  great  part, 
and  form  a  solution  which  gelatinizes  on  cooling.  Some  of  these  tissues, 
ciS  the  skin,  dissolve  easily,  and  almost  completely ;  others  dissolve  but 
partly,  and  leave  behind  a  quantity  of  coagulated  albumen.  In  most 
kinds  of  cartilage,  a  very  prolonged  boiling  is  necessary  to  extract  any 
sensible  quantity  of  gelatine.  These  various  tissues  are  thus  found  to 
consist  of  albumen  and  gelatine,  united  in  various  proportions,  and  each 
presenting  various  degrees  of  condensation  of  texture,  but  by  boiliffg  they 
may  be  completely  separated  from  each  other. 

The  gelatine  is  known  in  commerce  as  the  material  of  isinglass  and  of 
common  glue.  When  pure  it  is  colourless  and  transparent,  very  spa- 
ringly soluble  in  cold  water,  by  contact  with'  which,  however,  it  swells 
up  and  softens.  In  hot  water  it  dissolves  readily,  and  on  cooling,  forms 
so  strong  a  jelly,  that  with  yf^th  part  it  is  a  consistent  solid.  It  is  insolu- 
ble in  alcohol  and  ether.  When  a  solution  of  gelatine  is  long  exposed 
to  the  air,  or  frequently  heated  and  cooled,  it  undergoes  a  commencement 
of  putrefaction,  and  loses  its  property  of  gelatinizing.  The  composition 
of  gelatine,  by  Mulder's  analyses,  is  expressed  by  the  formula  CnHio 

The  action  of  reagents  on  gelatine  is  in  some  cases  of  high  interest. 
By  digestion  with  strong  sulphuric  acid,  as  with  caustic  potash,  the  same 
results  are,  obtained.  Ammonia  is  evolved,  a  white  crystalline  body 
{Leuci7ie)  and  a  sweet  substance  (Sugar  of  Gelatine)  are  formed.  They 
are  separated  from  each  other,  and  from  some  less  important  products, 
by  repeated  crystallizations.  From  its  alcoholic  solution,  Leucine  sep- 
arates in  brilliant  colourless  plates.  It  feels  greasy,  is  tasteless  and  ino- 
dorous ;  heated  to  336°,  it  sublimes  totally  unchanged.  It  dissolves  ia 
twenty-eight  parts  of  cold  water,  but  requires  625  parts  of  alcohol,  and  is 
insoluble  in  ether  ;  its  formula  is  C,2H,2 .  N.O4.  It  combines  with  nitric 
acid  to  form  Nitroleucic  Acid,  which  crystallizes  in  brilliant  needles,  and 
forms  with  bases  neutral  salts.    Its  formula  is  CjaHia .  N.04-}-N.05Aq. 

The  Sugar  of  Gelatine  crystallizes  from  its  solution  in  alcohol,  by  spon- 
taneous evaporation,  in  large  prisms,  which  are  colourless,  taste  sweet, 
and  feel  gritty  between  the  teeth.  It  is  decomposed  by  heat.  At  60°  it 
dissolves  in  five  parts  of  water,  but  it  is  sparingly  soluble  in  alcohol  and 
ether.  The  crystals  consist  of  C,6H,5  .  N40„-l-3  Aq.  It  forms,  with 
bases,  well-characterized  compounds,  and  unites  also  with  nitric  acid. 

When  acted  on  by  chlorine,  gelatine  is  converted  into  a  white  floccu- 
lent  substance,  insoluble  in  vvater,  but  dissolved  by  an  excess  of  gelatine. 
Its  composition  is  expressed  by  the  formula  C-^U^q  .  N8029H-C1.04,  con- 
sisting,  therefore,  of  four  atoms  of  unaltered  gelatine  and  one  atom  of 
chlorous  acid.  Gelatine  is  not  precipitated  either  by  solutions  of  ordina- 
ry or  of  basic  alum  ;  but  if  a  solution  of  common  salt  be  also  mixed,  the 
gelatine  falls  down,  combined  with  alumina,  as  it  decomposes  the  muri- 
ate of  alumina  which  is  then  formed.  On  this  principle  is  founded  the 
manufacture  of  white  leather,  by  a  kind  of  tanning  with  alum. 

The  most  important  compound  of  gelatine  is  that  with  tannic  acid, 
which  constitutes  ordinary  leather.     This  reaction  is  so  distinct,  that  one 


668    MANUFACTURE     OP     LBATHE  R. C  HONDRINE. 

part  of  gelatine  in  5000  of  water  is  at  once  detected  by  the  infusion  of 
galls.  The  constitution  of  the  precipitate  varies  according  as  one  or 
other  of  these  materials  is  employed  in  excess,  the  tannic  acid  and  ge- 
latine being  capable  of  uniting  in  at  least  three  different  proportions  ;  100 
parts  of  dry  gelatine  combine  with  136  parts  of  tannic  acid,  when  the 
latter  is  in  great  excess  :  this  compound  contains  an  atom  of  each  ingre- 
dient. 

The  technical  applications  of  gelatine  are  numerous,  and,  for  the  most 
part,  well  known.  For  glueing  together  wood,  paper,  &c.,  thickening 
colours,  filling  up  the  pores  of  writing  paper,  and  as  isinglass  and  calves* 
feet  jelly,  an  article  of  food,  it  is  abundantly  employed  ;  but  its  most  im. 
portaift  use  is  in  the  manufacture  of  leather.  The  skins  are  cleaned  by 
digestion  with  lime  and  scraping  with  a  knife,  from  the  hair  and  epider- 
mis  on  the  one,  and  the  loose  cellular  tissue  on  the  other  side,  and  then 
gteeped  in  pits  containing  an  infusion  of  oak  bark,  valonia,  sumach,  or 
other  of  the  substances  rich  in  tannic  acid  (p.  601).  At  first  the  tan- 
ning liquor  is  used  very  weak,  as  otherwise  the  surface  of  the  skin  would 
become  impervious,  and  the  interior  could  not  afterward  be  tanned  ;  but 
having  passed  through  a  succession  of  liquors  gradually  becoming  strong- 
er, the  skins  are  in  the  last  pit  interstratified  with  oak  bark,  and  so,  for  a 
considerable  time,  submitted  to  the  action  of  the  tannic  acid  in  its  high, 
est  state  of  concentration,  until  the  conversion  into  leather  is  complete 
throughout  the  entire  substance.  They  are  then  removed,  and  subjected 
to  finishing  and  cleaning  processes,  which  I  need  not  notice. 

Many  chemists  consider  that  gelatine  is  merely  a  product  of  the  de- 
composition of  albumen  or  fibrine  by  boihng  water,  and  not  a  true  con- 
stituent of  the  tissues.  I  believe  this  idea  to  be  incorrect  on  the  follow, 
ing  grounds :  First,  pure  fibrine,  or  albumen,  gives  no  gelatine  by  boil- 
ing ;  second,  in  the  process  of  tanning,  the  tannic  acid  combines  with  ge- 
latine in  a  skin  which  has  never  been  boiled  ;  and,  third,  that  we  can 
easily  understand  why  some  tissues  give  gelatine  more  easily  than  others 
by  the  different  degrees  of  condensation  in  their  structure  ;  but  I  rather 
consider  that  gelatine  bears  the  same  relation  to  the  organized  tissue  of 
the  skin  or  cellular  membrane  that  proteine  does  to  the  fibrine  of  the 
blood,  being  really  a  product  of  its  death  and  decomposition,  though  the 
only  representative  of  it  which  we  can  have. 

Chondrine. — Those  cartilages  in  which  bone  is  not  deposited,  are  re- 
solved by  boiling  into  a  substance  possessing  much  analogy  to  gelatine, 
but  still  distinguished  from  it  by  the  following  properties  :  it  precipitates 
solutions  of  alum,  sulphate  of  iron,  and  acetate  of  lead,  and  is  precipita. 
ted  by  acetic  acid,  none  of  which  bodies  have  any  action  on  ordinary  ge- 
latine, which,  however,  chondrine  resembles  in  all  its  other  characters  ; 
in  composition,  however,  it  differs,  its  formula  being,  by  Mulder's  anal- 
ysis,  CigHja.  NgO,;  it,  however,  contains  a  trace  of  sulphur,  its  complete 
formula  being  C220H260  •  N40O140+S.  The  physiologist  Miiller,  to  whom 
the  discovery  of  chondrine  is  due,  considers  that  the  skeleton  of  cartila- 
ginous fishes  yields  a  third  variety  of  gelatine. 

C.  Of  the  fatty  Constituents  of  the  Tissues, 

The  fatty  bodies  already  described  in  Chapter  XXIIL,  although  con- 
tributing essentially  to  the  support  of  the  animal  frame,  are  mere  secre. 
tions^  and  do  not  form  any  portion  of  its  organized  tissues.     The  sub- 


CEREBROTE,  CEREBROL,  CHOLESTERINE,  ETC.  669 

Stances  properly  included  under  the  present  head  are  the  constituents  of 
the  nervous  tissue,  such  as  it  is  found  in  the  brain,  the  apinal  cord,  and 
nerves. 

In  tlie  composition  of  the  brain  it  is  possible  to  distinguish  at  least 
three,  perhaps  five,  distinct  substances  of  a  fatty  nature ;  the  most  char- 
acteristic and  important  is  termed  Cerebrate  :  its  mode  of  preparation 
can  easily  be  gathered  from  its  characters  ;  it  is  a  white  powder,  taste- 
less and  inodorous,  feeling  not  at  all  greasy,  but  like  starch  ;  when  heat- 
ed, it  does  not  melt  until  it  has  become  brown,  and  in  great  part  decom- 
posed ;  it  is  insoluble  in  water,  sparingly  soluble  in  alcohol  or  ether  when 
cold,  but  abundantly  when  hot ;  on  cooling,  it  is  deposited  from  its  alco- 
holic solution  as  a  white  powder,  not  at  all  crystalline  ;  it  is  not  acted 
upon  by  alkalies.  In  composition  it  resembles  albumen,  containing  a 
large  quantity  of  nitrogen,  with  sulphur  and  phosphorus  in  minute  quan- 
tity, but  its  precise  formula  cannot  be  considered  as  being  yet  established. 

Cerebrol  is  a  liquid  reddish  oil,  having  the  odour  of  fresh  brain,  and  a 
disagreeable  rancid  taste.  It  is  soluble  in  all  proportions  in  ether  and 
in  oils,  but  only  moderately  so  in  alcohol.  It  contains  the  same  elements 
as  the  cerebrote,  and  apparently  in  nearly,  if  not  exactly,  the  same  pro- 
portions  ;  but  the  analyses  of  Couerbe,  who  alone  has  examined  their 
composition,  are  not  authentic  enough  to  be  brought  forward.  The  cer- 
ebrol  is  not  saponifiable,  nor  is  it  in  any  way  altered  by  digestion  with 
caustic  alkalies. 

In  addition  to  these  two  bodies,  the  brain  contains  a  large  quantity  of 
a  substance,  which,  from  having  been  first  discovered  as  a  constituent  of 
biliary  calcuU,  is  termed  Cholesterine :  it  is  insoluble  in  water,  but  dis- 
solves abundantly  in  boiling  alcohol,  from  which  it  crystallizes,  on  cool- 
ing, in  brilliant  plates  ;  it  melts  at  290°,  and  sublimes  partially  by  a 
stronger  heat ;  it  dissolves  readily  in  ether  ;  it  is  not  altered  by  caustic 
alkalies  ;  its  formula  is  CagHaoO.  By  treatment  with  hot  nitric  acid,  it 
is  converted  into  a  substance  which  crystallizes  in  yellow  needles,  and 
forms,  with  bases,  yellow  salts.  This  is  Cholesteric  Acid,  the  formula  of 
which  appears  to  be  CzeHao .  N.0,2. 

Couerbe  has  described  as  constituents  of  the  brain  two  other  fatty  bod- 
ies,  Cephalot  and  StearocenoL:  they  are  brown  coloured  resinous  bodies, 
which,  I  consider,  will  most  probably,  on  re-examination  of  the  subject, 
be  found  to  be  impure  or  decomposed  mixtures  of  cerebrote  and  cepha- 
lol.  I  hence  only  indicate  their  supposed  existence.  The  cholesterine 
I  look  upon  as  being  deposited  in  the  brain  as  ordinary  fat  is  in  the  cel- 
lular tissue,  or  in  the  substance  of  other  organs,  and  not  as  making  up  an 
essential  portion  of  the  nervous  tissue.  This  idea  is  strengthened  by  the 
fact  that  the  cholesterine  frequently  aggregates  in  the  brain  in  masses, 
forming  one  variety  of  the  fatty  tumours  of  that  organ. 

D.   Of  the  Saline  and  Extractive  Constituents  of  the  Tissues, 

We  find  in  all  the  animal  tissues  small  quantities  of  a  great  variety  of 
salts,  the  same  as  those  which  will  be  hereafter  noticed  as  existing  in  the 
blood,  to  the  presence  of  which  in  the  substance  of  the  tissues  they  are 
probably  due.  In  the  tissue  of  the  bones  and  teeth,  however,  these  sa- 
line matters  are  deposited  in  much  greater  quantity,  and  in  disease  and 
in  old  age  bony  deposites  occur  in  all  those  tissues  which  yield  true  ge- 
latine  on  boiling.  The  composition  of  the  bones  and  teeth  will  be  here- 
after noticed. 


670  S  K  I  N. E  P  I  D  E  R  M  I  S. H  O  R  N. 

The  extractive  matters  of  the  tissues,  like  the  extractive  matter  of 
plants  (p.  612),  do  not  pre-exist  as  such,  but  are  formed  by  the  decom- 
position, by  protracted  boiling  in  water,  of  the  fibrine,  albumen,  gelatine, 
(fee,  which  they  really  contain.  Berzelius  has  pointed  out  the  existence 
of  a  great  number  of  different  substances  that  are  thus  generated,  of 
which  two  need  here  only  require  notice.  For  the  first,  the  name  Ozma- 
zome  may  be  retained,  and  the  name  Zomidine  applied  to  the  second. 
Ozmazome  is  soluble  in  water,  and  also  in  absolute  alcohol  ;  it  cannot 
be  dried  by  heat,  but  forms  a  semifluid  of  an  acid  and  salty  taste,  which 
evolves  powerfully  the  odour  of  concentrated  decomposing  urine.  Its 
solution  in  water  is  yellow  ;  it  is  precipitated  by  the  salts  of  mercury, 
lead,  and  tin. 

The  zomidine  is  insoluble  in  alcohol ;  it  dries  down  to  a  brown  extract, 
of  a  strong  and  agreeable  odour  of  soup.  It  dissolves  in  water  in  all 
proportions.  Its  solutions  are  precipitated  by  the  salts  of  lead  and  tin, 
but  not  by  corrosive  sublimate  or  tincture  of  galls.  When  heated  it 
gives  out  an  odour  of  roasting  meat,  the  taste  and  smell  of  which  are 
indeed  due  to  its  formation.  Both  ozmazome  and  zomidine  contain  ni- 
trogen. 

Of  the  Composition  of  the  Tissues,  and  of  the  Secretions  in  Health  and  tn 

Disease, 

Having  described  thus  the  constituents  of  the  tissues  individually,  I 
shall  now  present  such  results  as  have  been  hitherto  obtained  as  to  the 
quantitative  composition  of  the  organized  tissues  formed  by  their  reunion, 
their  secretory  products,  and  morbid  alterations. 

Of  the  Skin,  Epidermis,  and  its  Modifications. — The  skin  of  animals 
is  a  congeries  of  finely-constructed  organs,  sensitive  and  secretory,  im- 
bedded in  a  peculiar  tissue,  which  is  one  of  those  most  easily  yielding 
gelatine,  whence  the  process  of  tanning  skins.  The  relative  proportions 
of  solid  and  liquid  matter  in  a  skin  freed  from  adhering  fat  and  cellular 
membrane,  but  soft  and  imbibed  with  its  natural  proportions  of  water, 
was  found  by  Wienhalt  to  be, 

Proper  cutaneous  tissues,  including  blood-  >  33,53' 

vessels  and  nerves 5 

Albumen 1-54 

Extractive  soluble  in  alcohol 083 

Do.       soluble  only  in  water  ....      760 
Water 57-50J 

On  the  surface  of  the  skin  there  is  secreted  a  substance,  which, 
though  varying  in  anatomical  structure  and  appearance  exceedingly,  as 
it  forms  the  fine  epidermis,  the  nails,  proper  horn,  the  tortoise-shell, 
feathers,  hairs,  &c.,  is  yet,  throughout  all  their  shapes,  identical  in  chem- 
ical character,  and  may  be  described  as  the  same  substance.  The  best 
example  of  horn  is  that  which  covers  the  process  of  the  frontal  bone  in 
the  ox.  It  varies  in  colour,  is  translucent,  tough,  and  elastic.  When 
heated  beyond  212°,  it  softens  without  being  decomposed,  and  may  then 
be  bent,  moulded,  and  soldered,  on  which  properties  many  of  its  uses 
depend.  It  is  scarcely  farther  acted  on  by  water  even  after  an  ebulli- 
tion of  several  days.  When  treated  by  strong  acids,  horn  is  softened, 
And  becomes  soluble  in  water.  Heated  with  solution  of  caustic  potash, 
it  evolves  ammonia,  dissolves,  and  the  liquor  contains  sulphuret  of  potas- 


10000. 


CELLULAR,     SEROUS,     AND     MUSCULAR    TISSUES.    671 

sium  and  an  organic  substance,  precipitable  by  an  acid.  The  composi- 
tion of  these  products,  or  of  horn  itself,  has  not  been  accurately  exam- 
ined. 

The  principal  mass  of  hair  is  composed  of  the  same  substance  as  horn, 
but  the  colour  is  due  to  an  oil,  which  may  be  extracted  by  ether.  If, 
by  virtue  of  the  sulphur  contained  in  hair,  a  solution  of  litharge  in  lime- 
water  blackens  the  hair,  nitrate  of  silver  blackens  the  hair  also,  but 
by  the  deposition  of  the  metal.  When  horn  or  hair  is  strongly  heated, 
it  fuses,  gives  off  carbonate  of  ammonia,  and  gases  of  a  characteristic 
disagreeable  smell  ;  if  air  be  present,  it  burns  with  a  brilliant  flame. 
The  perspiration  from  the  surface  of  the  skin  varies  in  nature  according 
to  the  part  of  the  body;  it  is  generally  acid,  contains  traces  of  albumen, 
fatty  matter,  and  the  salts  of  the  blood.  It  often  contains  a  volatile 
odorous  principle,  characteristic  of  the  animal  by  which  it  is  secreted. 

Of  the  Cellular  and  Serous  Tissues. — These  tissues  are  constituted  of 
gelatinous  material,  similar  to  that  in  the  skin,  and  hence  dissolve  by 
boiling  in  water,  being  converted  into  gelatine.  In  the  natural  condition 
of  these  membranes  their  surfaces  are  moistened  by  a  watery  liquid, 
which,  accumulating  in  excessive  quantity,  gives  rise  to  the  dropsies  of 
the  cavities  or  of  the  cellular  tissue.  This  serum  of  the  cavities  is  clear 
and  colourless.  It  reacts  alkahne  ;  its  specific  gravity  1*010  to  1*020; 
its  composition,  though  liable  to  fluctuate,  is,  in  general,  as  found  by 
Berzelius, 


Albumen 166^ 

Substance  soluble  in  alcohol  .    .      3-32 

Free  soda 0-28 

Alkaline  chlorides 609 

Earthy  phosphates 009 

Water 98756 


.100000  nearly. 


In  the  serum  of  dropsical  effusions  I  have  found  stearine,  elaine,  and 
urea.     This  observation  has  also  been  made  by  Marchand. 

The  cells  of  the  cellular  tissue,  in  which  fat  is  usually  deposited,  are 
often  filled  up  by  an  albuminous  material,  having  considerable  analogy 
to  caseiim.  It  is  thus  that  the  diffused  hardening  of  the  cellular  tissue 
and  the  local  white  tumours  have  their  origin.  Tendons,  aponeuroses, 
and  fibrous  membranes  are  similar  in  their  chemical  relations  to  the  cel- 
lular and  serous  tissues. 

Of  the  Muscular  Tissue. — From  what  has  been  already  said  of  fibrine, 
it  is  evidently  the  essential  element  of  the  muscular  tissue,  and  it  only  re- 
mains here  to  give  the  numerical  results  of  two  analyses  of  beef  muscle, 
made  by  Berzelius  and  Braconnot.     They  found  in  100  parts, 

Muscular  fibre  (with  vessels  and  nerves)    .  15-80  >  iq.iq 

Cellular  tissue  giving  gelatine 1-90  J  ^^ 

Soluble  albumen  and  colouring  matter    .    .  2-20    .  1-70 

Alcoholic  extract  with  salts 1-80    .  1-94 

Watery  extract  with  salts 105    .  0-15 

Phosphate  of  lime 008    . 

Water  and  loss 77*17    .  77-03 

Composition  of  the  Brain. — The  most  exact"  analyses  of  the  brain  thai 
we  possess  are  those  by  Lassaigne.  The  differently  coloured  portions 
differ  essentially  in  their  nature,  as  he  found  in  100  parts,    • 


d72  composition   of    the    bones. 


Medullary  Cortical 

Substance.  Substance, 

Albumen 99    .    .    7-5 

Colourless  fat 13-9    .    .    1-0 

Red  fat 09    .     .    3-7 

Ozmazome  and  organic  salts    ,  1-0    ..    1-4: 

Phosphates 1-3    ..    1-2 

Water 730..  852 


10000. 


Lion. 

Sheep. 

950 

800 

2-5 

19-3 

2-5 

0-7 

The  nerves  or  spinal  marrow  have  not  been  specially  analyzed. 

Composition  of  the  Bones. — Miiller  has  found  that,  prior  to  ossification, 
the  cartilage  of  the  bones  is  in  that  condition  which  yields  chondrine,  al- 
though it  is  afterward  totally  changed  into  the  gelatine  cartilage.  In 
the  vertebrated  animals  with  osseous  skeletons,  the  earthy  material,  in 
all  cases,  consists  principally  of  phosphate  of  lime  with  some  phosphate 
of  magnesia,  carbonates  of  lime  and  soda,  and  fluoride  of  calcium.  By 
digesting  a  bone  in  dilute  muriatic  acid,  all  of  thes#  inorganic  salts  are 
removed,  and  the  cartilage  remains,  preserving  perfectly  the  form  of  the 
bone.  By  burning  the  bone  in  a  moderate  current  of  air,  all  animal  mat- 
ter may  be  consumed,  and  the  earthy  material  then  remains  in  the  form 
of  the  bone,  and  perfectly  white  ;  100  parts  of  burned  bone  of  the  follow- 
ing animals  have  been  found  to  contain, 

Human  Bone.    Beef  Bone. 

Phosphate  of  lime  and  fluoride  )  og.j^  qo-70 

of  calcium J  cso  i 

Carbonate  of  lime  .    ....    103  2-16 

Carbonate  of  magnesia   ...      03  110). 

Carbonate  of  soda 30  5*74 ) 

But  these  proportions  vary  in  the  bones  of  different  individuals  of  the 
same  kind  of  animal. 

The  quantity  of  animal  matter  in  the  bones  varies  in  different  classes 
of  animals.  In  the  mammalia  it  is  generally  about  thirty-three  pei 
cent.  Thus  human  and  ox  bones,  deprived  of  their  marrow  and  perioa 
team,  and  dried  until  they  ceased  to  lose  weight,  gave  Berzelius, 

Human  Bone.      Beef  Bone. 

Cartilage  soluble  in  water    .    .    32- 17  )  33  30 

Vessels 1-13  ) 

Phosphate  of  lime  and  fluoride  >  m.qa  57-45 

of  calcium 5 

Carbonate  of  lime 11-30  3-85 

Phosphate  of  magnesia    .     .    .      1-16  285 

Soda  and  a  little  common  salt  .      1-20  3-45 

The  teeth  present,  in  their  constitution,  the  closest  analogy  to  boh<; 
The  principal  and  organized  substance  of  the  teeth  is  indeed  true  bone, 
containing,  however,  less  cartilage  (twenty-nine  per  cent.)  and  more 
phosphate  of  lime  (sixty-four  per  cent.)  than  the  other  bones.  The 
enamel,  which  is  an  inorganic  secretion  from  the  upper  surface  of  the 
bony  tooth,  is  almo&t  destitute  of  any  animal  matter,  the  analyses  of  Ber- 
zelius giving, 

Human  Enamel.    Beef  Enamel. 

Phosphate  of  lime  and  fluoride  of)  oq.r  o^.q' 

calcium ) 

Carbonate  of  lime 8-0         7-1 

Phosphate  of  magnesia  ....       15         3-0 

Soda "  1-4 

Animal  matter  and  water  ...       2-0         3-5  ^ 

The  proportion  of  fluoride  of  calcium  is  greater  in  enamel  than  in  com- 
mon bone,  and  the  animal  membrane  appears  to  belong  only  to  the  con- 
nexion of  the  enamel  with  the  subjacent  bony  tissue  of  the  tooth.     The 


100-00. 


Uoooo. 


BLOOD  C  O  A  G  U  L  U  M. S  E  R  U  M.  673 

exterior  crusla  petrosa  of  the  teeth,  which^exists  most  developed  in  her- 
biferous  animals,  has  the  same  composition  as  bone. 

In  the  invertebrate  animals,  the  internal  skeleton  is  replaced  by  an  ex- 
ternal  shell,  which  contains  cartilage,  with  earthy  salts,  similar  to  those 
of  proper  bone,  but  in  different  proportions,  the  carbonate  of  lime  prepon- 
derating. Thus  the  shells  of  crabs  and  lobsters  contain  from' fifty  to 
sixty  per  cent,  of  carbonate,  and  but  from  three  to  six  of  phosphate  of 
lime,  the  rest  being  animal  matter.  Oyster-shells  contain  but  a  trace  of 
animal  matter,  being  almost  pure  carbonate  of  lime ;  and  the  sul)stance 
termed  cuttle-fish  bone  has  the  same  composition  nearly  as  crab-shells. 

SECTION  11. 

OF    THE    COMPOSITION    OF   THE    BLOOD,  AND   THE   PHENOMENA    OF    RESPI- 
RATION. 

Blood  is,  in  the  higher  classes  of  animals,  an  opaque,  thick,  red  fluid ; 
its  specific  gravity  about  1*055  ;  it  has  a  salty  and  nauseous  taste,  and  a 
peculiar  smell,  resembling  that  of  the  animal  whence  it  had  been  derived. 

When  the  blood  of  any  red-blooded  animal  is  allowed  to  rest,  it  grad- 
ually  forms  a  soft  jelly,  from  which,  after  some  time,  a  thin  yellowish  fluid 
(serum)  separates,  while  the  red  jelly  or  coagulum  contracts  in  volume, 
and  acquires  greater  consistence.  If  this  coagulation  of  the  blood  takes 
place  slowly,  the  upper  portion  of  the  coagulum  becomes  white  or  pale 
yellow,  forming  thus  the  bvffy  coat.  There  is  no  doubt  that  the  blood, 
while  in  connexion  with  the  animal,  participates  in  its  life,  and  the  phe- 
nomena of  coagulation  are  to  be  referred  to  a  new  arrangement  of  its 
materials  consequent  on  the  loss  of  that  vitality. 

The  serum  of  the  blood,  when  coagulation  has  been  perfect,  is  of  a  yel- 
lowish,  sometimes  greenish  colour  ;  its  taste  is  dull  and  salty ;  its  spe- 
cific gravity  about  1*028;  it  is  thick-fluid,  like  olive  oil ;  when  heated  to 
140°,  it  coagulates. 

If  we  examine  under  the  microscope  the  appearance  presented  by 
blood,  we  find  that  it  consists  of  a  great  number  of  minute  red  particles 
swimming  in  a  nearly  colourless  liquor.  These  red  particles  are  flatten- 
ed  disks,  in  man  and  the  mammalia  round,  in  other  animals  elliptical. 
Their  size  is  variable,  being  in  man  from  ^^Vo^^  ^^  ? oVo^^^  ^^  ^"  ^'^^^^  ^"^ 
diameter,  but  larger  in  most  other  animals.  In  the  frog  they  are  about 
rrVe^h.  They  consist  of  a  central  colourless  nodule,  and  an  investing 
ring,  which  is  coloured  red  by  a  material  [Hematosine],  which  may  be 
dissolved  out  without  the  constitution  of  the  globule  being  otherwise  es- 
sentially altered. 

The  blood  contains  a  large  quantity  of  albumen^  partly  dissolved,  and 
remaining  in  the  serum  after  coagulation,  partly  in  a  solid  state,  forming 
the  great  mass  of  the  globules.  In  the  living  body  the  blood  contains 
also  fibrhie  in  solution,  but  this  separates  soon  after  extraction  from  the 
body  ;  it  assumes  a  solid  form,  and  investing,  as  a  sponge,  the  red  glob- 
ules, forms  with  them  the  coagulum.  The  fibrine  is  thus  the  element 
active  in  the  coagulation  of  the  blood,  the  globules  being  but  passively 
engaged  in  it.  In  addition  to  these  essential  organic  elements,  the  blood 
contains  a  variety  of  salts,  as  common  salt,  phosphates  of  magnesia,  am- 
monia,  and  lime,  lactates  of  soda  and  magnesia.  The  best  analyses  of 
the  blood  are  those  by  Lecanu,  and  the  results  for  blood  and  serum  are, 
that  they  contain, 

4Q 


674 


S  E  R  O  L  I  N  E. H  EMATOSINE. 


Blood  or  Man.  Serum  of  Mas. 

BJood  globules 1330 

Fibrine -21 

Albumen    .    ». C'5l  8-12 

Fatty  substances     . '37  -34 

Extractive  matters -30  -40 

Alkaline  salts -84  -75 

Earthy  salts -21  -OD 

Water 7802  9010 

Loss      . ;24        -14 

10000  100-00 

He  found  these  proportions  liable  to  fluctuation,  and  to  vary  according 
to  the  sex.  The  maxima  and  minima  of  each  constituent  which  he  found 
for  the  human  subject  of  each  sex  were, 


Constitnents. 

Male.            1           Female. 

Max. 

Mm.    j    Max. 

Mm. 

Water     .... 

80-5 

733  184-84 

75  00 

Albumen.     .     .     . 

6-3 

4-85|  68 

500 

Globules  .... 

18-6 

1105  1671 

714 

Fibrme    .... 

•4 

•20j     -31 

•20 

The  fatty  substance  of  the  blood  is  a  mixture  of  chqiesterine  with  stearic 
and  oleic  acids,  and  a  peculiar  fatty  substance,  termed  Seroline,  the  history 
of  which  is  yet  incomplete,  and  which  differs  from  cholesterine  most  in 
containing  nitrogen.  None  of  the  phosphuretted  fats  of  the  brain  appear 
to  exist  in  blood. 

The  chemical  history  of  fibrine  and  albumen  having  been  already  given, 
it  remains  only  to  describe  the  peculiar  colouring  matter,  for  the  most 
accurate  knowledge  we  possess  concerning  which  we  are  indebted  to 
Lecanu's  elaborate  researches  on  the  blood.  His  method  of  preparing 
hematosine  is  as  follows  : 

Blood,  which  has  been  freed  from  fibrine  by  beating  with  a  twig,  is  to 
be  mixed,  with  continual  agitation,  with  sulphuric  acid  diluted  with  its 
own  weight  of  water,  until  the  whole  mass  solidifies  to  a  brown  pulp, 
from  which  the  acid  liquor  is  to  be  then  drained  off  on  filtering  paper, 
and  the  last  portions  removed  by  washing  with  alcohol.  The  mass  thus 
obtained,  which  is  a  mixture  of  sulphates  of  albumen  and  of  hematosine, 
is  to  be  boiled  in  successive  portions  of  alcohol  as  long  as  this  becomes 
brown.  The  liquors,  being  filtered  when  cold,  are  to  be  neutralized  by 
ammonia,  by  which  albumen  and  much  sulphate  of  ammonia  are  precip- 
itated, while  a  compound  of  hematosine  and  ammonia  remains  dissolved. 
This  solution  is  to  be  then  evaporated  in  a  wateV-bath  to  dryness,  and  the 
residue  washed  with  water,  alcohol,  and  ether,  to  remove  the  salts  and 
fatty  matters  which  were  contained  in  it.  Being  then  redissolved  in  al- 
cohol by  means  of  ammonia,  evaporated  to  dryness,  and  washed  again 
w'llh  water,  the  hematosine  remains  pure,  but  in  its  coagulated  form. 

It  is  a  dark  brown  mass,  tasteless  and  inodorous  ;  when  heated,  it  does 
not  melt,  but  swells  up  and  evolves  ammoniacal  products ;  it  is  insoluble 
in  water,  alcohol,  and  ether ;  it  forms  with  the  mineral  acids  compounds 
which  are  insoluble  in  water,  but  soluble  in  alcohol.  By  caustic  alkalies 
it  is  dissolved  with  a  blood-red  colour,  and  these  combinations  are  soluble 
in  water,  alcohol,  and  ether.  Hematosine  contains  neither  phosphorus 
nor  sulphur,  but  iron  in  large  quantity  (6-64  per  cent.).  By  Mulder's 
analysis,  the  fotmula  of  hematosine  is  C44H22N3  .  OgFe.  It  hence  has  no 
connexion  with  proteine  or  albumen.     The  state  in  which  the  iron  exists 


HEMATOSINE,     GLOBULIN  E,     ETC.  675 

in  hcmatosine  has  been,  even  up  to  the  present  day,  an  object  of  much 
discussion  among  chemists ;  but  with  the  knowledge  we  now  possess  of 
hematosine  in  its  pure  form,  we  must  consider  the  iron  to  be  an  integral 
part  of  its  organic  constitution,  as  sulphur  is  in  albumen,  or  arsenic  in 
alkarsine ;  and  the  opinion  of  its  being  oxidized,  and  combined  with  the 
true  organic  element  as  a  kind  of  salt,  can  no  longer  be  supported.  If  j^ 
solution  of  hematosine  be  acted  on  by  chlorine  gas,  a  white  flocculent 
precipitate  is  produced,  and  the  solution  contains  chloride  of  iron. 

Although  hematosine  is  the  colouring  material  of  the  globules  of  the 
blood,  it  is  present  but  in  very  small  quantity ;  100  parts  of  dried  glob- 
ules containing  but  from  four  to  five  of  pure  hematosine.  In  the  blood 
globule,  the  hematosine  is  in  its  uncoagulated  state,  and  possesses  prop- 
erties somewhat  different  from  those  of  its  coagulated  form,  as  prepared 
by  the  process  above  given.  A  solution  of  the  coloured  blood  globules 
in  water,  when  exposed  to  the  air,  becomes  of  a  brighter  red  colour,  be- 
ing thus  partially  arterialized.  When  evaporated  at  a  temperature  of 
120°,  it  gives  a  dark  red  mass,  which  is  completely  soluble  in  cold  water. 
Its  solution  coagulates  at  155°,  leaving  the  liquor  clear  yellow.  It  is  co- 
agulated also  by  alcohol  and  by  acids.  The  hematosine  then  passes  into 
the  insoluble  condition  already  described. 

I  have  hitherto  spoken  of  the  colourless  ingredient  in  the  blood  glob- 
ules  as  being  albumen,  with  which,  indeed,  it  is  almost  identical  in  proper- 
ties, but  still  differs  in  some  points.  It  has  been  termed  Glohuline,  In 
its  uncoagulated  condition  it  cannot  be  separated  from  hematosine,  and 
is  there  distinguished  from  albumen  principally  by  being  insoluble  even 
in  a  very  dilute  saline  solution,  which  dissolves  albumen  readily.  It  ia 
hence  that  the  globules  swim  unaltered  in  the  serum  of  the  blood,  but  arc 
readily  dissolved  by  pure  water.  On  this  principle  is  founded  a  method 
of  is'jjciting  the  blood  globules.  If  the  blood,  when  extracted  from  the 
vein,  be  received  in  a  vessel  containing  a  solution  of  Glauber's  salt,  coag- 
ulation is  prevented,  as  the  fibrine  remains  dissolved,  and  by  filtering  the 
liquor  so  obtained,  the  serum  and  water  pass  off,  and  the  globules  remain 
mixed  only  with  a  little  of  the  salt.  The  globuline  cannot,  however,  be 
separated  from  the  hematosine  except  by  acids,  which,  as  described  in 
the  preparation  of  hematosine,  then  combine  with  the  globuline.  Mulder 
found  the  organic  element  in  the  sulphate  of  globuline  to  have  the  com- 
position  of  prote'ine  (see  p.  666). 

Alteration  of  the  Blood  in  Disease. — The  examination  of  the  state  of 
the  blood  in  disease,  although  presenting  important  relations  to  patholo- 
gy and  to  practice,  has  been  hitherto  conducted  in  a  manner  too  discon- 
nected and  superficial  to  afford  satisfactory  results.  This  branch  of 
chemical  pathology  has,  however,  been  taken  up  by  the  illustrious  An- 
dral,  who,  in  conjunction  with  M.  Gavaret,  has  published  the  results  of 
the  analysis  of  the  blood  in  360  cases  of  disease,  in  a  memoir,  from  whose 
publication  may  be  dated  the  commencement  of  a  true  pathology  of  this 
fluid. 

In  the  method  whicl^  by  the  advice  of  Dumas,  they  adopted,  the' quan- 
tity of  fibrine,  of  globules,  of  the  solid  materials  of  the  serum  (which  may 
be  considered  as  albumen),  and  the  quantity  of  water  in  each  specimen 
of  blood,  were  determined.  The  pure  hematosine  was  not  isolated,  and 
the  salts  were  considered  as  sufficiently  important  to  necessitate  their 
separation  only  in  certain  cases.     As  a  point  of  comparison,  they  assume 


676      ALTERATION     OF     THE     BLOOD     IN     DISEASE. 

as  the  standard  of  healthy  blood,  that  1000  parts  contain  790  of  water, 
127  of  globules,  three  of  fibrine,  and  eighty  of  solid  constituents  of  the 
serum,  of  whicii  eight  are  inorganic  ;  which  numbers  almost  coincide  with 
Lecanu's  analysis,  as  already  given.  Their  researches  have  enabled 
them  to  recognise  four  classes  of  diseases  in  which  the  composition  of 
the  blood  is  essentially  altered,  though  in  different  ways. 

The  first  class  presents  as  a  constant  alteration  an  increase  in  the 
quantity  of  jibrine ;  it  includes  diseases  remarkably  different  in  their  lo. 
cality  and  form,  but  all  belonging  to  the  class  of  acute  inflammations. 
In  some  cases  of  morbid  deposition,  as  in  tubercle  and  cancer,  a  similar 
increase  in  the  quantity  of  fibrine  is  found,  but  it  may  be  doubted  wheth. 
er  it  be  due  to  the  abnormal  growth,  or  to  the  inflammatory  action  which 
accompanies  it. 

In  the  second  class,  the  fibrine  remains  stationary,  or  even  diminishes 
in  quantity,  while  the  globules  increase  in  proportion  to  the  fibrine.  The 
diseases  which  belong  to  this  class  are  continued  fevers  without  local 
inflammation,  and  some  form  oi  cerebral  haemorrhages. 

In  the  third  class,  the  fibrine  remaining  unchanged,  there  is  a  remark- 
able diminution  in  the  quantity  of  the  globules  ;  of  these  diseases  chlorosis 
may  be  taken  as  the  example  ;  and  in  the  fourth  class,  it  is  no  longer 
the  fibrine  or  globules  which  are  the  subject  of  the  morbid  change,  but 
the  quantity  of  albumen  in  the  serum  is  diminished.  Of  this  class  of  af- 
fections Brighi's  disease  is  the  type. 

Without  entering  into  the  details  of  these  researches,  which  are  ex- 
cluded by  the  limited  extent  of  this  work,  I  shall  merely  present  in  the 
following  table  an  example  of  the  constitution  of  blood  in  each  of  these 
classes  of  morbid  alteration. 


Const  iiuems. 

Heallh. 

1st  CUs-. 

2d  Class. 

3d  Class. 

4!h  Class. 

Fibrine     .... 

3 

7 

2 

3 

3 

Globules  .... 

127 

125 

136 

47 

82 

Albumen      .     .     . 

72 

78 

69 

75 

58 

Salts 

8 

7 

7 

8 

7 

Water     .... 

790 

783 

786 

867 

850 

The  appearance  of  albumen  in  the  urine  in  Bright's  disease  is  evident- 
ly connected  with  its  diminution  in  the  serum.  The  oily  materials  which 
are  usually  found  in  the  blood,  and  the  remarkable  diminution  which  oc- 
curs,  not  so  much  in  the  globules  as  in  the  hematosine,  had  not  attracted 
Andral's  attention  in  the  memoir  now  described.  These  oily  substances 
are  of  the  same  nature  as  the  proper  fatly  matters  of  the  blood,  but  pres- 
ent in  excessive  quantity. 

It  has  been  observed  that  in  cholera  the  blood  becomes  so  thick  as  to 
arrest  the  circulation,  and  contains  from  thirty  to  forty-five  per  cent,  of 
solid  matter  ;  it  is  then,  also,  less  strongly  alkaline  than  healthy  blood. 
This  is  connected  probably  with  the  matters  vomited  and  evacuated, 
which  are  strongly  alkaline,  and  contain  a  quantity  of  albumen. 

The  blood  has  been  found  occasionally,  in  cases  of  diabetes  melUtuSj 
to  contain  traces  of  sugar;  the  great  discordance  of  the  results  obtained 
may  perhaps  result  from  the  sugar  being  contained  in  the  blood  only  for 
a  short  time  after  meals,  and  then  being  rapidly  evacuated  by  tlte  kid- 
neys. In  jaundice  the  green  colouring  matter  of  the  bile  has  been  ob- 
served in  the  serum  of  the  blood.  Other  observations  of  morbid  constit- 
uents of  the  blood  are  too  indefinite  to  justify  me  in  occupying  spac<» 


PHENOMENA     OF     RESPIRATION.  677 

with  them.  The  observation  of  Barruel,  that,  by  heating  the  blood  of 
any  animal  with  a  little  oil  of  vitriol,  the  odour  of  the  animal  is  so  pow- 
erfully evolved  as  to  be  easily  recognised,  appears  well  founded,  and  may 
be  useful  in  medico-legal  questions,  where,  however,  it  should  be  em- 
ployed with  exceeding  circumspection. 

Of  Respiration, — in  the  living  body,  the  blood  in  the  veins  and  arter- 
ies is  well  known  to  differ  remarkably  in  colour,  in  the  former  being  of 
a  dark  purple  red,  and  in  the  latter  of  a  bright  vermilion  colour.  The 
change  from  the  venous  to  the  arterial  state  is  effected  during  the  pas- 
sage of  the  blood  through  the  capillary  vessels  of  the  lungs,  where  it  is 
exposed  to  the  action  of  an  extensive  surface  of  atmospheric  air,  while 
the  arterial  blood,  in  traversing  the  general  capillary  system  of  the  body, 
assumes  the  dark  red  condition  in  which  it  is  returned  to  the  heart  by 
the  veins.  Even  out  of  the  body,  this  change  of  colour  is  produced 
when  venous  blood  is  exposed  to  the  air,  especially  if  agitated  therewith, 
and  still  more  with  pure  oxygen  ;  even  the  globules,  when  separated 
from  the  serum  and  dissolved  in  water,  become  brighter  in  colour,  and 
partially  arterialized  by  exposure  to  the  air.  Yet,  although  the  vital 
properties  of  the  blood  depend  essentially  upon  this  change  of  colour,  we 
are  not  yet  able  to  connect  it  with  any  alteration  in  the  composition  of 
the  constituents  of  the  blood,  or  even  in  their  relative  proportions.  Ar- 
terial  and  venous  blood  contain  sensibly  the  same  quantity  of  water, 
fibrine,  globules,  albumen,  and  salts  ;  and,  by  analysis,  the  composition  of 
these  bodies  is  found  to  be  identical,  no  matter  what  kind  of  blood  they 
are  derived  from.  To  trace  the  difference  of  nature  between  arterial 
and  venous  blood,  it  is  therefore  necessary  to  study  it  under  other  points 
of  view  than  its  proximate  or  elementary  composition,  so  far  as  we  have 
yet  examined  it. 

The  air  which  has  been  employed  in  respiration  is  found  to  have  un- 
dergone an  important  change  of  constitution  ;  its  volume  is  but  slightly, 
if  at  all,  altered  ;  but  a  quantity  of  oxygen  has  disappeared,  and  is  re- 
placed by  carbonic  acid,  in  generally  an  equal  volume.  Air  which  has 
been  once  respired  is  found  to  contain  from  three  to  four  per  cent,  of 
carbonic  acid  ;  and  if  the  same  quantity  of  air  be  continually  breathed, 
the  animal  dies,  with  all  symptoms  of  narcotic  poisoning,  when  the  car- 
bonic acid  has  accumulated  to  from  eight  to  ten  per  cent.  The  action  of 
the  air  in  expiration  is  therefore  to  remove  carbon  from  the  blood.  The 
quantity  so  taken  from  the  system  in  twenty.four  hours  is  very  large, 
and  makes  up  the  principal  portion  of  that  element  which  we  take  in 
with  our  Ibod  ;  yet  such  is  the  activity  with  which  its  assimilation  pro- 
ceeds, that  no  perceptible  change  in  the  solid  elements  of  the  blood  can 
be  detected. 

It  was  at  one  time  a  much  disputed  point  whether  the  carbon  so  separ- 
ated from  the  system  was  directly  secreted  from  the  lungs,  and  burned 
off,  as  it  were,  by  contact  with  the  oxygen  of  the  air,  or  whether  the 
oxygen  was  first  absorbed  by  the  blood,  and  carried  by  the  circulation  to 
every  portion  of  the  body,  where  it  combined  with  the  carbon,  which 
was  there  present  in  excess,  and  the  carbonic  acid  so  produced,  being 
dissolved  by  the  venous  blood,  was  thrown  off,  on  arriving  at  the  surface 
of  the  atmosphere,  in  the  lungs.  The  progress  of  science  has,  however, 
finally  decided  in  favour  of  the  latter  view,  to  which  the  fullest  confirma- 
tion has  been  given  by  the  careful  and  elaborate  experiments  of  Magnus. 


678  THEORY     OF     RESPIRATION. 

He  found  that  both  arterial  and  venous  blood  hold  dissolved  quantities 
of  gases,  oxygen,  nitrogen,  and  carbonic  acid,  which  amount  to  from  one 
tenth  to  one  twentieth  of  the  volume  of  the  blood.  The  proportions  of 
these  gases  to  each  other  are  different  in  arterial  and  venous  blood  j  the 
oxygen  in  arterial  blood  being  about  one  half  of  the  carbonic  acid,  while 
in  the  venous  blood  it  seldom  amounts  to  more  than  one  fifth.  The  dif- 
ference is  greatest  in  young  animals,  and  probably  is  proportional  to 
their  activity  of  nutrition.  The  quantity  of  nitrogen  appears  to  be  the 
same  in  both  kinds  of  blood,  making  from  one  fifth  to  one  tenth  of  the 
gaseous  mixture. 

The  physico-chemical  conditions  of  respiration  are  simply  explicable 
upon  these  results.  By  the  principle  of  gaseous  diffusion  (p.  267),  the 
fine  lining  pulmonary  membrane  being  permeable  to  gases  when  the 
venous  blood  arrives  at  the  surface  of  the  lungs,  a  portion  of  the  car- 
bonic acid  which  it  contains  is  evolved,  and  a  quantity  of  oxygen  gas  ab- 
sorbed in  place  of  it.  These  two  quantities  are  not  necessarily  equal  at 
each  moment,  though  ultimately  they  become  so,  and  hence  the  volume 
of  oxygen  absorbed  is  generally,  though  not  universally,  equal  to  that  of 
the  carbonic  acid  given  out.  There  appears,  from  the  presence  of  ni. 
trogen  in  equal  quantity  in  both  kinds  of  blood,  to  be  an  absorption  and 
evolution  of  that  gas,  simply  from  physical  laws,  and  independent  of  any 
direct  application  of  it  to  the  nutrition  of  the  animal;  hence  the  volume 
of  nitrogen  in  air  is  sometimes  increased,  and  at  others  diminished,  by 
respiration,  and  an  animal  evolves  much  nitrogen  when  respiring  an  ar. 
tificial  atmosphere  of  oxygen  and  hydrogen,  while  Bousingault  has 
shown  the  rate  of  nutrition  of  an  animal  to  be  proportional  to  the  quan- 
tity of  nitrogen  it  receives  as  food,  and  that  none  of  that  principle  is 
really  assimilated  from  the  air. 

It  is  still  not  by  any  means  easy  to  decide  upon  the  cause  of  the  change 
of  colour  which  occurs  in  the  blood  during  respiration;  for  this  should 
appear  connected,  not  merely  with  the  presence  of  certain  gases  in  the 
blood,  but  upon  a  true  change  in  the  constitution  of  the  hematosine,  which 
analysis  cannot  direct.  Stevens  first  directed  attention  to  the  remarka- 
ble influence  which  saline  bodies  have  upon  the  colour  of  the  blood.  If 
dark  venous  blood  be  put  in  contact  with  a  solution  of  common  salt, 
Glauber's  salt,  nitre,  or  carbonate  of  soda,  it  becomes  as  vermilion-col- 
oured as  if  it  had  been  truly  arterialized.  On  the  contrary,  the  presence 
of  carbonic  acid  impedes  this  action,  and  gives  to  blood,  so  reddened  by 
a  salt  not  in  excess,  the  dark  tint  of  venous  blood.  If  we  consider,  there- 
fore, the  arterial  tint  to  be  due  to  the  natural  combination  of  the  colour- 
ing matter  with  the  saline  constituents  of  the  serum,  this  will  be  darken- 
ed when,  by  passing  through  the  capillary  system,  the  blood  takes  up  an 
excess  of  carbonic  acid  ;  and  again,  in  the  lungs,  when  the  carbonic  acid 
is  replaced  by  oxygen,  the  vermilion  colour  is  restored,  not  by  any  active 
agency  of  the  oxygen,  but  by  the  natural  tint  of  saline  hematosine  be- 
coming evident.  Although  this  theory  of  the  change  of  colour  is  by  no 
means  free  from  objections,  it  appears  to  me  to  be  better  founded  than 
any  other  that  has  been  proposed. 

Animal  Heat. — The  phenomena  of  respiration  consisting  mainly  in 
the  conversion  of  carbon  into  carbonic  acid  by  union  with  oxygen,  the 
heat  which  is  developed  in  the  body  of  all  red-blooded  animals  has  been 
naturally  referred  to  that  source  ;  and  as  we  know  that  the  change 


MUCUS. GASTRIC     JUICE.  679 

from  the  arterial  to  the  venous  condition  of  the  blood  occurs  at  every 
point  of  the  system,  the  ahuost  complete  equality  of  temperature  through- 
out the  body  in  health  is  explained.  That  the  great  source  of  heat 
is  the  respiratory  process,  is  abundantly  proved  by  the  temperature  be- 
ing highest  in  those  animals,  and  in  the  same  animal  at  those  periods 
4Hien  The  circulation  is  most  rapid,  and  the  quantity  of  air  consumed  the 
greatest ;  but  it  has  been  calculated  that  the  heat  evolved  by  thecombus. 
tion  of  the  quantity  of  carbon  thrown  off  from  the  body  in  twenty-four 
hours  is  not  more  than  eight  tenths  of  the  quantity  generated  in  the  body 
during  that  time,  and  the  origin  of  the  remainder  must  be  found  in  the 
action  of  the  muscles  and  in  the  nervous  power,  which  appears  of  itself 
to  be  a  distinct  source  of  animal  heat. 

SECTION  III. 

COMPOSITION    OF   THE    DIGESTIVE    ORGANS   AND   OF   THEIR   SECRETIONS. 
CHEMICAL    PHENOMENA    OF    DIGESTION. 

Mucus. — The  lining  membrane  of  the  alimentary  canal  is  moistened 
with  a  liquid  possessing  many  characters  of  the  vegetable  mucus  (traga- 
canthine,  p.  530),but  containing  nitrogen.  It  is  a  thick  tenacious  sub- 
stance, which  contains,  dissolved  in  the  water  through  which  it  is  diffused, 
the  ordinary  salts  of  the  serum  of  the  blood  ;  it  swells  up  with  water  to 
a  considerable  mass,  but  without  dissolving ;  it  dissolves  in  alkaline  li- 
quors, and  is  precipitated  therefrom  on  the  addition  of  an  acid  and  by 
tincture  of  galls  ;  the  mucus  from  different  parts  of  the  mucous  membrane 
is,  however,  by  no  means  identical  in  properties. 

The  liquid  secreted  by  the  internal  surface  of  the  stomach,  the  Gasinc 
Juice,  which  exercises  an  important  influence  on  digestion,  differs  essen- 
tially in  its  characters  from  mucus.  When  the  stomach  is  empty  and 
contracted,  it  contains  only  ordinary  mucus  ;  but  if  even  indigestible  sub- 
stances  be  introduced,  and  still  more  after  taking  proper  food,  a  liquid  is 
abundantly  poured  out,  which  is  colourless  or  very  pale  yellow,  and  con- 
tains a  very  small  quantity  of  solid  matter  (two  per  cent.),  which  consists 
principally  of  inorganic  salts  (common  salt  and  sal  ammoniac,  with  a 
trace  of  a  salt  of  iron) ;  it  "s  specially  characterized  by  the  presence  of  a 
notable  quantity  of  free  muriatic  acid,  the  proportions  of  which  appear  to 
vary  with  the  activity  of  the  digestive  powers  at  the  time.  This  gastric 
juice  possesses  the  remarkable  property  of  softening  down  and  dissolving 
fibrine  and  albumen,  and  thus  converts  the  masses  of  food  into  the  uni- 
form pulp  [Chyme),  from  which  the  absorbing  vessels  of  the  small  intes- 
tines take  up  the  nutritious  elements. 

If  we  form  an  artificial  gastric  juice  by  mixing  together  the  muriatic 
acid  and  salts  in  the  proper  proportions,  it  is  found  to  be  totally  incapa- 
ble of  dissolving  the  materials  of  the  food,  and,  indeed,  to  be  quite  inac- 
tive towards  digestion.  The  organic  material  of  the  gastric  juice,  al- 
though its  quantity  be  so  minute,  is  therefore  essential  to  its  powers,  and 
these  may  be  perfectly  conferred  upon  the  previously  inactive  artificial 
juice  by  the  addition  of  a  little  of  the  mucus  of  the  stomach,  or  by  steeping 
in  the  acid  liquor,  for  a  short  time,  a  small  portion  of  a  mucous  membrane, 
and  filtering  the  liquor.  For  this  purpose  it  is  not  even  necessary  to  use 
the  mucous  membrane  of  the  stomach,  for  that  of  the  bladder  has  been  found 
to  act  equally  well.  The  substance  which  is  dissolved  out  of  the  membrane 
ia  these  cases  has  been  termed  Pepsine.     It  has  not  been  obtained  in  a 


680  PEPSIN  E,     SALIVA,    ETC. 

truly  isolated  or  pure  form,  but  its  properties  are  very  remarkable.  For 
«  its  full  activity  it  requires  the  presence  of  a  free  acid,  as  the  artificial  gas- 
tric juice  becomes  much  less  active  in  dissolving  food,  when  neutralized  by 
an  alkali,  though  it  retains  other  properties,  as  that  of  coagulating  milk  like 
rennet.  If  the  artificial  gastric  juice  be  precipitated  by  acetate  of  lead, 
the  precipitate  washed,  and  then  decomposed  by  sulphuret  of  hydrogen, 
the  solution  thus  obtained  possesses  all  the  digestive  powers  of  the  juice. 
Hence  the  pepsine  and  muriatic  acid  act  together  in  combining  with  oxide 
of  lead.  The  process  given  by  Schwann  for  preparing  the  best  artificial 
gastric  juice,  is  to  mix  water  with  2^  per  cent,  of  muriatic  acid,  of  spe- 
cific gravity  1*13,  and  digest  therein  the  mucous  membrane  of  a  stomach 
for  twenty-four  hours,  then  to  filter. 

Pepsine  appears  to  be  completely  decomposed  by  contact  with  alcohol, 
or  by  the  heat  of  boiling  water.  Its  powers  are  desti'oyed,  also,  by  de- 
oxidizing substances.  The  solution  of  albumen  and  fibrine  in  gastric 
juice  is  essentially  different  from  their  solution  in  muriatic  acid,  as  in  the 
former  case  the  quantity  of  acid  is  very  minute  in  relation  to  the  quantity 
of  material  dissolved,  and  after  solution  the  acid  still  remains  quite  un- 
combincd. 

Fremy  has  discovered  that  the  peculiar  fermentative  process,  which 
sometimes  spoils  the  manufacture  of  sugar,  and  which  I  have  described 
(p.  536)  as  the  mucous  fermentation,  is  capable  of  being  induced  by  con- 
tact with  mucous  membrane  (by  pepsine?).  He  has  found  that  sugar  of 
milk  may  thus  be  converted  to  an  unlimited  extent  into  lactic  acid,  no 
other  product  appearing.  The  vegetable  ferments  are  able  to  produce 
the  same  effect,  but  in  a  different  stage  of  decomposition  from  that  in 
which  they  induce  the  saccharine  or  alcoholic  fermentations. 

The  action  of  the  stomach  in  digestion  appears,  therefore,  to  be,  so  far 
as  our  actual  knowledge  extends,  a  purely  catalytic  fermentative  action; 
one  in  which  the  active  excitant  is  an  organic  substance  {Pepsine)  secre- 
ted by  the  mucous  surface,  and  whose  properties  are  developed  by  the 
presence  of  muriatic  acid,  which  is  secreted  at  the  same  time.  The  new 
products  into  which  the  food,  fibrine,  albumen,  gluten,  starch,  oils,  sugar, 
<Sz;c.,  are  converted,  and  which  collectively  constitute  the  white  uniform 
pulp  termed  by  physiologists  Chyme,  have  not  been  made  the  subject  of 
accurate  chemical  research. 

In  the  mouth  the  mass  of  nutritive  material  is  acted  on  by  a  liquid 
which  is  secreted  by  the  salivary  glands,  the  Saliva,  It  is  alkaline,  and 
holds  in  solution  not  one  per  cent,  of  solid  matter,  which  contains  some 
carbonate  of  soda  and  common  salt,  admixed  mucus,  a  trace  of  sulphocy- 
anid?  of  potassium,  and  a  peculiar  organic  body  termed  by  Tiedemann 
and  3melin  Salivary  Matter.  This  last  substance  is  soluble  in  water; 
its  solution  is  not  coagulated  by  heat,  nor  precipitated  by  tincture  of  galls, 
corrosive  sublimate,  acetate  of  lead,  nor  by  acids.  The  pancreas,  though 
so  similar  in  structure  to  the  salivary  glands,  has  a  different  secretion  ; 
it  contains  no  salivary  matter,  nor  any  sulphocyanide  of  potassium,  but 
albumen  and  some  salts ;  it  is  generally  slightly  acid. 

Composition  of  the  Bile. — The  precise  part  which  this  remarkable  se- 
cretion performs  in  the  animal  economy  is  not  yet  fully  known.  It 
has  been  the  subject  of  repeated  and  accurate  chemical  examination, 
although,  from  the  facility  with  which  its  elements  are  transformed  into 
other  bodies,  by  the  action  of  the  reagents  employed,  every  succeeding 


ANALYSES     OF     THE     BILE.  681 

analysis  has  led  to  different  results.  I  shall  only  notice  the  late  researches 
of  Gmelin,  Demar9ay,  and  Berzelius. 

In  the  elaborate  work  on  digestion,  undertaken  in  conjunction  with 
Tiedemann,  Gmelin  analyzed  principally  the  bile  of  the  ox,  from  which, 
however,  as  far  as  observations  have  been  made,  human  bile  does  not 
appear  essentially  to  diifer.  He  obtained  from  it  a  volatile  body  having 
the  odour  of  musk,  cholesterine,  margaric  and  oleic  acids,  a  peculiar  acid, 
the  Chollc  Acid;  colouring  matters.  Biliary  Resin,  Biliary  Sugar,  TaU' 
rine,  a  glutinous  substance,  caseiim,  salivary  matter,  ozmazome,  and  a 
number  of  salts  of  organic  and  inorganic  acids.  Dema^^ay  looks  upon 
all  of  these  substances  as  being  produced  by  the  reactions  used,  and  de- 
nies that  any  of  them  really  exist  in  the  bile.  He  considers  the  bile  to 
be  a  soda-soap  of  a  peculiar  fatty  acid,  the  Chole'ic  Acid,  that  is,  a  Cho. 
ledte  of  Soda,  The  cholei'c  acid  is  obtained  by  dissolving  one  part  of  the 
alcoholic  extract  of  ox-gall  in  100  parts  of  water,  and  mixing  the  solution 
with  two  parts  of  sulphuric  acid  diluted  with  ten  of  water.  By  gradual 
evaporation  of  the  liquor,  oily  drops  separate.  It  is  to  be  then  cooled, 
and  these  drops,  which  are  common  fat,  removed.  On  then  standing  for 
eight  or  ten  hours,  the  choleic  acid  gradually  separates,  and,  being  digest- 
ed with  ether  to  remove  some  adhering  fat,  is  pure.  It  is  a  brittle  yel- 
low-white mass,  tastes  bitter,  softens  by  a  heat  of  250°,  but  does  not 
really  melt ;  it  is  slightly  soluble  in  water,  but  abundantly  in  alcohol  and 
ether.  It  forms,  with  bases,  salts  which  do  not  crystallize  ;  its  formula 
was  found  to  be  C42H36  .  N.0,2. 

When  the  alcoholic  extract  of  the  gall  is  boiled  for  a  long  time  in  con- 
tact with  an  excess  of  muriatic  acid,  the  choleic  acid  is  decomposed,  and 
the  most  remarkable  products  are  the  Taurine  of  Gmelin,  and  a  new  acid, 
the  Cholo'idic  Acid.  The  latter  is  a  fatty  acid,  not  volatile,  yellow,  of  a 
bitter  taste  ;  it  forms  a  soft  mass  with  warm  water,  but  without  dissolving ; 
it  dissolves  readily  in  alcohol  and  ether,  and  these  solutions  redden  lit- 
mus. By  Dumas's  analysis  the  formula  of  this  body  appears  to  be  C33 
H33O7.  It  does  not  contain  nitrogen^  The  Taurine,  which  remains  in 
the  acid  liquor  from  which  the  cholofdic  acid  separates,  is  obtained  by 
evaporation,  and  mixing  with  alcohol,  from  which  solution  it  crystallizes 
gradually  in  six-sided  prisms,  which  are  perfectly  neutral ;  it  fuses  and  is 
decomposed  by  a  strong  heat ;  it  dissolves  in  twelve  and  a  half  parts  of 
cold,  and  in  less  of  boiling  water,  but  requires  573  parts  of  spirit  of  wine 
for  solution :  it  is  scarcely  acted  on  even  by  the  strongest  acids,  and  is 
not  precipitated  by  any  metallic  salt;  its  formula  is  remarkable,  being 
C4H7 .  N.0,0,  including  the  elements  of  binoxalate  of  ammonia  and  2  Aq. 

If  the  bile  be  treated  with  an  excess  of  a  strong  alkali,  the  choleic  acid 
is  totally  broken  up  into  ammonia  and  the  Cholic  Acid  of  Gmelin.  It 
crystallizes  from  its  hot  aqueous  solution  in  delicate  silky  needles,  of  a 
brilliant  white  colour;  its  taste  is  at  once  acid  and  sweet;  by  heat  it  is 
melted  and  decomposed ;  it  is  very  slightly  soluble  in  water,  but  copious- 
ly in  alcohol ;  its  solutions  redden  litmus  ;  it  contains  no  azote  ;  its  for- 
mula being,  as  determined  by  Dumas,  C42H360,o. 

Demar^ay's  examination  of  the  bile  appears  thus  quite  satisfactory  in 
showing  that  the  cholic  acid  and  the  taurine  are  secondary  products,  and 
he  considered  the  other  substances  found  by  Gmelin  to  be  choleic  or  cho- 
loidic  acids  in  an  impure  form.  But  Berzelius,  who  has  been  occupied  in 
the  re-examination  of  the  subject,  has  decided  that  the  choleic  acid  of 

4R 


682  COLOURING     aiATTER     OF     THE     BILE. 

Demar9ay  is  really  the  body  which  is  impure,  being  a  mixture  of  the  true 
biliary  substance  {Bilin,  GmcWn's  Biliary  Sugar)  with  the  biliary  resins. 
He  found  that  when  the  alcoholic  extract  of  the  bile  is  mixed  with  sul- 
phuric acid,  no  precipitate  appears  for  a  considerable  time,  showing  that 
the  substance,  which  really  exists  in  the  bile  combined  with  soda,  is  conti- 
pletely  soluble  in  water,  and  it  is  only  by  its  gradual  change  that  the  pre- 
cipitate (choleic  acid)  occurs.  By  digesling  this  substance  with  ether, 
he  removed  from  it  a  resin,  which,  by  possessing  acid  properties,  and  by 
means  of  combination  with  barytes,  is  shown  to  be  a  mixture  of  two  dis- 
tinct acid  resins,  Fellic  Acid  and  Cholinic  Acid,  The  material  insolu. 
ble  in  ether  is  the  true  Bilin;  it  is  not  acid,  of  a  bitter  taste,  soluble  in 
alcohol  and  water  in  all  proportions,  but  insoluble  in  ether ;  when  heat- 
ed, it  becomes  soft,  and  burns  like  a  resin  ;  its  watery  solution  is  rapidly 
decomposed,  especially  if  warmed  ;  by  contact  with  acids  or  alkalies,  it 
is  immediately  changed  in  constitution  ;  the  substances  produced  are  dif- 
ferent, according  as  the  degree  of  alteration  is  more  or  less  advanced. 
Those  more  important  are  the  following  : 

The  Biliary  Matter^  which  is  the  state  in  which  the  greater  part  of  the 
bilin  exists  in  ordinary  hile,  being  the  first  product  of  its  decomposition, 
is  a  white,  bitter  substance,  which  has  a  marked  acid  reaction,  and  is  de- 
composed by  oxide  of  lead  into  bilin  and  Bilifellmic  Acid,  which  is  the 
choleic  acid  of  Demarcay.  The  formation  of  taurine  is  accomj)anied  by 
that  of  another  body,  Dyslysin,  which  is  a  colourless  resinous  substance, 
very  sparingly  poluble  in  water.  The  fellinic  and  cholinic  acid  have 
been  noticed  o.bove. 

When  the  bile  has  been  kept  for  a  long  time,  it  is  decomposed  by  a 
kind  of  fermentation,  and  two  acids  formed,  termed  the  Fellanic  and 
Cholam'c  Acids :  they  are  white  earthy  powders  sparingly  soluble  in  wa- 
ter ;  the  former  melts  only  far  above  212° ;  the  latter  is  very  easily  fu- 
sible. 

The  Colouring  Matter  of  the  Bile  is  present  during  health  in  but  small 
quantity,  but  in  disease  it  sometimes  accumulates  so  as  to  produce  solid 
masses.  When  pure,  it  is  a  reddish-yellow  powder,  which  is  scarcely 
soluble  in  water  or  in  alcohol,  but  dissolves  easily  in  solution  of  caustic 
potash.  This  solution  is  of  a  clear  yellow  colour,  but  when  exposed  to 
the  air  it  becomes  deep  green,  absorbing  oxygen.  This  change  is  re- 
markably produced  by  nitric  acid,  and  it  is  indeed  the  reaction  by  which 
the  presence  of  the  bile  in  the  serum  of  the  blood,  in  the  urine,  in  the  skin 
and  eyes,  &;c.,  may  be  shown  in  cases  of  jaundice.  If  too  much  nitric 
acid  be  not  added  at  once,  the  yellow  liquor  becomes  at  first  green,  then 
blue,  violet,  and  finally  red,  all  these  changes  occurring  in  a  few  seconds. 
After  a  moment  the  red  colour  also  "disappears,  the  solution  becomes  yel- 
low, and  the  colouring  matter  is  found  to  be  totally  decomposed.  The 
solution  of  the  colouring  matter  in  potash  is  precipitated  by  muriatic  acid 
in  deep  green  flocculi,  which  dissolve  in  nitric  acid  with  the  effect  al- 
ready noticed,  and  are  soluble  in  caustic  ammonia  and  potash,  with  a 
rich  emerald. green  colour.  These  reactions  show  that,  by  a  process  of 
oxidizement  from  the  original  yellow  substance,  green  and  red  materials 
may  be  generated,  in  which  forms  the  colouring  matter  exists  naturally 
in  various  animals,  according  as  their  bile  is  yellow,  green,  or  reddish, 
and  also  gives  rise  to  the  concretions  of  various  kinds  that  are  deposited 
in  disease.  The  most  common  kind  of  gallstone  consists,  however,  of 
cholesterine. 


NATURE  OF  CHYLE  AND  LYMPH.        683 

This,  yellow  malerial  Berzelius  names  BUifulvin.  He  considers  the 
greeiT''colouring  matter  present  in  healthy  bile  to  be  identical  with  chlo- 
rophyll (p.  62i). 

Tne  bile  contains  generally  about  nine  per  cent,  of  solid  matter ;  but  in 
the  present  state  of  our  knowledge  of  its  constituents,  it  is  evidently  im- 
possible  to  assign  the  numerical  proportions  in  which  they  exist. 

The  substance  found  in  the  bile,  and  termed  Erythrogen  by  Bizio,  is 
too  apocryphal  to  require  any  notice. 

The  examination  of  the  farther  processes  of  digestion  involves  consid- 
erations too  purely  physiological  to  be  entered  into. 

Chyle  and  Lymph. — The  nutritive  materials  extracted  from  the  food 
by  the  absorbing  vessels  of  the  intestine  is  thrown  into  the  thoracic  duct, 
where  it  meets  with  another  fluid,  which  is  transmitted  to  the  same  vessel 
from  all  parts  of  the  body  by  the  colourless  veins  or  lymphatics.  The 
fluid  from  the  intestines  is  termed  Chyle,  that  from  the  body  generally  is 
termed  Lymph.  It  is  the  mixture  of  these  that  alone  has  been  examined, 
for  the  vessels  which^  carry  either  separately  are  too  minute  to  allow  of 
the  extraction  of  their  contents  in  a  pure  form. 

When  taken  from  the  thoracic  duct  a  thw  hours  after  a  meal,  when, 
probably,  the  chylous  element  prevails,  it  is  a  whitish,  opaque  liquid  like 
milk,  with  generally  a  reddish  shade  ;  a  short  time  after  separation  from 
the  body  it  coagulates  ;  the  clot  is  at  first  pale,  but  it  soon  becomes  light 
cinnabar  red  ;  the  milkiness  of  the  serum  is  due  to  the  presence  of  oil ;  it 
contains  albumen,  and  coagulates  by  heat.  Except  that  it  is  more  dilute, 
and  that  the  hematosine  is  for  the  most  part  absent  (not  yet  formed),  the 
chyle  and  lymph  have  the  same  composition  as  the  blood.  It  appears  to 
vary,  however,  with  the  nature  of  the  food,  as  Dr.  Prout  found  the  chyle 
of  dogs  fed  on  vegetables  to  contain  a  much  smaller  quantity  of  albumen 
than  when  they  had  had  animal  food.  Dr.  Prout  also  indicates  in  chyle  the 
existence  of  a  substance  which  he  terms  Incipient  Albumen,  which  is  not 
coagulated  by  heat,  except  after  the  addition  of  acetic  acid.  The  prop, 
erties  of  this  form  of  albumen,  however,  are  not  fully  known.  The  re- 
sults of  their  analyses  of  chyle  are  here  given  ;  that  by  Berzelius  was 
the  chyle  of  a  horse,  killed  some  time  after  having  fed  abundantly  with 
oats  ;  and  of  those  by  Dr.  Prout,  No.  1  was  from  a  dog  supported  on 
vegetable,  and  No.  2  of  a  dog  supported  on  animal  food.  100  parts  con- 
tained. 


Berzeliui.  Front.  No.  1.  No.  2. 

Dry  Clot    ....  078 

Albumen   ....  4*49 

Fatty  matters     .    .  1-67 


Extractive  matters 

and  salts    .     .    (    ^ "" 
Water 01  62 


Fibrine 06  0-8 

Incipient  Albumen  .     46  47 

Albumen    ....     04  46 

Oil  and  Sugar     .    .  trace  trace 

Salts 0-8  0-7 

Water 93-6  892 


SECTION  IV. 

CONSTITUTION   OF   THE   URINE   IN   HEALTH   AND   IN   DISEASE. 

The  nature  of  this  secretion  has  at  all  periods  been  an  object  of  con- 
siderable interest  to  the  physician  and  to  the  chemist,  from  the  indica- 
tions which  changes  in  its  composition  give  of  disease  of  important  or- 
gans, and  from  the  number  and  interest  of  the  organic  substances  it  con- 
tains. As  in  almost  all  other  branches  of  animal  chemistry,  Berzelius 
first  determined  accurately  its  constitution,  and  lately  Lecanu  has  ascer* 


10000 


b84  COMPOSITION     OF     URINE. UREA. 

tained  with  great  care  the  limits  to  which  the  proportions  of  its  ingredi- 
ents may  vary  in  health,  and  thus  established  a  correct  basis  of  compar 
ison  for  urine  in  the  various  conditions  of  disease. 

The  specific  gravity  of  urine  varies  from  1016  to  1030.  In  general, 
if  the  excretion  exceeds  in  quantity  thirty-two  ounces  in  twenty-four 
hours,  the  specific  gravity  falls  proportionally  below  1030;  but  if  the 
quantity  be  under  thirty-two  ounces,  the  specific  gravity  for  a  man  in  ac- 
tive heahh  is  generally  1030,  but  less  for  women.  The  important  organ- 
ic  constituents  of  the  urine  are  JJrea  and  Uric  Acid^  which  will  require 
a  detailed  and  special  examination ;  the  other  principles,  though  numer- 
ous, being  of  less  moment,  need  be  only  noticed  in  the  following  state- 
ment of  Berzelius's  general  analysis  of  the  urine.  He  found  100  parts 
to  contain, 

Water 93S00^ 

Urea 3010 

Free  lactic  acid,  lactate  of  ammonia,  and  )  v^\i 

animal  extract ) 

Uric  acid 1-00 

Mucus  of  the  bladder 0'33 

Sulphates  of  potash  and  soda 6-87 

Phosphates  of  soda  and  ammonia  ....  4-59 

Common  salt 4-45 

Sal  ammoniac 1-50 

Phosphates  of  lime  and  magnesia  .    ...  1-00 

Silica 003 

C7rea.— NA  .  O2H4  or  Ur.     Eq.  60  or  750. 

The  artificial  formation  of  this  remarkable  substance  in  various  ways, 
has  been  noticed  already  in  many  places  (as  511,  515).  It  may  be  ob- 
tained from  urine  by  evaporation  to  the  consistence  of  a  thick  sirup  in  a 
water-bath,  and  mixing  the  mass  remaining  with  three  times  its  volume 
of  nitric  acid,  specific  gravity  about  1*25,  which  had  been  perfectly  freed 
from  all  traces  of  nitrous  acid  which  it  might  contain,  as  this  last  instant- 
ly decomposes  urea.  The  liquor  forms  a  crystalline  pulp,  which,  being 
kept  carefully  cool,  may  be  freed  from  the  liquor  by  draining  and  press- 
ure between  folds  of  paper.  The  impure  crystallized  nitrate  of  urea  thus 
obtained  is  to  be  dissolved  in  a  small  quantity  of  boiling  water,  and  re- 
crystallized  by  cooling.  These  crystals  being  again  dissolved  in  water, 
are  to  be  digested  with  animal  charcoal  to  remove  the  colouring  matter, 
and  then  with  an  excess  of  carbonate  of  lead,  until  completely  neutral. 
The  solution  so  obtained,  being  evaporated  very  carefully  in  a  water- bath 
to  dryness,  is  to  be  treated  with  boiling  alcohol,  and  filtered.  The  pure 
urea  separates  from  the  alcoholic  solution,  on  cooling,  in  brilliant  white 
four-sided  prisms. 

Urea  is  much  more  simply  and  economically  obtained  by  the  transform- 
ation of  cyanate  of  ammonia,  for  which  purpose  the  process  given  by 
Liebig  answers  best. 

An  impure  cyanate  of  potash  is  prepared  by  roasting  yellow  prussiate 
of  potash  (as  described  p.  515),  and  this  is  mixed  with  a  solution  of  sul- 
phate of  ammonia  in  water,  and  the  whole  then  boiled  with  alcohol,  which 
dissolves  out  urea,  and  leaves  the  sulphate  of  potash  undissolved.  On 
cooling,  the  urea  crystallizes,  and  may  be  obtained  quite  pure  by  anoth- 
er crystallization  from  alcohol. 

The  taste  of  urea  is  fresh  like  nitre ;  its  reaction  is  quite  neutral  ;  it 
is  inodorous.     When  heated  to  220°,  it  melts,  and  at  a  higher  tempera- 


SALTS     OF     UREA. URIC     ACID.  685 

ture  is  decomposed,  giving  carbonic  and  cyanuric  acids  and  ammonia. 
It  dissolves  in  less  than  its  own  weight  of  water  at  60°,"  producing  great 
cold  ;  it  is  soluble  in  much  less  boiling  water.  If  the  urea  be  quite  pure, 
its  solution  remains  for  a  long  time  unaltered  ;  but  if  it  contains  any  tra- 
ces of  an  azotized  substance  which  putrefies,  this  acts  as  a  ferment,  and 
the  decomposition  extending  to  the  urea,  this  assimilates  the  elements  of 
water,  and  is  totally  converted  into  carbonate  of  ammonia,  N  C2  .  O2H4 
and  H4O4  producing  2(G.O  +N.H4O.).  It  is  this  decomposition  that 
renders  urine  alkaline  in  a  few  hours,  generally,  after  it  is  voided.  Urea 
dissolves  in  five  parts  of  cold  and  one  of  boiling  alcohol.  In  ether  it  is 
almost  insoluble. 

In  contact  with  strong  acids,  urea  is  decomposed,  giving  oflf  carbonic 
acid,  and  forming  an  ammoniacal  salt.  When  the  acids  are  dilute,  it  unites 
with  them,  although  without  neutralizing  them,  and  forms  crystalline 
compounds,  of  which  but  a  few  have  been  accurately  examined.  The 
oxygen  salts  of  urea  resemble  those  of  the  vegetable  alkalies,  melamine, 
ammonia,  &;c.,  in  containing  an  atom  of  associated  water. 

Nitrate  of  Urea  (Ur.H.O. -f-N.Og)  crystallizes  in  large  brilliant  plates 
by  the  cooling  of  its  solution.  It  is  pleasantly  acid,  and  is  soluble  in  al- 
cohol, but  much  more  so  in  water ;  if  heated  rapidly,  it  explodes.  It  is 
sparingly  soluble  in  dilute  nitric  acid,  whence  the  addition  of  a  great  ex- 
cess of  nitric  acid  serves  as  a  test  for  the  presence  of  urea,  this  salt  be- 
ing precipitated  in  bright  pearly  scales. 

Oxalate  of  Urea  (Ur.H.O.-j-CgOa)  crystallizes  in  long  rhomboidal 
tables.  It  tastes  acid  ;  it  is  copiously  soluble  in  boiling  water,  but  crys- 
tallizes almost  completely  out  on  cooling,  as  100  of  water  retain  but  4  of 
the  salt.     It  is  still  less  soluble  in  alcohol. 

Lactate  of  Urea  crystallizes  in  fine  plates  and  needles ;  it  is  very  solu- 
ble.  There  is  reason  to  consider  that  the  urea  is  naturally  combined 
with  lactic  acid  in  the  urine.    The  other  salts  of  urea  are  not  important. 

The  quantity  of  urea  secreted  in  health  appears  pretty  regular  in  the 
same  individual,  when  the  diet  remains  the  same,  and  not  to  depend  upon 
the  quantity  of  liquor  excreted.  It  varies,  however,  very  much  in  differ, 
ent  individuals,  and  is  much  more  abundant  in  men  in  active  age  than  in 
women  or  in  old  men.  Thus  Lecanu  found  the  quantity  of  urea  secreted 
in  twenty.four  hours,  by  men  in  the  prime  of  age,  to  vary  from  350  to 
500  grains  ;  in  women  it  varies  from  150  to  430  grains ;  while  with 
old  men  the  limits  were  80  and  180  grains.  In  children  the  quantity  is 
still  smaller,  and  infants  secrete  scarcely  a  trace  of  urea. 

Uric  Acid,  and  the  Bodies  derived  from  it. 

The  uric  acid  exists  in  the  urine  of  all  carnivorous  animals.  In  birds, 
leptiles,  and  many  insects,  it  is  voided  with  the  excrements,  and  the  urine 
is  in  such  a  slate  of  concentration  as  to  form  a  white  mass,  nearly  solid, 
which  consists  almost  totally  of  urate  of  ammonia.  In  the  small  islands 
of  the  South  Sea,  which  are  inhabited  by  great  flocks  of  aquatic  birds,  it 
accumulates  in  such  quantity  as  to  be  an  article  of  commerce,  being 
brought  to  South  America,  and  even  to  Europe,  under  the  name  o^ guano, 
and  used  as  manure.  In  many  diseases  it  is  generated  by  the  system  in 
abnormal  quantity,  and  constitutes,  free  or  combined  with  bases,  the  gouty 
and  arthritic  concretions,  and  many  forms  of  vesical  calculus. 

For  the  purposes  of  the  chemist,  the  uric  acid  is  most  easily  obtained 


686  URIC     A  C  I  D. ^A  L  L  A  N  T  O  I  N. A  L  L  O  X  A  N. 

from  the  white  solid  excrements  of  the  larger  serpents  in  the  menageries. 
This  is  to  be  boiled  in  a  solution  of  caustic  potash,  and  the  filtered  Jiquoi 
decomposed  by  the  addition  of  muriatic  acid  in  excess.  The  precipitate 
should  be  boiled  in  water  for  some  time,  then  well  washed  and  dried.  It 
crystallizes  in  minute  brilliant  white  scales,  which  are  very  slightly  solu- 
ble in  boiling  water ;  the  solution  reddens  litmus ;  it  is  tasteless  ;  it  dis- 
solves in  oil  of  vitriol,  forming  a  crystallizable  compound,  which  is  de- 
composed on  the  addition  of  water :  the  action  of  nitric  acid  is  different. 
When  heated,  it  is  decomposed,  giving  a  great  variety  of  products,  urea, 
hydrocyanic  and  cyanuric  acids,  carbonate  of  ammonia,  &;c.  Its  formu- 
la is  N4C,o  .  H^Og ;  its  salts  are  not  well  characterized  ;  those  of  the  al- 
kalies are  very  sparingly  soluble,  and  are  decomposed  by  all  acids  except 
the  carbonic  acid.  The  Urate  of  Ammonia  is  the  material  of  the  white 
excrement  (dry  urine)  of  birds  and  serpents.  The  Urate  of  Soda  is  the 
principal  material  of  gouty  deposites.  The  uric  acid  is  specially  inter- 
esting for  the  number  of  important  bodies  to  which  it  gives  origin  by  the 
action  of  reagents,  and  of  which  some  are  also  products  of  the  organiza- 
tion ;  for  our  accurate  knowledge  of  these  we  are  indebted  to  the  recent 
investi"[ations  of  Liebig  and  VVohler. 

Allantdin. — This  substance  exists  in  the  waters  of  the  allantoi's  of  the 
cow,  being  contained  in  the  urine  of  the  foetus,  from  which  it  may  be  ex- 
tracted  by  evaporation  and  crystallization.  It  is,  however,  much  more 
easily  formed  from  uric  acid.  Freshly-prepared  peroxide  of  lead  is  to  be 
added  to  uric  acid,  diffused  through  twenty  parts  of  boiling  water  as  long 
as  its  colour  is  destroyed.  The  boiling  liquor  is  to  be  filtered,  evapora- 
ted till  crystals  begin  to  form,  and  then  allowed  to  cool.  The  allantom 
crystallizes,  and  the  mother  liquor  contains  abundance  of  urea.  At  the 
same  time,  oxalate  of  the  protoxide  of  lead  is  produced,  2(N4C,o .  H4O6) 
and  5H.0.  with  4Pb.02,  producing  4(C203+Pb.O.) ;  with  urea,  2(Nj 
Cg  .  H4O.2),  and  allantoin,  N4C8  .  H5O5.  On  this  reaction  Liebig  founds 
a  theory  of  the  constitution  of  uric  acid,  to  which  I  shall  have  occasion 
again  to  recur.  He  considers  it  to  contain  urea  ready  formed,  and  a  hy- 
pothetic  substance,  for  which  he  proposes  the  names  of  Uril,  or  Cyanox- 
alic  Acid,  it  being  oxalic  acid  in  which  oxygen  is  replaced  by  cyanogen, 
CA+Cy.  Thus  uric  acid,  N4C,o  .  H406=N2C2  .  H402+2(C20,Cy.). 
In  forming  allantoin  on  this  view,  the  urea  is  set  free,  and  the  cyanox- 
alic  acid,  with  oxygen  and  water,  gives  oxalic  acid  and  allantoin. 

Allantoin  forms  rhombic  prisms,  which  contain  an  atom  of  water.  It 
is  sparingly  soluble  in  water,  and  perfectly  neutral.  By  boiling  with  a 
strong  alkali,  it  combines  with  the  elements  of  water,  giving  oxalic  acid 
and  ammonia.  It  does  not  form  a  definite  competed  with  any  base  but 
oxide  of  silver. 

Alloxan. — The  products  of  the  action  of  nitric  acid  on  uric  acid  present  consider- 
able interest,  from  their  number  and  connexion.  On  adding  one  part  of  uric  acid 
gradually  to  four  pans  of  strong  nitric  acid,  it  is  dissolved  with  much  heat,  and  co- 
pious disengagement  of  carbonic  acid  and  nitrogen.  The  lise  of  temperature  being 
prevented  as  much  as  possible,  the  liquor  solidifies  on  cooling  to  a  mass  of  granular 
crystals,  which  are  to  be  drained,  and  then  recrystallized  from  the  smallest  possible 
quantity  of  boiling  water.  This  is  Alloxan;  its  crystals  are  short  right  rhombic 
prisms,  brilliant  and  colourless.  In  dry  air  they  effloresce,  losing  6  Aq. ;  at  a  higher 
temperature  it  crystallizes  in  oblique  rhombic  prisms  which  are  anhydrous,  and  have 
the  formula  NjCs .  H4O10;  its  solution  in  M-ater  reddens  litmus,  and  stains  the  skin 
purple;  when  neutralized  by  an  alkali,  it  strikes  an  indigo-blue  colour  with  a  protc 
salt  of  iron;  it  is  decomposed  by  almost  all  reagents,  producing  a  series  of  bodies 
that  will  be  successively  examined;  its  origin  consists,  probably,  in  the  uryl  beicg 


ALLOXANIC     AND     MYCOMELINIC     ACIDS,    ETC.     687 

oxidized  by  oxygen  from  the  nitric  acid,  leaving  hyponitrous  acid,  which,  reacting 
on  the  urea,  gives  the  mixture  of  the  carbonic  acid  and  nitrogen  gases.  The  allox- 
an may  thus  be  considered  as  a  hydrated  deutoxide  of  uryl. 

AUoxanic  Addis  formed  by  acting  on  alloxan  with  strong  alkalies  or  by  barytesj 
when  separated  from  its  combinations  by  a  stronger  acid,  it  crystallizes  in  colour- 
less needles,  which  have  a  strong  acid  reaction;  its  alkaline  salts  are  soluble;  those 
with  the  earths  and  heavy  metallic  oxides  sparingly  soluble ;  it  is  insoluble  in  wa- 
ter ;  its  formula  is  N2C3 .  H2O8  when  dry,  tiie  alloxan  having  lost  the  elements  of 
two  atom.>  of  water.  When  a  solution  of  alloxanate  of  barytes  is  boiled,  or  when  a 
solution  of  alloxan  is  gradually  added  to  a  boiling  solution  of  sugar  of  lead,  another 
acid  is  formed,  JVLsoxaitc  Acid,  which  in  the  latter  case  precipitates  an  insoluble  salt 
of  lead,  and  the  liquor  contains  urea;  the  alloxan  breaking  up  into  N2C2 .  H4O2  and 
2C3O4,  which  is  the  constitution  of  the  mesoxalic  acid,  which  has  probably,  there- 
fore, an  isomeric  oxide  of  carbon  (C3O3)  for  its  base,  and  belongs  to  the  same  group 
as  the  mellitic  and  rhodizonic  acids  (p.  496).  By  oxidizing  agents,  the  mesoxalic 
acid  is  converted  into  carbonic  acid ;  thus,  with  a  solution  of  nitrate  of  silver,  ii 
gives  a  clear  yellow  precipitate,  which,  when  boiled,  is  converted  into  carbonic 
acid  and  metallic  silver. 

Mijconidtmc  Acid. — If  a  solution  of  alloxan  in  water  of  ammonia  be  heated,  a 
brownish-yellow  precipitate  falls,  which  is  mycomelinate  of  ammonia,  by  boiling 
which,  or  by  washing  with  dilute  sulphuric  acid,  the  ammonia  is  removed,  and  the 
mycomelinic  acid  remains  as  a  yellow  jelly,  which  dries  to  a  coarse  yellow  powder. 
It  is  sparingly  soluble  in  water;  its  salts  are  gelatinous,  sparingly  soluble  flocks; 
the  formula  of  the  acid  is  N4C8  .  H5O5,  being  isomeric  with  anhydrous  allantoVn. 

Panibanic  Acid. — If  alloxan  be  heated  with  an  excess  of  nitric  acid,  it  dissolves, 
nitrogen  gas  is  evolved,  and,  on  cooling,  the  new  acid  separates;  it  is  also  easily 
procured  from  uric  acid  by  using  an  excess  of  nitric  acid  ;  it  forms  colourless,  trans- 
parent, six-sided  prisms,  and  tastes  like  oxalic  acid.  It  is  partly  volatilized  and 
partly  decomposed  by  heat.  If  the  crystals  he  heated  to  212",  they  assume  a  reddish 
colour ;  the  formula  of  the  crystallized  acid  is  N2C6O4-1-2  Aq. ;  hence  alloxan  with 
20.  produces  2C.O2,  with  4H.0.  and  N2C6O4.  By  contact  with  bases,  this  acid  is 
decomposed,  producing  the  Oxaluric  Acid.  This  is  best  prepared  by  dissolving  pa- 
rabanic  acid  in  caustic  ammonia,  boiling,  and  then  letting  the  liquor  cool ;  it  forms 
a  mass  of  small  brilliant  white  crystals  of  oxalurate  of  ammonia.  The  oxaluric 
acid  is  also  a  product  of  other  reactions  on  uric  acid,  some  of  which  will  be  special- 
ly noticed  hereafter.  It  is  a  strong  acid,  and  is  obtained  free  by  dissolving  its  am- 
monia salt  in  boiling  water,  adding  an  excess  of  dilute  muriatic  acid,  and  rapidly 
cooling,  when  the  oxaluric  acid  separates,  as  a  white  or  slightly  yellow  powder;  if 
long  boiled  in  water,  it  is  decomposed  into  oxalic  acid  and  oxalate  of  urea,  of  which 
it  contains  the  elements,  its  formula  being  NoCe  .  HaOT-fAq. 

Tiiiomiric  Acid. — If  sulphurous  acid  gas  be  passed  through  a  saturated  solution 
of  alloxan  until  the  liquor  begins  to  smell  strongly  of  the  gas,  and  then  ammonia  be 
added  in  excess,  after  some  time  brilliant  white  rhombic  tables  form,  which  are 
thionurate  of  ammonia.  By  recrystallization,  this  salt  generally  becomes  pale 
rose-red,  but  is  not  altered  in  constitution.  To  obtain  the  acid  free,  a  solution  of 
this  ammonia  salt  is  to  be  precipitated  by  acetate  of  lead,  and  the  thionurate  of  lead 
decomposed  by  sulphuretted  hydrogen.  By  evaporation  of  the  liquor,  the  acid  re- 
mains as  a  white  semicrystalline  mass;  it  is  easily  soluble  in  water,  reddens  lit- 
mus strongly;  its  formula  is  N3C3 .  H7O14S2:  it  contains  thus  the  elements  of  one 
atom  of  alloxan,  one  oli  ammonia,  and  two  of  sulphurous  acid ;  it  is  a  bibasic  acidi 
If  a  strong  solution  of  thionuric  acid  be  boiled,  it  becomes  turbid,  and  soon  solidifies 
to  a  mass  of  brilliant  silky  crystals,  while  the  liquor  contains  much  sulphuric  acid; 
the  crystalline  substance  being  drained  and  washed  with  cold  water,  in  which  it 
scarcely  dissolves,  is  termed  Uramil;  it  is  white,  soluble  in  dilute  alkaline  liquors, 
and  precipitated  therefrom  unchanged  by  the  addition  of  an  acid,  but  by  strong  al- 
kalies it  is  decomposed,  ammonia  being  evolved,  and  uramilic  acid  formed.  The 
formula  of  uramil  is  N3C8 .  H-,06;  the  thionuric  acid  might  be  considered  as  bisul- 
phate  of  uramil.  The  Uramilic  Add  is  formed  by  the  action  of  acids  and  alka.lies 
on  uramil ;  it  crystallizes  in  colourless  needles,  which  dissolve  in  acids  and  alkalies, 
forming  with  the  latter  well-defined  salts;  its  formula  is  N.^Cie  .  H10O15. 

AU.vxuitin-'. — This  substance  is  formed  as  a  product  of  the  moderate  oxidation 
of  unc  acid,  or  it  may  be  obtained  by  acting  on  alloxan  with  deoxidizing  agents. 
Uric  acid  is  to  be  diffused  through  boiling  water,  and  the  dilute  nitric  acid  added 
until  a  perfect  solution  is  obtained.  On  filtering  and  cooling,  the  alloxantine  grad- 
ually crystaHizes.  The  mother  liquor  contains  much  urea.  If  sulphuretted  hydro- 
gen g  is'has  been  passed  through  a  solution  of  alloxan,  sulphur  is  deposited,  and  al- 
loxantine formed,  and  the  same  effect  is  produ:;ed  by  acidulating  the  solution  of  al- 


683  DIALURIC     ACID,     MUREXID,     ETC. 

loxan,  and  immersing  therein  a  slip  of  zinc ;  the  alloxan  is  deoxidized  by  the  nas- 
cent hydrogen.  By  the  galvanic  battery  alloxan  is  resolved  into  oxygen  and  allox- 
antine.  It  is  sparingly  soluble  in  cold,  but  much  more  in  boiling  water,  and  crys- 
tallizes in  short  oblique  rhombic  prisms  which  contain  3  Aq.,  which  tliey  lose  only 
by  a  heat  above  300"^.  The  solution  of  alloxaritine  reddens  litmus,  but  docs  not 
form  salts  with  bases,  being  immediately  decomposed  by  contact  with  them.  Its 
formula  is  N2C8 .  H5O10. 

By  oxidizing  bodies,  as  nitric  acid,  chlorine,  or  oxide  of  silver,  it  is  immediately 
converted  into  alloxan.  If  treated  by  an  excess  of  sulphuretted  hydrogen,  more  sul- 
phur is  set  free,  and  the  liquor  becomes  strongly  acid.  The  body  thus  formed,  if 
mixed  with  alloxan,  regenerates  alloxantine  from  both.  If  neutralized  by  carbonate 
of  amm.onia,  a  white  crystalline  precipitate  forms,  which  is  a  salt  of  ammonia,  of 
which  the  formula  is  NsCb  .  H-Os.  Liebig  considers  it  to  contain  a  body  which  he 
terms  the  DiaUric  Acid,  the  formula  of  which  is  N2C8O4,  being  isomeric  with  the 
cyanoxalic  acid  or  uryl  already  noticed.  The  Dialurate  of  Ammonia  is  therefore 
N2C8O4+N.H4O.+3  Aq.  It  may  be  produced  by  adding  hydrosuiphuret  of  ammo- 
nia to  a  saturated  solution  of  uric  acid  in  dilute  nitric  acid,  or  by  acting  on  alloxan 
with  zinc  and  muriatic  acid  in  excess.  Though  white  when  first  produced,  it  be- 
comes rose-red  by  drying,  and  at  212"  blood-red,  and  loses  ammonia.  It  is  by  no 
means  established  that  this  body  is  a  true  ammoniacal  salt  as  described  by  Liebig, 
or  that  the  dialuric  acid  really  exists.  Berzelius  looks  upon  it  as  a  compound  of 
alloxantine  and  alloxantine-amide. 

By  boiling  with  sal  ammoniac,  alloxantine  is  converted  into  uramil  and  alloxan, 
while  muriatic  acid  becomes  free.  By  the  action  of  oxygen  upon  an  ammoniacal 
solution  of  alloxantine,  uramil,  oxaluric  acid,  and  mycomelinic  acid  are  generated. 

Murezid. — This  remarkable  substance  may  be  produced  by  a  variety  of  reactions, 
none  of  which  are,  however,  quite  constant  in  their  result.  On  evaporating  a  solu- 
tion of  uric  acid  in  very  dilute  nitric  acid  until  the  liquor  becomes  flesh-red,  and 
then  adding  dilute  water  of  ammonia  in  slight  excess,  and  cooling,  the  murexid 
crystallizes.  In  this  process  a  very  slight  excess  or  deficiency  of  any  of  the  ingre- 
dients prevents  success,  and  Gregory  proposes,  as  the  most  certain  method,  to  dis- 
solve four  parts  of  alloxantine  and  seven  of  hydrated  alloxan  in  240  parts  of  boil- 
ing water  and  eighty  of  solution  of  carbonate  of  ammonia,  when  the  murexid  crys- 
tallizes by  gradual  cooling.  By  the  action  of  uramil  and  ammonia  it  may  also  be 
generated,  and  is  the  ordinary  source  of  the  purple  colours  that  are  produced  in 
many  of  the  reactions  already  described. 

The  Murexid,  the  name  of  which  is  derived  from  the  murex,  the  shell-fish  furnish- 
ing the  Tyrian  purple,  crystallizes  in  short  rhombic  prisms  of  a  garnet-red  colour, 
and  by  reflected  light  have  a  green  metallic  lustre.  It  dissolv^es  sparingly  in  cold, 
copiously  in  boiling  water;  it  is  insoluble  in  ether  and  alcohol.  Gregory  has  found 
that  it  is  sometimes  soluble,  and  at  others  insolulile  in  water  of  ammonia,  whence 
he  suggests  that  two  different  bodies  have  been  confounded  under  this  name.  It 
dissolves  in  caustic  potash,  with  an  indigo  blue  colour,  which  disappears  by  heat, 
ammonia  being  evolved;  it  does  not  appear  to  combine  with  bases;  its  formula  is 
NbCh  .  HeOg.  By  the  mineral  acids  and  by  sulphuretted  hydrogen  it  is  decompo- 
sed, ammonia,  alloxantine,  alloxan,  and  dialuric  acid  being  evolved,  besides  an- 
other body  termed  Murexan.  This  substance  is  more  abundantly  produced  by  dis- 
solving murexid  in  a  boiling  solution  of  potash,  and  when  the  blue  colour  has  to- 
tally disappeared,  adding  sulphuric  acid  in  excess.  It  precipitates  in  white  silky 
crystalline  scales;  its  formula  is  N2C6  .  H4O5;  it  dissolves  in  caustic  alkalies  with- 
out neutralizing  them.  If  its  solution  in  ammonia  be  exposed  to  the  air,  oxygen  is 
absorbed  and  murexid  regenerated. 

The  murexid  was  long  since  described  by  Prout  under  the  name  of  Puvpnratc  of 
Ammonia ;  and  Fritzsche  has  revived  the  idea  that  it  is  really  an  ammoniacal  salt 
of  a  distinct  acid,  Purpuric  Acid.  By  the  double  decomposition  of  murexid  with 
salts  of  potash,  barytes,  lead,  and  silver,  he  has  obtained  purpurates  of  these  bases, 
the  formula  of  whibh  shows  the  acid  to  be  composed  of  N5C16  .  H40i(.  The  mu- 
rexid is,  according  to  this  chemist,  composed  of  NeCie.  H80ii=N5Ci6  .  H4O10-I- 
N.H4O.  The  evidence  brought  forward  by  Fritzsche  against  Liebig's  view  is  very 
strong. 

In  the  urine  of  herbivorous  animals,  and  occasionally  in  children,  the  uric  acid  is 
replaced  by  a  different  body,  the  Hipjpiric  Acid,  which  exists  therein  combined  with 
soda.  The  urine  of  horses  and  com'S  is  to  be  evaporated  to  one  eighth  of  its  volume, 
and  mixed  with  muriatic  acid,  which  produces,  after  some  time,  a  yellowish  crys- 
talline precipitate.  This  is  to  be  dissolved  by  boiling  with  some  lime;  chloride  of 
iime  IS  to  be  added  to  the  liquor  until  it  is  nearly  decolorized,  and  the  smell  of  urine 
has  disappeared ;  being  then  digested  with  ivory  black  and  filtered,  the  pure  acid  is 


URINE    IN    DISEASE.  689 

separated  by  muriatic  acid.  By  the  cooling  of  the  liquor  it  crystallizes  in  delicate 
silky  needles  or  rhombic  prisms;  its  taste  is  very  slightly  bitter,  but  it  reddens  lit- 
mus strongly.  When  heated,  it  melts,  and  is  then  decomposed,  giving  a  crystalline 
sublimate  of  benzoic  acid  with  ammonia  and  prussic  acid..  It  is  very  sparingly 
soluble  in  cold,  but  copiously  in  boiling  water ;  very  soluble  in  alcohol.  By  nitric 
acid  and  other  oxidizing  agents,  it  is  decomposed,  and  benzoic  acid  is  formed.  Its 
salts  are  all  soluble  and  crystallize ;  they  resemble  the  benzoales  exactly.  The  for- 
mula of  the  crystallized  acid  is  N.Cis  •  HgOs+Aq.  The  constant  transformation  of 
this  acid  into  benzoic  acid  has  given  origin  to  many  theories  of  its  constitution.  It 
has  been  supposed  by  some  to  contain  benzoic  acid  ready  formed,  by  others  benza- 
mid,  and  by  others  oil  of  bitter  almonds,  but  none  of  these  views  have  even  much 
probability  in  their  favour. 

Of  the  Urine  in  Disease.     Urinary  Calculi. 

To  the  pathologist  and  physician,  the  indications  of  disease  of  the 
urinary  and  digestive  organs,  furnished  by  changes  in  the  composition 
of  the  urine,  are  most  valuable.  The  majority  of  the  substances  which 
are  taken  into  the  circulation,  but  are  incapable  of  assimilation  to  our 
organs,  are  thrown  off  by  this  secretion,  and  hence  a  variety  of  medicinal 
substances  may  be  traced  to  it  after  having  been  ingested,  sometimes  quite 
unaltered,  at  others  modified  in  their  nature.  Thus,  if  alkaline  salts  of  or- 
ganic acids  be  taken  into  the  stomach,  the  organic  material  is  oxidized, 
probably  during  the  action  of  respiration,  while  the  alkali  passes  into  the 
urine  in  the  state  of  carbonate.  If,  however,  the  organic  acid  be  taken 
uncombined,  it  escapes  decomposition,  and,  passing  into  the  urine,  pro- 
duces an  abundant  precipitate  of  salts  of  lime,  in  the  case  of  the  tartaric 
and  oxalic  acids. 

Iodide  of  potassium  and  iodine  pass  into  the  urine,  the  latter  as  hy- 
driodic  acid.  Some  organic  bodies,  as  asparagine  and  oil  of  turpentine, 
are  decomposed,  and  the  products  which  they  form  are  excreted,  giving 
to  the  urine  peculiar  odours,  in  the  latter  case  like  that  of  violets.  Ni- 
trate of  potash,  yellow  prussiate  of  potash,  and  most  other  alkaline  and 
earthy  salts,  pass  into  the  urine  unchanged.  The  majority  of  colouring 
matters  are  thrown  out  of  the  system  by  means  of  this  secretion,  while 
others,  as  cochineal  and  litmus,  are  not  so  given  off. 

The  mineral  acids,  alcohol,  camphor,  most  metallic  salts,  do  not  pass 
into  the  urine  in  any  sensible  degree. 

Urine  in  Diabetes. — The  most  remarkable  change  in  the  nature  of  the 
urine  occurs  in  diabetes  mellitus.  It  is  voided  in  great  quantity.  Its 
specific  gravity  is  very  high,  from  1030  to  1050,  and  it  is  found  to  con- 
tain  a  very  large  quantity  of  grape-sugar,  and  very  little  urea.  It  wsis 
supposed  that,  in  this  disease,  urea  ceased  to  be  formed  by  the  system, 
and  was  replaced  by  sugar  ;  but  I  have  shown  that,  although  the  quantity 
of  urea  is  very  small  4n  any  one  specimen  of  the  urine,  yet  the  total 
quantity  is  so  much  increased,  that  in  twenty-four  hours  the  natural 
quantity  of  urea  is  secreted  ;  the  secretion  of  sugar  being  an  act  of  faulty 
digestion,  and  totally  unconnected  with  the  urea.  These  results  have 
been  fully  confirmed  by  Macgregor.  The  diabetic  urine  sometimes  con- 
tains albumen,  which  arises  from  complication  of  other  forms  of  disease. 

As  the  average  composition  of  urine  in  diabetes,  the  following  may  be 
taken,  analyzed  by  myself.  Its  specific  gravity  was  1'0363  ;  it  contained 
in  1000  parts,  water  913,  sugar  60,  urea  6*5,  salts,  extractive  matters, 
and  uric  acid  20*5.  This  patient  made  in  volume  about  four  times  the 
healthy  quantity  of  urine  in  twenty-four  hours. 

Urine  in  Dropsies, — In  these  diseases,  particularly  where  associated 

4S 


690  URINARY     DEPOSITES    AND     CALCULI 

with  disease  of  the  kidneys,  the  urine  is  not  increased  in  quantity ;  its 
specific  gravity  is  very  low,  1005  to  1015,  and  it  contains  but  very  little 
urea,  but  generally  albumen,  and  sometimes  caseiim.  In  these  cases,  the 
urea,  which  is  deficient  in  the  urine,  is  found  in  the  serum  of  the  blood 
and  in  the  dropsical  effusions.  In  some  states  of  the  system,  which  do 
not  appear  connected  with  any  distinct  disease,  milk  passes  into  the  urine, 
in  which  as  well  the  butter  as  the  caseiim  may  be  detected.  Such  cases 
have  even  been  met  with  in  males.  In  jaundice  the  colouring  material 
of  the  bile  passes  abundantly  into  the  urine,  and  may  be  detected  by 
nitric  acid.  The  natural  elements  of  the  urine  are,  however,  not  altered 
in  quantity. 

Blue  and  Black  Urine. — The  urine  has  been  observed  coloured  deeply 
blue  by  a  peculiar  organic  substance,  which,  however,  has  not  been  ac- 
curately examined.  Braconnot  found  that  it  contained  nitrogen,  and  was 
reddened  by  acids,  and  the  colour  restored  by  aJkahes.  But  Sprangen- 
berg  found,  in  the  case  he  observed,  that  acids  dissolved  the  blue  sub- 
stance without  changing  its  colour.  Moncet  observed  in  the  urine  of  a 
child  a  black  matter  insoluble  in  water,  but  soluble  in  alkalies.  Prout, 
who  also  observed  this  substance,  termed  it  melanic  acid. 

In  many  states  of  the  system,  particularly  in  arthritic  rheumatism, 
there  is  a  great  tendency  to  the  formation  of  uric  acid,  and  the  urate  of 
ammonia  is  deposited  under  the  form  of  a  crystalline  precipitate  when 
the  urine  cools.  It  is  usually  mixed  with  more  or  less  of  a  yellowish-red 
body,  which  is  not  purpurate  of  ammonia  (murexid),  as  Prout  supposed, 
but  a  peculiar  organic  substance,  soluble  in  alcohol,  which  deserves  more 
minute  examination.  The  deposition  of  this  excess  of  matter  in  the 
joints  and  sheaths  of  the  tendons,  produces  the  gouty  concretions,  which 
consist,  for  the  most  part,  of  urate  of  soda. 

In  other  conditions  of  the  system,  the  formation  of  phosphatic  salts 
predominates,  and  precipitates  occur  in  the  urine  which  are  generally 
more  crystalline  and  less  highly  coloured  than  those  of  uric  acid  or  of 
urates.  As  these  different  conditions  of  the  secreting  organs  require 
different  modes  of  treatment,  it  is  necessary  to  be  able  simply  to  distin- 
guish between  these  two  kinds  of  sediment.  It  is  sufficient  to  remark, 
that  the  uric  acid  deposite  is  soluble  in  alkalies  and  insoluble  in  dilute 
acids,  while  the  phosphatic  sediments  dissolve  in  dilute  acids,  but  not  in 
alkaline  liquors,  even  though  decomposed  by  them. 

The  uric  acid  and  the  inorganic  salts  of  the  urine  are  afterward  de- 
posited in  the  bladder,  and  form  urinary  calculi. 

The  Uric  Acid  Calculus  is  probably  the  most  common.  It  is  recog- 
nised by  being  decomposed  by  heat ;  being  sellable  in  caustic  alkalies, 
and  precipitated  by  acids.  When  dissolved  in  nitric  acid,  evaporated 
and  moistened  with  water  of  ammonia,  it  gives  the  rich  purple  colour  of 
murexid. 

The  Urate  of  Ammonia  Calculus,  in  addition  to  the  characters  of  uric 
acid,  gives  off  ammonia  when  dissolved  in  solutions  of  caustic  potash. 

The  Phosphate  of  Lime  Calculus  fuses  with  difficulty,  or  not  at  all, 
before  the  blowpipe.  It  is  dissolved  by  muriatic  acid,  and  precipitated 
by  caustic  ammonia  from  this  solution  as  a  white  powder  not  crystal- 
line. 

The  Ammoniaco-magnesian  Phosphate  Calculus  is  generally  crystal- 
line  in  structure  ;  before  the  blowpipe  it  gives  off  ammonia,  and  ulti- 


CYSTIC    AND     XANTHIC     OXIDES,    ETC.  691 

mately  melts,  though  with  difficultj'.  It  also  gives  off  ammonia  when 
boiled  with  caustic  potash.  It  dissolves  in  dilute  acids,  and  is  precipita- 
ted as  a  crystalline  powder  on  the  addition  of  caustic  ammonia. 

The  two  latter  calculi  often  form  together,  and  produce  the  Triple 
Phosphate,  or  Fusible  Calculus.  This  melts  readily  before  the  blowpipe, 
and  if  dissolved  in  a  dilute  acid,  it  gives  with  oxalic  acid  a  precipitate  of 
oxalate  of  lime,  and  then,  with  an  alkali,  a  crystalline  deposite  of  ammo- 
niaco-magnesian  phosphate. 

All  of  these  various  deposites  may  occur  in  the  bladder,  either  success- 
ively, and  form  the  Alternating  Calculus,  or  together,  forming  the  Mixed 
Calculus.  The  recognition  of  these  species  will  depend  on  the  careful 
application  of  the  methods  by  which  each  component  may  be  known,  as 
already  described. 

It  is  not  very  unfrequent  to  meet  with  calculi  formed  of  materials  which 
do  not  exist  in  healthy  urine,  but  are  produced  by  the  decomposition  of 
its  natural  constituents.  Thus  the  Mulberry  Calculus,  so  called  from  its 
usual  external  form,  consists  of  oxalate  of  lime.  When  ignited  it  leaves 
caustic  lime,  which  browhs  wet  turmeric  paper  strongly,  dissolves  in 
muriatic  acid,  and  is  precipitated  by  adding  oxalate  of  ammonia.  Cal- 
culi have  been  found  also,  though  rarely,  consisting  of  carbonate  of  lime 
and  of  carbonate  of  magnesia. 

The  most  remarkable  calculi  of  this  class,  however,  are  those  formed 
of  the  Cystic  Oxide  and  Xanthic  Oxide,  substances  of  purely  organic  na- 
ture. The  latter  body  is  yellow,  soluble  in  alkalies,  and  is  precipitated 
by  the  addition  of  an  acid.  It  dissolves  in  nitric  and  sulphuric  acids,  but 
not  in  muriatic  or  oxalic  acids.  Its  formula  is  N4C,o  .  H4O4.  It  con- 
tains, therefore,  the  same  carbon,  nitrogen,  and  hydrogen  as  uric  acid, 
but  less  oxygen,  whence  the  name  Uric  Oxide  has  been  proposed  for  it. 
The  Cystic  Oxide  Calculus  consists  of  small  yellow  crystalline  plates, 
which  dissolve  in  alkalies,  and  crystallize  out  again  on  the  addition  of  an 
acid,  by  an  excess  of  which  the  cystic  oxide  is,  however,  redissolved. 
When  heated  strongly  it  is  decomposed,  evolving  sulphurous  acid  and 
ammonia.  It  forms  definite  salts  with  the  nitric  and  muriatic  acids.  Its 
formula  is  N.CeHe  .  O^. 

When  blood  is  effused  into  the  bladder,  the  fibrine  is  occasionally  ag- 
gregated as  a  calculus,  the  recognition  of  which  is  very  simple,  from  what 
has  been  said  of  the  properties  of  fibrine  (p.  663). 

Those  who  would  wish  for  more  detailed  information  of  the  properties 
of  calculi,  and  of  the  composition  of  the  urine  in  health  and  disease,  I 
would  refer  to  the  truly  classical  work  of  Doctor  Prout  on  the  Diseases 
of  the  Stomach  and  Urinary  Organs. 

SECTION  V. 

OF    THE    MILK,    AND    OTHER    NATURAL    AND    MORBID    PRODUCTS,    NOT 
INCLUDED    IN    THE    PRECEDING    SECTIONS. 

Some  of  the  most  remarkable  constituents  of  milk  have  been  al- 
ready described,  as  lactic  acid  (p.  536),  the  sugar  of  milk  (p.  535), 
the  butter,  fats  (p.  589).  It  only  remains  to  notice  the  general  com- 
position of  milk,  and  the  properties  of  the  Caseiim  or  curd.  It  is 
well  known  that,  by  standing,  milk  abandons  the  greater  part  of  its 
butter,  which  separates,  with  other  substances,  as  Cream.     Berzelius 


692 


COMPOSITION     OF     MILK,     ETC. 


found  the  cream  from  cows'  milk  to  have  specific  gravity  1'0244', 
and  to  consist,  in  100  parts,  of  4*5  of  butter,  separated  by  agitation, 
3'5  of  caseiJm,  with  some  butter,  separated  by  coagulation,  and  92 
of  whey.  The  skimmed  milk  had  a  specific  gravity  of  1*0348,  and 
contained  in  100  parts  : 

Caseous  matter  with  some  butter    ....    2-600"\ 

Sugar  of  milk 3-500 

Alcoholic  extract  with  lactic  acid  ....    0-600 

Chloride  of  potassium 0-170  !►  100-00. 

Alkaline  phosphates 0-025 

Earthy  phosphates  and  a  trace  of  iron      .    .    0230 
Water  f  . 92-875, 

The  following  table  presents  the  best  results  that  have  been  as  yet 
obtained  on  the  average  composition  of  the  milk  of  diflferent  animals : 


Specific  gravity  .    . 

Water 

Extractive     .    .     > 

Caseine     .... 

Butter 

Sugar   

Ashes  ....     1 

Human. 

Mares. 

Asses. 

Cowrs. 

Sheep. 

1-0380 

nog,. 

10323 

10395 

88-68 

1-82 
0-75 
8  75 

10322 

10320 

88-36 

1-24 

340 
253 
4-25 

022 

90  47 

1-95 
1-29 
629 

85-91 

700 
393 

2-87 

029 

532 

(Cream 

11-5) 

153 

5-8 

4-2 

65-74 

290 

17-40 
1620 

(Salts 
1-50) 

The  butter  of  human  milk  is  more  solid  than  that  of  the  cow,  and  appears  to  con- 
tain no  butyrine. 

The  Caseilm  or  Caseine  is  capable  of  existing  in  a  soluble  and  an 
.nsoluble  condition,  like  albumen.  In  milk  it  is  principally  dissolved, 
3ut  a  part  insoluble,  united  with  the  butter,  produces  the  emulsive 
appearance  of  the  milk.  On  adding  sulphuric  acid  to  skimmed  milk, 
the  caseine  precipitates,  combined  with  the  acid,  as  a  white  coagu- 
-um,  which,  being  washed  with  water  so  as  to  remove  all  adhering 
milk,  and  then  digested  with  carbonate  of  barytes,  the  caseine  dis- 
solves in  the  water,  and  may,  by  filtration,  be  freed  from  all  traces 
of  the  butter,  sulphuric  acid,  or  barytes.  The  caseine  may  also  be 
precipitated  by  alcohol,  and  when  the  curd  is  digested  with  ether 
to  remove  all  traces  of  butter,  it  miy  be  looked  ipon  as  pure. 

The  solution  of  caseine  in  water  js  thick,  like  mucilage  ;  it  smells 
as  boiled  milk,  and  dries  down  to  an  amber-coloured  mass,  which  is 
again  soluble  in  water.  The  solution  is  coagulated  by  all  acids, 
even  acetic  acid,  particularly  when  hot,  and  by  alcohol.  In  relation 
to  acids,  caseine  is  similar  to  albumen,  except  that  to  acetic  acid  ; 
the  constitution  of  its  precipitates  being  precisely  similar. 

The  coagulated  condition  of  caseine  is  not  produced  by  boiling, 
but  only  by  the  digestive  principle  (rennet,  pepsine),  as  already  de- 
scribed (p.  679).  When  thus  coagulated,  caseine  is  absolutely  un- 
distinguished from  coagulated  albumen  in  its  properties.  It  con- 
tains a  considerable  quantity  of  bone-earth  (phosphate  of  lime), 
amounting  to  five  or  six  per  cent., in  intimate  combination.  Its  or- 
ganic element  was  found  by  Mulder  to  be  proteme,  of  which  ten  at- 
oms are  combined  with  one  of  sulphur,  the  formula  of  caseine  being 
C400H310  •  N5oO,2o  +  S.  It  contains  no  phosphorus,  but  to  each  atom 
so  expressed,  two  atoms  of  bibasic  phosphate  of  lime. 

When  coagulated  caseine  containing  water  (cheese)  is  kept  for 


EGGS,    AMNIOS,    CONTENTS     OF     THE     EYE,    ETC.       693 

a  long  time,  it  undergoes  a  remarkable  kind  of  decomposition,  and 
a  substance,  crystallizable  and  soluble  in  water,  is  obtained,  termed 
by  Braconnot  jlposepedine.  By  Mulder's  experiments  it  appears, 
however,  to  be  impure  leucine  (p.  667)  ;  and  the  Caseous  Oxide  and 
Case'ic  Acid  of  Prout  appear  also  to  be  the  same  bodies  as  have  been 
already  noticed  as  formed  from  the  decomposition  of  the  other  pro- 
te'ine  substances. 

By  contact  with  caseine,  sugar  of  milk  is  rapidly  converted  into 
lactic  acid,  which  precipitates  the  caseine,  without,  however,  really 
coagulating  it  j  hence,  on  neutralizing  the  acid,  the  caseine  redis- 
solves,  and  may  react  on  a  new  quantity  of  sugar.  In  this  manner 
Freiry  lias  shown  that  the  Lactic  Fermentation  may  be  carried  on  to 
an  indefinite  extent. 

Constitution  of  Eggs. — The  shell  of  hens'  eggs  consists  of  from 
90  to  95  per  cent,  of  carbonate  of  lime,  one  to  five  of  phosphate  of 
lime,  and  two  to  five  of  animal  matter.  Internally  it  is  lined  by  a 
membrane  analogous  to  epidermis.  The  white  of  egg  is  a  concen- 
trated solution  of  albumen,  contained  in  the  cells  of  a  delicate  mem- 
brane, in  the  centre  of  which  the  yolk  is  suspended.  The  nutritive 
material  of  the  yolk  consists  of  albumen  and  an  oil ;  also  a  yellow 
colouring  matter  analogous  to  that  of  bile.  The  Oil  of  Eggs  is  ob- 
tained by  expressing  the  Ggg  boiled,  and  partly  torrefied  j  it  is  red- 
dish-yellow, thick,  and  solidified  by  coldj  it  soon  becomes  rancid; 
the  solid  portion  of,  it  appears  to  be  cholesterine ;  the  liquid  con- 
tains phosphorus  and  nitrogen,  and  is  not  saponifiable.  When  the 
young  animal  is  developed  during  incubation,  the  quantity  of  phos 
phoric  acid  in  its  bones  is  exactly  represented  by  the  quantity  of 
phosphorus  in  the  yoJk  and  white  ;  but  as  these  bodies  contain  very 
little  lime,  that  earth  must  be  derived  from  the  shell,  which  becomes 
thin  and  brittle  as  the  animal  advances  in  growth. 

Liquor  of  the  Amnios. — This  fluid,  in  which  the  foetus  is  immersed 
before  birth,  appears  to  be  identical  in  constitution  with  the  liquor 
effused  from  serous  surfaces  in  dropsy  (p.  671).  The  Liquor  of  the 
Allanto'is  of  the  cow,  which  is  really  the  urine  of  the  foetus,  is  of 
the  same  nature,  but  contains,  in  addition,  a  small  quantity  of  allan- 
toin,  the  artificial  formation  of  which  is  described  p.  686. 

Black  Pigment  of  the  Eye. — This  substance  is  insoluble  in  water 
and  alcohol.  It  is  decomposed  by  strong  acids  and  alkalies.  Caus- 
tic potash  dissolves  it,  forming  a  yellow  liquor,  from  which  acids 
throw  down  a  clear  brown  powder.  The  action  of  nitric  acid  is 
nearly  the  same.  The  Cuttle-fish  Ink  has  much  analogy  with  the 
black  matter  of  the  eye,  giving,  when  dried,  a  black  powder,  insol- 
uble in  water,  alcohol,  and  ether,  which  dissolves  in  nitric  acid  and 
potash  with  a  reddish-yellow  colour,  from  which  solution  a  yellow- 
ish powder  falls  when  it  is  neutralized.  The  true  nature  of  these 
black  colouring  matters,  and  their  relation  to  the  melanic  acid  of 
Prout,  which  sometimes  appears  in  the  urine,  would  deserve  atten- 
tive study. 

The  Humours  of  the  Eye  consist  of  water,  holding  in  solution  al 
bumen  in  small  quantity,  with  the  salts  which  usually  accompany 
it.     The  crystalline  lens  consists  of  albumen,  in  a  state  of  beautiful 


694  CERUMEN,     PUS,     AMBERGRIS,     ETC. 

and  complex  organization,  amounting  to  about  thirty-eight  per  cent, 
of  the  entire  mass,  which  contains  about  sixty  of  water. 

Cerumen.  Wax  of  the  Ear. — This  substance  contains  an  albumi- 
nous material  insoluble  in  water,  a  solid  and  a  liquid  fat  soluble  in 
ether,  and  a  deep  yellow  matter  soluble  in  alcohol  and  insoluble  in 
ether,  to  i(.'h\c\\  its  colour  and  very  disgusting  taste  are  due ;  an- 
other constituent,  which  appears  to  be  peculiar  to  this  secretion,  is 
brown,  insoluble  in  caustic  potash  ;  it  most  resembles  horn  in  its 
properties,  but  is  still  quite  distinct  from  that  body. 

Pus. — This  remarl^able  morbid  secretion  has  generally  a  specific 
gravity  of  1-030.  It  consists  of  a  clear  liquor,  in  which  float  a  great 
number  of  yellow  globules,  of  various  sizes,  the  largest  o^  which 
are  about  twice  the  size  of  the  globules  of  the  blood.  Pus  Joses 
by  drying  86*1  of  water  in  100  parts,  and  hence  contains  13'9  of 
solid  material,  from  which  alcohol  takes  5*9  of  fatty  and  extractive 
matters,  and  leaves  7'4i  per  cent,  of  a  residue,  which  consists  of 
coagulated  albumen,  the  solid  globules,  and  a  substance  peculiar 
to  pus. 

The  globules  of  pus  appear  to  consist  of  coagulated  albumen. 
The  serum  contains  two  liquids,  both  coagulable  by  heat.  One  is 
albumen,  the  9ther  Pyin^  which  is  characterized  by  being  coagula- 
ted both  by  heat,  by  acetic  acid,  and  by  a  solution  of  alum.  Giiter- 
bach,  who  has  recently  examined  pus  with  great  care,  finds  the  only 
certain  distinction  between  pus  and  mucus  to  be,  that  the  pus  glob- 
ules sink  always  in  water,  while  the  mucus  swims.  If  the  suspect- 
ed liquid  be  dried,  the  extraction  of  the  fatty  substance  by  ether 
should  decide  very  positively. 

Jlmbergris. — This  substance,  which  is  generally  found  floating  on 
the  seacoasts  of  tropical  islands,  is  known  to  be  an  intestinal  con- 
cretion of  the  spermaceti  whale,  analogous  to  the  gallstones  of 
cholesteVine  in  other  animals.  Its  principal  ingredient  is  the  Am- 
bre'ine,  which  is  obtained  by  solution  in  boiling  alcohol,  whence  it 
crystallizes,  on  cooling,  in  fine  needles.  It  is  white,  tasteless,  of  a 
very  agreeable  odour  j  it  is  not  saponifiable  ;  its  formula  is  C33H32O 
By  boiling  with  nitric  acid  it  produces  ambreic  acid,  which  crystal 
lizes  from  its  solution  in  alcohol  in  small  colourless  tables ;  it  red- 
dens litmus,  but  is  scarcely  soluble  in  water  ;  it  forms  well-defined 
yellow  salts  with  the  alkalies  j  its  formula  appears  to  be  C26H20 . 
N.0.2. 

SECTION  VI. 

OF    THE    PRESERVATION    AND    PUTREFACTION    OF    ANIMAL    MATTERS. 

From  the  greater  complexity  of  composition  of  animal  substances, 
their  decomposition  is  more  rapid,  and  its  products  more  diverse, 
than  in  the  case  of  organic  bodies  of  vegetable  origin ;  while  the 
carbon,  hydrogen,  and  oxygen  give  origin  to  the  various  kinds  of 
ulmine  and  other  substances  of  the  same  class,  the  nitrogen  is  gen- 
erally evolved  as  ammonia,  and  the  sulphur  as  sulphuretted  hydro- 
gen. It  is  the  presence  of  these  bodies  that  give  to  putrefying  sub- 
stances the  disagreeable  odour  by  which  that  process  is  distinguish- 
ed from  mere  mouldering  or  rotting. 


PUTREFACTION.  695 

Even  during  life  the  constituent  particles  of  the  "body  are  in  a 
continual  state  of  change,  being  absorbed  and  thrown  out  of  the 
system,  while  others  are  assimilated  in  their  place.  Any  part  of 
our  constituents,  liquid  or  solid,  which  becomes  unfitted  for  this 
vital  function,  is  thereby  killed,  and  must,  if  not  got  rid  of,  induce 
the  death  of  the  individual.  Hence  precisely  the  same  means  w:hich 
give  to  animal  substances  the  fixity  of  constitution  which  belongs 
to  true  chemical  compounds,  and  thus  preserve  them  from  decom- 
position by  the  disturbing  action  of  their  own  elements  (as  when 
we  coagulate  albumen  by  an  acid,  by  corrosive  sublimate,  or  by 
sulphate  of  copper),  produce,  if  applied  to  the  living  body,  the 
death  of  the  part  or  of  the  whole  being,  by  depriving  the  blood  or 
the  tissue  of  the  mutability  of  constitution  which  is  required  for  the 
functions  of  the  animal  frame. 

It  is  thus  that  the  generality  of  metallic  poisons  act  in  producing 
death.  Being  absorbed  into  the  system,  they  unite  with  the  albu- 
men and  fibrine  of  the  blood,  and,  converting  them  into  the  insolu- 
ble compounds  which  we  form  in  the  laboratory,  unfit  them  for  the 
continual  absorptive  and  secretive  offices  which,  as  organs,  vi'hile 
they  live  they  must  fulfil.  If  the  injury  be  local,  and  limited  in  ex- 
tent, the  part  so  coagulated  may  be  thrown  off,  and  after  a  certain 
time  the  functions  return  to  their  proper  order.  If  the  mass,  or  the 
importance  of  the  affected  parts  be  greater,  the  system  cannot  so 
get  rid  of  the  portions  which  have  thus  been  removed  from  the 
agency  of  life  to  submit  to  merely  chemical  laws ;  on  the  contrary, 
the  vital  powers  of  the  remaining  portions  of  the  animal  are  so  much 
weakened  in  the  effort  that  general  death  is  caused. 

For  putrefaction  it.  is  thus  necessary,  1st,  that  the  force  of  vitali- 
ty, which  governs  so  completely  the  mere  chemical  tendencies  of 
the  elements  of  our  tissues,  be  removed  ;  2d,  that  there  shall  not  be 
present  any  powerful  chemical  reagent  with  which  the  organized 
material  may  enter  into  combination,  and  thus  the  divellant  tenden- 
cies of  the  affinities  of  its  elements  be  overcome  ;  3d,  that  water  be 
present  in  order  to  give  the  necessary  mobility  j  4th,  that  oxygen 
be  present,  or  at  least  some  other  gas,  into  the  space  occupied  by 
which  the  gaseous  products  may  be  diffused  j  and,  lastly,  that  the 
temperature  shall  be  within  moderate  limits,  putrefaction  being  im- 
possible below  32°  and  above  182°. 

The  agency  of  the  first  of  these  preventive  powers  need  not  be 
farther  noticed.  The  second  is  extensively  employed  in  the  prepar- 
ation of  bodies  for  anatomical  purposes,  by  baths,  or  injections  into 
the  arteries,  of  solutions  of  corrosive  sublimate,  acetate  of  alumina, 
sulphate  of  iron,  tannin,  wood  vinegar,  and  kreosote  ;  this  last  body, 
however,  does  not  appear  to  act  by  direct  combinations,  but  by  the 
complete  (catalytic)  coagulation  it  produces  in  all  the  tissues  of  the 
body  that  have  proteine  for  their  base.  The  necessity  for  the  pres- 
ence of  water  is  shown  by  the  fact  that,  by  drying  the  animal  sub- 
stances, they  are  completely  preserved.  It  is  thus  that  the  bodies 
of  those  perishing  in  the  Arabian  deserts  are  recovered  years  sub- 
sequently, dried,  but  completely  fresh.  Alcohol  and  common  salt 
act  in  preserving  animal  bodies  by  their  affinity  for  water.  If  a 
piece  of  flesh  be  covered  with  salt,  the  wator  gradually  passes  from 


69(^  MIASM  S. C  O  N  T  A  G  I  O  N. 

the  pores  of  the  flesh,  and,  dissolving  the  salt,  forms  a  brine,  which 
does  not  wet  the  flesh  (p.  540),  but  trickles  off' its  surface;  the  wa- 
ter necessary  for  putrefaction  is  thus  removed.  The  mode  of 
strengthening  alcohol  in  a  bladder  (p.  540)  rests  on  the  same  prin- 
ciple. Fourth,  by  excluding  oxygen,  the  putrefactive  process  is  re- 
tarded, precisely  as  the  fermentative  action  of  the  gluten  in  grape- 
juice  (p.  538)  cannot  begin  until  a  small  quantity  of  oxygen  be  ab- 
sorbed. It  is  thus  that  meat  which  is  sealed  up  in  close  vessels, 
and  then  boiled  for  a  moment,  is  preserved  ',  the  small  quantity  ol 
oxygen  of  the  air  remaining  then  in  the  vessel  is  absorbed,  and  the 
product  of  that  minute  change  being  coagulated  by  the  heat,  it  can- 
not proceed  farther.  A  high  temperature  stops  putrefaction  by  co- 
agulating the  azotized  materials ;  a  temperature  below  32^,  by  freez- 
ing the  water,  acts  as  if  the  tissue  had  been  dried  j  in  both  cases 
putrefaction  is  arrested. 

During  putrefaction,  at  a  stage  prior  to  any  fetid  gas  being  evolv- 
ed, a  peculiar  organic  substance  is  generated,  possessed  of  intensely 
poisonous  properties,  and  the  blood  of  persons  who  have  died  from 
its  effects  is  found  to  be  quite  disorganized  and  irritating  when  ap- 
plied to  wounds.  The  blood  of  over-driven  cattle  is  found  to  pro- 
duce efl^ects  similar  to  those  of  venomous  reptiles,  and  the  wounds 
received  in  dissection  are  sometimes  followed  by  similar  fatal  con- 
sequences. The  communication  of  disease  in  this  way  has  recently 
been  very  ingeniously  ascribed  by  Liebig  to  the  general  principle 
of  the  communication  of  decomposition  by  contact  (p.  663).  The 
small  quantity  of  diseased  organic  matter  originally  introduced  into 
the  system  by  absorption,  acts  as  a  ferment,  and  reproduces  itself 
in  the  mass  of  blood  until  this  becomes  unfitted  for  the  performance 
of  its  functions,  and  the  animal  is  killed  ;  the  active  principle  being 
thus  copiously  present,  is  exuded  from  the  skin  and  lungs,  and  gives 
a  contagious  character  to  the  disease,  or  it  remains  only  in  the 
blood,  or  is  secreted  in  pustules,  &c.,  constituting  infection,  by  which 
the  disease  may  be  communicated  to  another  person. 

In  the  decomposition  of  vegetable  matter  in  marshes,  similar 
maleficent  products  may  be  evolved,  and  throwing  the  blood  of  the 
animal,  by  whom  they  are  absorbed,  into  fermentative  decomposi- 
tion, produce  the  effects  of  Malaria  and  Marsh  Miasm, 


INDEX. 


Absinthiine,  611. 
Absorption  of  Light,  45. 

of  Heat,  96. 

Acechloryl,  564. 
Acetal,  554. 
Acetone,  561. 
Acetyl,  654. 
Acid,  Acetic,  555. 

Adipic,  586. 

Aldehydic,  555. 

Althionic,  546. 

Aloetic,  612. 

Anchusic,  614. 

Anilie,  618. 

Antiraonious,  Antimonic,  385. 

Arsenic,  377. 

Arsenious,  376. 

Auric,  405. 

Azulmic,  518. 

Boletic,  604. 

^ Boracic,  326. 

Bromic,  318. 

Butyric,  589. 

Carbonic,  485. 

— —  Capric,  Caproic,  589. 

Catechutannic,  Catechuic,  603. 

Caincic,  605. 

Chloric,  304 

Chloroacetic,  564. 

Chlorochromic,  450. 

Chlorous,  305. 

Chromic,  372. 

Chrysammic,  613. 

Chrysolepic,  613. 

Cinchonic,  Cinchonatannic,  604. 

• Cinnamic,  572. 

Citric,  597. 

Colophonic,  579. 

Columbic,  375. 

Crenic,  Apocrenic,  640. 

Croconic,  496. 

Crotonic,  590. 

Cumenic,  Cumen-sulphuric,  575. 

Cyanic,  514. 

Cyanuric,  516. 

Delph>nic,  589. 

Elaidic,  586. 

Ellagic,  602. 

Ethionic,  546. 

Eugenic,  573. 

— —  Formic,  645. 

Fulminic,  515. 

Fungic,  604. 

Galhc,  601. 

Glucic,  534. 


4T 


Acid,  Hippuric,  688. 

Humous,  Humic,  639. 

Hydriodic,  315. 

Hydrobromic,  318. 

Hydrochloric,  307. 

Hydrocyanic,  517. 

Hydrofluoboric,  327. 

Hydrofluoric,  319. 

Hydrofluosilicic,  325. 

Hydroxanthic,  550. 

Hypoantimonius,  385. 

Hypochlorous,  304. 

Hyponitrous,  275. 

Hypophosphorous,  296. 

Hyposulphuric,  291. 

Hyposulphurous,  290. 

Iodic,  313. 

Isethionic,  546. 

Kinoic,  604. 

Krameric,  605. 

Lactucic,  604. 

Lipic,  586. 

Manganic,  356. 

Margaric,  583. 

Mellitic,  496. 

Metaphosphoric,  299. 

Methionic,  546. 

Molybdic,  451. 

Muriatic,  307. 

Myristic,  588. 

Nitric,  277. 

Nitromuriatic,  310. 

Nitrous,  276. 

Oleic,  584. 

Osmic,  374. 

Oxalic,  493. 

Oxalovinic,  550. 

Palmitic,  588. 

Paracyanic,  514. 

Perchloric,  306. 

Periodic,  314. 

Permanganic,  356. 

Phosphomesitic,  561. 

Phosphoric,  297. 

Phosphorous,  296. 

Picric,  618. 

Pimelic.  586. 

Pinic,  578. 

Purpuric,  688. 

Racemic,  596. 

Rhodizonic,  496. 

Saccharic,  532. 

Saccharohumic,  637. 

Sacchulmic,  532. 

Sebacic,  586, 


698 


INDEX. 


Acid,  Selenious,  Selenic,  294. 

Silicic.  322. 

Stannic,  370 

Stearic,  582. 

Succinic,  580. 

Sulphomesitic,  561. 

Sulphuric,  286. 

Sulphurous,  284. 

Sylvic,  578. 

Tannic,  597. 

Tantalic,  375. 

Tartaric,  592. 

Tellurous,  Telluric,  389. 

Titanic,  375. 

Tungstic,  374. 

Valerianic,  568. 

Vanadic,  373. 

Verdous  and  Verdic,  605. 

Acids,  Poiybasic,  413. 

Acroieon,  585. 

Actions  by  Contact,  235. 

Adhesion  of  Solids  to  Liquids,  19. 

Uroliths,  357. 

Affinity,  Chemical,  157. 

Order  of,  159. 


influenced  by  Cohesion,  164. 

Elasticity,  168. 

Light,  172. 


Measure  of,  202. 

Aggregation,  States  of,  16. 
Air,  Atmospheric,  262. 

Expansion  of,  48. 

Alabaster,  431. 
Albumen,  Animal,  663. 
Alcohol,  Ordinary,  540. 
Alem broth,  Salt  of,  461. 
Algarotti,  Powder  of,  453. 
Alkalies,  330. 
Alkalimetry,  489. 
Alkaline  Earths,  330, 
Alkarsine,  Alkargene,  563. 
AUantoine,  686. 
Alloxan,  686. 
Alloxantine,  687. 

Alum,  436. 

Aluminum,  Alumina,  349. 

Salts  of,  435. 

Amber,  579. 

Ambergris,  Ambreine,  694, 

Amldogene,  500. 

Amilic  Alcohol,  5671 
Ammeline,  526. 
Ammonia,  498. 

Ordinary  Salts  of,  507. 

Amygdaline,  569. 
Analcime,  40. 
Analysis,  Nature  of,  10, 

Organic,  482. 

Anatase,  375. 
Anhydrite,  431. 
Animal  Charcoal,  480. 

Electricity,  138. 

Antimonial  Powder,  454, 
Antimoniuret  of  Hydrogen,  388. 


Antimony,  384. 

Detection  of,  388. 

Oxide  of,  385. 

Salts  of,  453. 

Sulphurets  of,  386. 

Antimony  Crocus,  Glasses  of,  385. 

Apotheme,  612. 

Aqua-regia,  310. 

Arabine,  530. 

Aricine,  625, 

Arseniate  of  Iron,  452, 

Potash,  452. 

Silver,  461. 


Arsenic,  376, 

Acids  of,  377. 

Antidote  to,  384. 

Detection  of,  381. 

Salts  of,  451. 

Sulphurets  of,  379. 


Arsenite  of  Copper,  456. 

Potash,  452. 

Silver,  461. 


Arseniuret  of  Hydrogen,  378. 
Atmosphere,  262. 

Composition  of,  263, 

Effect  of  Respiration  ou, 

268. 

Extent  and  Form  of,  270. 

Pressure  of,  269. 


Atmospheric  Electricity,  126. 
Atomic  Theory,  217. 
Atoms,  Physical  and  Chemical,  219. 
Specific  Heat  of,  66. 


Atropine,  634. 
Aurates,  405. 
Azote,  260. 
Azure  Blue,  447. 


113. 


Balance,  Electrical, 
Barium,  342. 

Chloride  of,  429. 

Sulphuret  of,  344. 


Barytes,  342. 
Salts  of,  429. 


Batteries,  Constant,  136. 
Galvanic,  131. 


Bell  Metal,  393. 
Benzyle  Compounds,  570. 
Bile,  Constitution  of  the,  680. 
Bileine,  Bilifulvine,  682. 
Bismuth,  397. 

Oxides  of,  398. 

Salts  of,  458, 

Sulphuret  of,  398. 


Blende,  367. 
Blue,  Azure,  447. 

Thenard's,  447. 

Boihng  Points  of  Liquids,  83. 

Boracic  Acid,  Boron,  326. 

Boracite,  435, 

Borax,  428, 

Boron,  Fluoride  of,  327. 

Brass,  394, 

Bromates,  318. 


INDEX. 


69^ 


Bromide  of  Sulphur,  318. 
Bromine,  317. 

Chloride  of,  318. 

Bronze,  393. 
Brucine,  631. 

Cadmium  and  its  Compounds,  369. 

Salts  of,  448. 

Caffeine,  608. 

Calamine,  367. 

Calc  Spar,  345. 

Calcium  and  its  Oxides,  345. 

Salts  of,  430. 

Sulphuret,  347. 

Camphene,  576 
Cantharidine,  609. 
Caoutchouc,  Caoutchine,  580. 
Capacity  of  Bodies  for  Heat,  63. 
Caramel,  533. 
Carbon,  Forms  of,  476. 
Carbonates,  485. 
Carbonic  Acid,  485. 

Oxide,  492. 

Carburets,  485. 

Carmine,  616. 

Carthamine,  615. 

Caseiim,  Caseine,  691. 

Catalysis,  235. 

Cementation,  360. 

Cerebrot,  Cerebrol,  669. 

Cerium  and  its  Compounds,  351. 

Chalk,  345. 

Chameleon  Mineral,  356. 

Chemical  Action  of  Galvanism,  129. 

Affinity,  156. 

Formulae,  166. 

Nomenclature,  149. 

Rays  of  Light,  173. 

Chemistry,  Origin  and  Object  of,  9. 

Derivation  of,  10. 

Chloral,  564. 

Chlorate  of  Potash,  304,  424. 

Chloride  of  Aluminum,  435. 

Antimony,  453. 

Arsenic,  452. 

Barium,  429. 

Bismuth,  458. 

Boron,  326. 

Calcium,  430. 

Chrome,  449. 

Cobalt,  446. 

Copper,  455. 

Gold,  465. 

Hydrogen,  307. 

Iodine,  317. 

Iron,  444. 

Lead,  457. 

Magnesium,  434, 

■ Manganese,  443. 

Mercury,  461. 

Nickel,  446. 

Palladium,  466. 

Platinum,  466. 

Potassium,  421. 


Chloride  of  Rhodium,  466. 

Selenium,  311. 

Silicon,  323. 

Silver,  459. 

Sodium,  426. 

Strontium,  429. 

Sulphur,  310. 

Tin,  448. 

■  Titanium,  454. 

Zinc,  447. 

Chlorine,  300. 

Compounds  v^rith  Oxygen,  304 

Chlorophyll,  621. 
Chondrine,  668. 
Chromates  of  Lead,  458. 

Mercury,  464. 

Potash,  449. 

Chrome  Alum,  449. 
Iron,  371. 


Chromium,  371. 

Oxide,  Acid  of,  371. 


• Salts  of,  449. 

Chrysorhamnine,  615. 
Chyle  and  Chyme,  679. 
Cinchonine  and  its  Salts,  625. 
Cinnabar,  402. 

Factitious,  403. 

Circular  Polarization,  41. 
Classification  of  Bodies,  238. 
Cobalt,  366. 

Salts  of,  446. 


Cocculine,  609. 
Cohesion  and  Affinity,  163. 
Columbine,  609. 
Columbium,  375. 

Salts  of,  451. 


Combination,  Laws  of,  202. 
Combustion,  Slow,  173. 

Theories  of,  185. 

Communication  of  Motion,  235. 
Conduction  of  Heat,  91. 
Coneine,  635. 
Constant  Battery,  136. 
Contact,  Actions  by,  235. 
Cooling  of  Bodies,  103. 
Copper,  390. 

Alloys  of,  393. 

Oxides  of,  392. 

Pyrites,  390. 

Salts  of,  453. 

Sulphurets  of. 


Crystalline  Forms,  23. 
Crystals,  Dimorphous,  227. 

Isomorphous,  221. 

Polarization  by,  38. 

Systems  of,  26. 


Currents,  Galvanic,  126,  197. 
Cyanogen,  513. 


Daguerreotype  Images, 
Definite  Proportions,  2( 
Dew,  Nature  of,  104. 
Dex  rine,  331. 
Diamond,  477. 


175. 


700 


INDEX. 


Diastase,  651. 

Differential  Thermometer,  60. 
Dimorphism,  237. 
Distillation,  83. 
Divellent  Affinities,  157. 
Divisibility  of  Matter,  17. 
Double  Decomposition,  157. 

Refraction,  34. 

Dynamic  Electricity,  126. 

Ebullition,  83 
Elasticity  of  Gases,  19. 

Vapours,  78. 

and  Affinity,  168 

Elaterine,  609. 

Elayl,  552. 

Elective  Decomposition,  157. 

Electrical  Attraction,  112. 

Balance,  113. 

Battery,  120. 

Induction,  118. 

Electricity,  Distribution  of,  110. 

Dynamic,  126. 

Interference  of,  112. 

Nature  of,  106. 


—  of  the  Air,  125. 

—  Positive  and  Negative,  114. 

—  Statical,  107. 
Theories  of,  113. 


Electrics  and  Non- electrics,  107. 
Electro-chemical  Theories,  187. 
Electro-magnetism,  145. 
Electrolysis  and  Electrodes,  194. 
Electrotype,  130. 
Elements,  Nature  of,  9. 

Classification  of,  238. 

Emetine,  632. 

Epsom  Salt,  434. 

Equivalent  Decomposition,  206. 

Ethal,  591. 

Ether,  Luminiferous,  42. 

Sulphuric,  541. 

Etherene,  547. 

Ethers,  Theory  of  the,  544. 
Ethyl,  545. 

Eudiometer,  Use  of  the,  262. 
Evaporation,  77. 

Spontaneous,  87. 

Excitation,  Electrical,  106. 
Expansion  by  Heat,  46. 
of  Gases,  56. 

Liquids,  58. 

Solids,  60. 

Fermentation,  539. 

Fibrine,  603. 

Flame,  Constitution  of,  181. 

Flashing,  399. 

Flints,  321. 

Liquor  of,  437. 

Fluidity,  70. 
Fluoborates,  327. 
Fluoride  of  Boron,  327 
Calcium,  430. 


Fluoride  of  Hydrogen,  320. 

Phosphorus,  321. 

Silicon.  324. 


Fluorine,  319. 
Fluor  Spar,  430. 
Freezing  Mixtures,  71. 
Frost,  Nature  of,  104. 
Fulminates,  513. 
Fusion,  Liquefaction,  70. 

Galena,  395. 

Galvanic  Batteries,  Common,  134. 
Constant,  136. 


—  Circles,  128. 

—  Electricity,  126. 
Intensity,  131. 


Galvanism,  Contact  Theory  of,  133. 

Galvanoscope,  147,  195. 

Gases,  Conduction  of  Heat  by,  92. 

Liquefaction  of,  20. 

Specific  Gravity  of,  11. 

Heat  of,  69. 


Gelatine,  667. 

Glass,  Composition  of,  437. 
of  Antimony,  385. 


Glucinum,  Glucina,  351. 
Glucose,  533. 
Glycerine,  581. 
Glycyrrhizine,  535. 
Gold,  405. 

Gravity,  Nature  of,  11. 
Green,  Brunswick,  455. 

Emerald,  455. 

Scheele's,  455. 


Heat,  Central,  of  the  Earth,  104. 

Conduction  of  by  Solids,  92. 

Interference  of,  101. 

Latent  of  Liquids,  70. 

Vapours,  76. 

of  Liquefaction,  70. 

Polarization  of,  101. 

Radiation  of,  94. 

Reflection  and  Absorption  of,  9!4. 

Relation  of  to  Light,  102. 

Repulsive  Power  of,  46. 

Sources  of,  105. 

Specific  of  Atoms,  66. 

Gases,  69. 

Solids,  63. 


Transmission  of,  91. 

Heavy  Spar,  342. 

Hematite,  362. 

Hematosine,  674. 

Hematoxyline,  615. 

Hepar  Sulphuris,  339. 

Hydriodate  of  Phosphuretted  Hydrogen, 

316. 
Hydriodic  Acid,  315. 
Hydrobromic  Acid,  318. 
Hydrochloric  Acid,  307. 
Hydrofluoric  Acid,  320. 
Hydrofluosilic  Acid,  324. 
Hydrogen,  246. 


INDEX. 


701 


Hydrogen,  Antimoniuretted,  388. 

Arseniuretted,  378. 

Oxide  of,  253. 

Peroxide  of,  25|* 

Phosphuretted,  299. 

Seleniuretted,  294. 

Sulphuretted,  292. 

Hydro-oxygen  Blowpipe,  251. 
Hydruret  of  Arsenic,  378. 

Indigo,  Blue,  616. 
Inuline,  529. 
Iodine,  311. 

Compounds  of,  313. 

Iridium,  409. 

Salts  of,  466. 

Iron,  357. 

Magnetic  Oxide  of,  362. 

Malleable,  359. 

Oxides  of,  362. 

Passitivity  of,  361. 

Pyrites,  363. 

Salts  of,  444. 

Smelting  of,  359. 

Sulphurets  of,  363. 

Isomerism,  231. 
Isomorphism,  221. 
Isomorphous  Groups,  223. 

Kacodyl  Compounds,  562. 
Kalium,  337. 
Kermes  Mineral,  386. 
King's  Yellow,  379. 
Kupfer  Nickel,  365. 

Lac-sulphuris,  339. 
Lactine,  535. 
Lactucine,  611. 
Lamp,  Aphlogistic,  179. 

Safety,  183. 

liampblack,  479 

Lana  Philosophica,  367. 

Lanthanum,  351. 

Latent  Heat  of  Liquids,  70. 

Vapours,  76. 

Laws  of  Combination,  202. 

Lead,  394. 

Legumine,  538. 

Lichenine,  529. 

Light,  Chemical  Rays  of,  173. 

Wave  Theory  of,  42. 

Lignine,  529. 
Lime,  345. 

Salts  of,  430. 

Liquefaction,  70. 
Lithium,  342. 

Salts  of,  429. 

Lymph,  683. 

Madder,  Colouring  Bodies  of,  613. 
Magnesium,  348. 

Salts  of,  434. 

Magnetism,  143. 
Manganese,  352. 


Manganese,  Salts  of,  443. 
Mannite,  535. 
Marsh  Gas,  563. 
Meconine,  609. 
Melam,  526. 
Melamine,  526. 
Membrane,  Cellular,  671. 
Menthene,  578. 
Mercury,  402. 

Salts  of,  461. 

Mesitic  Ether,  561. 
Mesitylene,  561. 
Metal,  Bell,  393. 

Gun,  393. 

Speculum,  393. 

Metals,  Properties  of,  327. 
Methyl,  Salts  of,  644. 
Minium,  395. 
Molecular  Cohesion,  19. 
Molybdates,  373. 
Molybdenum,  373. 

Salts  of,  451. 


Mordants,  Action  of,  622. 
Morine,  615. 
Morphia,  627. 
Mosaic  Gold,  370. 
Mucus,  679. 

Multiple  Proportions,  207. 
Murexid,  688. 
Muriatic  Acid,  307. 
Myriospermine,  573. 

Napthaline,  647. 
Narcotine,  628. 
Natrium,  Natron,  342. 
Nickel,  365. 

Salts  of,  446. 


Nicotine,  635. 
Nitric  Oxide,  273. 
Nitrogen,  26. 
Oxides  of,  272. 


Nitrous  Oxide,  272. 
Nomenclature,  149. 

Oleine,  581. 
Olivine,  607. 
Ologist  Iron,  362. 
Orcine,  Orceine,  619. 
Organic  Analysis,  476. 
Bodies,  467. 


Orpiment,  379. 
Osmium,  374. 

Oxides  of,  374. 

Salts  of,  451. 


Oxamethane,  350. 
Oxides  of  Aluminum,  349. 

Antimony,  385. 

Arsenic,  377. 

Barium,  342. 

Bismuth,  397. 

Cadmium,  369. 

Calcium,  346. 

Cerium,  351. 

Chlorine,  304. 


W2 


7NDEX. 


Oxides  of  Chrome,  371. 

Cobalt,  366. 

Copper,  392. 

Glucinum,  351. 

Gold,  405. 

Hydrogen,  253. 

Iridium,  409. 

Iron,  362. 

Lead,  394. 

Lithium,  342. 

Magnesium,  348. 

Manganese,  353. 

Mercury,  403. 

Molybdenum,  373. 

Nickel,  365. 

Nitrogen,  272.     . 

Osmium,  374. 

Palladium,  406. 

Phosphorus,  296. 

. —  Platinum,  407. 

Potassium,  337. 

. Rhodium,  409. 

Silver,  401. 

Sodium,  340. 

Strontium,  344. 

Thorium,  351. 

Tin,  369. 

. Titanium,  375. 

Tungsten,  373. 

Uranium,  390. 

Vanadium,  373. 

Yttrium,  351. 

Zinc,  367. 

Zirconium,  351 

Oxychloride  of  Antimony,  453 
. Bismuth,  458. 

i^ Calcium,  430. 

. Chrome,  449. 

. Copper,  455. 

Lead,  457. 

Mercury,  462. 

PaUadium,  466. 


Oxygen,  241. 

Preparation  of,  241. 

Oxyhydrogen  Blowpipe,  251. 

Palladium,  406. 

Compounds  of,  406. 

Paracyanogen,  514. 
Pectirie,  605 
Perchlorates,  306. 
Periodates,  313. 
Permanganates,  357. 
Pewter,  397. 
Phenyl,  Hydrate  of,  648. 
Phloridzine,  607. 
Phosphates  of  Water,  297. 
Phosphites,  297. 
Phosphorus,  295. 

Compounds  of,  296. 

Photography,  175. 
Piperine.  608. 
Platinum,  407. 
Polarization,  Circular,  41. 


Polarization  of  Heat,  102, 
—  Light,  38. 


Polychrome,  610. 
Populine,  610. 
Porcelain,  Nature  of,  437. 
Potash,  337. 
Potassium,  336. 

Oxides  of,  337. 

Salts  of,  421. 

Sulphurets  of,  339. 


Proteine,  665. 
Puddling,  359. 
Purpurates,  688. 
Pus,  694. 
Putty,  370. 
Pyrites,  Copper,  390. 
Iron,  363. 


Pyrometer,  Daniell's,  54. 
Pyrophorus,  339. 
Pyroxylic  Spirit,  643. 

Quartation,  405. 
Quartz,  322. 
Quassine,  610. 
Quicksilver,  402. 
Quinine,  624. 

Radiation  of  Heat,  94. 
Light,  32. 


Radicals,  Compound, 
Nature  of,  233. 


Realgar,  379. 
Red  Lead,  394. 

Precipitate,  403. 

Reflection  of  Heat,  96. 

: Light,  32. 

Refraction  of  Heat,  100. 

Double,  34. 

Single,  32. 


Regular  System,  26. 
Respiration  of  Animals,  677. 
Rhodium,  409. 

Salts  of,  466. 

Rutile,  375. 
Rutiline,  Rufine,  607. 

Safety  Lamp,  183. 
Salop,  531. 

Salicyl  Compounds,  573. 
Salts,  Constitution  of,  410. 

Crystallization  of,  23. 

Isomorphism  of,  221. 

Solubility  of,  22. 

Salts  of  Alumina,  435. 

Antimony,  453. 

Arsenic,  452. 

Barium,  429. 

Bismuth,  458. 

Cadmium,  448. 

Calcium,  430. 

Chrome,  449. 

Cobalt,  446. 

Copper,  455. 

Gold,  465. 


INDEX. 


703 


Salts  of  Iridium,  466. 
Iron,  444. 

Lead,  457. 

Magnesium,  434. 

Manganese,  443. 

Mercury,  461. 

Molybdenum,  451. 

Nickel,  446. 

Osmium,  451. 

Palladium,  466. 

Platinum,  466. 

Potassium,  421. 

Rhodium,  466. 

Silver,  459. 

Sodium,  426. 

Strontium,  439. 

Tin,  448. 

Zinc,  447. 

Santaline,  615. 
Santonine,  610. 
Saponine,  611. 
Scillitine,  611. 
Selenium,  294. 

Compounds  of,  294. 

Senegine,  611. 

Silica,  322. 

Silicate  of  Alumina,  437. 

Cobalt,  447. 

Potash,  426. 

Soda,  429. 

Silicon,  321. 

Chloride  of,  323. 

Fluoride  of,  324. 

Silver,  399. 

Oxides  of,  401. 

Salts  of,  459. 

Sulphurets  of,  401. 

Simple  Bodies,  9. 

Table  of,  149. 

Skin,  Nature  of,  670. 
Slacked  Lime,  346. 
Smalts,  447. 
Smilacine,  611. 
Soap,  Manufacture  of,  590. 
Soda,  340. 

Detection  of,  340. 

Sodium,  340. 

Salts  of,  426. 

Solanine,  633. 
Solder,  396. 

Solids,  Conduction  of  Heat  by,  92. 

Expansion  of,  60. 

Specific  Gravity  of,  11. 

Specific  Heat,  63. 
Speculum  Metal,  393. 
Speiss,  365. 
Spermaceti,  591. 
Spirit  of  Salts,  307. 
Starch.  527. 
Steam,  Elasticity  of,  78. 

Latent  Heat  of,  76. 

Motive  Force  of,  89. 

Stearine,  582. 
Steel.  360. 


Stibium,  384. 
Strontium,  344. 

—  Oxides  of,  345. 

Salts  of,  429. 


Strychnine,  629. 
Sugar  of  Liquorice,  536. 
Sugarcane,  531. 
Sulphites,  284. 
Sulphocyanogeu,  525. 
Sulphosinapisine,  574. 
Sulphur,  282. 
Sulphurets  of  Aluminum,  350. 

Antimony,  386. 

Arsenic,  379. 

Barium,  344. 

Bismuth,  398. 

Cadmium,  369. 

Calcium,  347. 

. Chrome,  371. 

Cobalt,  367. 

Copper,  393. 

Gold,  405. 

Hydrogen,  292. 

Iron,  363. 

Lead,  395. 

Magnesium,  348. 

Manganese,  357, 

Mercury,  404. 

Molybdenum,  373. 

— Nickel,  366. 

Palladium,  407. 

Platinum,  407. 

Phosphorus,  299. 

—  Potassium,  339. 

— Selenium,  295. 

Silver,  401. 

•  Sodium,  342 

Strontium,  344. 

Tin,  370. 

■ Zinc,  368. 


Synthetic  Action  of  Galvanism, 
Systems  of  Crystallization,  26. 

Tantalum,  375. 
Telluret  of  Hydrogen,  389. 
Salts  of,  454. 


199 


Tellurium,  389. 

Compounds  of,  389. 


Temperature,  Nature  of,  49. 
Thebaine,  629. 
Theory,  Atomic,  217. 

of  Volumes,  213. 


Thermo-electricity,  139. 
Thermometer,  Nature  of  the,  49. 
Kinds  of,  50. 


Thermometric  Scales,  53. 
Thialol,  548. 
Thorium,  351. 
Tin,  369. 

Grain,  369. 

Oxides  of,  369. 

Tincal,  429. 
Titanium,  375. 
Transcalescence,  98. 


704 


INDEX 


Tragacanthine,  530. 
Transfer  of  Elements,  194 
Tungsten,  373. 

— Salts  of,  451. 

Types,  Chemical,  234. 

Ulmine,  from  Soil,  637. 
Uranium,  390. 

Salts  of,  454. 

Urea,  684. 
Urine,  689. 

Vanadium,  373. 

Salts  of,  451. 

Vaporization,  75. 
Vapours,  Elasticities  of,  78. 

Latent  Heat  of,  76. 

Volumes  of,  77. 

Veratrine,  631. 
Vermilion,  404. 
Vitriol,  Oil  of,  286. 
Voltaic  Electricity,  126. 


Volta's  Theory  of  Contact,  13S. 
Volumes,  Theory  of,  213. 

Water,  Composition  of,  253. 
Wave  Theory  of  Light,  42. 
Heat,  102. 


Wax,  592. 
Welding,  359. 
White,  Pearl,  458. 
Vitriol,  447. 


Xyloidine,  530. 

Yeast,  538. 
Yttrium,  351. 
Salts  of,  443. 


Zaflre,  366. 
Zinc,  367. 

Butter  of,  447. 

Zirconium,  351. 
Salts  of,  44S. 


THE  END 


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